Aetna considers metal-on-metal hip resurfacing a medically necessary alternative to total hip arthroplasty for physically active members with osteoarthritis of the hip, or osteonecrosis of the femoral head.

Please see appendix for contraindications for metal-on-metal hip resurfacing.

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.

The metal-metal femoral resurfacing technique developed by Amstutz, et al. (1986) has been proposed as an alternative to metal-on-metal total hip replacement.  In femoral resurfacing, the femoral head is reshaped and capped with a metal ball, but the femoral head is not removed as in total hip replacement.  Compared to total hip replacement, femoral resurfacing allows preservation of much more of the patient's own bone.  The advantages of femoral resurfacing over total hip replacement 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 total hip replacement.  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 total hip replacement) for patients with osteonecrosis of the femoral head, especially for young, active patients.

The UK 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 total hip replacement, 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 total hip replacement or other alternatives, which limit the conclusions one can draw about the comparative effectiveness of these procedures. 

The National Institute for Clinical Excellence recommended that metal on metal hip resurfacing be considered an option for people with advanced hip disease who would otherwise receive a conventional primary total hip replacement and are likely to live longer than the device is likely to last.

NICE notes 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.

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 one 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 two 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.

Appendix

Contraindications for metal-on-metal hip resurfacing:

• Individuals with infection or sepsis
• 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
• Females of child-bearing age because of unknown effect of metal ion release on the fetus
• Individuals with known moderate to severe renal insufficiency
• Individuals who are immunosuppressed with diseases such as AIDS or individuals receiving high doses of corticosteroids
• Individuals who are severely over-weight
• Individuals with known or suspected metal sensitivity.