Osteoarthritis (OA) is a non-inflammatory degenerative joint disease that occurs mainly in middle-aged and older individuals. Osteoarthritis of the knee occurs when the elastoviscous properties of the synovial fluid in the knee joint becomes diminished, resulting in less protection and shock absorption. Osteoarthritis of the knee is often characterized by pain that frequently requires medical and/or surgical intervention. In general, the pain associated with OA develops gradually, although sudden onset is also possible. The joint may become stiff and swollen, making it difficult to bend or straighten the knee. Pain and swelling are worse in the morning or after a period of inactivity. Pain may also increase after activities such as walking, stair climbing or kneeling. The pain may often cause a feeling of weakness in the knee, resulting in a "locking" or "buckling". Many arthritic patients note that changes in the weather also affect the degree of pain from arthritis.
Based on the criteria of the American College of Rheumatology (Altman et al, 1986), a diagnosis of OA of the knee can be rendered if patients experience knee pain and at least 5 of the following:
Crepitus (noisy, grating sound) on active motion
Erythrocyte sedimentation rate (ESR) less than 40 mm/hr
Less than 30 minutes of morning stiffness
No palpable warmth of synovium
Over 50 years of age
Rheumatoid factor less than 1:40 titer (agglutination method)
Synovial fluid signs.
The severity of OA is often described according to the Outerbridge scale, which classifies the articular degeneration of the knee by compartment in 4 grades: (i) Grade I refers to softening or blistering of the articular cartilage, (ii) Grade II describes fragmentation or fissuring in an area less than 1 cm, (iii) Grade III describes fragmentation or fissuring in an area greater than 1 cm, and (iv) Grade IV refers to cartilage erosion down to the bone.
Treatment of mild symptomatic OA entails patient education, non-pharmacological approaches such as exercises, lifestyle modifications, and use of supportive devices, as well as pharmacotherapies including non-opioid oral and topical analgesics. In patients who are unresponsive to this regimen, the use of non-steroidal anti-inflammatory drugs (NSAIDs) is appropriate. Intra-articular injections of steroids or viscosupplementation may be used for patients who fail conservative management. Patients with severe symptomatic OA of the knee may require surgical intervention, e.g., arthroscopic surgery, osteotomy, abrasion arthroplasty, subchondral penetration procedures, and laser/thermal chondroplasty.
Arthroscopy involves direct visualization of the joint by a videofiberoptic device. Arthroscopic lavage and/or debridement is often recommended when medical therapy fails to reduce osteoarthritic knee pain and improve functioning. Lavage entails either large or small volume saline irrigation of the knee. Debridement covers many types of arthroscopic surgery and may include but is not limited to variable amounts of the following treatments: partial synovectomy, decompression and resection of plicae/adipose tissue, partial menisectomy, chondroplasty, loose body removal, and/or osteophyte removal. In clinical practice, debridement is generally performed with low volume lavage or washout. The available evidence supporting the use of arthroscopic surgery for the treatment of symptomatic OA of the knee is largely retrospective and lacks validated health-related quality-of-life measures. In this regard, the reports by Baumgaertner and colleagues (1990), Ogilvie-Harris and Fitsialos (1991), Yang and Nisonson (1995), as well as Jackson and Dieterichs (2003) were case series studies, while that by Fond et al (2002) was a cohort observational study.
In contrast, findings of many randomized controlled studies indicate that arthroscopic lavage and/or debridement did not result in pain relief and improvement of functioning. Gibson et al (1992) studied the effect of arthroscopic lavage and debridement of the osteoarthritic knee. A total of 20 patients were randomly assigned to receive (i) lavage, or (ii) debridement. The primary outcome was objective evaluation of thigh muscle function in the affected quadriceps compared to that of the non-affected quadriceps before and after operation. There was some improvement in quadriceps isokinetic torque at 6 and 12 weeks after joint lavage but not after debridement. However, neither method significantly relieved patients' symptoms.
In a multi-center, randomized, controlled study, Ravaud et al (1999) assessed the effectiveness of joint lavage and intra-articular steroid injection, alone and in combination, in the treatment of patients with symptomatic knee OA. A total of 98 patients were randomly assigned to 4 treatment groups: (i) intra-articular placebo (1.5 ml of 0.9 % normal saline), (ii) intra-articular corticosteroids (3.75 mg of cortivazol in 1.5 ml), (iii) joint lavage and intra-articular placebo, and (iv) joint lavage and intra-articular corticosteroid. Outcome measures including severity of pain (100-mm visual analog scale [VAS]), global status (100-mm VAS), and Lequesne's functional index were evaluated at baseline, week 1, week 4, week 12, and week 24. There was no interaction between steroid injection and joint lavage. Patients who had undergone joint lavage had significantly improved pain VAS scores at week 24 (p < 0.020). In contrast, corticosteroid injection had no long-term effect (p < 0.313); corticosteroid injection was associated with a decrease in pain only at week 1 (p < 0.003) and week 4 (p < 0.020). However, there was no significant improvement in function at week 4 regardless of the assigned treatment as indexed by Lequesne's functional index.
In a multi-center, randomized, controlled study, Kalunian and associates (2000) examined if visually-guided arthroscopic irrigation is an effective therapeutic intervention in patients with early knee OA. A total of 90 patients were randomly assigned in a double-blind fashion to receive (i) arthroscopic irrigation with 3,000 ml of saline (treatment group), or (ii) the minimal amount of irrigation (250 ml) needed to perform arthroscopy (placebo group). The primary outcome variable was aggregate Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score. The study did not demonstrate an effect of irrigation on arthritis severity as measured by aggregate WOMAC scores, the primary outcome variable. The mean change in aggregate WOMAC score at 12 months was 15.5 (95 % confidence interval [CI]: 7.7 to 23.4) for the full irrigation group compared to 8.9 (95 % CI: 4.9 to 13.0) for the minimal irrigation group (p < 0.10).
In a prospective, randomized, placebo-controlled trial to determine whether a placebo effect might play a role in arthroscopic treatment of OA of the knee (Moseley et al, 1996), 5 subjects were randomized to a placebo arthroscopy group, 3 subjects were randomized to an arthroscopic lavage group, and 2 subjects were randomized to a standard arthroscopic debridement group. Patients who received the placebo surgery reported decreased frequency, intensity, and duration of knee pain. They also thought that the procedure was worthwhile and would recommend it to family and friends. Thus, there may be a significant placebo effect for arthroscopic treatment of osteoarthritis of the knee. The authors concluded that a larger study is needed to evaluate fully the effectiveness of an arthroscopic procedure for this condition. Recent evidence published in the New England Journal of Medicine (Moseley et al, 2002) confirms this earlier finding that arthroscopic lavage and/or debridement in patients with OA of the knee without other specific indications is no better than placebo surgery.
Moseley and colleagues (2002) carried out a randomized, placebo-controlled study to examine the effectiveness of arthroscopy for OA of the knee. A total of 180 patients with knee OA were randomly assigned to receive (i) arthroscopic debridement, (ii) arthroscopic lavage, or (iii) placebo surgery. Patients in the placebo group received skin incisions and underwent a simulated debridement without insertion of the arthroscope. Patients and assessors of outcome were blinded to the treatment-group assignment. Outcomes were assessed at multiple points over a 24-month period with the use of 5 self-reported scores -- 3 on scales for pain and 2 on scales for function -- and 1 objective test of walking and stair climbing. A total of 165 patients completed the trial. At no point did either of the intervention groups report less pain or better function than the placebo group. For example, mean (+/- SD) scores on the Knee-Specific Pain Scale (range of 0 to 100, with higher scores indicating more severe pain) were similar in the placebo, lavage, and debridement groups: 48.9 +/- 21.9, 54.8 +/- 19.8, and 51.7 +/- 22.4, respectively, at 1 year (p < 0.14 for the comparison between placebo and lavage; p < 0.51 for the comparison between placebo and debridement) and 51.6 +/- 23.7, 53.7 +/- 23.7, and 51.4 +/- 23.2, respectively, at 2 years (p < 0.64 and p < 0.96, respectively). Furthermore, the 95 % CIs for the differences between the placebo group and the intervention groups exclude any clinically meaningful difference. These researchers concluded that for patients with OA of the knee, the outcomes after arthroscopic lavage or arthroscopic debridement were no better than those after a placebo procedure.
In view of the findings of Moseley and associates, advocates of arthroscopic lavage and debridement suggest that may be these procedures are effective in subgroups of patients with knee OA including those at the early stages of OA, those with normal alignment as well as those with mechanical symptoms. However, Moseley and co-workers stated that they have performed an extensive subgroup analysis and did not find any differences to support the claim that outcomes of arthroscopic surgery for OA of the knee may be related to the severity of arthritis or alignment (Wray et al, 2002).
In a sham-controlled, randomized, double-blinded study, Bradley et al (2002) evaluated the effectiveness of tidal irrigation (TI) in comparison with a well-matched sham irrigation (SI) procedure as a treatment for OA of the knee. A total of 180 patients with knee OA were randomized to receive TI or SI, with clinical follow-up over the ensuing 12 months. The primary outcomes of interest were changes in pain and function, as measured by the WOMAC. Patients and the nurse assessor were blinded, and success of blinding was assessed. Although the study groups were otherwise comparable, the baseline WOMAC pain and physical functioning scores were higher (worse) in the SI group. After adjustment for baseline, there were no differences between the effects of SI and TI. Blinding was successful with approximately 90 % of SI and TI patients stating that they had received the TI procedure. The authors concluded that the improvement of these patients with knee OA following TI was due to a placebo effect.
Dervin and colleagues (2003) prospectively evaluated a cohort of patients (n = 126) with OA of the knee who were selected for arthroscopic debridement and determined which clinical criteria favor a sustained improvement in health-related quality of life after 2 years of follow-up. These researchers found that the prospectively evaluated quality-of-life benefit from arthroscopic debridement of the osteoarthritic knee is less than that reported in previous retrospective surveys on satisfaction. Additionally, clinical variables were only partially helpful for predicting a successful result after arthroscopic debridement.
The American College of Rheumatology (ACR) (2000) guidelines on OA of the hip and knee has concluded that “[n]o well-controlled trials of arthroscopic debridement with or without arthroplasty have been conducted, and the utility of this intervention for the treatment of knee osteoarthritis is unproven.” The ACR guidelines state that routine arthroscopic lavage with or without debridement should not be routinely recommended to patients with knee OA who have failed medical therapy. Arthroscopic removal of debris may, however, be useful for relief of pain and improvement in joint function in patients with mechanical symptoms due to loose bodies and meniscal tears. However, further studies in these types of patients are needed.
An assessment of arthroscopic lavage for knee osteoarthritis conducted by the Wessex Institute for Health Research and Development (Algood, 2002) summarized the evidence on arthroscopic lavage and debridement for osteoarthritis: "We found evidence from one good quality RCT [randomized controlled trial] that arthroscopic debridement or lavage did not improve patient reported pain and function at 2 years compared with sham arthroscopy for men with osteoarthritis of the knee. Two other, weaker, RCTs found that debridement and lavage did not improve symptoms compared with non-arthroscopic lavage. Another RCT found that arthroscopic lavage with 3,000 ml saline slightly improved pain compared with arthroscopic lavage with 250 ml saline. Another RCT found that arthroscopic debridement improved pain relief compared with arthroscopic lavage in people with isolated degenerative disease on the medial femoral condyle. We found no evidence that arthroscopic debridement or lavage improves symptoms compared with non-arthroscopic treatments."
In the Patient-Oriented Evidence that Matters (POEMs) of the Journal of Family Practice, Bailey (2002) stated that arthroscopy does not provide any benefit over sham surgery in reducing pain or physical functioning of patients with knee OA. In the Interpreting Key Trials section of the Cleveland clinic Journal of Medicine, Bernstein and Quach (2003) stated that the value of arthroscopy in treating patients with arthritic joints must be proved. Furthermore, in the American College of Physicians Journal Club, Gillespie (2003) stated that the study by Moseley et al (2002) made a case for questioning the value of arthroscopic lavage and debridement in active men younger than 65 years of age with OA of the knee. In addition, the Centers for Medicare and Medicaid Services (2003) will be issuing a national non-coverage determination stating that arthroscopic lavage alone is not reasonable and necessary for patients with OA of the knee; and that arthroscopic debridement is not reasonable and necessary for patients presenting with knee pain only or with severe OA (Outerbridge classification III or IV).
An assessment of arthroscopic lavage and debridement by the Medical Advisory Secretariat of the Ontario Ministry of Health and Long-term Care (2005) concluded: "Arthroscopic debridement of the knee has thus far only been found to be effective for medial compartmental OA. All other indications should be reviewed with a view to reducing arthroscopic debridement as an effective therapy. Arthroscopic lavage of the knee is not indicated for any stage of OA. There is very poor quality evidence on the effectiveness of debridement with partial meniscectomy in the case of meniscal tears in OA of the knee."
A randomized study by Kirkley et al (2008) published in the New England Journal of Medicine found that arthroscopic lavage and debridement for OA of the knee provided no additional benefit to optimized physical and medical therapy. The investigators conducted a single-center, randomized, controlled trial of arthroscopic surgery in patients with moderate-to-severe OA of the knee. Patients were randomly assigned to surgical lavage and arthroscopic debridement together with optimized physical and medical therapy or to treatment with physical and medical therapy alone. The primary outcome was the total Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score at 2 years of follow-up. Secondary outcomes included the Short Form-36 (SF-36) Physical Component Summary score. Of the 92 patients assigned to surgery, 6 did not undergo surgery. Of the 86 patients assigned to control treatment, all received only physical and medical therapy. After 2 years, there were no statistically significant differences in WOMAC scores or the SF-36 Physical Component Summary scores for the surgery group as compared with the control group. Analyses of WOMAC scores at interim visits and other secondary outcomes also failed to show superiority of surgery.
An accompanying study published in the New England Journal of Medicine found that incidental meniscal findings on MRI of the knee are common in the general population and increase with increasing age (Englund et al, 2008). MRI of the knee is often performed in patients who have knee symptoms of unclear cause. When meniscal tears are found, it is commonly assumed that the symptoms are attributable to them. However, there is a paucity of data regarding the prevalence of meniscal damage in the general population and the association of meniscal tears with knee symptoms and with radiographical evidence of osteoarthritis. Englund et al (2008) studied persons from Framingham, Massachusetts, who were drawn from census-tract data and random-digit telephone dialing. Subjects were 50 to 90 years of age and ambulatory; selection was not made on the basis of knee or other joint problems. The investigators assessed the integrity of the menisci in the right knee on 1.5-tesla MRI scans obtained from 991 subjects (57 % of whom were women). Symptoms involving the right knee were evaluated by questionnaire. The investigators found that the prevalence of a meniscal tear or of meniscal destruction in the right knee as detected on MRI ranged from 19 % among women 50 to 59 years of age to 56 % among men 70 to 90 years of age; prevalences were not materially lower when subjects who had had previous knee surgery were excluded. Among persons with radiographical evidence of OA, the prevalence of a meniscal tear was 63 % among those with knee pain, aching, or stiffness on most days and 60 % among those without these symptoms. The corresponding prevalences among persons without radiographical evidence of OA were 32 % and 23 %. Sixty-one percent of the subjects who had meniscal tears in their knees had not had any pain, aching, or stiffness during the previous month.
An accompanying editorial by Marx (2008) in the New England Journal of Medicine concluded that the study by Kirkley et al (2008), combined with other evidence, indicates that OA of the knee (in the absence of a history and physical examination suggesting meniscal or other findings) is not an indication for arthroscopic surgery and indeed has been associated with inferior outcomes after arthroscopic knee surgery. The editorialist stated, however, that OA is not a contraindication to arthroscopic surgery, and arthroscopic surgery remains appropriate in patients with arthritis in specific situations in which OA is not believed to be the primary cause of pain.
In a systematic review of outcomes of 3 treatments for OA of the knee: (i) intra-articular viscosupplementation, (ii) oral glucosamine, chondroitin or the combination, and (iii) arthroscopic lavage or debridement, Samson et al (2007) concluded that these 3 interventions are widely used in the treatment of OA of the knee, yet the best available evidence does not clearly demonstrate clinical benefit. Uncertainty regarding clinical benefit can be resolved only by rigorous, multi-center randomized controlled trials. Furthermore, a Cochrane review on arthroscopic debridement for knee OA, Laupattarakasem et al (2008) concluded that there is "gold" level evidence that arthroscopic debridement has no benefit for undiscriminated OA (mechanical or inflammatory causes).
In a review on surgical options for patients with OA of the knee, Lützner and colleagues(2009) stated that surgical treatments for knee OA include arthroscopy, osteotomy and knee arthroplasty; determining which of these procedures is most appropriate will depend on several factors, including the location and severity of OA damage, patient characteristics and risk factors. Arthroscopic lavage and debridement do not alter disease progression, and should not be used as a routine treatment for the osteoarthritic knee.
The American Association of Orthopaedic Surgeons’ clinical practice guideline on the treatment of OA of the knee (AAOS, 2008) does not recommend performing arthroscopy with debridement or lavage. Furthermore, it does not recommend performing needle lavage. Also, a recent Agency for Healthcare Research and Quality's (AHRQ, 2009) report summarized the evidence on the safety and effectiveness of 3 treatments for OA of the knee: (i) use of the supplements glucosamine hydrochloride, chondroitin sulfate, or combination of both; (ii) viscosupplementation; and (iii) arthroscopic lavage and debridement of the knee joint. The evidence evaluated comes mainly from comparisons of each therapeutic approach with a placebo. The AHRQ guideline concluded that glucosamine and chondroitin, viscosupplementation, as well as arthroscopic lavage with or without debridement do not lead to clinically meaningful improvement.
In a Cochrane review, Reichenbach and colleagues (2010) compared joint lavage with sham intervention, placebo or non-intervention control in terms of effects on pain, function and safety outcomes in patients with knee OAs. These investigators searched CENTRAL, MEDLINE, EMBASE, and CINAHL up to August 3, 2009, checked conference proceedings, reference lists, and contacted authors. They included studies if they were randomized or quasi-randomized trials that compared arthroscopic and non-arthroscopic joint lavage with a control intervention in patients with OA of the knee. Two independent review authors extracted data using standardised forms. They contacted investigators to obtain missing outcome information, and calculated standardized mean differences (SMDs) for pain and function, and risk ratios for safety outcomes. They combined trials using inverse-variance random-effects meta-analysis. These researchers included 7 trials with 567 patients; 3 trials examined arthroscopic joint lavage, 2 non-arthroscopic joint lavage and 2 tidal irrigation. The methodological quality and the quality of reporting was poor and these investigators identified a moderate-to-large degree of heterogeneity among the trials (I(2) = 65 %). They found little evidence for a benefit of joint lavage in terms of pain relief at 3 months (SMD -0.11, 95 % CI: -0.42 to 0.21), corresponding to a difference in pain scores between joint lavage and control of 0.3 cm on a 10-cm VAS. Results for improvement in function at 3 months were similar (SMD -0.10, 95 % CI: -0.30 to 0.11), corresponding to a difference in function scores between joint lavage and control of 0.2 cm on a WOMAC disability sub-scale from 0 to 10. For pain, estimates of effect sizes varied to some degree depending on the type of lavage, but this variation was likely to be explained by differences in the credibility of control interventions: trials using sham interventions to closely mimic the process of joint lavage showed a null-effect. Reporting on adverse events and drop-out rates was unsatisfactory, and they were unable to draw conclusions for these secondary outcomes. The authors concluded that joint lavage does not result in a relevant benefit for patients with knee OA in terms of pain relief or improvement of function.
Ronn et al (2011) noted that OA of the knee is common, and the chances of suffering from OA increase with age. Its treatment should be initially non-operative-and requires both pharmacological and non-pharmacological treatment modalities. If conservative therapy fails, surgery should be considered. Surgical treatments for knee OA include arthroscopy, cartilage repair, osteotomy, and knee arthroplasty. Determining which of these procedures is most appropriate depends on several factors, including the location, stage of OA, co-morbidities on the one side and patients suffering on the other side. Arthroscopic lavage and debridement is often carried out, but does not alter disease progression. If OA is limited to one compartment, uni-compartmental knee arthroplasty or unloading osteotomy can be considered. They are recommended in young and active patients in regard to the risks and limited durability of total knee replacement. Total arthroplasty of the knee is a common and safe method in the elderly patients with advanced knee OA.
In a cases-control study, Koh and Choi (2012) examined if isolated mesenchymal stem cells (MSCs) derived from the infra-patellar fat pad could effectively improve clinical results when percutaneously injected into arthritic knees. A total of 25 stem cell injections combined with arthroscopic debridement were administered to patients with knee OA. A mean of 1.89 × 10(6) stem cells were prepared with approximately 3.0 ml of platelet-rich plasma (PRP) and injected in the selected knees of patients in the study group. The mean Lysholm, Tegner activity scale, and VAS scores of patients in the study group improved significantly by the last follow-up visit. No major adverse events related to the injections were observed during the treatment and follow-up periods. The results were compared between the study and control groups, in which the patients had undergone arthroscopic debridement and PRP injection without stem cells. Although the pre-operative mean Lysholm, Tegner activity scale, and VAS scores of the study group were significantly poorer than those of the control group, the clinical results at the last follow-up visit were similar and not significantly different between the 2 groups. The authors concluded that the short-term results of this study are encouraging and show that infra-patellar fat pad-derived MSC therapy with intra-articular injections is safe, and provides assistance in reducing pain and improving function in patients with knee OA. These preliminary findings need to be validated by well-designed studies.
The effectiveness of arthroscopic partial meniscectomy for torn meniscus is unknown. Arthroscopic partial meniscectomy is performed in patients with symptomatic osteoarthritis of the knee who also have primary signs and symptoms of a torn meniscus. Guidelines from the American Academy of Orthopedic Surgeons (AAOS) state: "We are unable to recommend for or against arthroscopic partial meniscectomy in patients with osteoarthritis of the knee with a torn meniscus." The AAOS identified only a single study of arthroscopic partial meniscectomy that met criteria for inclusion in their analysis. The study, by Herrlin et al. (2007), compared arthroscopic partial meniscectomy followed by supervised exercise to supervised exercise alone and measured Knee injury and Osteoarthritis Outcome Score (KOOS) pain, symptoms, activities of daily life, sports/recreation, and quality of life subscales scores as outcomes. The study was downgraded from moderate- to low- strength because 40% of patients declined participation and the arthroscopic group had non-homogeneous preoperative KOOS scores. The authors reported no significant treatment benefits of meniscectomy using any of the outcomes at eight weeks and six months. Since there was only one low-strength study, the AAOS recommendation was graded inconclusive.
Additional studies of arthroscopic partial meniscectomy have been published since the AAOS guideline that have found no benefit to arthroscopic partial meniscectomy for torn meniscus. Sihvonen, et al. (2013) conducted a multicenter, randomized, double-blind, sham-controlled trial in 146 patients 35 to 65 years of age who had knee symptoms consistent with a degenerative medial meniscus tear and no knee osteoarthritis. Patients were randomly assigned to arthroscopic partial meniscectomy or sham surgery. The primary outcomes were changes in the Lysholm and Western Ontario Meniscal Evaluation Tool (WOMET) scores (each ranging from 0 to 100, with lower scores indicating more severe symptoms) and in knee pain after exercise (rated on a scale from 0 to 10, with 0 denoting no pain) at 12 months after the procedure. The investigators reported that, in the intention-to-treat analysis, there were no significant between-group differences in the change from baseline to 12 months in any primary outcome. The mean changes (improvements) in the primary outcome measures were as follows: Lysholm score, 21.7 points in the partial-meniscectomy group as compared with 23.3 points in the sham-surgery group (between-group difference, -1.6 points; 95% confidence interval [CI], -7.2 to 4.0); WOMET score, 24.6 and 27.1 points, respectively (between-group difference, -2.5 points; 95% CI, -9.2 to 4.1); and score for knee pain after exercise, 3.1 and 3.3 points, respectively (between-group difference, -0.1; 95% CI, -0.9 to 0.7). The investigators reported that there were no significant differences between groups in the number of patients who required subsequent knee surgery (two in the partial-meniscectomy group and five in the sham-surgery group) or serious adverse events (one and zero, respectively).
Katz, et al. (2013) conducted a multicenter, randomized, controlled trial involving symptomatic patients 45 years of age or older with a meniscal tear and evidence of mild-to-moderate osteoarthritis on imaging. The investigators randomly assigned 351 patients to surgery and postoperative physical therapy or to a standardized physical-therapy regimen (with the option to cross over to surgery at the discretion of the patient and surgeon). The patients were evaluated at 6 and 12 months. The primary outcome was the difference between the groups with respect to the change in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical-function score (ranging from 0 to 100, with higher scores indicating more severe symptoms) 6 months after randomization. In the intention-to-treat analysis, the mean improvement in the WOMAC score after 6 months was 20.9 points (95% confidence interval [CI], 17.9 to 23.9) in the surgical group and 18.5 (95% CI, 15.6 to 21.5) in the physical-therapy group (mean difference, 2.4 points; 95% CI, -1.8 to 6.5). At 6 months, 51 active participants in the study who were assigned to physical therapy alone (30%) had undergone surgery, and 9 patients assigned to surgery (6%) had not undergone surgery. The results at 12 months were similar to those at 6 months. The frequency of adverse events did not differ significantly between the groups.