Patellofemoral Bipolar Osteochondral Allograft Surgery Yields Similar Short- to Mid-term Outcomes As Unipolar Surgery: A Minimum 2-year Follow-up Study

Objectives: While osteochondral allograft (OCA) transplantation for tibiofemoral chondral lesions has been extensively studied, there is limited literature on outcomes following patellofemoral (PF) OCA transplantation, especially for the treatment of bipolar PF chondral lesions. This study aimed to compare graft failure rates, reoperation, and patient-reported outcomes (PROs) between patients undergoing unipolar and bipolar PF OCA transplantation with a minimum follow-up of two years. Methods: A retrospective review of PF OCA transplantations between 2015-2022 at a single institution was performed. Those with concomitant tibiofemoral OCA transplantation or < 2-year follow-up were excluded. Graft failure (conversion to total or PF knee arthroplasty or revision OCA), reoperation (second-look arthroscopy with graft or surrounding cartilage debridement), and pre- and post-operative International Knee Documentation Committee (IKDC) and Knee injury and Osteoarthritis Outcome Score (KOOS) subscale PRO scores were compared between unipolar and bipolar PF OCA patients. Categorical variable comparisons between groups were performed using Fisher’s exact tests. PRO score comparisons between groups were performed using Wilcoxon rank-sum tests or unpaired t-tests, depending on the normality of data as determined by the Shapiro-Wilk test. Kaplan-Meier survivorship analysis was performed for failure and reoperation, with comparisons between groups conducted using the log-rank test. All testing was two-sided, and significance was established as p < 0.05. Results: Thirty-six knees (24 unipolar, 12 bipolar) from 35/41 (85.4%) patients (68.57% female; age 33.59 ± 8.10 years; BMI 29.24 ± 5.28 kg/m 2 ) were included. Mean follow-up was 3.58 ± 1.39 years (3.87 ± 1.45 years unipolar vs 3.00 ± 1.10 bipolar, p = 0.05). There were no significant differences in baseline PROs, defect size ( p = 0.98), prior surgeries ( p = 0.53), previous cartilage repair ( p = 0.66), and concomitant ( p = 0.19) or prior tubercle osteotomy ( p = 0.48). Graft failure was similar (N = 1 (4.17%) unipolar vs N = 1 (8.3%) bipolar, p > 0.99) and survivorship did not significantly differ ( p = 0.16), with 100% unipolar and 91.7% bipolar grafts surviving 2-4 years postoperatively ( Figure 1 ). Reoperation-free survival was non-significantly lower among bipolar patients (92% in unipolar and bipolar at 2 years, 92% vs 76% at 3 years, and 92% vs 57% at 4.7 years, p = 0.15). PRO improvements from baseline at final follow-up were similar ( Figure 2 ). No significant differences in IKDC ( p = 0.74), KOOS Pain ( p = 0.64), and KOOS Sports ( p = 0.33) MCID achievement were observed ( Figure 3 ). Conclusions: Bipolar and unipolar PF OCA transplantation both yielded excellent and comparable graft survivorship and clinically significant functional improvement at short- to mid-term follow-up.