What Is the Best Way to Treat Focal Articular Cartilage Lesions of the Knee? Perhaps No Treatment at All

Commentary Focal cartilage lesions (FCLs) of the knee are common in an active population, as documented by Arøen et al., who found a 66% prevalence of these defects in 993 consecutive knee arthroscopies1. The increase in participation in sports that involve cutting, pivoting, and jumping, coupled with the risk of coexistent ligamentous and meniscal injury, only exacerbates the clinical impact of these lesions. The National Institutes of Health (NIH) consensus conference on osteoarthritis has noted a relative risk of 4.4 to 5.3 for knee osteoarthritis in high-demand pivoting athletes2. It is widely accepted that these articular cartilage lesions have a limited capacity to heal. The lack of vascularity, coupled with the inability of chondrocytes to replicate and signal the recruitment of extrinsic undifferentiated repair cells, negates the normal inflammatory and reparative response seen in other tissues. Therefore, a variety of reconstructive procedures have been devised over the past 3 decades to treat these biologically inert lesions. Unfortunately, the natural history of untreated FCLs of the knee is generally unknown, particularly in athletes, primarily due to an inability to accurately diagnose these lesions and follow them over time in a noninvasive manner. Widuchowski et al.3 retrospectively analyzed 2,931 patients with an isolated articular cartilage lesion documented at the time of knee arthroscopy. Outerbridge grade-3 or 4 lesions (articular cartilage fissuring with a diameter of >0.5 inches [1.3 cm] that either reaches subchondral bone [grade 3] or results in erosion of the articular surface that exposes subchondral bone [grade 4]) were noted in 152 (5.2%) of these patients. After 7 years of follow-up, they found good or satisfactory results following simple debridement and loose-body removal as well as when the cartilage lesions were left untreated. To better understand the long-term consequences of untreated and treated FCLs of the knee, the novel study performed by Birkenes et al. retrospectively analyzed 322 patients (328 knees) with a mean age of 36.8 years at the time of diagnosis who had an FCL documented during their knee arthroscopy. These patients were recruited from 6 major Norwegian hospitals and were treated by an unknown number of surgeons. The cohort was contacted 19.1 years after their index procedure to determine patient satisfaction as indicated by their Knee injury and Osteoarthritis Outcome Score (KOOS) Quality of Life (QoL) subscore, the need for subsequent cartilage surgery, and the risk of treatment failure as defined by a KOOS QoL of <50 or subsequent knee arthroplasty or osteotomy. After nearly 20 years, Birkenes et al. found that patients without subsequent knee arthroplasty or osteotomy had significantly better mean patient-reported outcome measures (Lysholm, KOOS, International Cartilage Regeneration and Joint Preservation Society [ICRS] visual analogue scale [VAS] for pain) at the time of final follow-up than preoperatively. Not surprisingly, medial and lateral femoral condylar lesions were associated with significantly better KOOS QoL scores than patellar lesions. Nearly 50% of the patients had treatment failure, and the main risk factors identified by multiple logistic regression were a body mass index of ≥25 kg/m2, >1 FCL, full-thickness lesions, and lower education level. The last factor has been associated with a higher risk of heavy manual labor, lower level of physical fitness, and lower socioeconomic status. Even though approximately 18% of the knees had undergone subsequent cartilage surgery, nonsurgical treatment had results equal to those of most surgical treatments. Interestingly, lesions treated with autologous chondrocyte implantation (ACI) had a higher KOOS QoL subscore and lower risk of failure but a higher risk of subsequent knee arthroplasty. However, the last finding may be related to the lack of availability of osteochondral allografts in Norway, which limited the available options to treat sizeable chondral defects resulting from a failed ACI procedure. A strength of this study was the large number of patients with FCLs of the knee treated by multiple surgeons, as this best resembles the normal clinical setting, which typically involves a heterogeneous mix of patients with a variety of coexistent pathologies, activity goals, and tolerance of symptoms. This is also the first study, to my knowledge, that compares the outcomes of patients who did and did not undergo treatment of an arthroscopically verified articular cartilage defect. Interestingly, the mean KOOS QoL subscore of this study’s patients was 58.1 at the time of final follow-up, which is strikingly similar to the value of 58.0 found by Kreuz et al.4. There are several limitations to this study that must be recognized. Standardized preoperative and postoperative weight-bearing and full-length alignment radiographs were not available to objectively determine the degree of osteoarthritis at baseline or the extent of joint deterioration over the 20-year period. There was also no objective measure of the patients’ physical activity, which would obviously affect the clinical outcome of an FCL of the knee. The results of the study may have been biased by several factors: only 65% of the eligible patients consented to participate, several of those who did participate failed to provide sufficient detail regarding their subsequent surgical procedures, and the number of study participants required by the power analysis was not met for all subgroup analyses. It should also be noted that the authors’ definition of failure—undergoing subsequent knee arthroplasty or osteotomy or having a KOOS QoL of <50—differs from that in prior research that considered any subsequent cartilage surgery as a failure5. The indications for a knee arthroplasty also may vary considerably between countries, as well as between regions within a country, and between patients and surgeons6. In summary, the study by Birkenes et al. causes one to reconsider whether all cartilage defects of the knee require surgical treatment. Although many details of their patient cohort are lacking, their nearly 20-year follow-up of untreated FCLs provides a unique contribution to the literature given the relative paucity of true “natural history” studies in orthopaedic surgery. These focal defects may do well without any specific treatment. However, additional long-term studies (ideally randomized controlled trials) are warranted, with validated patient-reported measures of knee function, symptom burden, and activity level in addition to objective measures of cartilage deterioration and the subsequent development of osteoarthritis. This information is vital to enable surgeons to counsel their active patients on the best way to treat an isolated cartilage lesion of the knee and to estimate the likelihood of success with or without treatment.