Joint Resurfacing

Number: 0661

Table Of Contents

Applicable CPT / HCPCS / ICD-10 Codes


Scope of Policy

This Clinical Policy Bulletin addresses joint resurfacing.

  1. Medical Necessity

    1. Aetna considers metal-on-metal hip resurfacing by means of a Food and Drug Administration (FDA)-approved device (e.g., Birmingham Hip Resurfacing (BHR) System, Cormet 2000) a medically necessary alternative to total hip arthroplasty for physically active non-elderly (less than 65 years of age) adult members when the following criteria are met:

      1. Member has advanced joint disease demonstrated by:
        1. Pain and functional disability that interferes with activities of daily living (ADLs) from injury due to osteoarthritis, avascular necrosis, or post-traumatic arthritis of the hip joint; and
        2. Limited range of motion (ROM), antalgic gait, and pain in hip joint with passive ROM on physical examination: and
        3. Radiographic or magnetic resonance imaging (MRI) supported evidence of severe osteoarthritis (as evidence by 2 or more of the following: subchondral cysts, subchondral sclerosis, periarticular osteophytes, joint subluxation, bone on bone articulation or joint space narrowing) of hip joint primarily affecting the femoral head, or osteonecrosis (avascular necrosis) of the femoral head when the disease is detected early and there is less than 50 % involvement of the femoral head; and
        4. Normal proximal femoral bone geometry and bone quality; and
        5. Member would otherwise require a conventional primary total hip replacement, but is likely to live longer than the functional lifespan of a traditional prosthesis; and
        6. History of of unsuccessful conservative therapy (non-surgical medical management) that is clearly addressed in the medical record (see Note). If conservative therapy is not appropriate, the medical record must clearly document why such approach is not reasonable: Members should have at least 12 weeks of non-surgical treatment documented in the medical record, including all of the following, unless contraindicated:
          1. Anti-inflammatory medications or analgesics; and
          2. Flexibility and muscle strengthening exercises, and
          3. Activity modification; and
          4. Supervised physical therapy (ADLs diminished despite completing a plan of care); and
          5. Weight reduction as appropriate; and
          6. Assistive device use, where appropriate; and
          7. Therapeutic injections into the hip, where appropriate.
      2. For members with significant conditions or co-morbidities, the risk/benefit of hip resurfacing should be appropriately addressed in the medical record.

      Aetna considers metal-on-metal hip resurfacing experimental and investigational for all indications other than those listed above. 

    2. Aetna considers hip resurfacing not medically necessary in persons with any of the following contraindications:

      1. Active infection of the joint or active systemic bacteremia that has not been totally eradicated; or
      2. Active skin infection (exception recurrent cutaneous staph infections) or open wound within the planned surgical site of the hip; or
      3. Allergy to metals used in resurfacing (e.g., cobalt, chromium or alumina); or
      4. Inactive and/or older individuals who are unlikely to require revisions of a traditional THR; or
      5. Morbid obesity (body mass index (BMI) greater than 40); or
      6. Member has inadequate bone stock to support the device; or
      7. Member has been diagnosed with avascular necrosis (osteonecrosis) of the femoral head where more than 50 % of the femoral head is affected; or
      8. Member has severe anatomic deformity of the femoral head; or
      9. Member is skeletally immature; or
      10. Persons with moderate-to-severe renal insufficiency (glomerular filtration rate [GFR] less than 60 mL/min/1.73 m2); or
      11. Multiple femoral neck cysts greater than 1 cm in diameter; or
      12. Vascular insufficiency, muscular atrophy, or neuromuscular disease severe enough to compromise implant stability or postoperative recovery; or
      13. Immunosuppression (i.e., AIDS) or high doses of corticosteroids; or
      14. Females of child-bearing age due to the unknown effect of metal ion release on the fetus.

    For criteria for revision of hip resurfacing arthroplasty, see CPB 0287 - Hip Arthroplasty.

  2. Experimental and Investigational

    The following procedures are considered experimental and investigational because their safety and effectiveness have not been established:

    1. Computer-assisted navigation for positioning during Birmingham hip resurfacing; 
    2. Facet joint resurfacing; 
    3. Knee resurfacing, partial knee resurfacing (e.g., Makoplasty), and isolated patellar resurfacing (e.g., UniCAP, HemiCAP);
    4. Metal-on-metal hip resurfacing for developmental dysplasia of the hip;
    5. Metal-on-polyethylene hip resurfacing implants;
    6. Metal resurfacing inlay implant for osteochondral talar defects after failed previous surgery; 
    7. Metatarsal phalangeal (MTP) toe joint resurfacing;
    8. Radiocapitellar joint/radiocapitellar joint replacement resurfacing; 
    9. Resurfacing capitate pyrocarbon implant for carpal injuries/wrist arthritis;
    10. Shoulder resurfacing, including total and hemi-resurfacing, for the treatment of glenohumeral arthritis, humeral head fractures, osteochondral lesions, and for all other indications.
  3. Related CMS Coverage Guidance

    This Clinical Policy Bulletin (CPB) supplements but does not replace, modify, or supersede existing Medicare Regulations or applicable National Coverage Determinations (NCDs) or Local Coverage Determinations (LCDs). The supplemental medical necessity criteria in this CPB further define those indications for services that are proven safe and effective where those indications are not fully established in applicable NCDs and LCDs. These supplemental medical necessity criteria are based upon evidence-based guidelines and clinical studies in the peer-reviewed published medical literature. The background section of this CPB includes an explanation of the rationale that supports adoption of the medical necessity criteria and a summary of evidence that was considered during the development of the CPB; the reference section includes a list of the sources of such evidence. While there is a possible risk of reduced or delayed care with any coverage criteria, Aetna believes that the benefits of these criteria – ensuring patients receive services that are appropriate, safe, and effective – substantially outweigh any clinical harms.

    Code of Federal Regulations (CFR):

    42 CFR 417; 42 CFR 422; 42 CFR 423.

    Internet-Only Manual (IOM) Citations:

    CMS IOM Publication 100-02, Medicare Benefit Policy Manual; CMS IOM Publication 100-03 Medicare National Coverage Determination Manual.

    Medicare Coverage Determinations:

    Centers for Medicare & Medicaid Services (CMS), Medicare Coverage Database [Internet]. Baltimore, MD: CMS; updated periodically. Available at: Medicare Coverage Center. Accessed November 7, 2023.

  4. Related Policies


Applicable CPT / HCPCS / ICD-10 Codes

Code Code Description

Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":

Hip resurfacing, metal-on-polyethylene hip resurfacing implants, Facet Joint Resurfacing, Radiocapitellar Joint/Radiocapitellar Joint Replacement Resurfacing:

No specific code

CPT codes covered if selection criteria are met:

27125 Hemiarthroplasty, hip, partial (e.g., femoral stem prosthesis, bipolar arthroplasty) [per AAOS for a femoral head resurfacing procedure, when only the head of the femur is replaced (a femoral component hemiarthroplasty)]
27130 Arthroplasty, acetabular and proximal femoral prosthetic replacement (total hip arthroplasty), with or without autograft or allograft [Hip resurfacing for arthroplasty]

Other CPT codes related to the CPB:

27033 Arthrotomy hip, including exploration or removal of loose or foreign body
27122 Acetabuloplasty; resection, femoral head (e.g., Girdlestone procedure)
27132 Conversion of previous hip surgery to total hip arthroplasty, with or without autograft or allograft
27360 Partial excision (craterization, saucerization, or diaphysectomy) bone, femur, proximal tibia and/or fibula (e.g., osteomyelitis or bone abscess)

HCPCS codes covered if selection criteria are met:

S2118 Metal-on-metal total hip resurfacing, including acetabular and femoral components

ICD-10 codes covered if selection criteria are met:

M16.0 - M16.12 Primary osteoarthritis, left hip
M16.2 - M16.7 Secondary osteoarthritis of hip
M16.9 Osteoarthritis of hip, unspecified
M87.051 - M87.059 Idiopathic aseptic necrosis, femur [avascular necrosis of the hip joint]
M87.150 - M87.159 Osteonecrosis due to drugs, pelvis and femur [avascular necrosis of the hip joint]
M87.251 - M87.256 Osteonecrosis due to previous trauma, pelvis and femur [avascular necrosis of the hip joint]
M87.350 - M87.353 Other secondary osteonecrosis, pelvis and femur [avascular necrosis of the hip joint]
M87.850 - M87.859 Other osteonecrosis, pelvis and femur [avascular necrosis of the hip joint]
M90.551 - M90.559 Osteonecrosis in diseases classified elsewhere, thigh [avascular necrosis of the hip joint]

ICD-10 codes not covered for indications listed in the CPB (not all-inclusive):

Q65.00 - Q65.6 Congenital dislocation of hip [developmental dysplasia]
Q65.01 [Q65.32 also required]
Q65.02 [Q65.31 also required]
Congenital dislocation of one hip with partial dislocation of other hip [developmental dysplasia]
Q65.89 Other specified congenital deformities of hip [developmental dysplasia]

ICD-10 codes contraindicated for this CPB:

A41.01 - A41.9 Other sepsis
A46 Erysipelas
D80.0 - D81.2, D81.4, D81.89 - D82.1
D83.0 - D84.9, D89.810 - D89.9
Certain disorders involving the immune mechanism
E66.01 Morbid (severe) obesity due to excess calories [BMI greater than 40]
G70.00 - G70.9
G73.1 - G73.3
Myasthenia gravis and other myoneural disorders [neuromuscular disease]
I73.9 Peripheral vascular disease, unspecified
I87.2, I87.8 - I87.9 Other disorders of veins
I99.8 Other disorder of circulatory system
M00.051 - M00.059
M00.151 - M00.159
M00.251 - M00.259
M00.851 - M00.859
Pyogenic arthritis, hip
M01.X51 - M01.X59 Direct infection of hip in infectious and parasitic diseases classified elsewhere
M62.50 - M62.59, M62.5A0 - M62.5A9 Muscle wasting and atrophy, not elsewhere classified
M62.84 Sarcopenia
N17.0 - N17.9 Acute kidney failure
N18.1 - N18.9 Chronic kidney disease (CKD)
N28.9 Disorder of kidney and ureter, unspecified [acute renal insufficiency]
Z79.51 - Z79.52 Long term (current) use of steroids
Z68.41 - Z68.45 Body mass index (BMI) 40 and over, adult

Shoulder Resurfacing, Facet Joint Resurfacing, Radiocapitellar Joint/Radiocapitellar Joint Replacement Resurfacing:

There are no specific codes for shoulder resurfacing:

CPT codes not covered for indication listed in the CPB (not all-inclusive):

23470 Arthroplasty, glenohumeral joint, hemiarthroplasty
23472     total shoulder (glenoid and proximal humeral replacement (eg, total shoulder))

ICD-10 codes not covered for indications listed in CPB (not all-inclusive):

M07.611 - M07.619 Enteropathic arthropathies, shoulder
M12.511 - M12.519 Traumatic arthropathy, shoulder
M12.811 - M12.819 Other specific arthropathies, not elsewhere classified, shoulder
M12.9 Arthropathy, unspecified [shoulder]
M13.0 Polyarthritis, unspecified [shoulder]
M13.111 - M13.119 Monoarthritis, not elsewhere classified, shoulder
M19.011 - M19.019 Primary osteoarthritis, shoulder
M19.111 - M19.119
M19.211 - M19.219
Secondary osteoarthritis, shoulder
M19.90 Unspecified osteoarthritis [shoulder]
M93.20 - M93.29 Osteochondritis dissecans [osteochondral lesions]
Numerous options Fracture of upper end of humerus [humeral head] [Codes not listed due to expanded specificity]

Wrist resurfacing:

CPT codes not covered for indication listed in the CPB (not all-inclusive):

Resurfacing capitate pyrocarbon implant – no specific code

ICD-10 codes not covered for indications listed in CPB (not all-inclusive):

M13.131 - M13.139 Monoarthritis, not elsewhere classified, wrist
M13.831 - M13.839 Other specified arthritis, wrist
M14.831 - M14.839 Arthropathies in other specified diseases classified elsewhere, wrist
M18.0 - M18.9 Osteoarthritis of first carpometacarpal joint
M19.031 - M19.039 Primary osteoarthritis, wrist
M19.131 - M19.139 Post-traumatic osteoarthritis, wrist
M19.231 - M19.239 Secondary osteoarthritis, wrist
S60.00XA - S69.92XS Injuries to the wrist, hand and fingers

No specific codes :

Knee or Partial Knee Resurfacing/Isolated Patellar Resurfacing, Facet Joint Resurfacing, Radiocapitellar Joint/Radiocapitellar Joint Replacement Resurfacing, Metal Resurfacing Inlay Implant for Osteochondral Talar Defects after failed previous surgery

ICD-10 codes not covered for indications listed in CPB (not all-inclusive):

M95.8 Other specified acquired deformities of musculoskeletal system [osteochondral talar defects]


Hip Resurfacing

Joint resurfacing arthroplasty, specifically hip resurfacing arthroplasty (HRA), may be considered as an alternative to conventional total hip replacement (THR). HRA does not remove the femoral head and neck or bone from the femur allowing for conversion to a THR, when necessary. The resurfacing procedure is designed for younger active individuals (typically less than 55 years of age) with viable bone in the proximal femur who is likely to outlive the prosthesis used in the THR procedure. Examples of U.S. Food and Drug Administration (FDA)-approved hip resurfacing systems include, but may not be limited to, Birmingham hip resurfacing system, Conserve Plus total hip resurfacing system, ReCAP HA Press-Fit femoral resurfacing head and Cormet hip resurfacing system.  

Hip resurfacing arthroplasty can either be categorized as a partial (hemi) or total resurfacing:

  • Partial HRA is the removal of the damaged surface of the femoral head, which is then resurfaced with a metal shell. The socket is left intact.
  • Total HRA involves both the femoral shell and the acetabulum (socket) cup. A metal shell is placed over the head of the femur as in a partial HRA; however, the damaged surface of the hip socket is also resurfaced.

Hip resurfacing has been promoted as an alternative to total hip replacement or for younger patients, to watchful waiting, and involves the removal and replacement of the surface of the femoral head with a hollow metal hemisphere.  This hemisphere fits into a metal acetabular cup.  The technique conserves femoral bone, maintains normal femoral loading and stresses.  Because of bone conservation, it may not compromise future total hip replacements (THRs).

The metal-metal femoral resurfacing technique developed by Amstutz et al (1986) has been proposed as an alternative to metal-on-metal THR.  In femoral resurfacing, the femoral head is re-shaped and capped with a metal ball, but the femoral head is not removed as in THR.  Compared to THR, femoral resurfacing allows preservation of much more of the patient's own bone.  The advantages of femoral resurfacing over THR is that it is less invasive, there is reduced thigh pain since there is no stem in the femoral canal, and that it may allow patients to be more active (an advantage especially for younger patients because the risk of dislocation is theoretically reduced because of the larger ball.  In addition, if the femoral resurfacing fails, the surgeon can perform a THR.  Unfortunately, the early designs tried by Amstutz had high failure rates.  In addition, there are theoretical concerns that resurfacing may increase the risk of avascular necrosis of the femoral head.  Femoral resurfacing may become a first choice procedure (relative to THR) for patients with osteonecrosis of the femoral head, especially for young, active patients.

The United Kingdom National Institute for Clinical Excellence (2002) systematically reviewed the literature supporting hip resurfacing.  The NICE review noted that only short-term (less than 5 years) outcomes data are available on metal-on-metal resurfacing hip arthroplasty.  Long-term data are important because for THR, failure rates have been noted to increase substantially beyond 10 years.  There are no randomized controlled clinical trials of metal-on-metal hip resurfacing arthroplasty.  In addition, there are no studies directly comparing the outcomes of metal-on-metal resurfacing hip arthroplasty to THR or other alternatives, which limit the conclusions one can draw about the comparative effectiveness of these procedures. 

The NICE recommended that metal-on-metal hip resurfacing be considered an option for people with advanced hip disease who would otherwise receive a conventional primary THR and are likely to live longer than the device is likely to last.

The NICE noted that, when considering a metal-on-metal hip resurfacing, surgeons should bear in mind:

  • How active the individual is
  • That the evidence resurfacing available at the moment for the clinical effectiveness and cost effectiveness of metal-on-metal hip comes mainly from studies that have involved people less than 65 years of age.

The NICE recommended that surgeons choose a device for hip resurfacing for which there is at least 3 years' evidence.  This evidence should show that the device is likely to meet a target of less than 1 in 10 devices needing replacing over 10 years.

In an assessment prepared for the Canadian Coordinating Office for Health Technology Assessment, Allison (2005) stated that minimally invasive hip resurfacing uses a smaller surgical incision and new techniques to expose the hip joint.  Possible advantages include less damage to soft tissue, muscle and bone; smaller scars; less blood loss; and shorter hospital stays and rehabilitation.  Possible disadvantages include damage to soft tissue, femur fracture, neurovascular damage, implant mal-position and a longer operating time.

Metal-on-metal resurfacing arthroplasty also represents an alternative for the treatment of patients with hip osteoarthritis.  Daniel and colleagues (2004) stated that the results of conventional hip replacement in young patients with osteoarthritis have not been encouraging even with improvements in the techniques of fixation and in the bearing surfaces.  Modern metal-on-metal hip resurfacing was introduced as a less invasive method of joint reconstruction for this particular group.  The authors presented their findings of a series of 446 hip resurfacings (n = 384) performed by one of the authors using cemented femoral components and hydroxyapatite-coated uncemented acetabular components with a maximum follow-up of 8.2 years (mean of 3.3 years).  Their survival rate, Oxford hip scores and activity levels were reviewed.  Six patients died due to unrelated causes.  There was 1 revision (0.02 %) out of 440 hips.  The mean Oxford score of the surviving 439 hips is 13.5.  None of the patients was told to change their activities at work or leisure; 31 % of the men with unilateral resurfacings and 28 % with bilateral resurfacings were involved in jobs that they considered heavy or moderately heavy; 92 % of men with unilateral hip resurfacings and 87 % of the whole group participate in leisure-time sporting activity.  The extremely low rate of failure in spite of the resumption of high level occupational and leisure activities provided early evidence of the suitability of this procedure for young and active patients with osteoarthritis.

Lilikakis et al (2005) reported preliminary results of an uncemented, hydroxyapatite-coated femoral implant for metal-on-metal hip resurfacing.  The pre-operative diagnosis was osteonecrosis in 1 patient, chondrolysis in 1 patient, and osteoarthritis in the remaining 64 patients (68 hips).  The survival rate of 70 implants after at least 2 years follow-up was 98.6 %, with an excellent clinical outcome.  There have been no femoral fractures, aseptic loosening, or radiolucencies around the stem.  Thinning of the femoral neck at the inferomedial cup-neck rim has been a frequent radiological finding but with no clinical implication so far.

Pollard et al (2006) compared the 5- to 7-year clinical and radiological results of the metal-on-metal Birmingham hip resurfacing with a hybrid total hip arthroplasty in 2 groups of 54 hips, matched for gender, age, body mass index and activity level.  Function was excellent in both groups, as measured by the Oxford hip score, but the Birmingham hip resurfacings had higher University of California at Los Angeles activity scores and better EuroQol quality of life scores.  The total hip arthroplasties had a revision or intention-to-revise rate of 8 %, and the Birmingham hip resurfacings of 6 %.  Both groups showed impending failure on surrogate end-points.  Of the total hip arthroplasties, 12 % had polyethylene wear and osteolysis under observation, and 8 % of Birmingham hip resurfacings demonstrated migration of the femoral component.  Polyethylene wear was present in 48 % of the hybrid hips without osteolysis.  Of the femoral components in the Birmingham hip resurfacing group which had not migrated, 66 % had radiological changes of unknown significance.

An assessment by the BlueCross BlueShield Association Technology Evaluation Center (BCBSA, 2007) concluded that metal-on-metal total hip resurfacing meets the TEC criteria.  The assessment found that a substantial body of evidence shows hip resurfacing "is associated with consistent and strong symptomatic and functional improvements at follow-up times up to 5 years."  The assessment also found that hip resurfacing results are comparable to those obtained with current generation total hip arthroplasty at similar time points in patients younger than 65 years of age.  The assessment noted that hip resurfacing differs procedurally from total hip arthroplasty in conserving a patient's native femoral bone neck.  When hip resurfacing patients subsequently require revision to total hip arthroplasty, the operation is technically similar to primary total hip arthroplasty and likely avoids the complications of revision of a primary total hip arthroplasty.  The assessment concluded, therefore, that the benefits comprise initial hip resurfacing results as good as total hip arthroplasty and a simpler revision to total hip arthroplasty when needed.  The assessment noted that, although longer-term (i.e., greater than 5 years) data on the relative durability of hip resurfacing compared to total hip arthroplasty are unavailable, current evidence is sufficient to conclude that hip resurfacing is a safe and effective means for initial surgical treatment in younger, properly selected patients who require a THR.  The assessment explained that primary use of hip resurfacing in the indicated patient subpopulation thus defers standard total hip arthroplasty.

By contrast, an assessment by the California Technology Assessment Forum (CTAF, 2007) found that metal-on-metal hip resurfacing does not meet CTAF criteria.  The CTAF assessment explained that there are no randomized clinical trials with either of the 2 currently approved devices that address the question of whether hip resurfacing is as safe and efficacious as total hip arthroplasty in comparable patients.  The assessmented noted that the peer-reviewed literature consists primarily of level 5 case series that report on the experience of a single surgeon operating at a single center with relatively short follow-up.  The assessment identified several important questions that remain unanswered about hip resurfacing.  These include questions about the long-term durability of hip resurfacing compared to total hip arthroplasty, questions about the short- and long-term results of total hip arthroplasty in persons who have undergone hip resurfacing, and whether there will be unforeseen long term complications that will make this revision more problematic than anticipated.  The assessment also questioned what are the long-term health consequences of increased low levels of circulating metal ions produced by hip resurfacing.  The assessment questioned whether outcomes of hip resurfacing will be as good as the procedure is disseminated and performed by less experienced surgeons.

In a controlled prospective study, Knecht et al (2004) examined if there are differences in function after resurfacing arthroplasty of the hip in patients with primary osteoarthritis compared to patients with secondary osteoarthritis due to developmental dysplasia of the hip (DDH).  Patients with primary osteoarthritis (n = 54, average age of 48.4 years) and osteoarthritis due to high-grade dysplasia (Eftekhar B, n = 34, average age of 55.8 years) were included in this study.  Standardized clinical (Harris hip score [HHS]) and radiographical examinations were performed at 6 weeks, 3 months, 6 months, and then every year after the operation.  All patients could be followed-up to 1.5 years (1 to 4 years) after surgery.  The average HHS improved to 82 to 95 points in both groups 3 months post-operatively.  Statistically significant differences could be found in the sub-scales "function" and "limp", where patients with DDH showed somewhat lower results after 6 (function) to 12 weeks (limp) post-operatively.  This is probably attributable to extended non-weight-bearing after acetabular reconstruction in these cases, as the difference disappeared with full weight-bearing.  Radiographically determined neck-shaft angles are slightly higher in dysplastic hips (142 degrees versus 135 degrees), but these researchers did not recognize any significant differences in implant positioning.  The authors concluded that the short-term to mid-term results showed no clinically relevant functional differences after surface replacement in patients with primary osteoarthritis of the hip and patients with secondary osteoarthritis due to higher grade dysplasia.  They stated that long-term observation is needed, however, to determine if these positive functional results are reflected by appropriate radiographical survival.

Amstutz and colleagues (2007) analyzed the mid-term results in a consecutive series of middle-aged patients with DDH treated with hybrid resurfacing joint arthroplasty.  Metal-on-metal hip resurfacing was carried out in 51 patients (59 hips), 42 of whom were female.  The average age at the time of surgery was 43.7 years.  Radiographical and clinical data were collected at 6 weeks, at 3 months, and at yearly follow-up visits.  Seven hips had Crowe type II DDH and 52 had type I.  The follow-up period ranged from 4.2 to 9.5 years (average of 6.0).  Initial stability was achieved in all but 3 hips.  The clinical outcomes, as rated with the University of California at Los Angeles (UCLA) hip score, improved significantly compared with the pre-operative ratings.  On the average, the pain rating improved from 3.2 to 9.3 points; the score for walking, from 6.0 to 9.7 points; the score for function, from 5.7 to 9.6 points; and the score for activity, from 4.6 to 7.3 points (all p = 0.0001).  The mean Short Form-12 (SF-12) mental score increased from 46.6 to 53.5 points, and the mean SF-12 physical score increased from 31.7 to 51.4 points (both p < 0.0001).  The mean post-operative HHS was 92.5 points.  On the average, the range of flexion improved from 106 degrees to 129.6 degrees; the abduction-adduction arc, from 41.9 degrees to 76.9 degrees; and the rotation arc in extension, from 32.1 degrees to 84.8 degrees (all p = 0.0001).  Four patients delivered a total of 6 healthy babies since the time of implantation of the prosthesis.  Radiographical analysis showed a decrease in the mean body weight lever arm from 118.5 mm pre-operatively to 103.9 mm post-operatively (p = 0.007).  There were 5 femoral failures requiring conversion to a total hip arthroplasty.  One hip showed a radiolucency around the metaphyseal femoral stem.  There were no complete acetabular radiolucencies, and all sockets remained well-fixed.  The authors concluded that the mid-term results of metal-on-metal resurfacing in patients with Crowe type I or II DDH were disappointing with respect to the durability of the femoral component.  However, the fixation of the porous-coated acetabular components without adjuvant fixation was excellent despite incomplete lateral acetabular coverage of the socket.  They stated that more rigorous patient selection and especially meticulous bone preparation are essential to minimize femoral neck fractures and loosening after this procedure.

Li and associates (2008) reported the findings of 21 consecutive patients (26 hips) with osteoarthritis secondary to DDH who underwent metal-on-metal hip resurfacing.  Average age at the time of surgery was 46.5 years (range of 37 to 59 years).  Six patients (28.6 %) were men and 15 (71.4 %) were women.  During the same period, another 21 patients (26 hips) with DDH secondary to osteoarthritis were treated with ceramic-on-ceramic total hip arthroplasty (THA).  Average patient age at the time of surgery was 48.2 years (range of 38 to 64 years).  At follow-up, no complications (e.g., dislocation, infection, or symptomatic deep venous thrombosis) occurred in the 2 groups.  No significant difference was noted in HHS between the 2 groups, but the average range of motion (ROM) of the hip resurfacing group was significantly better than the THA group (p < 0.05).  All patients reported significant pain relief on their operated hips, with the post-operative visual analog scale scores less than 2.  No signs of early loosening were observed on radiographs.  The authors concluded that the short-term results of the metal-on-metal hip resurfacing have been encouraging in the treatment of DDH, with better range of motion recovery than conventional THA.

Wang et al (2008) examined the clinical results of metal-on-metal hip resurfacing arthroplasty for patients with DDH.  A total of 34 cases of DDH (Crowe types I and II) were attempted to have metal-on-metal hip resurfacing arthroplasty.  There were 29 females (32 hips), 5 males (5 hips).  The average age was 45 years old (range of 26 to 57).  Radiographical and clinical evaluations were taken at 6 weeks, 3 months, 1 year and then once-yearly post-operatively.  The average HHS was 35 (range of 25 to 44).  Hip flexion was 101 degrees, abduction 24 degrees, adduction 15 degrees.  Three patients were turned to THA during operations; 31 patients (34 hips) received hip resurfacing surgery.  These 31 patients were followed for an average of 21.4 months (range of 12 to 33 months).  The average HHS was 94 (range of 82 to 100) at the latest follow-up, and there was statistical difference compared with the pre-operative score (p < 0.01).  Hip flexion increased to 133 degrees, abduction to 48 degrees, adduction to 26 degrees.  No radiolucency line was found at both acetabular and femoral sides in all the patients.  The average abduction angle of acetabular cup was 43 degrees (range of 40 to 53), and the average stem shaft angle was 139 degrees (range of 130 to 145).  The authors concluded that the short-term result is excellent.  They stated that mid-term to long-term results for hip resurfacing arthroplasty in patients with DDH are being awaited.

McBryde et al (2008) performed metal-on-metal hip resurfacing for DDH in 96 hips in 85 patients (78 in women and 18 in men) with a mean age at the time of surgery of 43 years (range of 14 to 65).  These cases were matched for age, gender, operating surgeon and date of operation with a group of patients with primary osteoarthritis who had been treated by resurfacing, to provide a control group of 96 hips (93 patients).  A clinical and radiological follow-up study was performed.  The dysplasia group were followed for a mean of 4.4 years (range of 2.0 to 8.5) and the osteoarthritis group for a mean of 4.5 years (range of 2.2 to 9.4).  Of the dysplasia cases, 17 (18 %) were classified as Crowe type III or IV.  There were 5 (5.2 %) revisions in the dysplasia group and none in the osteoarthritic patients.  Four of the failures were due to acetabular loosening and the other sustained a fracture of the neck of femur.  There was a significant difference in survival between the 2 groups (p = 0.02).  The 5-year survival was 96.7 % (95 % confidence interval [CI]: 90.0 to 100) for the dysplasia group and 100 % (95 % CI: 100 to 100) for the osteoarthritic group.  There was no significant difference in the median Oxford hip score between the 2 groups at any time during the study.  The medium-term results of metal-on-metal hip resurfacing in all grades of DDH are encouraging, although they are significantly worse than in a group of matched patients with osteoarthritis treated in the same manner.

Naal and associates (2009) evaluated 24 patients (32 hips; mean age of 44.2 years) after hip resurfacing performed for osteoarthritis secondary to DDH.  These investigators used the HHS, the UCLA activity scale, and a sports and activity questionnaire.  A radiographical analysis also was performed.  They followed patients a minimum of 28 months (mean of 43 months; range of 28 to 60 months).  The HHS improved from a mean of 54.7 to 97.3 and UCLA activity levels increased from a mean of 5.3 to 8.6.  All patients returned to sports activity at a mean of 11 weeks after surface replacement.  There were no major differences in pre-operative and post-operative participation in the most common sports and activities.  Two of the 32 replacements (6 %) failed.  These researchers detected femoral radiolucencies in 10 of the remaining 30 hips.  Despite satisfactory outcomes in clinical scores, return to sports, and hip biomechanics, the failure rate of 6 % was disappointing.  The authors concluded that additional follow-up is important to assess if failure rates increase in these young, active patients.

Prosser and colleagues (2010) stated that the outcome of modern resurfacing remains to be determined.  The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) started collection of data on hip resurfacing at a time when modern resurfacing was started in Australia.  The rate of resurfacing has been higher in Australia than in many other countries.  As a result, the AOANJRR has one of the largest series of resurfacing procedures.  This study was undertaken to determine the results of this series and the risk factors associated with revision.  Data from the AOANJRR were used to analyze the survivorship of 12,093 primary resurfacing hip replacements reported to the Joint Replacement Registry between September 1999 and December 2008.  This was compared to the results of primary conventional THR reported during the same period.  The Kaplan-Meier method and proportional hazards models were used to determine risk factors such as age, sex, femoral component size, primary diagnosis, and implant design.  Female patients had a higher revision rate than males; however, after adjusting for head size, the revision rates were similar.  Prostheses with head sizes of less than 50 mm had a higher revision rate than those with head sizes of 50 mm or more.  At 8 years, the cumulative per cent revision of hip resurfacing was 5.3 (4.6 to 6.2), as compared to 4.0 (3.8 to 4.2) for total hip replacement.  However, in osteoarthritis patients aged less than 55 years with head sizes of 50 mm or more, the 7-year cumulative per cent revision for hip resurfacing was 3.0 (2.2 to 4.2).  Also, hips with dysplasia and some implant designs had an increased risk of revision.  The authors concluded that risk factors for revision of resurfacing were older patients, smaller femoral head size, patients with developmental dysplasia, and certain implant designs.

Hartmann and colleagues (2012) examined if the long-term survival rate of hip resurfacing is comparable to that of conventional THA and certain factors can be identified that influence serum ion concentration 10 years post-operatively.  These investigators specifically assessed
  1. the 10-year survivorship in the whole cohort and in male and female patients,
  2. serum concentrations of metal ions in patients with hip resurfacing who had not undergone revision surgery, and
  3. potential influencing factors on the serum ion concentration. 

These researchers retrospectively reviewed their first 95 patients who had 100 hip resurfacings performed from 1998 to 2001.  The median age of the patients at surgery was 52 years (range of 28 to 69 years); 49 % were men.  They assessed the survival rate (revision for any reason as the end point), radiographical changes, and serum ion concentrations for cobalt, chromium, and molybdenum.  The correlations between serum ion concentration and patient-related factors (age, sex, body mass index [BMI], activity) and implant-related factors (implant size, cup inclination, stem-shaft angle) were investigated.  The minimum follow-up was 9.3 years (mean of 10 years; range of 9.3 to 10.5 years).  The 10-year survivorship was 88 % for the total cohort.  The overall survival rate was greater in men (93 %) than in women (84 %).  Median serum ion levels were 1.9 μg/L for chromium, 1.3 μg/L for cobalt, and 1.6 μg/L for molybdenum.  Radiolucent lines around acetabular implants were observed in 4 % and femoral neck thinning in 5 %.  The authors concluded that although their overall failure rate was greater than anticipated, the relatively low serum ion levels and no revisions for pseudotumors in young male patients up to 10 years post-operatively provide some evidence of the suitability of hip resurfacing in this subgroup.

Vendittoli et al (2013) compared metal-on-metal hip resurfacing with 28-mm diameter metal-on-metal THR.  A total of 219 hips in 192 patients aged between 18 and 65 years were randomized to 28-mm metal-on-metal uncemented THRs (107 hips) or hybrid hip resurfacing (HR, 112 hips).  At a mean follow-up of 8 years (6.6 to 9.3), there was no significant difference between the THR and HR groups regarding rate of revision (4.0 % (4 of 99) versus 5.8 % (6 of 104), p = 0.569) or re-operation rates without revision (5.1 % (5 of 99) versus 2.9 % (3 of 104), p = 0.428).  In the THR group, 1 recurrent dislocation, 2 late deep infections and 1 peri-prosthetic fracture required revision, whereas in the HR group 5 patients underwent revision for femoral head loosening and 1 for adverse reaction to metal debris. The mean University of California, Los Angeles activity scores were significantly higher in HR (7.5 (S.D. 1.7) versus 6.9 (S.D. 1.7), p = 0.035), but similar mean Western Ontario and McMaster Universities Osteoarthritis Index scores were obtained (5.8 (S.D. 9.5) in HR versus 5.1 (S.D. 8.9) in THR, p = 0.615) at the last follow-up.  Osteolysis was found in 30 of 81 THR patients (37.4 %), mostly in the proximal femur, compared with 2 of 83 HR patients (2.4 %) (p < 0.001).  At 5 years the mean metal ion levels were less than 2.5 μg/L for cobalt and chromium in both groups; only titanium was significantly higher in the HR group (p = 0.001).  The authors concluded that although revision rates and functional scores were similar in both groups at mid-term, long-term survival analysis is needed to determine whether one procedure is more advantageous than the other.

While traditional THR involves removing the head and neck of the femur, surface replacement preserves this bone.  With a traditional THR, after this bone is removed, a prosthetic ball attached with a stem is inserted within the thigh bone.  For surface replacement arthroplasty (SRA) of the hip, only the joint surfaces are removed during surgery, most of the normal bone is preserved, the medullary canal is not opened, and the implants utilized are of small volume (Wagner, 1978)

Schachter and Lamont (2009) stated that treatment of the young patient with degenerative disease of the hip has historically been a difficult problem for the orthopedist; THA in the young patient has generally produced inferior results as compared to older patients; SRA was initially developed over 50 years ago to treat degenerative disease of the hip.  It has regained enthusiasm over the last 10 to 15 years as an alternative to THA for the treatment of degenerative disease of the hip in younger patients.  The modern metal-on-metal bearing provides improved wear characteristics over its metal-on-polyethylene predecessor.  Multiple studies have demonstrated mid-term results of metal-on-metal SRA, which are comparable to THA.  The authors concluded that the long-term survival data of SRA remains to be seen, as does the long-term effect of elevated levels of metal ions in the serum, urine, and lymphatics.  These investigators stated that further research needs to be conducted regarding the effects of metal ions, vascular insult, and comparative studies with THA using comparable bearing surfaces.

Laaksonen and associates (2017) examined the main findings of clinical studies that have evaluated outcomes of the articular surface replacement (ASR) Hip System.  These investigators performed a systematic literature search to identify all articles published between January 2008 and June 2015 that included ASR hip resurfacing arthroplasty (ASR HRA) or ASR THA (ASR XL THA) outcomes according to the PRISMA statement.  A total of 56 studies were assessed.  The prevalence of adverse local tissue reactions (ALTRs) and revision rates were found to be high; ALTR prevalence varied from 12.5 % to 69 % (mean of 33.5 %).  Mean revision rate for any reason at 4-year to 7-year follow-up was 13.8 % (range of 5.6 % to 31%) for ASR HRA and 14.5 % (range of 0 % to 37 %) for ASR XL THA.  Femoral head size of less than 53 mm was found to correlate with higher blood metal ion levels.  Femoral head size  of greater than 44 mm was not associated with higher ALTR prevalence or revision rates in ASR XL THA.  High blood metal ion levels (greater than 7 μg/L cobalt (Co), greater than 7 μg/L chromium (Cr)) were associated with higher failure rates and bearing-related complications.  The role of cup positioning was found to be controversial.  The authors concluded that ALTR prevalence and failure rates were high.  High blood metal ion levels were a risk factor for ALTR and failure.  Surprisingly, the role of cup positioning and large femoral head size in ASR XL THA were controversial.  These findings should be considered in the clinical follow-up and risk stratification of patients with the ASR Hip System.

Sibia and King (2018) stated that the ASR mono-block metal-on-metal acetabular component was recalled due to a higher than expected early failure rate.  In a retrospective, single-center, single-surgeon study, these investigators evaluated the survivorship of the device and variables that may be predictive of failure at a minimum of 5-year follow-up.  This review was conducted in patients who received the DePuy Synthes ASR XL acetabular hip system from December 2005 to November 2009.  Mean values and percentages were calculated and compared using the Fisher's exact test, simple logistic regression, and Student's t-test.  The significance level was p ≤ 0.05.  This study included 29 patients (24 men, 5 women) with 32 ASR XL acetabular hip systems.  Mean age and BMI were 55.2 years and 28.9 kg/m², respectively.  Mean post-operative follow-up was 6.2 years.  A total of 2 patients (6.9 %) died of an unrelated cause and 1 patient was lost to follow-up (3.4 %), leaving 26 patients with 28 hip replacements, all of whom were available for follow-up.  The 5-year revision rate was 34.4 % (10 patients with 11 hip replacements).  Mean time to revision was 3.1 years.  Age (p = 0.76), gender (p = 0.49), BMI (p = 0.29), acetabular component abduction angle (p = 0.12), and acetabulum size (p = 0.59) were not associated with the increased rate for hip failure.  Blood cobalt (7.6 versus 6.8 µg/L, p = 0.58) and chromium (5.0 versus 2.2 µg/L, p = 0.31) levels were not significantly higher in the revised group when compared with those of the unrevised group.  In the revised group, a 91 % decrease in cobalt and 78 % decrease in chromium levels were observed at a mean of 6 months following the revision.  The authors concluded that this study demonstrated a high rate of failure of ASR acetabular components used in THA at a minimum of 5 years of follow-up.  In the absence of reliable predictors of early failure, continued close clinical surveillance and laboratory monitoring of these patients are needed.  Moreover, these investigators noted that metal levels dropped quickly after revision, and the revision surgery can generally be performed with slightly larger primary components.  Symptomatic patients with ASR hip replacements, regardless of blood metal-ion levels, were candidates for the revision surgery; and not all failed hips exhibited substantially elevated metal levels.  Asymptomatic patients with high blood metal-ion levels should be closely followed-up and revision surgery should be strongly considered, consistent with recently published guidelines.

Hellman and colleagues (2019) noted that SRA, compared with traditional THA, is more expensive and carries unique concern related to metal ions production and hypersensitivity.  Additionally, SRA is a more demanding procedure with a decreased margin for error compared with THA.  To justify its use, SRA must demonstrate comparable component survival and some clinical advantages.  These researchers carried out a systematic review to examine the differences in complication rates, patient-reported outcomes, stress shielding, and hip biomechanics between SRA and THA.  A systematic review of the literature was completed using Medline and Embase search engines.  Inclusion criteria were level-I to level-III articles that reported clinical outcomes following primary SRA compared with THA.  An initial search yielded 2,503 potential articles for inclusion.  Exclusion criteria included review articles, level-IV or level-V evidence, less than 1 year's follow-up, and previously reported data.  A total of 27 articles with 4,182 patients were available to analyze.  Fracture and infection rates were similar between SRA and THA, while dislocation rates were lower in SRA compared with THA; SRA demonstrated equivalent patient-reported outcome scores with greater activity scores and a return to high-level activities compared with THA; SRA more reliably restored native hip joint biomechanics and decreased stress shielding of the proximal femur compared with THA.  The authors concluded that in young active men with osteoarthritis (OA), there was evidence that SRA offered some potential advantages over THA, including: improved return to high-level activities and sport, restoration of native hip biomechanics, and decreased proximal femoral stress shielding.  These investigator stated that continued long-term follow-up is needed to evaluate ultimate survivorship of SRA.

In a randomized study with 15 years of follow-up, Vendittoli and colleagues(2020) compared clinical scores and revision and complication rates after HR with those after THA.  A total of 203 hips were randomized to 28-mm metal-on-metal (MoM) THA (99 hips) or to HR (104 hips).  Main outcome measures compared between groups were the WOMAC score, the revision rate, and the complication rates.  The radiographic findings were also assessed.  After a mean follow-up of 15 years (range of 14 to 16 years), 9 (4.4 %) of the 203 patients were lost to follow-up and 15 (7.4 %) had died.  The Kaplan-Meier survivorship, with revision for any reason as the end-point, was 89.2 % (95 % CI: 82.3 % to 96.1 %) for HR and 94.2 % (95 % CI: 89.3 % to 99.1 %) for THA (p = 0.292).  The reasons for revision included infection (3 patients), recurrent dislocation (1 patient), and adverse reaction to metal debris (ARMD) (1 patient) in the THA group and ARMD (2 patients) and femoral head loosening (7 patients) in the HR group.  With aseptic revision as the end-point, the Kaplan-Meier survivorship was significantly higher in the THA group (97.4 % versus 89.2 %; p = 0.033).  No dislocation occurred in the HR group compared with 4 in the THA group (p = 0.058).  Both groups achieved a similar mean WOMAC score (10.7 in the HR group and 8.8 in the THA group; p = 0.749), FJS (87.1 and 85.3, respectively; p = 0.410), UCLA activity score (6.3 and 6.4, respectively; p = 0.189), and overall joint perception (p = 0.251).  The authors concluded that the specific HR and MoM 28-mm THA implants used in this study showed good long-term survival and function.  The overall rates of complications and revisions were similar in both groups but were of different types.  These investigators stated that as it provided better femoral bone preservation and biomechanical reconstruction, HR may continue to have a role in selected patients when performed by experienced surgeons and using validated implants.

Shoulder Resurfacing

Shoulder resurfacing arthroplasty was designed as a possible alternative to conventional total shoulder replacement and reportedly replaces a smaller portion of the humeral head than the conventional shoulder replacement surgery. Supposedly, this procedure is viewed as a potential alternative for people who are younger, physically active and have advanced or end stage degenerative joint disease or arthritis. Total shoulder replacement is not an option for rotator cuff tear that is not repairable. An example of an FDA-approved device for shoulder resurfacing arthroplasty includes, but may not be limited to, the Copeland resurfacing head.

Shoulder resurfacing is a more conservative approach to conventional total shoulder replacement (TSR) surgery for the treatment of glenohumeral arthritis, humeral head fractures, and osteochondral lesions.  It is being explored as an option for shoulder replacement, especially in younger, more active adults.  Resurfacing replaces only the damaged or diseased part of the humeral head instead of the entire joint.  During shoulder resurfacing, the humeral head is re-shaped and replaced with a metal covering, or cap, thus preserving the bone of the proximal part of the humerus.  Shoulder resurfacing can be performed with devices that provide complete or partial coverage and can be done alone (hemi-resurfacing) or in combination with glenoid replacement (total shoulder resurfacing).  If the glenoid is replaced, a polyethylene glenoid replacement prosthesis or an interposed soft-tissue graft is used.  Shoulder resurfacing is potentially less traumatic, less invasive, and preserves more bone.  Since the bone stock has been maintained, revision to a conventional TSR can be undertaken, if needed.

Several prosthetic designs are currently available in the United States.  The implants are constructed from cobalt-chromium or a titanium-alloy.  Some have a ceramic surface coating, while others provide a titanium porous coating on the undersurface where the implant rests against the bone. Examples of brands of shoulder resurfacing include Copeland Extended Articulating Surface (EASTM) Resurfacing Heads, DePuy Global Cap, CTA Resurfacing Shoulder Humeral Head, Axiom Shoulder Resurfacing System, and HemiCAP (also referred to as Contoured Articular Prosthetic (CAP) Humeral Head Resurfacing Prothesis).

The Interlok/HA Copeland Resurfacing Heads (Biomet, Inc., Warsaw, IN) received 510(k) marketing clearance from the U.S. Food and Drug Administration in 2001.  These devices are intended for uncemented use and are designed to maintain maximum bone stock by removing minimal bone and replacing only the defective surface.  The spherical humeral heads contain a tapered, fluted stem for fixation with an interlok and a hydorxyapatite surface finish to the stem and inside spherical radius. 

Levy and Copeland (2001) reported their experience using the Copeland Mark-2 prosthesis (Biomet, Inc., Warsaw, IN) during cementless surface replacement arthroplasty in a case-series study of 103 treated shoulders with a mean follow-up of 6.8 years.  The authors reported that 93.9 % of the patients considered their shoulder to be much better or better than before the operation.  Radiological review showed no evidence of radiolucency in 61 of 88 humeral implants (69.3 %).  Eight shoulders required revision (7.7 %), 5 of which were revised to a stemmed humeral component.  Mild subluxation of the humeral head was observed in 15 shoulders, moderate superior migration was observed in 7, and severe superior subluxation with obliteration of the acromiohumeral interval was observed in 8.

In another case-series study of the Copeland prosthesis by the same investigators (Levy and Copeland, 2004), 79 cementless surface replacement arthroplasties (total shoulder resurfacing = 42, hemiarthroplasty = 37) were performed for primary osteoarthritis of the shoulder.  The mean follow-up was 7.6 years (range of 48 months to 13 years) for total shoulder resurfacing and 4.4 years (range of 24 months to 6.5 years) for hemiarthroplasty.  The investigators reported that 89.9 % of the patients considered the shoulder to be much better or better as a result of the operation.  Radiological review showed 1 humeral implant and 3 glenoid implants had evidence of loosening.  Four revisions were performed in the total shoulder resurfacing group.  No revision surgery was needed in the hemiarthroplasty group.

A case-series study (52 patients, 56 shoulders) by Thomas et al (2005) of humeral head surface replacement hemiarthroplasty using the Copeland prosthesis for treatment of osteoarthritis (n = 20), rheumatoid arthritis (n = 26), rotator cuff arthropathy (n = 1), and post-traumatic arthrosis (n = 1) with a mean follow-up of 34 months (mean age of 68 years) reported comparable results to Copeland's series.

These small case-series reports with the Copeland prosthesis indicated that most patients experienced improvements in motion, pain, and strength in the short- and mid-term; however, overlap in patients between the same investigators is likely and there are no randomized controlled studies comparing outcomes to traditional shoulder replacement surgery.

Fuerst et al (2007, 2008) evaluated the mid-term results of the DUROM cup (Zimmer, Switzerland) surface replacement in a cohort of 35 patients (42 shoulders) with rheumatoid arthritis affecting the glenohumeral joint.  Thirty-five shoulders in 29 patients (average age of 61.4 years) were evaluated prospectively after an average follow-up period of 73 months.  The mean Constant score for the 35 shoulders increased from 20.8 points pre-operatively to 64.3 points at a mean of 73.1 months post-operatively.  There were 3 revisions:
  1. to replace an implant that was too large,
  2. to treat glenoid erosion, and
  3. due to loosening of the implant. 

Over the 5-year follow-up period, proximal migration of the cup increased in 63 % of the shoulders, and the glenoid depth increased in 31 %.  The authors concluded that these mid-term results of the cemented DUROM cup are very encouraging and that the advantage of cup arthroplasty is the less complex bone-sparing surgery and in the event of failure of the implant, other reliable salvage options remain.

Buchner et al (2008) compared short-term functional results after cementless surface replacement of the humeral head (CUP) with those obtained after TSR for osteoarthritis of the shoulder.  A total of 22 patients (average age of 61.4 years) with primary osteoarthritis who obtained surface replacement of the humeral head were compared to a control group of 22 TSR patients (average age of 61.1 years).  Patients in the CUP group showed significantly better peri-operative results (time of surgery, blood loss, days of in-patient treatment) compared to the patients in the TSR group.  Both groups showed significant improvement in clinical function and pain reduction and had high subjective satisfaction rates; however, the TSR group showed a statistically significant improvement in mobility, abduction, and range of motion compared to the CUP group at 12 months.  Two CUP implants had to be removed during the follow-up period owing to secondary glenoidal erosion.  The authors concluded that at short-term follow-up, surface replacement is technically less demanding and provided only slightly inferior results to TSR.

Raiss et al (2010) reported the results from a prospective study of cementless humeral surface replacement arthroplasty in 23 patients (26 implants) less than 55 years of age treated with cementless humeral surface replacement with a mean follow-up of 2.5 years.  Ten patients had post-traumatic osteoarthritis, 7 had primary osteoarthritis, and 6 had osteonecrosis.  Patients were evaluated using the Constant score, shoulder motion, and subjective satisfaction.  The mean Constant score increased significantly from 33 points pre-operatively (8 to 69 points) to 61 points post-operatively (25 to 83 points; p < 0.0001), adjusted to age and gender from 38 % (8 to 86 %) to 70 % (28 to 114 %; p < 0.0001).  Significant improvement for the whole cohort was found regarding patients' pain, activity, mobility, shoulder flexion and abduction, and internal and external rotation (p < 0.001).  In 1 case, re-operation was necessary due to a superficial wound infection, and in another case, implant revision to a TSR was performed because of glenoid erosion.  The authors concluded that cementless humeral surface replacement arthroplasty is a viable bone-preserving treatment option for young and active patients and that later conversion to TSR is possible; however, long-term investigations are necessary to confirm these observations.

Biological glenoid resurfacing with or without prosthetic humeral head replacement has been suggested as a means to avoid the potential complications of polyethylene use in younger patients with glenohumeral arthritis.  A variety of biologic surfaces, including anterior capsule, autogenous fascia lata, and Achilles tendon allograft, have been used; however, there is little evidence in the peer-reviewed literature that these biological grafts can provide a durable bearing surface over time.  Poor clinical outcomes related to persistent post-operative infection have also been reported (Elhassan et al, 2009).

de Beer and colleagues (2010) analyzed the intermediate-term findings of arthroscopic debridement and biological resurfacing of the arthritic glenoid in a middle-aged population using an acellular human dermal scaffold.  Between 2003 and 2005, a total of 32 consecutive patients underwent an arthroscopic debridement and biological glenoid resurfacing for glenohumeral arthritis.  The diagnoses included primary osteoarthrosis (n = 28), arthritis after arthroscopic reconstruction for anterior instability (n = 1) and inflammatory arthritis (n = 3).  All shoulders were assessed clinically using the Constant and Murley score, and results graded according to Neer's criteria.  Statistical analysis was performed to determine significant parameters and associations.  A significant improvement (p < 0.0001) in each parameter of the subjective evaluation component (severity of pain, limitation in daily living and recreational activities) of the Constant score was observed.  The Constant and Murley score increased significantly (p < 0.0001) from a median of 40 points (range of 26 to 63) pre-operatively to 64.5 (range of 19 to 84) at the final assessment.  Overall, the procedure was considered as "successful outcome" in 23 patients (72 %) and as a "failure" in 9 patients (28 %).  According to Neer's criteria, the result was categorized as excellent in 9 (28 %), satisfactory in 14 (44 %) and unsatisfactory in 9 (28 %).  Within the unsatisfactory group, there were 5 conversions to prosthetic arthroplasty.  A standard magnetic resonance imaging was performed on 22 patients in the successful outcome group; glenoid cartilage was identified in 12 (thick in 5, intermediate in 1, thin in 6) and could not be identified in 10 patients (complete/incomplete loss in 5, technical difficulties in 5).  Overall, 5 complications included transient axillary nerve paresis, foreign-body reaction to biological material, inter-layer dissociation, mild chronic non-specific synovitis and post-traumatic contusion.  Dominance of affected extremity and generalized disease (diabetes, rheumatoid arthritis, generalized osteoarthritis) was associated with an unsatisfactory outcome (p < 0.05).  The authors cocnluded that arthroscopic debridement and biological resurfacing of the glenoid is a minimally invasive therapeutic option for pain relief, functional improvement and patient satisfaction in glenohumeral osteoarthritis, in the intermediate-term.  Long-term data are needed to ascertain the value of shoulder resurfacing.

Elser et al (2010) discussed surgical decision making and up-to-date summaries of the current techniques available to treat both focal chondral defects and more massive structural osteochondral defects of the shoulder.  These techniques include microfracture, osteoarticular transplantation (osteochondral autograft transfer system [OATS]), autologous chondrocyte implantation, bulk allograft reconstruction, as well as biologic resurfacing.  The authors stated that as new approaches to glenohumeral cartilage repair and shoulder joint preservation evolve, there continues to be a heightened need for collaborative research and well-designed outcomes analysis to facilitate successful patient care.

While shoulder resurfacing appears to be a promising new procedure for the treatment of glenohumeral arthritis, humeral head fractures, and osteochondral lesions, long-term data from randomized controlled studies are lacking.  Further studies to assess the long-term outcomes and to evaluate alternative surface bearing materials, especially on the glenoid side are needed.

Gobezie et al (2011) noted that the treatment of advanced, bipolar glenohumeral osteoarthritis in the young patient is particularly challenging because of the expected failure of a traditional shoulder arthroplasty within the patient's lifetime.  These investigators have had early success performing osteochondral allograft resurfacing of the humeral head articular surface and glenoid articular surface, and they described a new all-arthroscopic technique for performing this procedure.  In the context of their new procedure, these researchers have reviewed the available literature on the topic of biologic resurfacing with osteochondral allograft and have provided an overview of the relevant findings.  Although only short-term follow-up data are available, their results in young patients have been promising in terms of regained motion, minimal pain, and accelerated rehabilitation.  The authors believed that this new arthroscopic biologic shoulder resurfacing technique has the potential to be superior to other available treatments for this patient population because it preserves bone stock, limits damage to surrounding structures, and allows for early rehabilitation.  They stated that although longer-term follow-up is needed, early results have been greatly encouraging.

Longo et al (2011) stated that young patients with degenerative shoulder disease are a therapeutic challenge.  To try to delay a shoulder arthroplasty, biological interpositional arthroplasty has been proposed to provide a biologically active bearing surface that could eventually results in the formation of fibrocartilage, fibrous tissue, or hyaline cartilage.  Anterior capsule, autogenous fascia lata, Achilles tendon allograft, lateral meniscus allograft, human dermis, and porcine small intestine submucosa have been used as interposition material, either alone or in combination with a hemiarthroplasty or humeral resurfacing procedure.  Some investigators have reported favorable long-term results, although others have found this procedure unreliable.  Several variables are unknown at present, such as the best biological resurfacing device, healing potential, possible antigenic responses, optimal fixation technique or position, aftercare restrictions.  The authors concluded that further prospective studies with long follow-up are necessary to provide data that will help to define the role of biological glenoid resurfacing in young patients with glenohumeral arthritis.

Lee and colleagues (2013) noted that there is a lack of consensus in treating glenohumeral arthritis in younger patients.  Hemi-arthroplasty has historically been favored because of complications associated with total shoulder arthroplasty.  Biologic resurfacing of the glenoid has been investigated as a potential treatment that would decrease glenoid erosion and pain, the major complications of hemi-arthroplasty.  These investigators reported on 19 shoulders treated with meniscal allograft glenoid resurfacing and shoulder hemi-arthroplasty.  All patients were followed-up for a minimum of 2 years post-operatively (mean of 4.25 years) with Disabilities of the Arm, Shoulder and Hand (DASH), Simple Shoulder Test (SST), and visual analog scale (VAS) scores.  In addition, these researchers compared the outcomes related to pre-operative concentric versus eccentric glenoid wear.  At final follow-up, the mean score for the DASH questionnaire was 28; SST, 8; and VAS, 3.5.  Whereas the eccentric wear group (DASH score, 19.4; SST score, 9.1; VAS score, 2.5) exhibited better shoulder function and pain scores compared with the concentric wear group (DASH score, 37.6; SST score, 8.4; VAS score, 4.1), the difference was not statistically significant (p = 0.098, p = 0.647, and p = 0.198, respectively).  There were 6 complications (32 %), all resulting in repeat surgery.  Three patients underwent total shoulder arthroplasty and 1 shoulder had revision hemi-arthroplasty, whereas synovectomy was performed in another shoulder.  The 6th patient underwent lysis of adhesions and capsular release.  The authors concluded that with long-term follow-up, they have observed that biologic resurfacing of the glenoid with meniscal allograft exhibited inconsistent results and high complication rates.  They stated that strong consideration should be given to performing total shoulder arthroplasty in patients in whom all conservative treatment options have failed.

Merolla and associates (2013) reported clinical and radiographic mid-term outcomes in a population of 60 patients, aged 50 years or younger, who underwent shoulder resurfacing in osteoarthritis.  The mean age was 48 ± 8.4 years, 36 were male and 24 female, dominant arm in 43 cases.  Glenoid arthritis was treated in 36 cases (60 %) using a meniscus allograft in 22 cases, biologic patch in 4 cases and microfractures in 10 cases.  Clinical and radiographic assessment was performed with Constant-Murley score and standard X-ray.  At an average follow-up of 44 months, the mean values of the constant score increased 30 points (p < 0.05), the pain decreased of 4.56 points (p < 0.05) and the Simple Shoulder Test increased 4.3 points (p < 0.05).  These researchers found lower scores (p > 0.05) in 9 patients (15 %) treated for glenoid arthritis using homologous meniscus (7 cases) and biologic patch (2 cases).  A significant narrowing of joint space (5.92 mm post-operative versus 1.65 mm at 37 months) (p < 0.05) was found in the 22 cases treated with meniscus interposition.  In 4 cases with type A2 pre-operative glenoid morphology and in 9 cases type B1; these investigators registered significantly lower scores compared with the overall study population (p < 0.01).  There were 5 unsatisfied patients (7 %) – they underwent meniscus removal and glenoid reaming in 3 cases, and conversion in total shoulder arthroplasty in 2 cases.  The authors concluded that resurfacing arthroplasty is an effective device in young patients with advanced glenohumeral arthropathy; however, the high rate of post-operative glenoid erosion and the failure of biologic allograft lead them to consider glenoid replacement as the best option to improve clinical outcomes.

Sweet and colleagues (2015) stated that humeral head defects such as degenerative disease or avascular necrosis are often treated with stemmed hemi-arthroplasty or total shoulder arthroplasty. Despite its historical and clinical significance, stemmed humeral head replacement poses inherent technical challenges to placing spherical implants at the anatomically correct head height, version, and neck-shaft angle. In a case-series study, these investigators evaluated humeral head inlay arthroplasty as a joint-preserving alternative that maintains the individual head-neck-shaft anatomy. Humeral head inlay arthroplasty also allows intra-operative surface mapping and placement of a contoured articular component that is matched to the patient's defect size, location, and individual surface geometry. This retrospective case series included 19 patients (20 shoulders), with an average age of 48.9 years (range of 32 to 58 years; 3 women and 16 men). Pre-operative diagnoses were osteoarthritis in 16 shoulders and osteonecrosis in 4 shoulders. Pre- and post-operative evaluations included physical examination, radiographic assessment, the American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, the Simple Shoulder Test, a pain VAS, and patient satisfaction rating. The mean follow-up period was 32.7 months (range of 17 to 66 months). The mean American Shoulder and Elbow Surgeons score improved from 24.1 to 78.8, mean Simple Shoulder Test score from 3.95 to 9.3, mean VAS score from 8.2 to 2.1, mean forward flexion from 100° to 129°, and mean external rotation from 23° to 43° (p < 0.001 for all). Radiographic follow-up showed no evidence of peri-prosthetic fracture, component loosening, osteolysis, or device failure. Patient shoulder self-assessment was 90 % poor before surgery and improved to 75 % good-to-excellent at last follow-up; 20 % of patients self-rated as somewhat good-to-somewhat poor, and 5 % self-rated as poor; 90 % of patients were satisfied with the choice of the procedure. Three patients had post-operative complications unrelated to the implants, including a partial rotator cuff tear treated with physical therapy, pre-existing glenoid wear treated with arthroscopic debridement and microfracture, and infection complicated by subscapularis rupture requiring several subsequent surgical procedures but with retention of the implant. The authors concluded that humeral head inlay arthroplasty is effective in providing pain relief, functional improvement, and patient satisfaction. They noted that rather than delaying shoulder arthroplasty to end-stage osteoarthritis, humeral head inlay arthroplasty is a promising new direction in primary shoulder arthroplasty for younger and active patients with earlier stage disease. This retrospective case-series study provided level 4 evidence regarding the clinical value of the HemiCAP implant for shoulder arthroplasty.

Schmidutz and colleagues (2015) noted that cementless-surface-replacement-arthroplasty (CSRA) of the shoulder aims for functional joint restoration with minimal bone loss. Good clinical results have been reported, but due to the radiopaque metal shell no data are available on the structure, osseous integration, and bone stock under the implant. In this study, a total of 14 hemi-CSRAs (4 manufacturers) with 2 geometries (crown [n = 7]/stem [n = 7] fixation) were retrieved from patients undergoing revision due to glenoidal erosion. Histological sections cutting through the implant center and bone were analyzed. Quantitative histo-morphometry evaluated the bone-implant-contact and compared the bone-area to native humeral retrievals (n = 7). The bone-implant-interface was further assessed by scanning-electron-microscopy (SEM) and energy-dispersive-x-ray (EDX). Qualitative histology revealed a reduced and inhomogeneous bone stock. Obvious signs of stress shielding were observed with bone predominantly visible at the stem and implant rim. Quantitative histo-morphometry confirmed the significantly reduced bone-area (9.2 ± 3.9 % [crown 9.9 ± 4.3 %, stem 8.6 ± 3.6 %]) compared to native humeri (21.2 ± 9.1 %; p < 0.05). Bone-implant-contact was 20.5 ± 5.8 % (crown 21.8 ± 6.2 %, stem 19.2 ± 5.6 %), which was confirmed by SEM and EDX. The authors concluded that CRSA showed satisfactory bone ingrowth at the interface suggesting sufficient primary stability to allow osseous integration. Moreover, they stated that clear signs of stress shielding with an inhomogeneous and reduced bone stock were observed; and the impact on the long-term-results is unclear requiring further investigation.

Geervliet and colleagues (2017) reported the mid-term results of the Global C.A.P. uncemented resurfacing shoulder prosthesis (DePuy Synthes).  From January 2007 to December 2009, a total of 48 humeral cementless resurfacing prostheses were performed.  All patients were diagnosed with primary gleno-humeral osteoarthritis (OA).  Patients were contacted for review; the Constant Score, VAS score, Dutch Simple Shoulder Test, SF-12 scores and physical examination were assessed both pre-operatively and yearly post-operatively.  Complications and revision surgery were documented.  Radiographs were evaluated for component size, offset, inclination, height, loosening and subluxation.  A total of 46 patients (12 men) with a mean age of 72 years (range of 59 to 89) were included.  At a mean 6.4-year follow-up (range of 5 to 8), the Constant Score, VAS score and the Dutch Simple Shoulder Test scores improved significantly (p < 0.05) from baseline; 3 patients were lost to follow-up; 1 patient died and 2 patients were not able to attend the follow-up appointments, due to other health-related issues; 11 patients (23 %) had a revision operation.  The authors concluded that the most important findings of this study of the Global C.A.P. shoulder resurfacing arthroplasty were an increase of ROM, a reduction of pain complaints, but a concerning high rate of revision after mid-term follow-up.  Level of Evidence = IV.

In a retrospective, single-center study, Soudy and associates (2017) examined clinical and computed-tomography (CT) outcomes at least 2 years after humeral head resurfacing to treat concentric gleno-humeral OAs.  This study included 40 Copeland and 65 Aequalis humeral resurfacing heads implanted between 2004 and 2012.  Mean patient age at diagnosis was 64 years.  The diagnoses were OA with an intact (68 %) or torn (21 %) rotator cuff, avascular necrosis (5 %), OA complicating chronic instability (3 %), post-traumatic OA (2 %), and chronic inflammatory joint disease (1 %).  Validated clinical scores, radiographs, and CT before surgery and at last follow-up were compared.  During the mean follow-up of 56 months, complications occurred in 24 implants.  Revision surgery with reverse shoulder replacement was required in 18 cases, after a mean of 43.6 months, to treat glenoid wear or a rotator cuff tear.  At last follow-up, for the implants that did not require revision surgery, the mean Constant score was 64/100.  The implants had a mean varus of 5° and mean retroversion of -13.3°.  The mean increase in glenoid cavity depth was 2.4 mm.  Mean increases in medial and lateral humeral offset were 1.9 mm and 2.7 mm, respectively.  Pre-operative factors significantly associated with failure were rotator cuff tear (p = 0.017) and glenoid erosion (p = 0.001).  The authors found a high failure rate related to glenoid wear or progressive rotator-cuff impairment, although CT showed no evidence of implant mal-position or over-stuffing.  Previous studies of stemmed humeral head implants showed better outcomes.  They concluded that given the low medium-term prosthesis survival rate, they now reserve humeral head resurfacing for concentric OA without glenoid erosions or rotator cuff damage.  Level of Evidence = IV.

Knee / Partial Knee / Patellar Resurfacing

Knee resurfacing arthroplasty was designed as an alternative to conventional total knee replacement. Reportedly, these devices do not require that bone tissue be removed. This technology is purportedly viewed as an alternative for individuals who are:

  • Between 40 and 60 years
  • Have early stage osteoarthritic damage which is confined to the inside of the knee
  • Overweight
  • Physically active.

Examples of FDA-approved knee resurfacing systems include, but may not be limited to, the HemiCAP patello-femoral resurfacing prosthesis and the UniCAP compartmental resurfacing implant system.

The UniCAP Bipolar Knee Resurfacing System (Arthrosurface, Inc., Franklin, MA) was introduced in 2008 as an alternative to allow for a delay in traditional joint replacement procedures. It utilizes intraoperative, 3-dimensional joint surface mapping to fit and implant defect-sized components that are matched to the individual joint surface (Miniaci, 2014).

Available evidence for focal resurfacing of the knee joint is limited to small studies without internal comparison groups and with limited followup. The Work Loss Data Institute’s guideline on “Knee & leg (acute & chronic)” (2013) listed focal joint resurfacing (Arthrosurface HemiCAP/UniCAP) as one of the interventions that were considered, but not recommended.

Dhollander et al (2015) described the clinical and radiographical outcome of the HemiCAP resurfacing system as a salvage treatment for a failed index cartilage procedure.  A total of 14 patients were treated consecutively and clinically prospectively followed for a mean period of 26.1 ± 12.8 months.  All patients were previously treated for their cartilage lesion.  Radiographical data were analyzed based on the Kellgren and Lawrence system.  The patients involved in this study demonstrated a gradual clinical improvement in time.  However, radiographically significant osteoarthritic changes were observed during the follow-up period.  The position of the HemiCAP® resurfacing system was adequate in all cases, and no signs of loosening were observed during the follow-up period.  The authors concluded that the HemiCAP resurfacing system is feasible as a salvage treatment for a failed index cartilage procedure and resulted in a gradual clinical improvement.  However, the favorable clinical outcome was not confirmed by the radiographical findings.

Imhoff et al (2015) prospectively evaluated the clinical, radiographic, and sports-related outcomes at 24 months after isolated and combined patellofemoral inlay resurfacing (PFIR).  Between 2009 and 2010, 29 consecutive patients with patellofemoral osteoarthritis (OA) were treated with the HemiCAP Wave Patellofemoral Resurfacing System. Based on preoperative findings, patients were divided into 2 groups: group I, isolated PFIR (n = 20); and group II, combined PFIR with concomitant procedures to address patellofemoral instability, patellofemoral malalignment, and tibiofemoral malalignment (n = 9).  Patients were evaluated preoperatively and at 24 months postoperatively.  Clinical outcomes included the Western Ontario and McMaster Universities Arthritis Index (WOMAC), subjective International Knee Documentation Committee (IKDC), pain VAS, Tegner activity score, and a self-designed sports questionnaire.  Kellgren-Lawrence grading was used to assess progression of tibiofemoral OA.  The Caton-Deschamps Index was used to assess differences in patellar height.  The investigators reported that 27 patients (93 %) were available for 24-month follow-up; 81 % of the patients were either satisfied or very satisfied with the overall outcome.  Significant improvements in the WOMAC, subjective IKDC, and Pain VAS were seen in the overall patient cohort and in both subgroups.  The median Tegner score and sports frequency showed a significant increase in the overall patient cohort and in group II.  The number of sports disciplines increased significantly in both subgroups.  No significant progression of tibiofemoral OA or changes in patellar height were observed.

Bollars et al (2012) reported on a consecutive case series of 27 patients treated with the Arthrosurface HemiCAP Focal Femoral Condyle Resurfacing Prosthesis between 2004 and 2008.  Outcome measures included the Knee Injury and OA Outcome Score (KOOS), IKDC, Hospital for Special Surgery Knee Score (HSS) and WOMAC as well as physical and radiographic evaluation.  The investigators reported that 19 patients met the inclusion/exclusion criteria, 18 were available for review at a median follow-up of 34 months (range of 20 to 57).  The median age was 49 years (range of 43 to 78); 63 % had early arthritis, 5.2 % localized osteonecrosis, and 31.6 % had a focal traumatic full thickness defect.  The follow-up total WOMAC score averaged 90.1 ± 9.3.  The KOOS showed very good to excellent scores in all domains and also when compared to age-matched normative data.  Significant improvement was seen with the HSS Score.  On IKDC examination, 83.4 % had normal or nearly normal results.

Marcacci et al (2011) presented preliminary clinical and radiographic results in a case series of 13 consecutive patients who received  arthroscopic-assisted focal resurfacing of medial tibio-femoral compartment.  Mean follow-up was 29 months.  All patients were treated with the presented procedure for Ahlback grade 3 medial compartment OA.  Subjective evaluation was based on a VAS for pain self-assessment.  Objective clinical evaluation was based on Hospital for Special Surgery score.  Range of motion was evaluated with a manual goniometer.  Radiographic evaluation compared hip-knee-ankle angle pre- and post-operatively.  The investigators stated that clinical and functional results were satisfactory.  Hospital for Special Surgery score and visual analog scale for pain self-assessment showed significant improvements (p < 0.0001 and p = 0.0002, respectively).  Range of motion and axial alignment were not significantly different respect to pre-operative values.

Makoplasty partial knee resurfacing is used for knee osteoarthritis that affects only 1 or 2 components of the knee.  However, there is insufficient evidence that Makoplasty improves health outcomes in patients undergoing knee surgery.

In a pilot study, Lonner et al (2010) compared the post-operative radiographical alignment of the tibial component with the pre-operatively planned position in 31 knees in 31 consecutive patients undergoing unicompartmental knee arthroplasty (UKA) using robotic arm-assisted bone preparation and in 27 consecutive patients who underwent unilateral UKA using conventional manual instrumentation to determine the error of bone preparation and variance with each technique.  Radiographically, the root mean square error of the posterior tibial slope was 3.1 degrees when using manual techniques compared with 1.9 degrees when using robotic arm assistance for bone preparation.  In addition, the variance using manual instruments was 2.6 times greater than the robotically guided procedures.  In the coronal plane, the average error was 2.7 degrees +/- 2.1 degrees more varus of the tibial component relative to the mechanical axis of the tibia using manual instruments compared with 0.2 degrees +/- 1.8 degrees with robotic technology, and the varus/valgus root mean square error was 3.4 degrees manually compared with 1.8 degrees robotically.  The authors concluded that further study is needed to examine if a reduction in alignment errors of these magnitudes will ultimately influence implant function or survival.

Werner et al (2014) stated that in comparison with standard surgical techniques robotic-assisted surgery has the advantages of increased surgical accuracy, reproducibility, optimization of component position, and improved patient outcomes in UKA and THA procedures.  The MAKO Tactile Guidance System (TGS; MAKO Surgical Corp, Fort Lauderdale, FL) facilitates robotic-assisted arthroplasty procedures currently implemented in many operating rooms.  The benefits of this technology are evident, but have not been shown to improve patient outcomes and justify the added financial burden imposed.  The authors concluded that further research is needed to determine if this technological advancement will translate into improvements in longevity and clinical outcomes.

Hansen et al (2014) performed a retrospective review in a matched group of patients on the use of robotic-assisted UKA implantation versus UKA performed using standard operative techniques to assess differences between procedures.  While both techniques resulted in reproducible and excellent outcomes with low complication rates, the results demonstrate little to no clinical or radiographic difference in outcomes between cohorts.  Average operative time differed significantly with, and average of 20 minutes greater in, the robotic-assisted UKA group (p = 0.010).  The minimal clinical and radiographic differences lend to the argument that it is difficult to justify the routine use of expensive robotic techniques for standard medial UKA surgery, especially in a well-trained, high-volume surgeon.  The authors concluded that further surgical, clinical and economical study of this technology is needed.

An assessment by the Canadian Agency for Drugs and Technologies in Health (CADTH, 2011) concluded that there is insufficient evidence regarding the clinical effectiveness, safety, and impact of the use of the MAKO’s RESTORIS line of implants and the MAKOplasty procedure.

The ECRI Institute (2013) found insufficient published clinical evidence that addresses how well the MAKOplasty robotic-assisted partial knee resurfacing procedure works for patients with early to mid-stage osteoarthritis. In addition, they found insufficient published clinical study results to indicate whether the MAKOplasty procedure is better or worse than alternative procedures for patients with early to mid-stage osteoarthritis.

In a prospective study, Eshnazarov and co-workers (2016) compared radiological outcomes after total knee arthroplasty (TKA) with or without patellar resurfacing in patients with grade IV osteoarthritis on patella-femoral joint. A total of 123 cases with Kellgren-Lawrence grade IV osteoarthritis on patella-femoral joint were enrolled for this study.  At the operating room, they were randomly assigned to undergo patella resurfacing (62 cases) or patella retention (61 cases).  Among them, 114 cases that could be followed for more than 2 years were included in this study (resurfacing group; 59 cases, retention group; 55 cases).  Pre-operative and post-operative radiological outcomes (mechanical femoro-tibial angle, patellar tilt and congruence angles) were evaluated and compared between 2 groups.  Pre-operative radiological measures showed insignificant difference between patellar tilt (p = 0.13), mechanical femoro-tibial angles (p = 0.62) and congruence angle (p = 0.37).  Despite the difference performed methods of surgery, post-operative radiological assessment outcomes between 2 groups were almost identical  -- patellar tilt (p = 0.47), mechanical femoro-tibial angles (p = 0.34) and congruence angle (p > 0.05).  The authors stated that the almost the same satisfactory radiological outcomes obtained after patella resurfacing and retention groups after TKA allowed them to conclude that, primary TKA without patella resurfacing is a good therapeutic option in patients with high-grade osteoarthritis of the patella-femoral joint.

Aunan et al (2016) noted that recent research on outcomes after TKA has raised the question of the ability of traditional outcome measures to distinguish between treatments. In a single-center, randomized, double-blind study, these researchers compared functional outcomes in patients undergoing TKA with and without patellar resurfacing, using the KOOS as the primary outcome and 3 traditional outcome measures as secondary outcomes.  A total of 129 knees in 115 patients (mean age of 70 years; range of 42 to 82; 67 females) were evaluated.  Data were recorded pre-operatively, at 1 year, and at 3 years, and were assessed using repeated-measures mixed models.  The mean sub-scores for the KOOS after surgery were statistically significantly in favor of patellar resurfacing: sport/recreation, knee-related quality of life, pain, and symptoms.  No statistically significant differences between the groups were observed with the Knee Society clinical rating system, with the Oxford knee score, and with VAS for patient satisfaction. The authors concluded that in the present study, the KOOS, but no other outcome measure used, indicated that patellar resurfacing may be beneficial in TKA.

Ali and colleagues (2016) stated that knee pain after TKA is not uncommon. Patellar retention in TKA is one cause of post-operative knee pain, and may lead to secondary addition of a patellar component. Patellar resurfacing in TKA is controversial.  Its use ranges from 2 % to 90 % worldwide.  In this randomized study, these investigators compared the outcome after patellar resurfacing and after no resurfacing.  They performed a prospective, randomized study of 74 patients with primary osteoarthritis who underwent a Triathlon CR TKA.  The patients were randomized to either patellar resurfacing or no resurfacing.  They filled out the VAS pain score and KOOS questionnaires preoperatively, and VAS pain, KOOS, and patient satisfaction 3, 12, and 72 months post-operatively.  Physical performance tests were performed pre-operatively and 3 months post-operatively.  The authors found similar scores for VAS pain, patient satisfaction, and KOOS 5 subscales at 3, 12, and 72 months post-operatively in the 2 groups.  Physical performance tests 3 months post-operatively were also similar in the 2 groups.  No secondary resurfacing was performed in the group with no resurfacing during the first 72 months.  The authors concluded that patellar resurfacing in primary Triathlon CR TKA is of no advantage regarding pain, physical performance, KOOS 5 subscales, or patient satisfaction compared to no resurfacing.  None of the patients was re-operated with secondary addition of a patellar component within 6 years.  They noted that according to these results, routine patellar resurfacing in primary Triathlon TKA appears to be unnecessary.

van Jonbergen et al (2016) noted that when secondary patellar resurfacing is performed, a uniformly and widely used scoring system that is validated for anterior knee pain caused by a retro-patellar degeneration will give more insight into the results of this procedure. The cause of anterior knee pain following TKA is not always related to the patella itself.  Other causes have been identified (e.g., an insufficient posterior cruciate ligament in the case of a posterior cruciate-retaining TKA or an internally rotated femoral and/or tibial component).  Treatment of anterior knee pain following primary TKA with secondary patellar resurfacing is a controversial procedure with uncertain outcomes.  These investigators systematically reviewed the available peer-reviewed literature on patient satisfaction and functional outcomes of secondary resurfacing.  The authors performed a systematic computerized database search of the Cochrane Database of Systematic Reviews, Medline, and Embase in October 2014.  The quality of the included studies was assessed using the Grading of Recommendations Assessment, Development and Evaluation approach.  A total of 15 articles met the inclusion criteria.  In total, 148 (64 %) of 232 patients were satisfied with the outcomes of secondary patellar resurfacing.  A statistically significant improvement in knee scores was noted in all 9 studies that reported functional outcomes, although no clinically significant improvement in knee scores was observed.  Reported complications included infections and impaired wound healing, patellar instability, and patellar fracture.  The authors concluded that because the available evidence is of generally low quality, the results of this systematic review only support a weak recommendation for secondary patellar resurfacing if patient satisfaction and clinically important improvement of functional outcomes are the desired end-points.

Toro-Ibarguen et al (2016) noted that secondary patellar resurfacing (SPR) is a procedure that can be used in patients with persistent anterior knee pain (AKP) after a primary TKA. These investigators analyzed the clinical and functional outcomes as well as the complications of this procedure and identified predictive factors for a favorable outcome.  A total of 46 patients who underwent SPR for persistent AKP after primary TKA were retrospectively studied.  The patient's mean age was 68 years (range of 36 to 86).  The average follow-up time after SPR was 74 months (range of 24 to 197).  Demographic data, Knee Society Score scale, ROM, pain improvement (VAS), overall satisfaction, and complications were recorded.  The statistical analysis was performed using STATA tm/SE v10.  There was an improvement of the Knee Society scale (from 54 ± 11 to 64 ± 16 points; p < 0.05).  However, in 59 % of the cases, there was no pain improvement, and 65 % of patients were not satisfied; 4 patients showed complications, and in 2 cases, re-operation was necessary.  These researchers did not find any pre-operative predictive factor for a favorable outcome after SPR.  The authors concluded that despite improvement of the Knee Society scale, many patients continued with AKP and were dissatisfied with this procedure; therefore, the authors do not recommend it in this clinical scenario.

van Jonbergen and colleagues (2016) stated that when secondary patellar resurfacing is performed, a uniformly and widely used scoring system that is validated for anterior knee pain caused by a retro-patellar degeneration will give more insight into the results of this procedure.  The cause of anterior knee pain following TKA is not always related to the patella itself.  Other causes have been identified, such as an insufficient posterior cruciate ligament in the case of a posterior cruciate-retaining TKA or an internally rotated femoral and/or tibial component.  Treatment of anterior knee pain following primary TKA with secondary patellar resurfacing is a controversial procedure with uncertain outcomes.  These investigators reviewed the available peer-reviewed literature on patient satisfaction and functional outcomes of secondary resurfacing.  They performed a systematic computerized database search of the Cochrane Database of Systematic Reviews, Medline, and Embase in October 2014.  The quality of the included studies was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.  A total of 15 articles met the inclusion criteria; 148 (64 %) of 232 patients were satisfied with the outcomes of secondary patellar resurfacing.  A statistically significant improvement in knee scores was noted in all 9 studies that reported functional outcomes, although no clinically significant improvement in knee scores was observed.  Reported complications include infections and impaired wound healing, patellar instability, and patellar fracture.  The authors concluded that because the available evidence was of generally low quality, the results of this systematic review only supported a weak recommendation for secondary patellar resurfacing if patient satisfaction and clinically important improvement of functional outcomes are the desired end-points.

Laursen (2017) reported the outcome of a prospective cohort study of 18 patients with large trochlea lesions or isolated OA treated with the HemiCAP-Wave implant and presented with up to a 6-year survival rate, and hypothesized short-to mid-term reduced pain and improved function.  Indication for treatment with the HemiCAP-Wave implant was a symptomatic, large cartilage lesion in trochlea demonstrated by MRI or arthroscopy, which was ICRS grades 3 to 4 and larger than 4 cm2.  Patients were followed for 2 years with American Knee Society Subjective outcome Scores (AKSS), pain scores and radiographic evaluations and for up to 6 years with complications and re-operations.  At the 1- and 2-year follow-up mean AKSS clinical score, the mean AKSS function score and mean pain score improved significantly.  Within 6 years, a high number of the implants (28 %) were revised to arthroplasty due to the progression of cartilage lesions, OA or increased knee pain.  The authors concluded that the findings of the present study demonstrated an improved short- to mid-term clinical outcome and reduced pain; but high mid-term revision rate after patello-femoral inlay resurfacing using the HemiCAP-Wave implant.  arthroplasty treatment.  Level of Evidence = IV.

Marcovigi et al (2017) stated that unicompartmental knee arthroplasty (UKA) has proven to be an effective surgical procedure, but its survivorship is still negatively affected by inaccuracy in component positioning, implant and limb alignment.  Robotic surgery has been introduced in order to minimize such technical errors.  These investigators evaluated clinical and surgical outcomes after a 3 years' experience of robotic assisted UKA with the Mako Robotic Arm.  A total of 77 patients undergoing  UKA with robotic instrumentation (65 medial UKAs, 8 lateral UKAs) and with a clinical follow-up of 3 to 37 months were included in the present study.  A complete clinical evaluation with KOOS, Forgotten Joint Score (FJS)-12 and SF-12 was administered to all patients pre- and post-operatively.  Post-operative HKA angle and surgical time were also recorded.  Mean post-operative KOOS score was 81.32 (SD 17.19), while the mean FJS-12 score was 75.51 (SD 30.12) and the mean SF-12 Physical Score 42.25 (SD 9.97). 91 % to 88 % of post-operative results were considered satisfactory.  Only 1 UKA failure was reported (1.3 %) caused by peri-prosthetic infection.  In medial UKAs mean post-operative HKA angle in extension was 3.9° varus (SD 2.5°), with no case of over-correction; in lateral UKAs mean post-operative HKA angle in extension was 1.9° valgus (SD 1.9°) with 1 case (13 %) of over-correction.  Mean skin-to-skin surgical time decreased from 83.2 minutes (SD 13.0) to 70.0 minutes (SD 10.9) along the learning curve.  The authors concluded that robotic UKA has provided an improvement both in clinical and technical results, determining satisfactory clinical outcomes and a low-risk of post-operative complications.  This was a single-center study with a small sample size (n = 77) and short- to mid-term follow-up (3 to 37 months).

Blyth et al (2017) reported on a secondary exploratory analysis of the early clinical outcomes of a randomized clinical trial comparing robotic arm-assisted UKA for medial compartment osteoarthritis (OA) of the knee with manual UKA performed using traditional surgical jigs.  This followed reporting of the primary outcomes of implant accuracy and gait analysis that showed significant advantages in the robotic arm-assisted group.  A total of 139 patients were recruited from a single-center.  Patients were randomized to receive either a manual UKA implanted with the aid of traditional surgical jigs, or a UKA implanted with the aid of a tactile guided robotic arm-assisted system.  Outcome measures included the American Knee Society Score (AKSS), Oxford Knee Score (OKS), Forgotten Joint Score, Hospital Anxiety Depression Scale, University of California at Los Angeles (UCLA) activity scale, Short Form-12, Pain Catastrophizing Scale, somatic disease (Primary Care Evaluation of Mental Disorders Score), pain visual analog scale (VAS), analgesic use, patient satisfaction, complications relating to surgery, 90-day pain diaries and the requirement for revision surgery.  From the 1st post-operative day through to week 8 post-operatively, the median pain scores for the robotic arm-assisted group were 55.4 % lower than those observed in the manual surgery group (p = 0.040).  At 3 months post-operatively, the robotic arm-assisted group had better AKSS (robotic median 164, interquartile range (IQR) 131 to 178, manual median 143, IQR 132 to 166), although no difference was noted with the OKS.  At 1 year post-operatively, the observed differences with the AKSS had narrowed from a median of 21 points to a median of 7 points (p = 0.106) (robotic median 171, IQR 153 to 179; manual median 164, IQR 144 to 182).  No difference was observed with the OKS, and almost 50 % of each group reached the ceiling limit of the score (OKS greater than 43).  A greater proportion of patients receiving robotic arm-assisted surgery improved their UCLA activity score.  Binary logistic regression modeling for dichotomized outcome scores predicted the key factors associated with achieving excellent outcome on the AKSS: a pre-operative activity level of greater than 5 on the UCLA activity score and use of robotic-arm surgery.  For the same regression modeling, factors associated with a poor outcome were manual surgery and pre-operative depression.  The authors concluded that robotic arm-assisted surgery resulted in improved early pain scores and early function scores in some patient-reported outcomes measures, but no difference was observed at 1 year post-operatively.  Although improved results favored the robotic arm-assisted group in active patients (i.e., UCLA greater than or equal to 5), these did not withstand adjustment for multiple comparisons.  Moreover, these investigators stated that any future multi-center, randomized trials, in addition to studying clinical effectiveness, should also include a full health economic assessment of the cost-effectiveness of the technology.

The authors stated that this study had several drawbacks.  The sample size was relatively small (n = 139) as the study was originally devised to determine the accuracy of the robotic-arm system.  Without correction for multiple comparisons, statistically significant findings may be spurious (Type I error).  Similarly, adjustment for multiple comparisons could introduce Type II errors (false negatives, where true differences are not observed due to the more stringent test to detect significant differences p < 0.005).  In addition, the implants differed between the 2 groups in the study: fixed bearing for the robotic arm-assisted group and mobile bearing for the manual surgery group.  There were recognized differences in kinematics between these implant designs.  The pragmatic decision to use these implants was based on the lack of availability of a mobile bearing implant for use with the Mako system, and a desire to compare the robotic-arm technology with the current benchmark treatment for UKA, which, in the United Kingdom at least, is the Biomet Oxford Unicompartmental Knee System (Zimmer Biomet, Warsaw, Indiana).  This limitation in the study design made it impossible to determine if the differences observed were due to the differences in the implants or due to the robotic-arm surgical technique.  A 3rd drawback was that the cohort of patients has not yet reached the relevant time-point at which to assess the impact on implant survivorship that may develop due to the increased accuracy that robotic-arm technology affords.  Only per-protocol data were available for analysis as patients who were treated with total knee arthroplasty were not followed-up.  There was therefore a risk to the integrity of the randomized groups from attrition bias.  The final drawback of the study related to the use of standard outcome measures that were ineffective at differentiating degrees of excellence in clinical outcome.  The decision to use the AKSS and OKS was based on both scores being widely accepted in the orthopedic community.  Differences in outcome might yet be demonstrated by a quantitative assessment of kinematics using gait analysis.

Millar et al (2018) stated that recently, systems have been developed to improve alignment of UKA implants, although improvement in function has been difficult to document.  The MAKO RIO robotic surgery system has previously shown improvements in in knee flexion during weight acceptance (WA) in comparison to conventional methods at a 1-year follow-up.  This study aimed to determine if these improvements remained at 5 years follow-up.  A total of 25 MAKO and 21 conventional knees were tested using 3-D gait analysis to measure knee kinematics.  Results demonstrated that the MAKO group achieved significantly greater knee flexion in WA than the conventional group which was consistent with results at 1-year.  This could be due to the improved accuracy of prosthesis implantation offered by the MAKO system.  This was a small study (n = 25 for MAKO) with mid-term follow-up (5 years).

Deese et al (2018) noted that UKA originated in the 1950's.  There have been many enhancements to the implants and the technique, improving the precision and accuracy of this challenging operation.  Specifically for Robotic Arm Interactive Orthopedic System (Rio; Mako Stryker, Fort Lauderdale, FL), there are many studies reporting clinical outcomes, but the authors’ search offered nothing regarding patient reported outcomes using validated surveys.  Patients with onlay tibial components presenting for routine follow-up of robotic-arm assisted UKA performed between May 2009 and September 2013 were invited to participate.  Four joints had simultaneous patella femoral resurfacing.  Knee Injury and Osteoarthritis Outcomes Score (KOOS) and the 2011 Knee Society Scores were collected.  Radiographic evidence of OA in the non-operative knee compartments was documented.  A total of 81 patients presented for follow-up and consented to participate.  Mean follow-up was 54 months.  Mean patient reported KOOS activities of daily living and pain scores were each 90.  Knee Society 2011 mean objective score was 96 and mean function score 81.  There was 1 revision to total knee at 40 months post-op for pain after injury; 77 % reported their knee always felt "normal", 20 % sometimes, and only 3 % reported that it never felt normal.  The authors concluded that the literature on UKA failure rates suggested that UKA may be a less forgiving procedure than total knee arthroplasty; and robotic-arm assisted surgery has been reported to improve the accuracy of implant placement.  These researchers stated that based on their prospectively collected positive patient outcomes, they have achieved good results from performing robotic-arm assisted UKA on select patients.

Rauck et al (2018) stated that “Bell et al's "Improved Accuracy of Component Positioning with Robotic-Assisted Unicompartmental Knee Arthroplasty: Data from a Prospective, Randomized Controlled Study" compared the accuracy of a robotic-assisted UKA using the MAKO Robotic Interactive Orthopedic Arm (RIO) system to a conventional UKA using standardized instrumentation”.  This review examined the authors' findings and their relevance to clinical practice.  Bell et al concluded that the MAKO RIO system led to more accurate implantation of both the tibial and femoral components in UKA in the sagittal, coronal, and axial planes.  This well-designed, level I study suggested what many arthroplasty surgeons assumed about robotic assistance, which admittedly was of unknown clinical significance at this time.  Evaluating this article in the context of the current literature provided valuable insight into areas in need of future investigation.  The effect of implant positioning on long-term clinical outcomes and implant survivorship remains unclear.  The authors concluded that long-term follow-up studies are needed to determine the role of robotic-assisted arthroplasty in the future.

Grassi and colleagues (2018) stated that the need of patellar resurfacing in TKA is a subject of debate.  In a systematic review of overlapping meta-analyses, these investigators analyzed current evidence regarding patellar resurfacing and non-resurfacing in TKA.  They carried out a systematic literature search in March 2017 in PubMed, CINAHL and Cochrane Library.  Inclusion criteria were meta-analysis of randomized controlled trials (RCTs) that compared TKA with and without patellar resurfacing considering as outcomes re-operations rate, complications, anterior knee pain, functional scores.  The quality of meta-analyses was evaluated with AMSTAR score and the most relevant meta-analysis was determined by applying the Jadad algorithm.  A total of 10 meta-analyses, published between 2005 and 2015, were included in the systematic review; 2 studies found a significantly increased Knee Society Score in the resurfacing group.  According to 4 meta-analyses, anterior knee pain incidence was lower in resurfacing group; 6 of the included studies described a greater risk of re-intervention in the non-resurfacing groups.  The overall quality of included studies was moderate.  The most relevant meta-analysis reported no differences in functional scores and incidence of anterior knee pain between the groups.  The authors concluded that comparable outcomes were found when comparing patellar resurfacing and non-resurfacing in TKA.  The higher risk of re-operations following non-resurfacing should be interpreted with caution due to the methodological limitations of the meta-analyses regarding search criteria, heterogeneity and the inherent bias of easier indication to re-operation when the patella was not resurfaced.  There was no clear superiority of patellar resurfacing compared to patellar retention.

Longo and associates (2018) noted that patellar resurfacing in TKA remains controversial.  In a systematic review and meta-analysis, these researchers examined this technique through an analysis of comparative studies in the current literature.  They performed a comprehensive search of PubMed, Medline, Cochrane, CINAHL, and Embase databases using various combinations of the keywords "knee", "replacement", "prosthesis", "patella", "resurfacing" and "arthroplasty".  All articles relevant to the subject were retrieved, and their bibliographies were hand searched for further references relevant to primary patellar resurfacing in TKA.  Only articles published in peer-reviewed journals were included in this systematic review.  The percentage for a re-operation was 1 % for the patellar resurfacing group (17/1636) and 6.9 % for the non-resurfacing group (118/1,699) (odds ratio [OR] 0.18, 95 % CI: 0.11 to 0.29, p < 0.00001).  The patellar resurfacing group showed a significantly higher postop Knee Society Score (KSS) pain (OR 1.52, 95 % CI: 0.68 to 2.35, p = 0.004) and post-operative HSS score (OR 4.35, 95 % CI: 3.21 to 5.49, p < 0.00001), over the non-resurfacing group.  The authors concluded that based on the outcome scores of KSS (pain), KSS (function), and Hospital for Special Surgery HSS score, postoperative patellar resurfacing TKAs have performed better than non-resurfaced TKAs.  The lower secondary operation and revision rates for patellar resurfaced TKAs also demonstrate that this technique was the more effective option.  However, the full impact of patellar resurfacing still needs to be critically evaluated by larger RCTs with long-term follow-up.

Maney and co-workers (2019) noted that surgeons may "usually" resurface the patella during TKA, "rarely" resurface, or "selectively" resurface on the basis of certain criteria.  It is unclear which of these 3 strategies yields superior outcomes.  Utilizing New Zealand Joint Registry data, these investigators examined what proportion of surgeons employed each of the 3 patellar resurfacing strategies, which strategy was associated with the lowest overall revision rate, and which strategy was associated with the highest 6-month and 5-year Oxford Knee Score (OKS).  A total of 203 surgeons who performed a total of 57,766 primary TKAs from 1999 to 2015 were categorized into the 3 surgeon strategies on the basis of how often they resurfaced the patella during primary TKA; with "rarely" defined as less than 10 % of the time, "selectively" as greater than or equal to 10 % to less than or equal to 90 %, and "usually" as greater than 90 %.  For each strategy, the cumulative incidence of all-cause revision was calculated and utilized to construct Kaplan-Meier survival curves.  The mean 6-month and 5-year postoperative OKS for each group were utilized for comparison.  Overall, 57 % of surgeons selectively resurfaced, 37 % rarely resurfaced, and 7 % usually resurfaced.  The usually resurfacing group was associated with the highest mean OKS at both 6 months (38.57; p < 0.001) and 5 years post-operatively (41.34; p = 0.029), followed by the selectively resurfacing group (6-month OKS, 37.79; 5-year OKS, 40.87) and the rarely resurfacing group (6-month OKS, 36.92; 5-year OKS, 40.02).  Overall, there was no difference in the revision rate per 100 component years among the rarely (0.46), selectively (0.52), or usually (0.46) resurfacing groups (p = 0.587).  Posterior-stabilized TKAs that were performed by surgeons who selectively resurfaced had a lower revision rate (0.54) than those by surgeons who usually resurfaced (0.64) or rarely resurfaced (0.74; p < 0.001).  The authors concluded that usually resurfacing the patella was associated with improved patient-reported outcomes, however, there was no difference in overall revision rates among the 3 strategies.

Koh and colleagues (2019) stated that anterior knee pain after TKA is often unexplained, spurring ongoing debates on the need for patellar resurfacing.  It was hypothesized that a contemporary patella-friendly implant would restore patella-femoral kinematics more physiologically than outdated implants and that there would be no perceived or clinically demonstrable differences due to resurfacing of patella (RP).  This prospective, bilateral randomized trial was performed in 49 patients scheduled for the same-day bilateral TKAs.  One knee was subjected at random to RP while withholding RP on the opposing side (non-RP).  A recently approved single-radius femoral prosthesis featuring a deep, elongate trochlear groove with lateral tilt and a high lateral flange was implanted bilaterally in all patients.  Mean follow-up duration was 5 years.  Group comparisons were based on patient-reported outcomes [anterior knee pain, FJS, and side preference], physician-rated results [Feller patella-femoral (PF) score], radiographic patellar position, patella-related complications, and need for re-operation.  There were no differences in mid-term rates of anterior knee pain (RP 8 %; non-RP 4 %; n.s.), FJS (all n.s.), or side preference (RP 47 %; non-RP 45 %; n.s.), nor did the groups differ by Feller PF score (all n.s.) or radiographic patellar position (all n.s.).  No secondary resurfacings of non-RP or RP revisions were needed.  The authors concluded that patients were incapable of distinguishing if RP was carried out, casting doubt on its benefits.  These researchers stated that surgeons may thus forego RP during TKA when using contemporary patella-friendly TKA implants.  Level of Evidence = I.

Christopher and co-workers (2019) stated that osteolysis of the patella following TKA is both uncommon and poorly described in the literature.  These investigators described 3 cases of TKA with patella resurfacing that later presented with AKP with patellar osteolysis without evidence of patellar implant failure: 2 males and 1 female patient, all with bilateral knee OA.  Osteolysis of the patella was identified radiographically between 2 and 16 years from the index procedure.  The authors theorized that high pressures across the PF joint, in obese or muscular patients, may play a role in the formation of these patellar osteolytic lesions.  These researchers suspected that the prevalence of this phenomenon is under-recognized in the literature and may increase with longer term follow-up and awareness.  They hoped that this series will raise awareness of this phenomenon and promote further research into understanding the pathogenesis of patellar osteolysis.

Crawford and associates (2020) noted that patellar resurfacing in primary TKA remains a controversial topic.  These investigators examined if patellar resurfacing affects early complications and outcomes with a symmetric femoral component design.  They carried out retrospective review from 2015 to 2019 of all primary TKAs performed with the Klassic Knee System (Total Joint Orthopedics, Inc., Salt Lake City, UT) yielding a cohort of 526 patients (674 knees).  Patients were compared based on whether the patella was resurfaced (391 knees, 58 %) or unresurfaced (283 knees, 42 %).  Pre- and post-operative ROM, UCLA activity score, and Knee Society clinical (KSC), functional (KSF) and pain (KSP) scores were evaluated between groups.  Manipulation under anesthesia (MUA) and revisions were evaluated.  The resurfaced group was significantly younger and had significantly more female patients, but they had no differences in pre-operative BMI, knee ROM, or KSS; 1-year minimum follow-up was available in 240 patients.  Mean follow-up was 7 months (range of 1 to 35 months, SD ±7 months).  MUAs were performed on 12 knees (4.2 %) in the unresurfaced group and 37 knees (9.5 %) in the resurfaced group (p = 0.01); 1 patient (0.3 %) in the unresurfaced group underwent a revision 1.5 years after the index surgery for a patellar resurfacing and polyethylene exchange.  No other revisions were performed in either group.  In patients with 1-year minimum follow-up, there was no significant difference in ROM or clinical or functional outcomes between groups.  The authors concluded that patients who underwent a primary TKA with the TJO Klassic Knee System with a resurfaced patella had a significantly higher incidence of MUA than those with an unresurfaced patella.  At most recent follow-up, there was no significant difference in mean ROM or clinical outcome scores.

Butnaru and colleagues (2020) stated that understanding the risk factors associated with post-operative pain and worse outcome could guide surgeons on whether primary patellar resurfacing is warranted during TKA.  These researchers examined if clinical scores and pain after TKA without patellar resurfacing are correlated with patellar shape and post-operative patellar position and kinematics.  Radiographs as well as anterior knee pain according to the pain VAS (pVAS) were collected pre- and post-operatively for 100 knees aged 68 ± 7.7 years that received uncemented TKA without patellar resurfacing.  At a minimum follow-up of 12 months the FJS, the OKS as well as the flexion ROM and the presence of J-sign during active extension were recorded.  Uni- and multi-variable linear regression analyses were performed to determine associations between the collected clinical scores and patient demographic and radiographic data.  Post-operative OKS (79 ± 14.4) was worse for Wiberg Type III patellae (β = -11.4, p = 0.020, compared with Type II).  Anterior pVAS (2 ± 2) was greater in knees with J-sign during extension (β = 2.8, p < 0.001).  None of the other radiographic measurements (patellar tilt, congruence angle and lateral patellar displacement) were correlated with post-operative OKS or anterior pVAS.  The authors concluded that incongruent patellar shape (Wiberg Type III) was associated with worse clinical scores, and abnormal kinematics (J-sign) with increased pain after TKA without patellar resurfacing.  Thus, these researchers recommended routine resurfacing for Wiberg Type III patellae, although further studies are needed to confirm whether resurfacing truly improves clinical scores and pain in this subgroup.

van Raaij and co-workers (2021) noted that there is some evidence that PF joint OA causes AKP following TKA.  These researchers hypothesized that patellar resurfacing in primary TKA for patients with symptomatic tri-compartmental knee OA yields better clinical results after 2 years than non-resurfacing.  They carried out a single-center RCT comparing 40 patients receiving 42 cruciate retaining TKAs with (n = 21) or without patellar resurfacing (n = 21).  Primary outcome was the specific PF joint score HSS Baldini and secondary outcomes were the KSS and the KOOS.  After 2 years no significant differences between both groups and between the groups in time for HSS Baldini, KSS, and KOOS were found.  HSS Baldini score improved significantly after 6 weeks in both groups (p < 0.001) and did not improve in time afterward.  At final follow-up the HSS Baldini mean score improved from a pre-operative mean of 39 to 88 (difference of 49 points; p < 0.001)) for without patellar resurfacing group, and from a pre-operative mean of 37 to 81 for patellar resurfacing group (difference of 47 points; p < 0.001); 1 patient in the patellar resurfacing group underwent a soft tissue re-alignment procedure because of patellar subluxation; 2 patients in without patellar resurfacing group received secondary patellar button placement.  The authors concluded that patellar resurfacing in primary TKA for patients with symptomatic tri-compartmental OA had no beneficial effect over non-resurfacing and appeared unnecessary.  A special PF joint outcome measurement tool (HSS Baldini) and common knee scores showed no better knee function or AKP outcomes for the patellar resurfacing group over the without patellar resurfacing group in time and after 2 years of follow-up.

Grela et al (2022) noted that patellar resurfacing is optional during TKA.  Some surgeons always resurface the patella, some never resurface, and others selectively resurface.  Which resurfacing strategy provides optimal outcomes is unclear.  In a systematic review and meta-analysis, these investigators examined the effectiveness of patellar resurfacing, no resurfacing, and selective resurfacing in primary TKA.  Medline, Embase, Web of Science, the Cochrane Library, and bibliographies were searched to November 2021 for RCTs comparing outcomes for 2 or more resurfacing strategies (resurfacing, no resurfacing, or selective resurfacing) in primary TKA.  Observational studies were included if limited or no RCTs existed for resurfacing comparisons.  Outcomes assessed were (PROMs, complications, and further surgery.  Study-specific relative risks [RR] were aggregated using random-effects models; and quality of the evidence was evaluated by means of GRADE.  These researchers identified 33 RCTs involving 5,540 TKAs (2,727 = resurfacing, 2,772 = no resurfacing, 41 = selective resurfacing).  Patellar resurfacing reduced anterior knee pain compared with no resurfacing (RR = 0.65 (95 % CI: 0.44 to 0.96)); there were no significant differences in PROMs.  Resurfacing reduced the risk of revision surgery (RR = 0.63, CI: 0.42 to 0.94) and other complications (RR = 0.54, CI: 0.39 to 0.74) compared with no resurfacing.  Quality of evidence ranged from high to very low.  Limited observational evidence (5 studies, TKAs = 215,419) suggested selective resurfacing increased the revision risk (RR = 1.14, CI: 1.05 to 1.22) compared with resurfacing.  Compared with no resurfacing, selective resurfacing had a higher risk of pain (RR = 1.25, CI: 1.04 to 1.50) and lower risk of revision (RR = 0.92, CI: 0.85 to 0.99).  The authors concluded that level-1 evidence supported TKA with patellar resurfacing over no resurfacing.  Resurfacing has a reduced risk of anterior knee pain, revision surgery, and complications, despite PROMs being comparable.  Moreover, these researchers stated that although selective resurfacing is the most common strategy currently used by U.K. surgeons and in many other countries, there is very little published research evidence available to support this approach.  These investigators recommended large, high-quality RCTs involving selective patellar resurfacing and always resurfacing to establish the role of selective resurfacing, as limited observational data suggested selective resurfacing may not have clinical benefits over other strategies.

Simpson et al (2023) stated that modern TKA femoral components are designed to provide a more optimal articular surface for the patella whether or not it has been resurfaced.  Previous systematic reviews comparing outcomes of patellar resurfacing and no resurfacing combine both historic and modern designs.  In a systematic review and meta-analysis, these investigators examined the effect of patellar resurfacing in modern "patellar friendly" implants on incidence of anterior knee pain, PROMs, complication rates, and re-operation rates compared with un-resurfaced patellae in primary TKA.  Medline, PubMed and Google scholar studies were examined using SIGN assessment tool and data analysis was carried out using Review Manager 5.2 on only RCTs.  The search terms were: arthroplasty, replacement, knee (Mesh), TKA, prosthesis, patella, patellar resurfacing, patellar retaining.  A total of 32 RCTs were identified that reported the type of TKA implant used: 11 used modern "patellar friendly" implants; and 21 older "patellar non-friendly" implants.  Among "patellar friendly" TKAs there were no significant differences in anterior knee pain rates between resurfaced and un-resurfaced groups.  Patellar resurfacing with "patellar friendly" implants had significantly higher clinical (MD -0.77, p = 0.007) and functional (MD -1.87, p < 0.0001) KSS than un-resurfaced counterparts but these did not exceed the MCID.  Resurfacing with "patellar friendly" implants was not associated with a significant (p = 0.59) difference in the OKS, in contrast when a "patellar non-friendly" implant was used there was a significant difference (MD 3.3, p = 0.005) in favor of resurfacing.  There was an increased risk of re-operation for un-resurfaced TKAs with "non-patellar friendly" implants (odds ratio 1.68, 95 % CI: 1.03 to 2.74, p = 0.04), but not for un-resurfaced patellae with "patellar friendly" implants (OR 1.17, CI: 0.59 to 2.30).  The authors concluded that patellar resurfacing in combination with a modern patellar friendly implant was not associated with a lower rate of anterior knee pain, complications, or re-operations compared to not resurfacing, nor did it give a clinically significant improvement in knee specific function.  In contrast, patellar resurfacing in combination with a "non-friendly" TKA implant was associated with a significantly better OKS and lower re-operation rate.  These researchers noted that implant design should be acknowledged when patellar resurfacing is being considered.

Metatarsophalangeal Toe Joint Resurfacing

Metatarsophalangeal (MTP) toe joint resurfacing was designed to resurface the damaged surface of the metatarsal head caused by arthritis (eg, hallux rigidus, post-traumatic arthritis). This resurfacing purportedly provides a "contoured cap" that matches the individual’s cartilage surface, which reportedly protects the remaining cartilage to prevent further damage to the joint. The metatarsophalangeal joints (MTP) are the joints between the heads of the metatarsal bones and bases of the proximal phalanges. The first MTP joint is commonly known as the big toe joint. Hallux rigidus is restricted mobility of the big toe due to stiffness of the MTP joint especially when due to arthritic changes in the joint. 

Examples of FDA-approved devices for MTP joint resurfacing include, but may not be limited to, CAP great toe resurfacing hemi-arthroplasty implant and the OsteoMed metatarsal resurfacing implant system.

Facet Joint Resurfacing

In a feasibility study, de Kelft (2016) evaluated the safety and the clinical and radiologic performance of a bilaterally implanted FENIX facet resurfacing device.  A total of 8 consecutive patients with proven single segmental bilateral lumbar facet joint OA as unique pain generator received a bilateral implantation of the FENIX device.  Correct device placement and mobility preservation were assessed on x-ray at 6 weeks and at 6, 12, and 24 months after implantation.  Magnetic resonance imaging (MRI) at 12 and 24 months after surgery assessed the bony ingrowth and CT-single photon emission computed tomography (SPECT) was repeated at 6 months to assess evolution of the pre-operative inflamed facet joints.  The Oswestry disability index (ODI), VAS pain score, and the need for analgesic medication were the parameters used for clinical assessment.  At 24 months after surgery, 7 of the 8 patients were found to have all implants in place and all assessed parameters were found to be normal.  Patients experienced significant pain relief and functionality improvement.  Mobility was maintained and no Modic changes were noted, either at the index or at the adjacent levels.  No "hot" lesions at the implanted levels were observed on CT-SPECT; 1 of the 48 (2 %) implants was found to be dislocated at 6 months follow-up.  The authors concluded that the FENIX facet resurfacing technique might be considered in the future as a surgical treatment of well-selected patients suffering from chronic low back pain (LBP) because of facet joint OA.

Radiocapitellar Joint / Radiocapitellar Joint Replacement Resurfacing

Schmidt (2017) noted that coronal shear fracture type IV of the distal part of humerus is a very rare injury with articular complexity potentially leading to post-traumatic OA.  One option for surgical treatment of advanced unicompartmental radiocapitellar OA is resurfacing radiocapitellar joint replacement.  These investigators reported the case of a 62-year old woman who sustained a coronal shear fracture type IV of the distal part of left humerus that was primarily treated with open reduction and internal fixation (ORIF) using headless compression screws; 3 years post-operatively, there was a migration of one screw into radiocapitellar joint that led to circular deep cartilage defect of radial head; 4 years after ORIF, a distinctive radiocapitellar OA has evolved leading to a resurfacing radiocapitellar joint replacement using the Lateral Resurfacing ElbowTM (LRE) system.  At the 2-year follow-up after that procedure, there was an excellent subjective and functional outcome.  Radiographically, no loosening or subsidence of implant without any signs of over-stuffing could be found.  The patient reported that she would have the same procedure again.  The authors concluded that the goal of unicompartmental radiocapitellar replacement is to obtain stability in elbow joint by avoiding cubitus valgus with subsequent instability of the distal radioulnar joint, and it does not alter the unaffected ulno-humeral joint.  Additionally, the feature of the LRETM system is that the radial head is not excised, and so will receive the anatomical length of the overall radius articulating with the capitellum by preserving the annular ligament.  These researchers noted that in the literature only 3 publications could be found in which short-term results with the use of the LRETM system have been described; thus, further studies are needed to validate this concept.

Resurfacing Hemiarthroplasty of the Shoulder

Ibrahim and colleagues (2018) reported the outcome of resurfacing hemiarthroplasty (RHA) in a cohort of patients with juvenile idiopathic arthritis (JIA) affecting the shoulder joint.  A total of 14 un-cemented RHA procedures were performed for 11 consecutive patients who required surgery because of JIA.  Mean age at surgery was 36.4 years.  Mean clinical follow-up was 10.4 years (range of 5.8 to 13.9 years).  A significant humeral head defect (up to 40 % surface area) was found in 5 shoulders and filled with autograft from the distal clavicle or femoral head allograft.  At latest follow-up, no patient required revision.  There was excellent relief from pain.  The mean Oxford Shoulder Score and Constant-Murley Score improved significantly.  No shoulder had a poor outcome, and 6 had a very good or excellent outcome.  Worse outcome was associated with an intra-operative finding of significant humeral head erosion; 2 shoulders required early arthroscopic sub-acromial decompression, but there were no other re-operations.  There were no instances of radiographic implant loosening or proximal migration.  Painless glenoid erosion was seen in 5 shoulders but was not associated with worse outcome.  The authors concluded that the mid-term results of RHA for JIA were at least comparable to those for stemmed hemiarthroplasty, with the added benefit of bone conservation.  This was a small study (n =  11 patients) with mid-term (10.4 years); these findings need to be validated by well-designed studies with larger sample size and long-term follow-up.

Computer-Assisted Navigation During Birmingham Hip Resurfacing

Vigdorchik and colleagues (2018) stated that inaccurate positioning of acetabular and femoral components during Birmingham Hip Resurfacing (BHR) can lead to increased wear, edge-loading, and failure of the prosthesis, a consequence of substantial concern for young and active patients seeking long- term, post-operative survival of the joint.  In turn, sizing of the acetabular component during BHR is limited by the size of the native femoral neck, and reaming of the acetabulum should be minimized to optimize the bony architecture for potential subsequent arthroplasties.  These researchers noted that computer-assisted navigation systems (CAS) can improve the accuracy of component selection and positioning during total hip arthroplasty (THA); however, evidence for the usefulness of CAS in BHR is lacking.  They summarized a case of BHR performed with navigation to assist with component positioning.  A 34-year old man, a martial arts instructor, presented with a constant and localized pain in the left hip and groin.  Following the examination, the patient was diagnosed with left hip impingement and OA.  Due to his age and active lifestyle, the patient elected to undergo BHR rather than THA.  The navigation tool was used to assist with acetabular reaming and to confirm final cup placement.  Post-operatively, standard, antero-posterior pelvic radiographs showed a final cup position of 39.0° inclination and 24.7° anteversion, which was confirmed by the navigation tool.  A pre-operative leg length differential of 3 mm was measured from pre-operative radiographs; however, leg lengths were equalized following BHR.  The authors concluded that this case demonstrated the value of a novel surgical navigation tool during BHR, allowing for increased specificity when preparing the acetabulum and optimizing the accuracy of acetabular component positioning while limiting the volume of excavated bone.  Increased accuracy and the potential bone-sparing benefits of CAS may be advantageous for young and active patients seeking less invasive surgical intervention.  These investigators stated that computer-assisted navigation may assist with the accuracy of acetabular component selection and positioning during BHR.  These preliminary findings need to be validated by well-designed studies.

Metal Resurfacing Inlay Implant for Osteochondral Talar Defects After Failed Previous Surgery

Vuurberg and colleagues (2018) noted that treatment of osteochondral talar defects (OCDs) after failed previous surgery is challenging.  Promising short-term results have been reported with use of a metal resurfacing inlay implant.  In a case-series study, these researchers evaluated the mid-term clinical effectiveness of the metal implant for OCDs of the medial talar dome after failed previous surgery.  They prospectively studied all patients who met the inclusion criteria and received a metal resurfacing inlay implant between 2007 and 2014.  The primary outcome measure was implant survival, as measured by re-operation rate; secondary outcome measures were numeric rating scales (NRS) for pain at rest and during walking, running, and stair climbing; the Foot and Ankle Outcome Score (FAOS); the American Orthopaedic Foot and Ankle Society (AOFAS) Ankle Hindfoot Scale; the 36-Item Short Form Health Survey (SF-36); return-to-work and return-to-sports; and radiographic evaluation.  This study included 38 patients with a mean age of 39 years (SD, ± 13 years) and a mean follow-up of 5.1 years (SD, ± 1.5 years); 2 patients (5 %) underwent revision surgery by means of an ankle arthrodesis (2 and 6 years post-operatively).  In 8 patients, computed tomography scanning was conducted to assess post-operative complaints.  These scans showed impression of the tibial plafond (n = 4), a small tibial cyst (less than 2.5 mm; n = 1), and cyst formation around the implant screw (n = 4).  A total of 21 re-operations were performed, including medial malleolar screw removal (n = 12), arthroscopic removal of bony anterior impingement (n = 7), and calcaneal re-alignment osteotomy (n = 2).  All secondary outcome measures improved significantly, apart from pain at rest, the FAOS symptoms subscale, and the SF-36 mental component scale.  The mean time for return-to-sport was 4.1 months (SD, ± 3 months), and 77 % of patients resumed sporting activities post-operatively.  Only 1 patient did not return to work post-operatively.  Radiographs at final follow-up showed cyst formation (n = 2), subchondral peri-prosthetic radiolucency (n = 2), and non-preexisting joint space narrowing (n = 2).  The authors concluded that this study showed that the metal implant is an effective technique when assessed at mid-term follow-up for OCDs of the medial talar dome after failed previous surgery.  Moreover, these investigators stated that to determine long-term outcomes concerning implant failure and patient satisfaction, more cases and a longer follow-up period are needed.  Level of evidence = IV.

The authors stated that the findings of this study were limited, as no gold standard or reference therapy is available for failed secondary surgery for OCDs to allow comparison of these results.  Furthermore, these  results did not show significant score improvements between the pre-operative assessment and the 6- to 8-year follow-up for the FAOS pain, sports, and quality of life (QOL) scales and the AOFAS scale despite significant score changes at earlier follow-up time-points.   This may be related to a lower number of patients due to a shorter follow-up, which decreased the study power.  The period studied (2007 to 2014) meant that not enough patients reached the 6- to 8-year follow-up (n = 15) compared with the initial power calculation of 20 patients, and thus the study had a lack of power. This 6- to 8-year follow-up was included to provide an indication of long-term outcome.  A final drawback was that the technique requires a medial malleolar osteotomy to reach the defect, automatically excluding lateral lesions from this therapeutic option.


In a prospective study, Song et al (2011) compared the outcomes of robotic-assisted total knee arthroplasty (RA-TKA) and conventional TKA in same patient simultaneously.  It was hypothesized that the robotic-assisted procedure would produce better leg alignment and component orientation, and thus, improve patient satisfaction and clinical and radiological outcomes.  A total of 30 patients underwent bilateral sequential TKA.  One knee was replaced by robotic-assisted implantation and the other by conventional implantation.  Radiographic results showed significantly more post-operative leg alignment outliers of conventional sides than robotic-assisted sides (mechanical axis, coronal inclination of the femoral prosthesis, and sagittal inclination of the tibial prosthesis).  Robotic-assisted sides had non-significantly better post-operative knee scores and range of motion (ROM).  Robotic-assisted sides needed longer operation times (25 mins, SD ± 18) and longer skin incisions.  Nevertheless, post-operative bleeding was significantly less for robotic-assisted sides.  The authors concluded that the better alignment accuracy of RA-TKA and the good clinical results achieved may favorably influence clinical and radiological outcomes.

The authors stated that this study had several drawbacks that require consideration.  Although this study was carried out in a randomized, prospective manner, patients were able to deduce from skin incisions which procedure had been used on which knee, and this could have significantly impacted these findings.  Furthermore, the relatively small number of patients (n = 30) recruited could have weakened the power or the analysis.  Furthermore, although these researchers found that blood loss for robot-assisted knees was significantly less than for conventional knees, these researchers only measured the amount of post-operative drainage, which only provided a crude measure of actual blood loss.  Finally, these investigators performed a 6-degree conventional TKA correction in every case without considering the pre-operative femoral anatomy.

Song et al (2013) noted that several studies have shown mechanical alignment influences the outcome of TKA.  Robotic systems have been developed to improve the precision and accuracy of achieving component position and mechanical alignment.  These investigators examined if robotic-assisted implantation for TKA would improve clinical outcome; mechanical axis alignment and implant inclination in the coronal and sagittal planes; the balance (flexion and extension gaps); as well as reduced complications, post-operative drainage, and operative time when compared to conventionally implanted TKA over an intermediate-term (minimum 3-year) follow-up period.  They prospectively randomized 100 patients who underwent unilateral TKA into 1 of 2 groups: 50 using a robotic-assisted procedure and 50 using conventional manual techniques.  Outcome variables considered were post-operative ROM, Western Ontario and McMaster Universities Arthritis Index (WOMAC) scores, Hospital for Special Surgery (HSS) knee scores, mechanical axis alignment, flexion/extension gap balance, complications, post-operative drainage, and operative time.  Minimum follow-up was 41 months (mean of 65 months; range of 41 to 81 months).  There were no differences in post-operative ROM, WOMAC scores, and HSS knee scores.  The robotic-assisted group resulted in no mechanical axis outliers (greater than ± 3° from neutral) compared to 24 % in the conventional group.  There were fewer robotic-assisted knees where the flexion gap exceeded the extension gap by 2 mm.  The robotic-assisted procedures took an average of 25 mins longer than the conventional procedures but had less post-operative blood drainage.  There were no differences in complications between groups.  The authors concluded that robotic-assisted TKA appeared to reduce the number of mechanical axis alignment outliers and improve the ability to achieve flexion-extension gap balance, without any differences in clinical scores or complications when compared to conventional manual techniques.

The authors stated that this study had several drawbacks.  First, there were differences between the groups in the goals for alignment of the femoral component, which could affect limb alignment and ligament balance.  A 6-degree valgus cut relative to the patient’s anatomic femoral canal was the goal in every conventional case without considering any variation in the patient’s pre-operative femoral anatomy; in the ROBODOC1-assisted group, the femoral component was aligned to the patient’s individual femoral mechanical axis.  A fixed femoral resection angle, however, was reportedly associated with errors in coronal alignment over a population due to individual differences.  Second, the goal for femoral rotation was different in the 2 groups: in the ROBODOC1-assisted group, the femoral component was aligned with the trans-epicondylar axis, while in the conventional group, it was aligned 3 externally to the posterior condylar axis.  According to the literature, the best rotation alignment for the femoral component has been parallel to the trans-epicondylar axis.  This axis was identifiable on most CT scans but was difficult for surgeons to identify manually during surgery.  Several studies have shown using 3 of external rotation to the posterior condylar axis may accurately estimate the femoral flexion axis only 65 % to 80 % of the time.  Therefore, using a fixed 3 rotational alignment in the conventional group could have resulted in some of the differences found in this group.  Third, these researchers did not measure total blood loss (TBL), only the post-operative drainage amount, which did differ.  However, drainage reportedly correlated with actual blood loss, and since the tourniquet was kept inflated until after wound closure, the post-operative drainage should closely approximate actual blood loss.  Fourth, these researchers only measured the flexion and extension gaps once intra-operatively and without patellar relocation.  Fifth, the surgeon was not blinded to the procedure when making the intra-operative measurements of PCL tension, which could have resulted in potential bias when making these measurements.  Sixth, the 2 groups had differing lengths of time to latest follow-up.  However, because these investigators were interested in considering most recent outcomes, they decided to use the latest follow-up available with a minimum of 3 years.  Furthermore, this study had insufficient power to detect small differences in complication rates.  A final drawback was the inability to assess cost-effectiveness.  The cost of the ROBODOC1 device varies by country.  This study was performed in Korea and the cost structure is not readily generalizable to other countries.  As the ROBODOC1 system with TKA is not available for sale in the U.S. at this time, it was difficult to accurately assess its cost.

Bell et al (2016) stated that higher revision rates have been reported in patients who have undergone unicompartmental knee arthroplasty (UKA) compared with patients who have undergone TKA, with poor component positioning identified as a factor in implant failure.  A robotic-assisted surgical procedure has been proposed as a method of improving the accuracy of component implantation in arthroplasty.  In a prospective, randomized, single-blinded, controlled trial, these researchers examined the accuracy of component positioning in UKA comparing robotic-assisted and conventional implantation techniques.  A total of 139 patients were randomly assigned to treatment with either a robotic-assisted surgical procedure using the MAKO Robotic Interactive Orthopedic Arm (RIO) system or a conventional surgical procedure using the Oxford Phase-3 unicompartmental knee replacement (UKR) with traditional instrumentation.  A post-operative computed tomographic (CT) scan was performed at 3 months to evaluate the accuracy of the axial, coronal, and sagittal component positioning.  Data were available for 120 patients, 62 who had undergone robotic-assisted UKA and 58 who had undergone conventional UKA.  Intra-observer agreement was good for all measured component parameters.  The accuracy of component positioning was improved with the use of the robotic-assisted surgical procedure, with lower root mean square errors and significantly lower median errors in all component parameters (p < 0.01).  The proportion of patients with component implantation within 2° of the target position was significantly greater in the group who underwent robotic-assisted UKA compared with the group who underwent conventional UKA with regard to the femoral component sagittal position (57 % compared with 26 %, p = 0.0008), femoral component coronal position (70 % compared with 28 %, p = 0.0001), femoral component axial position (53 % compared with 31 %, p = 0.0163), tibial component sagittal position (80 % compared with 22 %, p = 0.0001), and tibial component axial position (48 % compared with 19 %, p = 0.0009).  The authors concluded that robotic-assisted surgical procedures with the use of the MAKO RIO led to improved accuracy of implant positioning compared with conventional UKA surgical techniques.  Moreover, these researchers stated that the potential for detection bias limited the strength of this conclusion.  Although they demonstrated increased accuracy, further follow-up of the study cohort is needed to examine if the improved accuracy of component positioning would result in improved clinical outcomes.

The authors stated that this study had several drawbacks.  First, although, intuitively, improvement in the accuracy of component positioning in UKA would have been expected to be beneficial, improved accuracy of component implantation has not yet been shown to lead to improved clinical performance or survivorship.  Second, although these investigators found good intra-observer agreement in the measurement of the component alignment parameters using post-operative CT scans, the potential for error existed between the identification of anatomic landmarks in the pre-operative and post-operative CT scans by the research engineer and investigators.  Third, with the observers being aware of the treatment group assignment, a substantial potential for detection bias existed.

Marchand et al (2017) noted that robotic arm-assisted TKA (RA-TKA) presents a potential, new added value for orthopedic surgeons.  In today’s healthcare system, a major determinant of value can be assessed by patient satisfaction scores.  These researchers analyzed patient satisfaction outcomes between RA-TKA and manual total knee arthroplasty (M-TKA). Specifically, these researchers used the WOMAC to compare pain scores, physical function scores, and total patient satisfaction outcomes in M-TKA and RA-TKA patients at 6 months post-operatively.  In this study, 28 cemented RA-TKAs performed by a single orthopedic surgeon at a high-volume center were analyzed.  The first 7 days were considered as an adjustment period along the learning curve; 20 consecutive cemented RA-TKAs were matched and compared with 20 consecutive cemented M-TKAs performed immediately.  Patients were administered a WOMAC satisfaction survey at 6 months post-operatively.  Satisfaction scores between the 2 cohorts were compared and the data were analyzed using Student’s t-tests.  A p-value < 0.05 was used to determine statistical significance.  The mean pain score, standard deviation (SD), and range for the manual and robotic cohorts were 5 +/- 3 (range of 0 to 10) and 3  3 (range of 0 to 8, p < 0.05), respectively.  The mean physical function score, SD, and range for the manual and robotic cohorts were 9 +/- 5 (range of 0 to 17) and 4 +/- 5 (range of 0 to 14, p ¼ 0.055), respectively.  The mean total patient satisfaction score, SD, and range for the manual and robotic cohorts were 14 points (range of 0 to 27 points, SD: +/- 8) and 7  8 points (range of 0 to 22 points, p < 0.05), respectively.  The authors concluded that the results from this study further highlighted the potential of this new surgical tool to improve short-term pain, physical function, and total satisfaction scores; thus, it appeared that patients who undergo RA-TKA could expect better short-term outcomes when compared with patients who undergo M-TKA.  Moreover, these researchers stated that since this technology is relatively new, additional studies correlating clinical outcomes and patient satisfaction are needed.

Pearle et al (2017) noted that successful clinical outcomes following UKA depend on lower limb alignment, soft tissue balance and component positioning, which can be difficult to control using manual instrumentation.  Although robotic-assisted surgery more reliably controls these surgical factors, studies assessing outcomes of robotic-assisted UKA are lacking.  In a prospective, multi-center study, these researchers examined outcomes of robotic-assisted UKA.  A total of 1,007 consecutive patients (1,135 knees) underwent robotic-assisted medial UKA surgery from 6 surgeons at separate institutions between March 2009 and December 2011.  All patients received a fixed-bearing metal-backed onlay implant as tibial component.  Each patient was contacted at minimum 2-year follow-up and asked a series of 5 questions to determine survivorship and patient satisfaction.  Worst-case scenario analysis was performed whereby all patients were considered as revision when they declined participation in the study.  Data was collected for 797 patients (909 knees) with average follow-up of 29.6months (range of 22 to 52months).  At 2.5-years of follow-up, 11 knees were reported as revised, which resulted in a survivorship of 98.8 %; 35 patients declined participation in the study yielding a worst-case survivorship of 96.0 %.  Of all patients without revision, 92 % was either very satisfied or satisfied with their knee function.  The authors concluded that in this multi-center study, robotic-assisted UKA was found to have high survivorship and satisfaction rate at short-term follow-up.  These researchers stated that prospective comparison studies with longer follow-up and higher follow-up rate are needed in order to compare survivorship and satisfaction rates of robotic-assisted UKA to conventional UKA and TKA.

The authors stated that this study had several drawbacks.  The most important drawback was that 20 % of patients were lost to follow-up.  Most of these patients could not be included because they could not be reached by serial phone calls.  However, a small percentage of patients declined to participate, which included a potential bias; thus, a worst-case scenario survivorship analysis was performed, which showed comparable survivorship to that reported in registries and most manual cohort studies.  A follow-up rate of 80 % was not unexpected in a multi-center study of this scale performed in the U.S.  With a follow-up rate of 80 %, this study still reported the survivorship and satisfaction rate of 909 robotic-assisted UKA procedures and was, to the authors’ knowledge, the largest U.S. multi-center study reporting outcomes following UKA surgery.  Findings in this study reported that outcomes of robotic-assisted UKA surgery were between superior to similar to conventional UKA; thus, future studies are needed to further compare outcomes of both procedures.  A 2nd drawback was that this study only assessed survivorship and satisfaction rate of robotic-assisted UKA surgery, while functional and radiographic outcomes were not obtained.  Several other studies have previously reported radiologic outcomes and accuracy of robotic-assisted UKA surgery.  furthermore, several recent studies have reported the short-term functional outcomes of robotic-assisted surgery.  A 3rd drawback was that due to the nature of a multi-center study and the different surgeon case volumes, standardization of surgical indication was not part of the study design and no distinct exclusion criteria were specified for this study.  However, because surgical indications were left to the discretion of the multiple surgeons in the study, these outcomes may be generalizable to the robotic UKA experience in the U.S.  A 4th drawback was that medical notes were not reviewed; and that all data was patient-reported, which may contain a potential bias.  Lastly, follow-up was relatively short and long-term follow-up is needed.  This study is ongoing with patient contact planned at 5 and 10 years post-operatively.

Chowdhry et al (2017) stated that UKA is an under-utilized implant for medial tibiofemoral arthritis despite proven benefits in performance and reduced complications.  This is likely related to registry recorded higher revision rates compared with TKA.  These researchers felt that better component alignment resulting from the usage of computer-assisted surgery should improve longer-term functional results and survival of UKAs.  Between August 2003 and June 2007, a total of 265 medial UKAs were carried in 264 consecutive patients using navigation.  A total of 88 women and 176 men with an average age of 51.7 (± 4.63) years were assessed for function and survival over a follow-up period of 92.6 (63 to 120) months (7.7 years).  The final survival rate over 5 years for this cohort was 97.6 % at 5 years.  The authors concluded that computer-assisted UKA, to treat medial tibiofemoral joint arthritis, produced 5-year survival rates that were comparable with TKA.  This study addressed the use of computer-assisted UKA; not robotics-assisted UKA.

The authors stated that this study had several drawbacks.  First, there was no comparative group.  Second, it was possible that the improved survival figures of this cohort were due to the fact that the operating surgeon was a high volume UKR surgeon.  A comparison with conventionally implanted UKR’s by the same surgeon would have clarified this issue.  Third, an analysis of component alignment was performed, but again there was no group to compare it to, and pre-operative alignment was not evaluated.  Fourth, only a single observer carried out radiographic measurements.  Fifth, despite the fact that an equal number of revisions were performed with both types of implant used, 2 different implants were used in this cohort.  Variations in implant design and mobile versus fixed bearing serve as potential sources of bias in this study.

Liow et al (2017) noted that despite reduction in radiological outliers in previous randomized trials comparing RA-TKA versus conventional TKA, no differences in short-term functional outcomes were observed.  These researchers examined if there was improvement in functional outcomes and quality-of-life (QoL) measures between R-TKA and conventional TKA.  All 60 knees (31 robotic-assisted; 29 conventional) from a previous randomized trial were available for analysis.  Differences in ROM, Knee Society (KSS) knee and function scores, Oxford Knee scores (OKS), SF-36 subscale and summative (physical PCS/mental component scores MCS) were analyzed.  Furthermore, patient satisfaction, fulfilment of expectations and the proportion attaining a minimum clinically important difference (MCID) in KSS, OKS and SF-36 were studied.  Both RA-TKA and conventional TKA displayed significant improvements in majority of the functional outcome scores at 2 years.  Despite having a higher rate of complications, the RA-TKA group displayed a trend towards higher scores in SF-36 QoL measures, with significant differences in SF-36 vitality (p = 0.03), role emotional (p = 0.02) and a larger proportion of patients achieving SF-36 vitality MCID (48.4 % versus 13.8 %, p = 0.009).  No significant differences in KSS, OKS or satisfaction/expectation rates were noted.  The authors concluded that subtle improvements in patient QoL measures were observed in RA-TKA when compared to conventional TKA.  This finding suggested that QoL measures may be more sensitive and clinically important than surgeon-driven objective scores in detecting subtle functional improvements in RA-TKA patients.  Moreover, these researchers stated that long-term follow-up, registry data and survivorship studies are needed before widespread adoption of robotic technology in orthopedics can occur.  Level of Evidence = II.

This study had several drawbacks.  First, this study examined a small sample size with 31 RA-TKA patients and 29 conventional TKA patients.  However, the use of pre-operative power analysis, relative homogeneity of groups pre-operatively and randomized design mitigated this issue.  Second, the lack of blinding of patients may have resulted in reporting bias, with the robotic-assisted group providing better patient-reported outcome measures (PROM).  However, an extensive battery of HRQoL instruments and corresponding MCID thresholds were utilized which showed consistent, convergent improvements in the robotic-assisted group.  Third, although both groups had no significant differences in pre-op HRQoL cores, development of potential undetected co-morbidities during the 2-year follow-up may have confounded these findings in terms of the subtle differences in HRQoL measures between the 2 groups.  Lastly, radiological findings at 2 years were not presented, and potential radiological changes such as early loosening, change in the MA or joint line measurements could not be determined.  However, previous measurements were performed at 6 months, at a time when implants were expected to be well fixed for radiological assessment.  The American College of Radiology has recommended that routine repeat radiographs at early follow-up for well-functioning patients may not be necessary; however, more frequent follow-up is needed if patients present with signs of failure, sepsis or subnormal peri-prosthetic bone quality.  All study patients were assessed by the physicians and physiotherapists at their last follow-up visit, with radiographs performed for any suspected complications, which have been reported in this study.

In a prospective cohort study, Kayani et al (2018) compared early post-operative functional outcomes and time to hospital discharge between conventional jig-based total knee arthroplasty (TKA) and robotic-arm assisted TKA.  This trial included 40 consecutive patients undergoing conventional jig-based TKA followed by 40 consecutive patients receiving robotic-arm assisted TKA.  All surgical procedures were performed by a single surgeon using the medial parapatellar approach with identical implant designs and standardized post-operative inpatient rehabilitation.  Inpatient functional outcomes and time to hospital discharge were collected in all study patients.  There were no systematic differences in baseline characteristics between the conventional jig-based TKA and robotic-arm assisted TKA treatment groups with respect to age (p = 0.32), gender (p = 0.50), body mass index (BMI; p = 0.17), American Society of Anesthesiologists score (p = 0.88), and pre-operative hemoglobin level (p = 0.82).  Robotic-arm assisted TKA was associated with reduced post-operative pain (p < 0.001), decreased analgesia requirements (p < 0.001), decreased reduction in post-operative hemoglobin levels (p < 0.001), shorter time to straight leg raise (p < 0.001), decreased number of physiotherapy sessions (p < 0.001) and improved maximum knee flexion at discharge (p < 0.001) compared with conventional jig-based TKA.  Median time to hospital discharge in robotic-arm assisted TKA was 77 hours (interquartile range (IQR) 74 to 81) compared with 105 hours (IQR 98 to 126) in conventional jig-based TKA (p < 0.001).  The authors concluded that robotic-arm assisted TKA was associated with decreased pain, improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based TKA.

The authors stated that there are several limitations of this study that need to be considered when interpreting the findings.  First, all patients received general anesthetic, which was not keeping in with current trends in enhanced recovery programs, and this may have reduced the overall rehabilitation time in both treatment groups.  Second, the reported early functional outcome measures were not correlated to long-term clinical outcomes or implant survivorship.  Third, patients and observers recording outcomes of interest could not be blinded as patients in the robotic group had an additional incision over the proximal tibia for the insertion of the registration pins.  Fourth, the use of historical controls may have introduced bias into the study due to increasing drive for faster rehabilitation and reduced length of stay.  Improved outcomes in the robotic group may therefore not be exclusively due to surgical technique.  Fifth, pre-operative grading of the arthritis and radiological outcomes were not analyzed in this study.

Marchand et al (2018) stated that although robotic-assisted total knee arthroplasty (TKA) has the potential to accurately reproduce neutral alignment, it is still unclear if this correction is attainable in patients who have severe varus or valgus deformities.  These investigators examined a single surgeon's experience with correcting coronal deformities using the robotic-assisted TKA device.  Specifically, they looked at correction of varying degrees of varus and valgus deformity in patients who underwent robotic arm-assisted TKA (RA-TKA).  A total of 330 robotic-assisted TKA cases performed by a single surgeon were analyzed.  Pre-operative CT scans were registered to the robotic-assisted software to create a three-dimensional (3D) rendering from which coronal alignment was measured.  Post-operative coronal alignment measurements were taken in the operating room (OR) using the robotic-assisted device after trial component placement.  The robotic-assisted device uses optical tracking from navigation probes placed on the distal femur and proximal tibia.  The robotic-assisted software could register these probes as bony landmarks to measure coronal alignment in the distal plane of the femoral component and proximal plane of the tibial component.  A total of 261 cases were of varus knees, 46 cases were of valgus knees, and 23 cases had 0° pre-operative alignment.  Severe deformity was defined as 7° or greater deformity.  Pre-operative neutral alignment was defined as 0°, while post-operative neutral alignment was defined as 0° ± 3°.  There were 129 patients with and initial severe varus and 7 patients with an initial severe valgus deformity of 7° or greater.  Patients were divided into varus or valgus cohorts, and analysis was performed on the overall cohort, as well as non-severe (less than 7°) and severe (7° or greater) deformity cohorts.  All 132 knees with initial varus deformity of less than 7° were corrected to neutral (mean 1°, range of -1 to 3°).  A total of 82 knees (64 %) with 7° or greater varus deformity were corrected to neutral (mean 2°, range of 0 to 3°).  However, approximately 30 % of patients with severe deformity who were not corrected to neutral were still corrected within a couple of degrees of neutral.  There were 7 knees with 7° or greater valgus deformity, and all were corrected to neutral (mean 2°, range of 0 to 3°).  The authors concluded that the findings of this study demonstrated that all knees were corrected in the appropriate direction within a few degrees of neutral, and no knees were over-corrected.  The implication of this ability to achieve alignment goals on clinical outcomes will need to be evaluated in future studies.  The results from this study demonstrated the potential for the robotic-assisted device during TKA in helping surgeons achieve a pre-operatively planned desired neutral alignment.

Marchand et al (2019a) noted that although several studies highlighted the advantages of RA-TKA, few examined its intra-operative outcome.  These researchers analyzed the RA-TKA's ability to assist with intra-operative correction of: (i) flexion and (ii) extension gaps, as well as its ability to (iii) accurately predict implant sizes.  Furthermore, in this RA-TKA cohort, length of stay (LOS), complications, and re-admissions were evaluated.  A total of 335 patients who underwent RA-TKA were included.  The robotic software virtually measured the intra-operative pre-bone cut extension and flexion gaps.  Differences in medial versus lateral pre-bone cut extension and flexion gaps were calculated.  A total of 155 patients (46 %) had an extension gap difference of between -2 and 2 mm (mean, -0.3 mm), while 119 patients (36 %) had a flexion gap difference of between -2 and 2 mm (mean, -0.6 mm).  Post-bone cut differences in medial versus lateral flexion and extension gaps were measured.  Balanced knees were considered to have a medial and lateral flexion gap difference within 2 mm.  The robot-predicted implant size was also compared with the final implant size.  In additional, LOS, complications, and re-admissions were assessed.  All patients achieved a post-bone cut extension gap difference between -1 and 1 mm (mean, -0.1 mm).  A total of 332 patients (99 %) achieved a post-bone cut flexion gap difference of between -2 and 2 mm (mean, 0 mm).  For 98 % of prostheses, the robotic software predicted within 1 implant size the actual tibial or femoral implant size used.  The mean LOS was found to be 2 days.  No patients suffered from superficial skin infection, pin site infections or fractures, soft tissue damage, and no robotic cases were converted to manual TKA due to intra-operative complications.  A total of 8 patients (2.2 %) were re-admitted; however, none was directly related to robotic use.  The robotic software and use of a pre-operative computed tomography (CT) substantially helped with intra-operative planning and accurate prediction of implant sizes.  Thus, based on the results of this study, the RA-TKA device did, in fact, provide considerable intra-operative assistance.  Moreover, these researchers state that there is still a need to further evaluate the impact of all these benefits on long-term outcomes and survival.

Marchand et al (2019b) stated that RA-TKA has been shown to potentially have certain pre- and intra-operative advantages over manual techniques.  Although there are many studies on the alignment advantages when using the robotic-arm assisted (RAA) system for TKA, there have been questions regarding patient-reported outcomes.  These researchers used this index to compare: (i) total; (ii) physical function; and (iii) pain scores for manual versus RAA patients.  They compared 53 consecutive RAA to 53 consecutive manual TKAs.  No differences in pre-operative scores were found between the cohorts.  Patients were administered a modified WOMAC satisfaction survey pre-operatively, and at 1-year post-operatively.  Univariate analyses and multi-variate models with stepwise backward linear regression were used to evaluate the associations between outcome scores and surgical technique, age, sex, as well as body mass index (BMI).  The RAA cohort had significantly improved mean total (6 ± 6 versus 9 ± 8 points, p = 0.03) and physical function scores (4 ± 4 versus 6 ± 5 points, p = 0.02) when compared to the manual cohort.  The mean pain score for the RAA cohort [2 ± 3 points (range of 0 to 14 points)], was also lower than that for the manual cohort [3 ± 4 points (range of 0 to 11 points) (p = 0.06)].  On backward linear regression analyses, RAA was found to be significantly associated with more improved total (beta coefficient [β]-0.208, SE [standard error] 1.401, p < 0.05), function (β = 0.216, SE = 0.829, p < 0.05), and pain scores (β-0.181, SE = 0.623, p = 0.063).  The RAA technique was found to have the strongest association with improved scores.  The authors concluded that with newer surgical technologies constantly being introduced, it is imperative to continue to evaluate these new modalities, especially in their abilities to improve patient satisfaction outcomes.  The findings of this study suggested that RAA patients may have short-term improvements at minimum 1-year post-operative; however, longer-term follow-up with greater sample sizes are needed to further validate these findings.

Pietrzak et al (2019) stated that patient dissatisfaction after TKA is a concern.  Surgical error is a common, avoidable cause of failed TKA.  Correct femoral and tibial component sizing improves implant longevity, clinical outcomes, knee balance, and pain scores.  These researchers hypothesized that pre-operative 3D templating for RA-TKA is more accurate than 2D digital templating.  Prospectively collected data from 31 RA-TKAs were assessed to determine accuracy pertaining to implant sizing and positioning.  All cases undergoing RA-TKA undergo pre-operative CT-scans as per protocol.  A total of 3 blinded observers retrospectively templated these knees for TKA using standard radiographs.  They compared whether 2D templating was as accurate as CT-guided templating.  Post-operative radiographs were then evaluated for sizing and positioning.  Intraclass correlation coefficients (ICCs) and the effect of learning curve were assessed.  Pre-operative femoral component 3D templating and retrospective blinded 2D templating accuracies were 96.6 % and 52.9 %, respectively (χ 2: 17.965; odds ratio [OR]: 24.957, 3.250 to 191.661; p < 0.001).  Tibial component 3D and 2D templating accuracies were 93.1 % and 28.7 %, respectively (χ 2: 36.436; OR: 33.480, 7.400 to 151.481; p < 0.001).  ICC for the 3 radiograph observers was 0.920 (95 % CI: 0.652 to 0.890; p < 0.001) for the femur and 0.833 (0.717 to 0.911; p < 0.001) for the tibia, showing excellent agreement.  The authors concluded that pre-operative CT-based templating for RA-TKA more accurately predicted the size of implants compared with traditional 2D digital templating; this may improve OR efficiency and cost containment; and warrants further investigation.

Sultan et al (2019) noted that despite the demonstrated success of modern TKA, it remains a procedure that involves sophisticated pre-operative planning and meticulous technique to reconstruct the mechanical axis, achieve ideal joint balance, and restore maximal ROM.  Recently, RA-TKAs have emerged as a promising new technology offering several technical advantages, and it is achieving excellent radiological results, including establishing the posterior condylar offset ratio (PCOR) and the Insall-Salvati Index (ISI).  Studies have demonstrated that these parameters were surgically modifiable, and their accurate restoration (fewer mean differences) correlate with improved final joint ROM.  However, there is a paucity of studies that evaluate these parameters in light of performing RA-TKA.  These researchers compared: (i) PCOR; and (ii) ISI restoration in a cohort of patients who underwent RA-TKA versus M-TKA.  They evaluated a series of 43 consecutive RA-TKA (mean age of 67 years; range of 46 to 79 years) and 39 M-TKA (mean age of 66 years; range of 48 to 78 years) performed by 7 fellowship-trained joint reconstructive surgeons.  All surgeries were performed using medial para-patellar approaches by high-volume surgeons.  Using the Knee Society Radiographic Evaluation System, pre-operative and 4-to-6-week post-operative radiographs were analyzed to determine the PCOR and patella height based on the ISI.  The mean post-operative PCOR was larger in M-TKA when compared to the RA cohort (0.53 versus 0.49; p = 0.024).  The absolute MD between pre- and post-operative PCOR was larger in M-TKA when compared to RA-TKA (0.03 versus 0.004; p = 0.01).  Furthermore, the number of patients who had post-operative ISI outside of the normal range (0.8 to 0.12) was higher in the M-TKA cohort (12 versus 4).  The authors concluded that patients who underwent RA-TKA had smaller mean differences in PCOR, which has been previously shown to correlate with better joint ROM at 1 year following surgery.  In addition, these patients were less likely to have values outside of normal ISI, which meant they were less likely to develop patella baja leading to restricted flexion and overall decreased ROM.  Moreover, these researchers stated that future studies are needed to compare these clinical outcomes in patients.

The authors stated that this study had several drawbacks including its relatively small sample size (n = 43).   Also, the radiological analysis was only limited to studying differences in PCOR and ISI without reporting on other parameters. 

Kayani and Haddad (2019) stated that robotic technology enables TKA to be undertaken with improved accuracy of implant positioning and reduced periarticular soft-tissue injury compared with conventional jig-based TKA.  This has translated to improved inpatient functional rehabilitation and earlier time to hospital discharge compared with conventional jig-based TKA.  Robotic technology offers potential for further research by providing objective data on gap measurements and knee kinematics following specific ligamentous releases; and provides an avenue for executing pre-planned implant positioning and alignment with greater precision and reproducibility for study purposes.  These advantages must be acknowledged while respecting the limitations of robotic TKA, which include additional costs for installation and maintenance of the robotic machine, additional radiation exposure, and paucity of long-term data showing any functional benefit over conventional jig-based TKA.  The results of further high-quality studies with longer term follow-up on functional outcomes, implant survivorship, complications, and cost-effectiveness are awaited.

Clement et al (2019) compared the knee-specific functional outcome of robotic unicompartmental knee arthroplasty (rUKA) with manual total knee arthroplasty (mTKA) for the management of isolated medial compartment osteoarthritis (OA).  Secondary aims were to compare length of hospital stay (LOS), general health improvement, and satisfaction between rUKA and mTKA.  A powered (1:3 ratio) cohort study was performed.  A total of 30 patients undergoing rUKA were propensity score matched to 90 patients undergoing mTKA for isolated medial compartment arthritis.  Patients were matched for age, sex, body mass index (BMI), and pre-operative function.  The Oxford Knee Score (OKS) and EuroQol five-dimension questionnaire (EQ-5D) were collected pre-operatively and 6 months post-operatively.  The Forgotten Joint Score (FJS) and patient satisfaction were collected 6 months post-operatively; LOS was also recorded.  There were no significant differences in the pre-operative demographics (p ⩾ 0.150) or function (p ⩾ 0.230) between the groups.  The 6-month OKS was significantly greater in the rUKA group when compared with the mTKA group (difference 7.7, p < 0.001).  There was also a greater 6-month post-operative EQ-5D (difference 0.148, p = 0.002) and FJS (difference 24.2, p < 0.001) for the rUKA when compared to the mTKA.  No patient was dissatisfied in the rUKA group and 5 (6 %) were dissatisfied in the mTKA, but this was not significant (p = 0.210); LOS was significantly (p < 0.001) shorter in the rUKA group (median of 2 days, inter-quartile range (IQR) 1 to 3) compared to the mTKA (median of 4 days, IQR 3 to 5).  The authors concluded that patients with isolated medial compartment arthritis had a greater knee-specific functional outcome and generic health with a shorter length of hospital stay after rUKA when compared to mTKA.  Moreover, these researchers stated that these functional results should be confirmed in future prospective comparative studies.

The authors stated that the major drawback of this study was the non-randomization of the surgical intervention (group) between 2 different hospitals.  The 3 surgeons (JTP, GM, PS) worked between the 2 hospitals but rUKA is not available in one, and patients in that institution were offered an mTKA or an mUKA.  There were only 12 mUKAs performed in the non-rUKA center during the study period.  The authors felt that this low rate of mUKA was reflected in the U.K., with only 8 % of primary knee arthroplasties being a UKA3 and was as low as 3 % in some regions.  This low rate of uptake for mUKA did, however, allow the comparison of the different interventions between the 2 groups that had the same pattern of joint disease (medial compartment), which would have not been possible if rUKA was available in both centers.  Previous studies comparing the outcome of UKA with TKA often match for patient variables and pre-operative score but not for disease pattern, with some patients in the TKA group having bi- and tri-compartmental disease.  The length of follow-up was short, reporting only 6-month data, and this may change with longer follow-up and should be assessed in future studies.  However, the majority of the improvement in the OKS occurs in the first 6 months, with only a 1 to 2-point further increase by 12 months.  Six-month data were collected by the NJR.  Comparative studies of UKA versus TKA using this data found a 1.5-point difference in the post-operative OKS between the groups, which was not clinically significant as is it was less than the MCID.  In contrast, the current study at this same time-point found a statistically and clinically (being more than the MCID) significantly greater OKS in the rUKA group and supports a better “early” functional outcome, but whether this will be observed into the mid-to-longer term remains unknown.  The 3:1 group ratio could also be raised as a limitation of the study.  This ratio was chosen because of the availability of data from the 2 centers included.  The hospital used to select the matched mTKA cohort was a large-volume arthroplasty center whereas the hospital performing rUKA was a smaller-volume center.  However, one advantage of the larger number of mTKAs being available with 6-month outcomes was the ability to propensity score match to the smaller defined rUKA group, which enabled a powered comparative study to be conducted.  The propensity score matching did not include patient co-morbidities, which was a limitation, but did include the EQ-5D, which is a marker of generic physical and mental health.  Also, tourniquet was used in the mTKA but not routinely for the rUKA.  While this has been shown to influence early functional outcome, these differences were not observed 6 months post-operatively.

Ren et al (2019) stated that in the field of prosthetics, the ultimate goal is to improve the clinical outcome by using a technique that prolongs the longevity of prosthesis.  Active rTKA is one such technique that is capable of providing accurate implant position and restoring mechanical alignment.  Although relevant studies have been performed, the differences in the efficacy and reliability between rTKA and conventional mTKA have not yet been adequately discussed.  These researchers referenced articles, including randomized controlled trials (RCTs) and comparative retrospective research, from PubMed, Embase, Cochrane Library and Web of Science to compare rTKA with mTKA.  Data extraction and quality assessment were conducted for each study.  Statistical analysis was performed using Revman V. 5.3.  A total of 7 studies with a total of 517 knees undergoing TKA were included.  Compared with conventional surgery, rTKA showed better outcomes in precise mechanical alignment (mean difference [MD]: − 0.82, 95 % confidence interval [CI]: −1.15 to − 0.49, p < 0.05) and implant position, with lower outliers (p < 0.05), better functional score (Western Ontario and McMaster University, Knee Society Score functional score) and less drainage (MD: − 293.28, 95 % CI: − 417.77 to − 168.79, p < 0.05).  No significant differences were observed when comparing the operation time, range of motion (ROM) and complication rates.  The authors concluded that the current research demonstrated that rTKA surgeries were more capable of improving mechanical alignment and prosthesis implantation when compared with conventional surgery.  Moreover, these researchers stated that further studies are needed to examine the potential benefits and long-term clinical outcomes of rTKA.

Zhang et al (2019) noted that rUKA has been recommended for treatment of unicompartmental knee OA.  However, its safety and effectiveness remain controversial compared with conventional UKA.  In a meta-analysis, these investigators re-evaluate the effects of rUKA on clinical functional outcomes.  PubMed, Embase, and Cochrane Library databases were searched to screen the relevant studies.  Continuous data (surgical time, knee excursion during weight acceptance, American knee society score [AKSS], Oxford knee score [OKS], forgotten joint score [FJS], VAS, and ROM were pooled using a standardized mean difference (SMD) with their corresponding 95 % CIs to estimate the effect size, while dichotomous data (complication rate, revision rate) were pooled to obtain the relative risk (RR) with a 95 % CI by STATA 13.0 software.  A total of 11 studies involving 498 patients undergoing rUKA and 589 patients receiving conventional UKA were included.  The pooled results demonstrated that robotic-assisted could significantly reduce the complication rate (RR: 0.62, 95 % CI: 0.45 to 0.85; p = 0.0041) and improved the knee excursion during weight acceptance (SMD: 0.62, 95 % CI: 0.25 to 1.00; p = 0.001), but prolonged the surgical time (SMD: 0.74, 95 % CI: 0.40 to 1.08; p < 0.001).  No significant difference in the revision rate, AKSS, OKS, FJS, VAS, and ROM between robotic-assisted and conventional UKA groups.  The authors concluded that the findings of this meta-analysis demonstrated rUKA may be a safe and effective surgical procedure for treatment of unicompartmental knee OA.

The authors concluded that there were several limitations in this current meta-analysis.  First, the sample size was not large for several clinical parameters, such as the revision rate, AKSS, OKS, FJS, VAS, and ROM, which may influence the assessment of the difference between robotic-assisted and conventional UKA.  Second, the follow-up time was heterogeneous among different studies, which may also affect the results of follow-up related outcomes.  Third, some studies were not RCT, which may lead to some potential bias.  Accordingly, these findings should be further confirmed by more RCTs and large-scale studies.

The study by Cool et al (2019) was a cost-effectiveness analysis.  The authors concluded that the findings of this study showed robotic-assisted TKA (rTKA) to be associated with significantly lower 90-day episode-of-care (EOC) costs.  These lower rTKA patient costs were likely attributable to the significantly lower index costs, increased likelihood of being discharged to home shorter LOS and decreased re-admission rates, when compared with mTKA patient costs.  Additional contributing factors may include a number of robotic-arm assisted clinical, radiographic and patient outcome advantages.  These researchers stated that future studies should build on these findings by performing hospital and surgeon-specific cost analyses as well as an analysis from the provider perspective.  Furthermore, these data could stimulate further discussions regarding healthcare cost-containment with operating-room technology utilization.  Based on these findings, robotic-arm assisted surgery appeared to be cost-effective and provide added value for payers.  As a result of these findings, robotic-arm assisted surgery can be an effective tool in managing existing value-based care programs while also offering value given its potential to promote efficiencies through the EOC journey.

The authors stated that this study was not without limitations.  As a large administrative claims database study, it was difficult to precisely identify the desired study population of interest as well as their clinical progressions.  Specific to this study, identifying patients who underwent rTKA based on coding for a CT-scan performed 60 days prior to TKA at an out-patient setting substantially reduced the number of patients who could be included for analysis.  The sample size was also limited, as the study time period was early in the adoption for rTKA in the U.S. and the Medicare SAF data had a significant lag between the provision of services and the availability of the data.  Additionally, it was possible that some of the cases identified had been incorrectly coded, although the literature indicated this would only be likely in a small minority of cases.  In addition, other clinical factors, such as the type and duration of anesthesia, the anti-coagulation prescribed, and other risk factors were not assessed.  However, these researchers performed a propensity score match in order to account for age, sex, race, geographic region and high-cost co-morbidities with the goal of minimizing confounding factors between study cohorts.  This study evaluated all-cause re-admissions, consistent with Medicare's definition in their Bundled Payment Programs.  Future studies could analyze individual causes for re-admission or more specific complications (e.g., pin-site infections, peri-prosthetic fractures, etc.).  Unfortunately, the dataset in this analysis did not provide the level of granularity needed to facilitate a specific evaluation of pin-site complications, however existing literature showed the incidence with similar fixation types to be as low as 0.065 to 0.64 %.  Finally, this analysis examined the economic impact of rTKA to a payer and did not account for capital equipment investment(s) or the pre-operative CT-scan.

Hampp et al (2019) examined if robotic-arm assisted TKA (RATKA) allows for more accurate and precise bone cuts and component position to plan compared with manual TKA (MTKA).  Specifically, these researchers evaluated the following:
  1. final bone cuts,
  2. final component position, and
  3. a potential learning curve for RATKA.

On 6 cadaver specimens (12 knees), a MTKA and RATKA were performed on the left and right knees, respectively.  Bone-cut and final-component positioning errors relative to pre-operative plans were compared.  Median errors and standard deviations (SDs) in the sagittal, coronal, and axial planes were compared.  Median values of the absolute deviation from plan defined the accuracy to plan.  SDs described the precision to plan.  RATKA bone cuts were as or more accurate to plan based on nominal median values in 11 out of 12 measurements.  RATKA bone cuts were more precise to plan in 8 out of 12 measurements (p ≤ 0.05).  RATKA final component positions were as or more accurate to plan based on median values in 5 out of 5 measurements.  RATKA final component positions were more precise to plan in 4 out of 5 measurements (p ≤ 0.05).  Stacked error results from all cuts and implant positions for each specimen in procedural order showed that RATKA error was less than MTKA error.  The authors concluded that although this study analyzed a small number of cadaver specimens, there were clear differences that separated these 2 groups.  When compared with MTKA, RATKA demonstrated more accurate and precise bone cuts and implant positioning to plan.  These researchers stated that this cadaveric study provided preliminary evidence supporting the use of robotic-arm assisted systems in TKA; ongoing clinical studies will hopefully show that this novel technology will result in enhanced clinical outcomes.

The study by Cotter et al (2020) was another cost analysis.  These investigators compared 90-day EOC costs for mTKA and rTKA.  A retrospective review of an institutional database from April 2015 to September 2017 identified consecutive mTKAs and rTKAs using a single implant system performed by 1 surgeon.  The rTKA platform became available at the authors’ institution in October 2016.  Prior to this date, all TKAs were performed with mTKA technique.  After this date, all TKAs were performed using robotic-assistance without exception.  Sequential cases were included for both mTKA and rTKA with no patients excluded.  Clinical and financial data were obtained from medical and billing records; 90-day EOC costs were compared.  Statistical analysis was performed by departmental statistician.  A total of 139 mTKAs and 147 rTKAs were identified.  No significant differences in patient characteristics were noted.  Total intra-operative costs were higher ($10,295.17 versus 9,998.78, respectively, p < 0.001) and in-patient costs were lower ($3,893.90 versus 5,587.40, respectively, p < 0.001) comparing rTKA and mTKA; LOS was reduced 25 % (1.2 versus 1.6 days, respectively, p < 0.0001) and prescribed opioids were reduced 57 % (984.2 versus 2,240.4 morphine milligram equivalents, respectively, p < 0.0001) comparing rTKA with mTKA; 90-day EOC costs were $2,090.70 lower for rTKA compared with mTKA ($15,629.94 versus 17,720.64, respectively; p < 0.001).  The higher intra-operative costs associated with rTKA were offset by greater savings in post-operative costs for the 90-day EOC compared with mTKA.  Higher intra-operative costs were driven by the cost of the robot, maintenance fees, and robot-specific disposables.  Cost savings with rTKA were primarily driven by reduced instrument pan re-processing fees, shorter LOS, and reduced prescribed opioids compared with mTKA technique.  The authors concluded that rTKA demonstrated improved value compared with mTKA based on significantly lower average 90-day EOC costs and superior quality exemplified by reduced LOS, less post-operative opioid requirements, and reduced post-discharge resource utilization.

Mancino et al (2020) noted that TKA is a highly successful operation that improves patients’ quality of life (QOL) and functionality.  Yet, up to 20 % of TKA patients remain unsatisfied with the functional outcomes.  Robotic TKA has gained increased attention and popularity in order to improve patient satisfaction and implant survivorship by increasing accuracy and precision of component implantation.  In a systematic review, these investigators compared implant survivorship, complication rates, clinical outcomes, and radiological outcomes between rTKA RA and conventional mTKA.  Articles were referenced from the U.S. National Library of Medicine (PubMed/Medline), Embase, and the Cochrane Database of Systematic Reviews.  A total of 9 comparative studies with 1,199 operated knees in 1,159 patients were included, 614 underwent active or semi-active rTKA compared to 585 mTKA.  Improvements in the rTKA group were reported for early functional outcomes, radiographic outliers (rTKA 16 % versus mTKA 76 %) and radiolucent lines (rTKA 0 % versus mTKA 35 %).  No significant differences between the 2 groups were reported in overall survivorship (rTKA 98.3 % versus mTKA 97.3 %), complication rate (rTKA 2.4 % versus mTKA 1.4 %) and operative time (rTKA 88 mins versus mTKA 79 mins).  Despite higher costs, rTKA offered better short-term clinical outcomes when compared to conventional mTKA with reduction in radiographic outliers and reduced risks of iatrogenic soft tissues injuries (reduced blood loss and post-operative drainage).  Moreover, these researchers stated that further high-quality long-term studies of modern robotic systems are needed to evaluate how the increased accuracy and reduced outliers affect the long-term survivorship of the implants and the clinical outcomes.

In a systematic review and meta-analysis, Agarwal et al (2020) examined if rTKA resulted in improved clinical and radiological outcomes; and assessed the breadth and depth of studies conducted on this topic.  These researchers carried out a Preferred Reporting Items for Systematic Reviews and Meta-Analyses systematic review using 4 databases (Medline, Embase, Cochrane, and Web of Science) to identify all clinical studies that examined clinical or radiological outcomes using rTKA.  The Critical Appraisal Skills Program checklist for cohort studies was used for critical appraisal and evaluation of all 22 studies that met the inclusion criteria.  All studies reviewed determined that knee arthroplasty improved clinical outcomes; 12 studies found statistically better clinical outcomes with rTKA compared with conventional mTKA, whereas 9 studies found no difference; 1 study did not examine clinical outcomes.  When assessing radiological outcomes, 14 studies reported that rTKA resulted in more consistent and accurate post-operative mechanical alignment, whereas 2 studies reported no difference; 6 studies did not examine radiological outcomes.  The authors concluded that although knee arthroplasty is one of the most commonly performed orthopedic operations, the level of patient satisfaction varies.  The meta-analyses conducted in this systematic review showed that rTKA resulted in greater improvements in post-operative Hospital for Special Surgery score and Western Ontario and McMaster Universities scores compared to conventional mTKA.  Furthermore, it showed that rTKA resulted in more accurate post-operative alignment of prostheses.  These together can explain the improved post-operative outcomes.  Moreover, these researchers stated that more randomized controlled trials must be conducted before this technique is integrated into routine clinical practice.

Ofa et al (2020) examined the differences between RA-TKA and non-RA-TKA on peri-operative and post-operative complications and opioid consumption.  An administrative database was queried from 2010 to Q2 of 2017 for primary TKAs performed via robot-assisted surgery versus non-robot-assisted surgery.  Systemic and joint complications and average morphine milligram equivalents were collected and compared with statistical analysis.  Patients in the non-robotic TKA cohort had higher levels of prosthetic revision at 1-year after discharge (p < 0.05) and higher levels of MUA at 90 days and 1-year after discharge (p < 0.05).  Furthermore, those in the non-robotic TKA cohort had increased occurrences of deep vein thrombosis (DVT), altered mental status, pulmonary embolism, anemia, acute renal failure, cerebrovascular event, pneumonia, respiratory failure, and urinary tract infection (UTI) during the inpatient hospital stay (all p < 0.05) and at 90 days after discharge (all p < 0.05).  All of these categories remained statistically increased at the 90-days post-discharge date, except pneumonia and stroke.  Patients in the non-robotic TKA cohort had higher levels of average morphine milligram equivalents consumption at all time periods measured (p < 0.001).  The authors concluded that the use of robotics for TKA found lower revision rates, lower incidences of MUA, decreased occurrence of systemic complications, and lower opiate consumption for post-operative pain management.  Moreover, these researchers stated that continued research and expansion on long-term data for robotics in knee arthroplasty procedures will help establish the future role of robotics in orthopedic operating rooms..  Level of Evidence = III.

The authors noted that a potential drawback of this study was that during the time period of data collection, the only FDA–approved robotic platform during this collection for TKA was the Stryker Mako Robotic-arm Assist (Stryker Corporation, Kalamazoo, MI).  Furthermore, by measuring complication measurements at 1 year, this study was limited to short-term outcomes.  Similarly, examination of systemic complications was limited to a 90-day evaluation.  In addition, there exists a possibility of coding bias with the manual entry of diagnosis and procedural codes used for this study.  Codes between ICD-9 and ICD-10 do not exactly match.  To address possible coding bias and the lack of continuity between ICD-9 and ICD-10 codes, a code translator was used to match corresponding codes.  Despite the use of multi-variate logistic regression to diminish the effect of confounders, there still remains the chance of other confounders influencing the data.  Although this study could have incorporated more elements into the adjustment to control for other confounders, the decision to control for age, BMI, gender, CCI, tobacco use, and diabetes mellitus was only because these represented “high-impact” confounders.  Finally, another limitation was that patients in both cohorts could not be identified by the type of anesthesia received (general versus spinal or epidural).  With the Current Procedural Terminology (CPT) coding, there is no stratification between general or regional anesthesia, as anesthesia only codes for time units.

Smith et al (2021) stated that approximately 20 % of the patients are dissatisfied with the results of their TKA.  Computer technology has been introduced for TKA to provide real-time intra-operative information on limb alignment and exact flexion/extension gap measurements.  These researchers examined if patient satisfaction could be improved with the use of RA technology following primary TKA.  A total of 120 consecutive patients undergoing RA-TKA with real-time intra-operative alignment and gap balancing information were compared with a prospective cohort of 103 consecutive patients undergoing TKA with manual jig-based instruments during the same time period.  There were no differences between groups with age, gender, baseline KSS knee and function scores, follow-up, and ASA scores.  TKAs were carried out using same technique, implant design, anesthesia, and post-operative treatment protocols.  Patient satisfaction survey using KSS and Likert scoring system were obtained at 1-year follow-up.  Likert scoring system demonstrated 94 % of the patients in the RA group were either very satisfied or satisfied versus 82 % in the manual instruments TKA group (p = 0.005).  RA-TKA group had better average scores of all 5 satisfaction questions although not significant.  RA-TKA group had a better average overall satisfaction score of 7.1 versus 6.6 in the manual instrument group, p = 0.03.  KSS function scores were significantly better at 6 weeks and 1 year post-operatively (p = 0.02, 0.005), and KSS knee scores were significantly better at 1 year post-operatively (p = 0.046).  There were multiple reasons for patient dissatisfaction following primary TKA.  Using intra-operative computer technology with RA surgery for patients undergoing a primary TKA, a significant improvement in patient satisfaction was demonstrated compared with TKA using conventional manual jig-based instruments.  The authors concluded that RA surgery provided several advantages in TKA including real-time information in millimeters to help obtain balanced gaps, accurate bone cuts, reduced soft tissue injury, and achieve the target alignment that may lead to improved patient satisfaction.  Moreover, these researchers stated that future work in addition to a prospective randomized study with longer follow-up will help determine the efficacy of this technology in primary TKA.

Marchand et al (2021) noted that advanced imaging used in RA-TKA, such as CT-based 3D planning, may provide an accurate means of implant sizing pre-operatively.  These researchers examined pre-operative CT-based implant planning accuracy for RA- TKA in patients who have (i) varus deformities, (ii) valgus deformities, (iii) neutral alignment, and (iv) retained hardware.  A total of 393 patients underwent a RA-TKA by a single surgeon received pre-operative CT scans.  The surgeon reviewed the CT-based model pre-operatively and recorded the expected size of the components.  The final implants used in each case were recorded and compared with the surgeon's pre-operative plan.  In all groups of patients, the surgeon's CT-based implant plan was within 1 size of the implant utilized 100 % of the time for both the tibiae and femora.  Overall, the surgeon was exactly matched in 319 (81 %) and 315 (80 %) cases for the femoral and tibial components, respectively.  For the femoral component, the mean age for patients in whom the original plan was exactly matched was younger than those whose implants were up-sized and older than patients those implants were down-sized (p = 0.024).  Other patient demographics and pre-operative knee alignment were not associated with predictive accuracy for femoral or tibial components.  These findings demonstrated how pre-operative CT-based, 3D planning for RA-TKA was accurate to within 1 size of the components in every case (100 %), and exactly matched in 80 %.  The results of this study were important because they demonstrated how CT-based pre-operative implant planning for TKA was reliable and accurate across all native knee alignments and other patient-specific factors.  Furthermore, they built on a previous study by the same single surgeon, demonstrating that predictive ability could improve over time.  This may be important as researchers move toward more out-patient surgery with less ability for prostheses inventory at ambulatory sites.

This study had several drawbacks including its non-randomized design and single-surgeon experience, such that these findings may not be generalizable to other surgeons.  These researchers stated that future studies should include multiple surgeons and surgical centers to improve the generalizability of these results.  Future studies should also examine differences in operative times, procedure costs, and other potential impacts on the surgical procedure that may be associated with accurately predicting implant size pre-operatively.

Zhang et al (2022a) noted that haptic RA-TKA seeks to leverage 3D planning, intra-operative assessment of ligament laxity, and guided bone preparation to establish and achieve patient-specific targets for implant position.  These researchers compared: (i) operative details, (ii) knee alignment, (iii) recovery of knee function, and (iv) complications during adoption of this technique to their experience with manual TKA.  They compared 120 RA-TKAs performed between December 2016 and July 2018 to 120 consecutive manual TKAs performed between May 2015 and January 2017.  Operative details, LOS, and discharge dispositions were collected.  Tibio-femoral angles, Knee Society Scores (KSS), and ranges of motion (ROM) were assessed until 3 months post-operatively.  Manipulations under anesthesia (MUA), complications, and re-operations were tabulated.  Mean operative times were 22 mins longer in RA-TKA (p < 0.001) for this early cohort; but decreased by 27 mins (p < 0.001) from the first 25 RA-TKA cases to the last 25 RA-TKA cases.  Less articular constraint was used to achieve stability in RA-TKA (93 % versus 55 % cruciate-retaining, p < 0.001; 3 versus 35 % posterior stabilized (PS), p < 0.001; and 4 % versus 10 % varus-valgus constrained, p = 0.127).  RA-TKA had lower LOS (2.7 versus 3.4 days, p < 0.001).  Discharge dispositions, tibio-femoral angles, KSS, and knee flexion angles did not differ, but MUA were less common in RA-TKAs (4 versus 17 %, p = 0.013).  These investigators observed less use of constraint, shorter LOS, and fewer MUA in RA-TKA, with no increase in complications.  Operative times were longer, particularly early in the learning curve, but improved with experience.  All measured patient-centered outcomes were equivalent or favored the newer technique, suggesting that RA-TKA with patient-specific alignment targets did not compromise initial quality.  Observed differences may relate to improved ligament balance or diminished need for ligament release.  These preliminary findings need to be validated by well-designed studies.

The drawbacks of this study included its retrospective, non-randomized design; clinical assessment was not blinded; sex differed between groups that may have introduced bias; as well as its short-term follow-up (5 months I the manual group).

In a systematic review and meta-analysis, Zhang et al (2022b) compared the accuracy of component positioning, alignment and balancing techniques employed, patient-reported outcomes, and complications of RA-TKA) with M-TKA and the associated learning curve.  Searches of PubMed, Medline and Google Scholar were performed in October 2020 using PRISMA guidelines.  Search terms included "robotic", "knee" and "arthroplasty".  The criteria for inclusion were published clinical research articles reporting the learning curve for RA-TKA and those comparing the component position accuracy, alignment and balancing techniques, functional outcomes, or complications with M-TKA.  There were 198 articles identified, following full text screening, 16 studies satisfied the inclusion criteria and reported the learning curve of RA-TKA (n = 5), component positioning accuracy (n = 6), alignment and balancing techniques (n = 7), functional outcomes (n = 7), or complications (n = 5); 2 studies reported the learning curve using CUSUM analysis to establish an inflexion point for proficiency that ranged from 7 to 11 cases and there was no learning curve for component positioning accuracy.  The meta-analysis showed a significantly lower difference between planned component position and implanted component position, and the spread was narrower for RA-TKA compared with the M-TKA group (femur coronal: mean 1.31, 95 % CI: 1.08 to 1.55, p < 0.00001; tibia coronal: mean 1.56, 95 % CI: 1.32 to 1.81, p < 0.00001); 3 studies reported using different alignment and balancing techniques between M-TKA and RA-TKA, 2 studies used the same for both group and 2 studies did not state the methods used in their RA-TKA groups.  RA-TKA resulted in better KSS compared to M-TKA in the short-to-mid-term follow-up (95 % CI: - 1.23 to -0.51], p = 0.004).  There was no difference in arthrofibrosis, superficial and deep infection, wound dehiscence, or overall complication rates.  RA-TKA demonstrated improved accuracy of component positioning and patient-reported outcomes.  The learning curve of RA-TKA for operating time was between 7 and 11 cases.  The authors concluded that future well-powered studies on RA-TKAs should report on the knee alignment and balancing techniques used to enable better comparisons on which techniques maximize patient outcomes.  Level of evidence III.

The authors stated that this study had several drawbacks.  First, the inclusion criteria, such as English language, may have excluded relevant studies.  Second, the methodology has known limitations regarding the type of studies included (non-blinded, non-randomized prospective and retrospective cohort studies) and the difficulties in assessing the analyses without access to the raw data.  Third, there was an important variability between the studies with respect to the type of outcome measurement used, the follow-up period and cohorts evaluated.  Moreover, there are not yet any published RCTS.  The studies on RA-TKAs were few and mainly have short-term follow-up.  Future studies with longer term follow-up will be needed to provide more conclusive findings in assessing the outcomes and benefits.  Another drawback was that 2 studies were excluded in the forest plot for functional outcomes of KSS scores because the spread of the data was not available for pooled analysis.  Furthermore, the overall WOMAC score collected by Marchand et al (2019b) used a modified scale rather than the original WOMAC.  These may have introduced bias into the analysis.

King et al (2022) examined the patient experience and short-term clinical outcomes associated with the hospital stay of patients who underwent RA-TKA.  These findings were compared with a cohort of patients who underwent TKA without robotic assistance performed by the same surgeon prior to the introduction of this technology.  A cohort of consecutive patients undergoing primary TKA for the diagnosis of osteoarthritis (OA) by a single fellowship-trained orthopedic surgeon over a 39-month period was identified.  Patients who underwent TKA during the year that this surgeon transitioned his entire knee arthroplasty practice to robotic assistance were excluded to eliminate selection bias and control for the learning curve.  All patients received the same prosthesis and post-operative pain protocol.  Patients that required intubation for failed spinal anesthetic were excluded.  A final population of 492 TKAs was identified.  Of these, 290 underwent TKA without robotic assistance and 202 underwent RA-TKA.  Patient demographic characteristics and short-term clinical data were analyzed.  RA-TKA was associated with shorter LOS (2.3 versus 2.6 days, p < 0.001), a 50 % reduction in morphine milligram equivalent utilization (from 214 to 103, p < 0.001), and a mean increase in procedure time of 9.3 mins (p < 0.001).  There was 1 superficial infection in the non-robotic cohort and there were no deep post-operative infections in either cohort.  There were no MUA in the robotic cohort while there were 6 in the non-robotic cohort.  Furthermore, there were no significant differences in emergency department visits, re-admissions, or return to the OR.  The authors concluded that this analysis corroborated existing literature suggesting that RA-TKA can be correlated with improved short-term clinical outcomes.  This study reported on a single surgeon's experience with regard to analgesic requirements, LOS, pain scores, and procedure time following a complete transition to RA-TKA.  These results underscored the importance of continued evaluation of clinical outcomes as robotic arthroplasty technology continues to grow.

This study had several drawbacks including the results were based on the practice of a single, high-volume, fellowship-trained surgeon, such that these findings may not be generalizable to other practices.  Also, patient-reported outcome measures were inconsistently collected during the study period.  These researchers stated that future research should evaluate how a transition to RA-TKA would impact patient-reported outcome measure.  Finally, these results were based on one platform of robotic assistance, and may not apply to all types of RA-TKA currently available to arthroplasty surgeons.

Partial Femoral Condyle Focal Resurfacing (HemiCAP-UniCAP) for the Treatment of Full-Thickness Cartilage Defects

Elbardesy et al (2021) stated that knee osteochondral defects are a common problem among young and active patients; thus, effective joint preserving surgeries is essential to prevent or even delay the onset of OA for these group of patients.  In a systematic review and meta-analysis, these investigators examined the available evidence for the effectiveness of femoral condyle resurfacing (HemiCAP / UniCAP) in the treatment of patients with focal femoral condyle cartilage defect.  Using the search terms : HemiCAP, UniCAP, Episurf, focal, femoral, condyle, inlay and resurfacing, these researchers reviewed the PubMed and Embase and the Cochrane Database of Systematic Reviews (CDSR) to find any articles published up to March 2020.  The short-term follow-up of the HemiCAP showed a 6.74 % revision rate; however, 29.13 % loss of follow-up let these investigators considered these results with caution especially if the revision rate progressively increased with time to 19.3 % in 5 to 7 years with inadequate evidence for the long-term results except the data from the Australian Joint Registry 2018, where the cumulative revision rate was 40.6 % (33.5 5 to 48.4 %) at 10 years.  The UniCAP used for defect that was more than 4 cm2 had a high revision rate (53.66 %), which was considered an unacceptable revision rate in comparison to another similar prosthesis such as Uni-Knee Arthroplasty (UKA).  The evidence from published studies and the meta-analysis suggested that partial resurfacing of the femoral condyle (HemiCAP) did not support its usage as a tool for the treatment of the focal cartilage defect in middle-aged patients.  Furthermore, the UniCAP as femoral condyle resurfacing had very high revision rate at 5 to 7 years (53.66 %) making the authors to recommend against its usage.

Resurfacing Capitate Pyrocarbon Implant for Carpal Injuries / Wrist Arthritis

Fulchignoni et al (2020) noted that up to 10 years ago, to treat patients with chronic wrist pain due to advanced stages of arthritis, surgeons had 4 main solutions: partial or total wrist arthrodesis, total wrist prosthesis and proximal row carpectomy (PRC).  Since 2010, a new technique has been described in literature using the Resurfacing Capitate Pyrocarbon Implant (RCPI), combined to PRC.  In a literature review, these researchers examined the indications, outcomes and complications associated with RCPI.  They carried out an electronic literature research on pertinent articles.  Surgical technique, results and complications described in those articles were presented.  The authors concluded that RCPI could be considered as a good alternative to arthrodesis and total wrist arthroplasty, at any ages, when PRC alone would not be indicated.  Moreover, these researchers stated that the drawbacks of this review included the small number of articles published on the use of RCPI combined with PRC in advanced stage of wrist OA and Kienbock’s disease, the short follow-up of some of the patients included is those articles, as well as the non-uniformity of methods for collecting results in the different publications.

In a retrospective study, Ferrero et al (2020) reported on 2 comparable groups of patients with advanced carpal arthritis treated with either PRC combined with a pyrocarbon resurfacing of the capitate (31 patients) or a 4-corner arthrodesis and dorsal plating (26 patients).  Follow-up time was 46 months (24 to 118).  Except for a modestly higher radial wrist deviation in the patients treated with 4-corner arthrodesis, there were no significant differences in outcomes between the groups.  Asymptomatic progression of OA in the lunate fossa was observed in 4 cases in both groups; 2 cases were converted to a total wrist arthrodesis in the pyrocarbon group compared with 1 case in the 4-corner arthrodesis group.  The authors concluded that although 4-corner arthrodesis remained the reference standard in the treatment of wrist OA with involvement of the mid-carpal joint, PRC combined with pyrocarbon resurfacing of the capitate was an alternative option.  It could even be used in selected cases with erosion of the lunate fossa.  Level of Evidence = III.

The authors stated that this study had several drawbacks.  These researchers acknowledged the relatively small number of subjects involved in each group, and the retrospective nature of the study did not allow for documentation of pre-operative ROM.  Another drawback was that the procedures were carried out by different surgeons; however, all surgeons had a high level of expertise and used the method of their preference.  Finally, a longer follow-up, especially for the PRC–RCPI patients, may provide additional information regarding the reliability of these techniques.  These investigators stated that concerns remain regarding the costs of the RCPI implant and its durability in the long-term, especially when it is used in young patients.

Rocchi et al (2021) stated that PRC is a long-time, well-accepted, easy-to-reproduce procedure for the treatment of several painful degenerative conditions of the wrist, when capitate pole and radius lunate fossa are preserved.  It has been reported to relieve pain and preserve a substantial wrist ROM, although a partial loss of strength has to be expected because of the decreased length of the carpus.  Since 2010, a new technique has been described in the literature using the RCPI, combined with PRC.  This implant has been designed to perform PRC even in the presence of degenerate joint surfaces; thereby, resolving the limited indications of this procedure.  However, if a resection of the capitate pole is carried out to set up the implant, similar to PRC it may not positively influence the recovery of strength.  The authors proposed an RCPI technique without any capitate bone resection, to preserve as much as possible the carpus length and so to improve the functional recovery.  These researchers described the surgical technique and preliminary results were presented.

Marcuzzi et al (2022) noted that Resurfacing Capitate Pyrocarbon Implant (RCPI) has been introduced in the surgical practice as an alternative method to restore wrist motion, strength and functions in patients suffering from wrist OA.  It has already been well described in the literature as a treatment for advanced stages of degenerative wrist diseases that follow scaphoid's and lunate's injuries such as scapho-lunate advanced collapse, scaphoid non-union advanced collapse, and advanced stages of Kienbock’s disease.  These investigators extended the use of RCPI to other selected cases of complicated wrist injuries, spreading out from the classic indications for which the device was designed.  These researchers discussed 8 cases with serious outcomes of carpal injuries treated with RCPI as salvage procedure between 2005 and 2013 by the 1st author of this study.  Among the 8 particular selected cases, at a mean follow-up of 4.3 years (range of 2 to 11) only 1 was considered a failure and underwent a total wrist arthrodesis, resolving pain after all.  The remaining 7 cases reported good results; ROM, VAS for pain, subjective satisfaction and radiographical outcomes were reported.  The authors concluded that as a result of this heterogeneous clinical experience, validated by long-term follow-ups in most cases, they think that the use of a RCPI can be suggested as an option in the outcomes of various carpal injuries.

Glossary of Terms

Table: Glossary of Terms
Term Definition
Conservative therapy Non-surgical medical management


Contraindications for metal-on-metal hip resurfacing:

  • Females of child-bearing age because of unknown effect of metal ion release on the fetus
  • Individuals who are immunosuppressed with diseases such as AIDS or individuals receiving high doses of corticosteroids
  • Individuals who are severely over-weight
  • Individuals who are skeletally immature
  • Individuals with any vascular insufficiency, muscular atrophy, or neuromuscular disease severe enough to compromise implant stability or post-operative recovery
  • Individuals with bone stock inadequate to support the device
  • Individuals with infection or sepsis
  • Individuals with known moderate-to-severe renal insufficiency
  • Individuals with known or suspected metal sensitivity.


The above policy is based on the following references:

Hip Resurfacing

  1. Alberta Heritage Foundation for Medical Research (AHFMR). Metal-on-metal surface replacement of the hip for congenital hip dysplasia. Technote 23. Edmonton, AB: AHFMR; 2000.
  2. Alberta Heritage Foundation for Medical Research (AHFMR). Metal-on-metal hip resurfacing for young, active adults with degenerative hip disease. Technote TN 33. Edmonton, AB: AHFMR; 2002. 
  3. Allison C. Minimally invasive hip resurfacing. Issues Emerg Health Technol. 2005;(65):1-4.
  4. American Academy of Orthopaedic Surgeons (AAOS). Technology Overview. Modern metal on metal hip resurfacing [website]. Rosemont, IL:  AAOS; December 4, 2009.
  5. American Academy of Orthopaedic Surgeons (AAOS). Technology Overview. Modern metal on metal hip implants [website]. Rosemont, IL: AAOS; December 2, 2011.
  6. American College of Occupational and Environmental Medicine (ACOEM). Hip and groin disorders. Occupational Medicine Practice Guidelines. Elk Grove Village, IL: ACOEM; 2011.
  7. Amstutz HC, Antoniades JT, Le Duff MJ. Results of metal-on-metal hybrid hip resurfacing for Crowe type-I and II developmental dysplasia. J Bone Joint Surg Am. 2007;89(2):339-346.
  8. Amstutz HC, Campbell P, Le Duff MJ. Metal-on-metal hip resurfacing: What have we learned? Instr Course Lect. 2007;56:149-161.
  9. Amstutz HC, Dorey F, O'Carroll PF. THARIES resurfacing arthroplasty. Evolution and long-term results. Clin Orthop. 1986;(213):92-114.
  10. Amstutz HC, Grigoris P, Safran MR, et al. Precision-fit surface hemiarthroplasty for femoral head osteonecrosis. Long-term results. J Bone Joint Surg Br. 1994;76(3):423-427.
  11. Amstutz HC, Noordin S, Campbell PA, et al. Precision fit surface hemiarthroplasty for femoral head osteonecrosis. In: Osteonecrosis: Etiology, Diagnosis, and Treatment. JP Jones Jr, JR Urbaniak, eds. Rosemont, IL: American Academy of Orthopaedic Surgeons; 1997:373-383.
  12. Amstutz HC. Present state of metal-on-metal hybrid hip resurfacing. J Surg Orthop Adv. 2008;17(1):12-16.
  13. Beaule PE, Schmalzried TP, Campbell P, et al. Duration of symptoms and outcome of hemiresurfacing for hip osteonecrosis. Clin Orthop. 2001;385:104-117.
  14. Bernath V. Hip resurfacing in patients with osteoarthritis. Evidence Centre Critical Appraisal. Clayton, VIC: Centre for Clinical Effectiveness (CCE); 2002.
  15. Bisset AF. Hip resurfacing in younger people with osteoarthritis. STEER: Succint and Timely Evaluated Evidence Reviews. Bazian Ltd., eds. London, UK: Wessex Institute for Health Research and Development, University of Southampton; 2001;1(8):1-7.
  16. BlueCross BlueShield Association (BCBSA), Technology Evaluation Center (TEC). Metal-on-metal total hip resurfacing. TEC Assessment Program. Chicago, IL: BCBSA; June 2007;22(3).
  17. Bogoch ER, Fornasier VL, Capello WN. The femoral head remnant in resurfacing arthroplasty. Clin Orthop. 1982;167:92-105.
  18. Bozic KJ, Pui CM, Ludeman MJ, et al. Do the potential benefits of metal-on-metal hip resurfacing justify the increased cost and risk of complications? Clin Orthop Relat Res. 2010;468(9):2301-2312.
  19. Bradley GW, Freeman MA, Revell PA. Resurfacing arthroplasty. Femoral head viability. Clin Orthop. 1987;(220):137-141.
  20. Cabanela ME. Bipolar versus total hip arthroplasty for avascular necrosis of the femoral head: A comparison. Clin Orthop. 1990;261:59.
  21. California Technology Assessment Forum (CTAF). Metal-on-metal total hip resurfacing as an alternative to total hip arthroplasty. A Technology Assessment. San Francisco, CA: CTAF; October 17, 2007.
  22. Campbell P, Mirra J, Amstutz HC. Viability of femoral heads treated with resurfacing arthroplasty. J Arthroplasty. 2000;15(1):120-122.
  23. Canadian Coordinating Office of Health Technology Assessment (CCOHTA). Metal-on-metal hip resurfacing. Pre-assessment No. 19. Ottawa, ON: CCOHTA; March 2003.
  24. Cimon K, Hodgson A. Metal-on-metal hip resurfacing. Health Technology Inquiry Service (HTIS). Ottawa, ON: Canadian Agency for Drugs and Technologies in Health (CADTH); April 16, 2007.
  25. Daniel J, Pynsent PB, McMinn DJ. Metal-on-metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis. J Bone Joint Surg Br. 2004;86(2):177-184.
  26. De Smet K, Campbell PA, Gill HS. Metal-on-metal hip resurfacing: A consensus from the Advanced Hip Resurfacing Course, Ghent, June 2009. J Bone Joint Surg Br. 2010;92(3):335-336.
  27. Frankel ES, Urbaniak JR.  Osteonecrosis. In: Ruddy: Kelley's Textbook of Rheumatology. 6th ed., Ch. 112. St. Louis, MO: W. B. Saunders Company; 2001:1661.
  28. Garbuz DS, Tanzer M, Greidanus NV, et al. The John Charnley Award: Metal-on-metal hip resurfacing versus large-diameter head metal-on-metal total hip arthroplasty: A randomized clinical trial. Clin Orthop Relat Res. 2010;468(2):318-325.
  29. Glyn-Jones S, Gill HS, McLardy-Smith P, Murray DW. Roentgen stereophotogrammetric analysis of the Birmingham hip resurfacing arthroplasty. A two-year study. J Bone Joint Surg Br. 2004;86(2):172-176.
  30. Hartmann A, Lützner J, Kirschner S, et al. Do survival rate and serum ion concentrations 10 years after metal-on-metal hip resurfacing provide evidence for continued use? Clin Orthop Relat Res. 2012;470(11):3118-3126.
  31. Hashimoto R, Dettori JR, Henrikson RB, et al. Hip resurfacing. Health Technology Assessment. Prepared for the Washington State Health Care Authority Health Technology Assessment Program by Spectrum Research, Inc. Olympia, WA: Washington State Health Care Authority; October 23, 2009.
  32. Hellman MD, Ford MC, Barrack RL. Is there evidence to support an indication for surface replacement arthroplasty? Bone Joint J. 2019;101-B(1_Supple_A):32-40.
  33. Hing C, Back D, Shimmin A. Hip resurfacing: Indications, results, and conclusions. Instr Course Lect. 2007;56:171-178.
  34. Howie DW, Cornish BL, Vernon-Roberts B. The viability of the femoral head after resurfacing hip arthroplasty in humans. Clin Orthop. 1993;291:171-184.
  35. Hungerford MW, Mont MA, Scott R, et al. Surface replacement hemiarthroplasty for the treatment of osteonecrosis of the femoral head [abstract]. J Bone Joint Surg. 1998;80A:1656.
  36. Jantzen C, Jørgensen HL, Duus BR, et al. Chromium and cobalt ion concentrations in blood and serum following various types of metal-on-metal hip arthroplasties: A literature overview. Acta Orthop. 2013;84(3):229-236.
  37. Jiang Y, Zhang K, Die J, et al. A systematic review of modern metal-on-metal total hip resurfacing vs standard total hip arthroplasty in active young patients. J Arthroplasty. 2011;26(3):419-426.
  38. Knecht A, Witzleb WC, Beichler T, Günther KP. Functional results after surface replacement of the hip: Comparison between dysplasia and idiopathic osteoarthritis. Z Orthop Ihre Grenzgeb. 2004;142(3):279-285.
  39. Krackow KA, Mont MA, Maar DC. Limited femoral endoprosthesis for avascular necrosis of the femoral head. Orthop Rev. 1993;22:457-463.
  40. Laaksonen I, Donahue GS, Madanat R, et al. Outcomes of the recalled articular surface replacement metal-on-metal hip implant system: A systematic review. J Arthroplasty. 2017;32(1):341-346.
  41. Lavigne M, Therrien M, Nantel J, et al. The John Charnley Award: The functional outcome of hip resurfacing and large-head THA is the same: A randomized, double-blind study. Clin Orthop Relat Res. 2010;468(2):326-336.
  42. Li J, Xu W, Xu L, Liang Z. Hip resurfacing for the treatment of developmental dysplasia of the hip. Orthopedics. 2008;31(12). pii:
  43. Lilikakis AK, Vowler SL, Villar RN. Hydroxyapatite-coated femoral implant in metal-on-metal resurfacing hip arthroplasty: Minimum of two years follow-up. Orthop Clin North Am. 2005;36(2):215-222, ix.
  44. McBryde CW, Shears E, O'Hara JN, Pynsent PB. Metal-on-metal hip resurfacing in developmental dysplasia: A case-control study. J Bone Joint Surg Br. 2008;90(6):708-714.
  45. McGrory B, Barrack R, Lachiewicz PF, et al. Modern metal-on-metal hip resurfacing. J Am Acad Orthop Surg. 2010;18(5):306-314.
  46. McKenzie L, Vale L, Stearns S, McCormack K. Metal on metal hip resurfacing arthroplasty. Eur J Health Econ. 2003;4(2):122-129.
  47. Moroni A, Cadossi M, Bellenghi C, et al. Resurrection of hip resurfacing: What is the evidence? Expert Rev Med Devices. 2006;3(6):755-762.
  48. Naal FD, Schmied M, Munzinger U, et al. Outcome of hip resurfacing arthroplasty in patients with developmental hip dysplasia. Clin Orthop Relat Res. 2009;467(6):1516-1521.
  49. National Horizon Scanning Centre (NHSC). Metal on metal resurfacing hip arthroplasty (hip resurfacing) -- horizon scanning review. New and Emerging Technology Briefing. Birmingham, UK: NHSC; 2000.
  50. National Institute for Clinical Excellence (NICE). Guidance on the use of metal on metal hip resurfacing arthroplasty. Technology Appraisal Guidance No.44. London, UK: NICE; 2002.
  51. National Institute for Health and Care Excellence (NICE). Technology Appraisal Guidance. Total hip replacement and resurfacing arthroplasty for end-stage arthritis of the hip. London, UK: NICE; February 26, 2014.
  52. Nelson CL, Walz BH, Gruenwald JM. Resurfacing of only the femoral head for osteonecrosis: Long-term follow-up study. J Arthroplasty. 1997;12:736-740.
  53. Ontario Ministry of Health and Long-Term Care, Medical Advisory Secretariat (MAS). Metal-on-metal total hip resurfacing arthroplasty. Health Technology Policy Assessment. Toronto, ON: MAS; February 2006.
  54. Pollard TC, Baker RP, Eastaugh-Waring SJ, Bannister GC. Treatment of the young active patient with osteoarthritis of the hip. A five- to seven-year comparison of hybrid total hip arthroplasty and metal-on-metal resurfacing. J Bone Joint Surg Br. 2006;88(5):592-600.
  55. Prosser GH, Yates PJ, Wood DJ, et al. Outcome of primary resurfacing hip replacement: Evaluation of risk factors for early revision. Acta Orthop. 2010;81(1):66-71.
  56. Schachter AK, Lamont JG. Surface replacement arthroplasty of the hip. Bull NYU Hosp Jt Dis. 2009;67(1):75-82.
  57. Scott RD, Urse JS, Schmidt R, et al. Use of TARA hemiarthroplasty in advanced osteonecrosis. J Arthroplasty. 1987;2:225-232.
  58. Sehatzadeh S, Kaulback K, Levin L. Metal-on-metal hip resurfacing arthroplasty: An analysis of safety and revision rates. Ont Health Technol Assess Ser. 2012;12(19):1-63.
  59. Shimmin A, Beaule PE, Campbell P. Metal-on-metal hip resurfacing arthroplasty. J Bone Joint Surg Am. 2008;90(3):637-654.
  60. Shimmin AJ, Bare JV. Comparison of functional results of hip resurfacing and total hip replacement: A review of the literature. Orthop Clin North Am. 2011;42(2):143-151.
  61. Sibia US, King PJ. Minimum 5-year follow-up of articular surface replacement acetabular components used in total hip arthroplasty. Am J Orthop (Belle Mead NJ). 2018;47(6).
  62. Smith TO, Nichols R, Donell ST, Hing CB. The clinical and radiological outcomes of hip resurfacing versus total hip arthroplasty: A meta-analysis and systematic review. Acta Orthop. 2010;81(6):684-695.
  63. Snyder D, Chapell R, Bruening W, et al. Horizon scan on hip replacement surgery. Technology Assessment. Prepared for the Agency for Healthcare Research and Quality (AHRQ) by ECRI Evidence-based Practice Center (Contract No. 290-02-0019). Rockville, MD: AHRQ; December 22, 2006.  
  64. Stulberg BN, Trier KK, Naughton M, Zadzilka JD. Results and lessons learned from a United States hip resurfacing investigational device exemption trial. J Bone Joint Surg Am. 2008;90 Suppl 3:21-26.
  65. Su EP, Ho H, Bhal V, et al. Results of the first U.S. FDA-approved Hip resurfacing device at 10-year follow-up. J Bone Joint Surg Am. 2021;103(14):1303-1311.
  66. Tooke SM, Amstutz HC, Delaunay C. Hemiresurfacing for femoral head osteonecrosis. J Arthroplasty. 1987;2(2):125-133.
  67. U.S. Food and Drug Administration (FDA). 510(k) summary: ReCap HA press-fit femoral resurfacing head. Silver Spring, MD: FDA; June 29, 2007.
  68. U.S. Food and Drug Administration (FDA). FDA Executive Summary Memorandum. Metal-on-metal hip implant systems. Silver Spring, MD: FDA; 2012.
  69. U.S. Food and Drug Administration (FDA). Summary and effectiveness data: Cormet hip resurfacing system. Silver Spring, MD: FDA; February 22, 2007.
  70. U.S. Food and Drug Administration (FDA). Summary and effectiveness data: Conserve plus total hip resurfacing hip system. Silver Spring, MD: FDA; November 3, 2009.
  71. U.S. Food and Drug Administration (FDA). The Birmingham Hip Resurfacing (BHR) System, Smith & Nephew, Inc., Memphis, TN. Summary of Safety and Effectiveness Data. PMA No. 040033. Rockville, MD: FDA; May 9, 2006. 
  72. Vale L, Wyness L, McCormack K, et al. A systematic review of the effectiveness and cost-effectiveness of metal-on-metal hip resurfacing arthroplasty for treatment of hip disease. Health Technol Assess. 2002;6(15):1-109.
  73. Vale L, Wyness L, McCormack K, et al. Systematic review of the effectiveness and cost-effectiveness of metal on metal hip resurfacing arthroplasty for treatment of hip disease.  Aberdeen, UK: University of Aberdeen; November 28, 2001. 
  74. van der Weegen W, Hoekstra HJ, Sijbesma T, et al. Survival of metal-on-metal hip resurfacing arthroplasty: A systematic review of the literature. J Bone Joint Surg Br. 2011;93(3):298-306.
  75. Vendittoli PA, Riviere C, Roy AG, et al. Metal-on-metal hip resurfacing compared with 28-mm diameter metal-on-metal total hip replacement: A randomised study with six to nine years' follow-up. Bone Joint J. 2013;95-B(11):1464-1473.
  76. Vendittoli PA, Shahin M, Riviere C, et al. Hip resurfacing compared with 28-mm metal-on-metal total hip replacement: A randomized study with 15 years of follow-up. J Bone Joint Surg Am. 2020;102(Suppl 2):80-90.
  77. Vigdorchik JM, Elbuluk A, Benson JR, Muir JM. Birmingham hip resurfacing using a novel mini-navigation system: A case report. J Orthop Case Rep. 2018;8(1):48-52.
  78. Wang Q, Zhang XL, Jiang Y, et al. Hip resurfacing arthroplasty for secondary osteoarthritis after developmental dysplasia of hip. Zhonghua Wai Ke Za Zhi. 2008;46(17):1293-1296.
  79. Woon RP, Johnson AJ, Amstutz HC. Results of Conserve Plus® metal-on-metal hip resurfacing for post-traumatic arthritis and osteonecrosis. Hip Int. 2012;22(2):195-202.
  80. Work Loss Data Institute. Hip and pelvis (acute and chronic). Encinitas, CA: Work Loss Data Institute; 2013.

Shoulder Resurfacing

  1. American Academy of Orthopaedic Surgeons (AAOS)e. The treatment of glenohumeral joint osteoarthritis.Guideline and Evidence Report. Rosemount, IL: AAOS; December 4, 2009.
  2. American College of Occupational and Environmental Medicine (ACOEM). Shoulder disorders. Occupational Medicine Practice Guidelines. Elk Grove Village, IL: ACOEM; 2011.
  3. Bailie DS, Llinas PJ, Ellenbecker TS. Cementless humeral resurfacing arthroplasty in active patients less than fifty-five years of age. J Bone Joint Surg Am. 2008;90(1):110-117.
  4. Biomet. Copeland humeral resurfacing head [website]. Warsaw, IN; Biomet; 2009. Available at: Accessed November 9, 2009.
  5. Buchner M, Eschbach N, Loew M. Comparison of the short-term functional results after surface replacement and total shoulder arthroplasty for osteoarthritis of the shoulder: A matched-pair analysis. Arch Orthop Trauma Surg. 2008;128(4):347-354.
  6. Burgess DL, McGrath MS, Bonutti PM, et al. Shoulder resurfacing. J Bone Joint Surg Am. 2009;91(5):1228-1238.
  7. de Beer JF, Bhatia DN, van Rooyen KS, Du Toit DF. Arthroscopic debridement and biological resurfacing of the glenoid in glenohumeral arthritis. Knee Surg Sports Traumatol Arthrosc. 2010;18(12):1767-1773.
  8. Elhassan B, Ozbaydar M, Diller D, et al. Soft-tissue resurfacing of the glenoid in the treatment of glenohumeral arthritis in active patients less than fifty years old. J Bone Joint Surg Am. 2009;91(2):419-424.
  9. Elser F, Braun S, Dewing CB, Millett PJ. Glenohumeral joint preservation: Current options for managing articular cartilage lesions in young, active patients. Arthroscopy. 2010;26(5):685-696.
  10. Fuerst M, Fink B, Rüther W. The DUROM cup humeral surface replacement in patients with rheumatoid arthritis. J Bone Joint Surg Am. 2007;89(8):1756-1762.
  11. Fuerst M, Fink B, Rüther W. The DUROM cup humeral surface replacement in patients with rheumatoid arthritis. Surgical technique. J Bone Joint Surg Am. 2008;90 Suppl 2 Pt 2:287-298.
  12. Geervliet PC, van den Bekerom MPJ, Spruyt P, et al. Outcome and revision rate of uncemented glenohumeral resurfacing (C.A.P.) after 5-8 years. Arch Orthop Trauma Surg. 2017;137(6):771-778.
  13. Gobezie R, Lenarz CJ, Wanner JP, Streit JJ. All-arthroscopic biologic total shoulder resurfacing. Arthroscopy. 2011;27(11):1588-1593.
  14. Ibrahim EF, Rashid A, Thomas M. Resurfacing hemiarthroplasty of the shoulder for patients with juvenile idiopathic arthritis. J Shoulder Elbow Surg. 2018;27(8):1468-1474.
  15. Krishnan SG, Reineck JR, Nowinski RJ, et al. Humeral hemiarthroplasty with biologic resurfacing of the glenoid for glenohumeral arthritis. Surgical technique. J Bone Joint Surg Am. 2008;90 Suppl 2 Pt 1:9-19.
  16. Lee BK, Vaishnav S, Rick Hatch GF 3rd, Itamura JM. Biologic resurfacing of the glenoid with meniscal allograft: Long-term results with minimum 2-year follow-up. J Shoulder Elbow Surg. 2013;22(2):253-260.
  17. Lee KT, Bell S, Salmon J. Cementless surface replacement arthroplasty of the shoulder with biologic resurfacing of the glenoid. J Shoulder Elbow Surg. 2009;18(6):915-919.
  18. Levy O, Copeland SA. Cementless surface replacement arthroplasty of the shoulder. 5- to 10-year results with the Copeland mark-2 prosthesis. J Bone Joint Surg Br. 2001;83(2):213-221.
  19. Levy O, Copeland SA. Cementless surface replacement arthroplasty (Copeland CSRA) for osteoarthritis of the shoulder. J Shoulder Elbow Surg. 2004;13(3):266-271.
  20. Levy O, Funk L, Sforza G, Copeland SA. Copeland surface replacement arthroplasty of the shoulder in rheumatoid arthritis. J Bone Joint Surg Am. 2004;86-A(3):512-518.
  21. Longo UG, Berton A, Alexander S, et al. Biological resurfacing for early osteoarthritis of the shoulder. Sports Med Arthrosc. 2011;19(4):380-394.
  22. Merolla G, Bianchi P, Lollino N, et al. Clinical and radiographic mid-term outcomes after shoulder resurfacing in patients aged 50 years old or younger. Musculoskelet Surg. 2013;97 Suppl 1:23-29.
  23. Mullett H, Levy O, Raj D, et al. Copeland surface replacement of the shoulder. Results of an hydroxyapatite-coated cementless implant in patients over 80 years of age. J Bone Joint Surg Br. 2007;89(11):1466-1469.
  24. National Institute for Health and Care Excellence (NICE). Shoulder resurfacing arthroplasty. London, UK: NICE; July 28, 2010.
  25. Raiss P, Kasten P, Baumann F, et al. Treatment of osteonecrosis of the humeral head with cementless surface replacement arthroplasty. J Bone Joint Surg Am. 2009;91(2):340-349.
  26. Raiss P, Pape G, Becker S, et al. Cementless humeral surface replacement arthroplasty in patients less than 55 years of age. Orthopade. 2010;39(2):201-208.
  27. Savoie FH 3rd, Brislin KJ, Argo D. Arthroscopic glenoid resurfacing as a surgical treatment for glenohumeral arthritis in the young patient: Midterm results. Arthroscopy. 2009;25(8):864-871.
  28. Schmidutz F, Sprecher CM, Milz S, et al. Resurfacing of the humeral head: An analysis of the bone stock and osseous integration under the implant. J Orthop Res. 2015;33(9):1382-1390.
  29. Soudy K, Szymanski C, Lalanne C, et al. Results and limitations of humeral head resurfacing: 105 cases at a mean follow-up of 5 years. Orthop Traumatol Surg Res. 2017;103(3):415-420.
  30. Sweet SJ, Takara T, Ho L, Tibone JE. Primary partial humeral head resurfacing: Outcomes with the HemiCAP implant. Am J Sports Med. 2015;43(3):579-587.
  31. Thomas SR, Sforza G, Levy O, Copeland SA. Geometrical analysis of Copeland surface replacement shoulder arthroplasty in relation to normal anatomy. J Shoulder Elbow Surg. 2005;14(2):186-192.
  32. Thomas SR, Wilson AJ, Chambler A. et al. Outcome of Copeland surface replacement shoulder arthroplasty. J Shoulder Elbow Surg. 2005;14(5):485-491.
  33. U.S. Food and Drug Administration (FDA). Copeland resurfacing heads. Summary and effectiveness data: Silver Spring, MD: FDA; February 9, 2006.
  34. U.S. Food and Drug Administration (FDA). Interlok/HA Copeland Resurfacing Heads. 510(k) Summary. K010635. Biomet, Inc. Warsaw, IN. Rockville, MD: FDA; August 20, 2001. 
  35. Uribe JW, Botto-van Bemden A. Partial humeral head resurfacing for osteonecrosis. J Shoulder Elbow Surg. 2009;18(5):711-716.
  36. Widnall JC, Dheerendra SK, Macfarlane RJ, Waseem M. The use of shoulder hemiarthroplasty and humeral head resurfacing: A review of current concepts. Open Orthop J. 2013;7:334-337.
  37. Wirth MA. Humeral head arthroplasty and meniscal allograft resurfacing of the glenoid. J Bone Joint Surg Am. 2009;91(5):1109-1119.

Knee Resurfacing

  1. Agarwal N, To K, McDonnell S, Khan W. Clinical and radiological outcomes in robotic-assisted total knee arthroplasty: A systematic review and meta-analysis. J Arthroplasty. 2020;35(11):3393-3409.
  2. Ali A, Lindstrand A, Nilsdotter A, Sundberg M. Similar patient-reported outcomes and performance after total knee arthroplasty with or without patellar resurfacing. Acta Orthop. 2016;87(3):274-279.
  3. Aunan E, Næss G, Clarke-Jenssen J, et al. Patellar resurfacing in total knee arthroplasty: Functional outcome differs with different outcome scores. Acta Orthop. 2016;87(2):158-164.
  4. Bell SW, Anthony I, Jones B, et al. Improved accuracy of component positioning with robotic-assisted unicompartmental knee arthroplasty: Data from a prospective, randomized controlled study. J Bone Joint Surg Am. 2016;98(8):627-635.
  5. Blyth MJG, Anthony I, Rowe P, et al. Robotic arm-assisted versus conventional unicompartmental knee arthroplasty: Exploratory secondary analysis of a randomised controlled trial. Bone Joint Res. 2017;6(11):631-639.
  6. Bollars P, Bosquet M, Vandekerckhove B, et al. Prosthetic inlay resurfacing for the treatment of focal, full thickness cartilage defects of the femoral condyle: A bridge between biologics and conventional arthroplasty. Knee Surg Sports Traumatol Arthrosc. 2012;20(9):1753-1759. 
  7. Butnaru M, Sigonney G, Muller JH, et al. Wiberg Type III patellae and J-sign during extension compromise outcomes of total knee arthroplasty without patellar resurfacing. Knee. 2020;27(3):787-794.
  8. Canadian Agency for Drugs and Technologies in Health (CADTH). MAKO’s RESTORIS Implants and MAKOplasty Procedure for early to mid-stage osteoarthritic knee disease: Clinical and cost-effectiveness, health service delivery, and safety. Rapid Response Reports. Ottawa, ON: CADTH; July 21, 2011.
  9. Chowdhry M, Khakha RS, Norris M, et al. Improved survival of computer-assisted unicompartmental knee arthroplasty: 252 cases with a minimum follow-up of 5 years. J Arthroplast.. 2017;32(4):1132-1136.
  10. Christopher ZK, Deckey DG, Chung AS, Spangehl MJ. Patellar osteolysis after total knee arthroplasty with patellar resurfacing: A potentially underappreciated problem. Arthroplast Today. 2019;5(4):435-441.
  11. Clement ND, Bell A, Simpson P, et al. Robotic-assisted unicompartmental knee arthroplasty has a greater early functional outcome when compared to manual total knee arthroplasty for isolated medial compartment arthritis. Bone Joint Res. 2019;9(1):15-22.
  12. Cool CL, Jacofsky DJ, Seeger KA, et al. A 90-day episode-of-care cost analysis of robotic-arm assisted total knee arthroplasty. J Comp Eff Res. 2019;8(5):327-336.
  13. Cotter EJ, Wang J, Illgen RL. Comparative cost analysis of robotic-assisted and jig-based manual primary total knee arthroplasty. J Knee Surg. 2020.
  14. Crawford DA, Hurst JM, Morris MJ, Berend KR. Does patellar resurfacing in primary total knee arthroplasty increase the risk of manipulation? Surg Technol Int. 2020;36:299-303.
  15. Deese JM, Gratto-Cox G, Carter DA, et al. Patient reported and clinical outcomes of robotic-arm assisted unicondylar knee arthroplasty: Minimum two year follow-up. J Orthop. 2018;15(3):847-853.
  16. Dhollander AA, Almqvist KF, Moens K, et al. The use of a prosthetic inlay resurfacing as a salvage procedure for a failed cartilage repair. Knee Surg Sports Traumatol Arthrosc. 2015;23(8):2208-2212.
  17. ECRI Institute. MAKOplasty robotic-assisted partial knee resurfacing for treating osteoarthritis. ECRI Institute Research Highlights for August 28, 2013. On the Front Line. Plymouth Meeting, PA: ECRI; 2013. 
  18. Eshnazarov KE, Seon JK, Song EK. Comparison of radiological assessments patellar resurfacing with retention for grade IV osteoarthritis in patellofemoral joint accomplished total knee arthroplasty. Vestn Rentgenol Radiol. 2016;97(1):28-32.
  19. Grassi A, Compagnoni R, Ferrua P, et al. Patellar resurfacing versus patellar retention in primary total knee arthroplasty: A systematic review of overlapping meta-analyses. Knee Surg Sports Traumatol Arthrosc. 2018;26(11):3206-3218.
  20. Grela M, Barrett M, Kunutsor SK, et al. Clinical effectiveness of patellar resurfacing, no resurfacing and selective resurfacing in primary total knee replacement: Systematic review and meta-analysis of interventional and observational evidence. BMC Musculoskelet Disord. 2022;23(1):932.
  21. Hampp EL, Chughtai M, Scholl LY, et al. Robotic-arm assisted total knee arthroplasty demonstrated greater accuracy and precision to plan compared with manual techniques. J Knee Surg. 2019;32(3):239-250.
  22. Hansen DC, Kusuma SK, Palmer RM, Harris KB. Robotic guidance does not improve component position or short-term outcome in medial unicompartmental knee arthroplasty. J Arthroplasty. 2014;29(9):1784-1789.
  23. Imhoff AB, Feucht MJ, Meidinger G, et al. Prospective evaluation of anatomic patellofemoral inlay resurfacing: Clinical, radiographic, and sports-related results after 24 months. Knee Surg Sports Traumatol Arthrosc. 2015;23(5):1299-1307.
  24. Kayani B, Haddad FS. Robotic total knee arthroplasty: Clinical outcomes and directions for future research. Bone Joint Res. 2019;8(10):438-442.
  25. Kayani B, Konan S, Tahmassebi J, et al. Robotic-arm assisted total knee arthroplasty is associated with improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based total knee arthroplasty: A prospective cohort study. Bone Joint J. 2018;100-B(7):930-937.
  26. King CA, Jordan M, Bradley AT, et al. Transitioning a practice to robotic total knee arthroplasty is correlated with favorable short-term clinical outcomes -- A single surgeon experience. J Knee Surg. 2022;35(1):78-82.
  27. Koh IJ, Kim MS, Sohn S, et al. Patients undergoing total knee arthroplasty using a contemporary patella-friendly implant are unaware of any differences due to patellar resurfacing. Knee Surg Sports Traumatol Arthrosc. 2019;27(4):1156-1164. 
  28. Laursen JO. High mid-term revision rate after treatment of large, full-thickness cartilage lesions and OA in the patellofemoral joint using a large inlay resurfacing prosthesis: HemiCAP-Wave®. Knee Surg Sports Traumatol Arthrosc. 2017;25(12):3856-3861.
  29. Liow MHL, Goh 3GSH, Wong MK, et al. Robotic-assisted total knee arthroplasty may lead to improvement in quality-of-life measures: A 2-year follow-up of a prospective randomized trial. Knee Surg Sports Traumatol Arthrosc. 2017;25(9):2942-2951.
  30. Longo UG, Ciuffreda M, Mannering N, et al. Patellar resurfacing in total knee arthroplasty: Systematic review and meta-analysis. J Arthroplasty. 2018;33(2):620-632.
  31. Lonner JH, John TK, Conditt MA. Robotic arm-assisted UKA improves tibial component alignment: A pilot study. Clin Orthop Relat Res. 2010;468(1):141-146.
  32. Mancino F, Cacciola G, Malahias M-A. What are the benefits of robotic-assisted total knee arthroplasty over conventional manual total knee arthroplasty? A systematic review of comparative studies. Orthoped Review. 2020;12:S1.
  33. Maney AJ, Koh CK, Frampton CM, Young SW. Usually, selectively, or rarely resurfacing the patella during primary total knee arthroplasty: Determining the best strategy. J Bone Joint Surg Am. 2019;101(5):412-420.
  34. Marcacci M, Bruni D, Zaffagnini S, et al. Arthroscopic-assisted focal resurfacing of the knee: Surgical technique and preliminary results of 13 patients at 2 years follow-up. Knee Surg Sports Traumatol Arthrosc. 2011;19(5):740-746. 
  35. Marchand KB, Salem HS, Mathew KK, et al. The accuracy of computed tomography-based, three-dimensional implant planning in robotic-assisted total knee arthroplasty. J Knee Surg. 2022;35(14):1587-1594.
  36. Marchand RC, Sodhi N, Anis H, et al. 1-year patient outcomes for robotic-arm assisted vs. manual total knee arthroplasty. J Knee Surg. 2019b;32:1063-1068.
  37. Marchand RC, Sodhi N, Bhowmik-Stoker M, et al. Does the robotic arm and preoperative CT planning help with 3D intraoperative total knee arthroplasty planning? J Knee Surg. 2019a;32(8):742-749.
  38. Marchand RC, Sodhi N, Khlopas A, et al. Coronal correction for severe deformity using robotic-assisted total knee arthroplasty. J Knee Surg. 2018;31(1):2-5.
  39. Marchand RC, Sodhi N, Khlopas A, et al. Patient satisfaction outcomes after robotic arm-assisted total knee arthroplasty: A short-term evaluation. J Knee Surg. 2017;30(9):849-853.
  40. Marcovigi A, Zambianchi F, Sandoni D, et al. Robotic-arm assisted partial knee arthroplasty: A single centre experience. Acta Biomed. 2017;88(2 -S):54-59.
  41. Millar LJ, Banger M, Rowe PJ, et al. A five-year follow up of gait in robotic assisted vs conventional unicompartmental knee arthroplasty. Gait Posture. Gait Posture 2018;65 Suppl 1:31-32.
  42. Miniaci A. UniCAP as an alternative for unicompartmental arthritis. Clin Sports Med. 2014;33(1):57-65.
  43. Ofa SA, Ross BJ, Flick TR, et al. Robotic total knee arthroplasty vs conventional total knee arthroplasty: A nationwide database study. Arthroplast Today. 2020;6(4):1001-1008.
  44. Pearle AD, van der List JP, Lee L, et al. Survivorship and patient satisfaction of robotic-assisted medial unicompartmental knee arthroplasty at a minimum two-year follow-up. Knee. 2017;24(2):419-428.
  45. Pietrzak JRT, Rowan FE, Kayani B, et al. Preoperative CT-based three-dimensional templating in robot-assisted total knee arthroplasty more accurately predicts implant sizes than two-dimensional templating. J Knee Surg. 2019;32(7):642-648.
  46. Rauck RC, Blevins JL, Cross MB. Component placement accuracy in unicompartmental knee arthroplasty is improved with robotic-assisted surgery: Will it have an effect on outcomes? HSS J. 2018;14(2):211-213.
  47. Ren Y, Cao S, Wu J, et al. Efficacy and reliability of active robotic-assisted total knee arthroplasty compared with conventional total knee arthroplasty: A systematic review and metaanalysis. Postgrad Med J. 2019;0:1-9.
  48. Simpson CJ, Ng N, Ndou S, et al. Patellar resurfacing was not associated with a clinically significant advantage when a modern patellar friendly total knee arthroplasty is employed: A systematic review and meta-analysis. Knee. 2023;41:329-341.
  49. Smith AF, Eccles CJ, Bhimani SJ, et al. Improved patient satisfaction following robotic-assisted total knee arthroplasty. J Knee Surg. 2021;34(7):730-738.
  50. Song E-K, Seon J-K, Park S-J, et al. Simultaneous bilateral total knee arthroplasty with robotic and conventional techniques: A prospective, randomized study. Knee Surg Sports Traumatol Arthrosc. 2011;19(7):1069-1076.
  51. Song E-K, Seon J-K, Yim J-H, et al. Robotic-assisted TKA reduces postoperative alignment outliers and improves gap balance compared to conventional TKA. Clin Orthop Relat Res. 2013;471(1):118-126.
  52. Sultan AA, Samuel LT, Khlopas A, et al. Robotic-arm assisted total knee arthroplasty more accurately restored the posterior condylar offset ratio and the Insall-Salvati Index compared to the manual technique: A cohort-matched study. Surg Technol Int. 2019;34:409-413.
  53. Toro-Ibarguen AN, Navarro-Arribas R, Pretell-Mazzini J, et al. Secondary patellar resurfacing as a rescue procedure for persistent anterior knee pain after primary total knee arthroplasty: Do our patients really improve? J Arthroplasty. 2016;31(7):1539-1543.
  54. U.S. Food and Drug Administration (FDA). 510(k) summary: HemiCAP patella femoral resurfacing prosthesis. Silver Spring, MD: FDA; March 15, 2006.
  55. van Jonbergen HPW, Boeddha AV, M van Raaij JJ. Patient satisfaction and functional outcomes following secondary patellar resurfacing. Orthopedics. 2016;39(5):e850-e856.
  56. van Raaij TM, van der Meij E, de Vries AJ, van Raay JJAM. Patellar resurfacing does not improve clinical outcome in patients with symptomatic tricompartmental knee osteoarthritis. An RCT study of 40 patients receiving primary cruciate retaining total knee arthroplasty. J Knee Surg. 2021;34(14):1503-1509.
  57. Werner SD, Stonestreet M, Jacofsky DJ. Makoplasty and the accuracy and efficacy of robotic-assisted arthroplasty. Surg Technol Int. 2014;24:302-306.
  58. Work Loss Data Institute. Knee & leg (acute & chronic). Encinitas, CA: Work Loss Data Institute; November 29, 2013. 
  59. Zhang F, Li H, Ba Z, et al. Robotic arm-assisted vs conventional unicompartmental knee arthroplasty. A meta-analysis of the effects on clinical outcomes. Medicine (Baltimore). 2019;98(35):e16968.
  60. Zhang J, Matzko CN, Sawires A, et al. Adoption of robotic-arm-assisted total knee arthroplasty is associated with decreased use of articular constraint and manipulation under anesthesia compared to a manual approach. J Knee Surg. 2022a;35(8):849-857.
  61. Zhang J, Ndou WS, Ng N, et al. Robotic-arm assisted total knee arthroplasty is associated with improved accuracy and patient reported outcomes: A systematic review and meta-analysis. Knee Surg Sports Traumatol Arthrosc. 2022b;30(8):2677-2695.

MTP Resurfacing

  1. U.S. Food and Drug Administration (FDA). 510(k) summary: OsteoMed metatarsal resurfacing implant system. Rockville, MD: FDA; February 21, 2008.
  2. U.S. Food and Drug Administration (FDA). Summary and effectiveness data: Merete toe mobile anatomical great toe resurfacing system. Rockville, MD: FDA; May 8, 2008.
  3. U.S. Food and Drug Administration (FDA). Summary and effectiveness data: CAP great toe resurfacing hemi-arthroplasty. Rockville, MD: FDA; February 18, 2004.

Facet Joint Resurfacing

  1. de Kelft EV. Lumbar facet resurfacing: First experience with the FENIX implant. Clin Spine Surg. 2016;29(9):E475-E481.

Radiocapitellar Joint/Radiocapitellar Joint Replacement Resurfacing

  1. Schmidt I. A complicated course of a coronal shear fracture type IV of the distal part of humerus resulting in resurfacing radiocapitellar joint replacement. Open Orthop J. 2017;11:248-254.

Metal Resurfacing Inlay Implant for Osteochondral Talar Defects

  1. Vuurberg G, Reilingh ML, van Bergen CJA, et al. Metal resurfacing inlay implant for osteochondral talar defects after failed previous surgery: A midterm prospective follow-up study. Am J Sports Med. 2018;46(7):1685-1692.

Partial Femoral Condyle Focal Resurfacing (HemiCAP-UniCAP) for the Treatment of Full-Thickness Cartilage Defects

  1. Elbardesy H, Nagle M, Simmons L, Harty J. The partial femoral condyle focal resurfacing (HemiCAP-UniCAP) for treatment of full-thickness cartilage defects, systematic review and meta-analysis. Acta Orthop Belg. 2021;87(1):93-102.

Resurfacing Capitate Pyrocarbon Implant for Carpal Injuries / Wrist Arthritis

  1. Ferrero M, di Summa PG, Giacalone F, et al. Salvage of advanced carpal collapse: Proximal row carpectomy with pyrocarbon resurfacing of the capitate versus four-corner arthrodesis. J Hand Surg Eur Vol. 2020;45(7):687-692.
  2. Fulchignoni C, Caviglia D, Rocchi L, et al. Resurfacing capitate pyrocarbon implant after proximal row carpectomy: A literature review. Orthop Rev (Pavia). 2020;12(Suppl 1):8679.
  3. Marcuzzi A, Fulchignoni C, Teodori J, Rocchi L. Resurfacing capitate pyrocarbon implant as salvage procedure in several serious outcomes of carpal injuries. Clinical experience and follow-up. Acta Biomed. 2022;92(S3):e2021536.
  4. Rocchi L, Fulchignoni C, Marcuzzi A, et al. Resurfacing capitate pyrocarbon implant without capitate pole resection to improve clinical results in the treatment of chronic wrist arthritis. Tech Hand Up Extrem Surg. 2021;25(4):213-218.