Does Medial Patellofemoral Osteoarthritis Influence Outcome Scores and Risk of Revision After Fixed-bearing Unicompartmental Knee Arthroplasty?

Background Patellofemoral osteoarthritis (OA) and anterior knee pain sometimes are considered contraindications for unicompartmental knee arthroplasty (UKA). However, several studies have demonstrated excellent patientreported outcome scores in patients with patellofemoral OA treated with medial mobile-bearing UKA. Because these studies assessed the outcome of mobile-bearing UKA only, we were interested to see whether that finding also applies to fixed-bearing medial UKA. Questions/purposes (1) Does patellofemoral OA influence patient-reported outcome scores after medial fixed-bearing UKA? (2) Does untreated medial patellofemoral OA increase the revision rate after medial fixed-bearing UKA? Methods: Between 2008 and 2015, one surgeon performed 308 medial fixed-bearing UKAs of a single design. Of those, 80 (26%) had patellofemoral OA of at least moderate severity (ICRS III or IV), and 228 (74%) did not. During that period, the surgeon did not use patellofemoral OA as a contraindication to UKA. In all, 13 patients (10%) in the patellofemoral OA group were lost before 2-year minimum followup, and 20 (11%) in the control group (without patellofemoral OA) were lost; all other patients were available, seen in the last 5 years, and included in this retrospective study. Mean (+/- SD) followup in the patellofemoral OA group was 39 +/- 25 months, and it was 41 +/- 23 in the control group. There were 100 women and 120 men. Patients had a mean age +/- SD of 65 +/- 10 years and mean +/- SD BMI of 29 +/- 4.5 kg/m.The intraoperative status of the patellofemoral joint was assessed using the International Cartilage Repair Society (ICRS) classification. The primary study endpoint was the Forgotten Joint Score (FJS-12); we also compared scores on the Lonner PatelloFemoral Score (LPFS), Oxford Knee Score (OKS) and Short-Form 12 (SF-12). With the numbers available, we had 80% power to detect a difference of 12.3 points on the Forgotten Joint Score. A secondary endpoint was femoral or tibial component revision for any reason verified over the phone for each included patient. Results: With the numbers available, there was no difference in FJS-12 score between the UKA with patellofemoral OA group and the group without patellofemoral OA 71 +/- 29 versus 77 +/- 26, mean difference - 6; 95% CI, -16 to 4.5; p = 0.270). Likewise, with the numbers available, we saw no differences in LPFS, OKS and SF-12. There was no difference in survivorship from all-cause revision at 4 years between the patellofemoral OA group and the group without patellofemoral OA (98%; 95% CI, 85.8-99.7 versus 99.5%; 95% CI, 96.0-99.2%; p = 0.352). Conclusions: Patients with medial osteoarthritis in this single-center study generally benefitted from medial fixed-bearing UKA with good-to-excellent outcomes scores at short term, whether or not medial patellofemoral wear is present.