Autologous Chondrocyte Implantation in the Patella

Abstract

Background: Cartilage defects in the patella are common, and a subset of patients does not respond to nonoperative measures. While most cartilage repair techniques have demonstrated good outcomes in the femoral condyles, the patellofemoral compartment poses special challenges. Hypothesis: Repair of patellar cartilage defects with autologous chondrocyte implantation (ACI) will provide lasting improvements in pain and function. Study Design: Case series; Level of evidence, 4. Methods: Patients were treated at 1 of 4 participating cartilage repair centers with ACI for cartilage defects in the patella; bipolar (patella + trochlea) defects were included as well. All patients were followed prospectively for at least 4 years with multiple patient-reported outcome instruments, including the International Knee Documentation Committee, Short Form–12, modified Cincinnati Rating Scale, Western Ontario and McMaster Universities Osteoarthritis Index, and Knee Society scores. Treatment failure was defined as structural failure of the graft combined with pain requiring revision surgery. Results: A total of 110 patients were available for analysis. As a group, they experienced both statistically significant and clinically important improvements in pain and function in all physical outcome scales. The International Knee Documentation Committee improved from 40 ± 14 preoperatively to 69 ± 20 at the last follow-up; the Cincinnati Rating Scale, from 3.2 ± 1.2 to 6.2 ± 1.8; and the Western Ontario and McMaster Universities Osteoarthritis Index, from 50 ± 22 to 29 ± 22 (all P < .0001). Ninety-two percent of patients stated that they would choose to undergo ACI again, and 86% rated their knees as good or excellent at the time of final follow-up. Nine patients (8%) were considered treatment failures, and 16% reported that their knees were not improved. Conclusion: Cartilage repair in the patellofemoral joint is arguably not without its challenges. Autologous chondrocyte implantation remains off-label in the patella, a fact that needs to be discussed with prospective patients during the informed consent process. However, when performed with attention to patellofemoral biomechanics, self-rated subjective good and excellent outcomes can be achieved in more than 80% of patients treated with ACI, even in a patient population with large and frequently bipolar defects such as the one presented in this study. However, final functional scores, although significantly improved, still reflected residual disability in this challenging group of patients.