ANTERIOR KNEE PAIN AFTER PATELLOFEMORAL JOINT REPLACEMENT: REVISION IS NOT THE ANSWER. A FIVE-YEAR SURVIVORSHIP AND FUNCTIONAL OUTCOMES STUDY

Patellofemoral joint (PFJ) replacement is a bone-preserving knee surgical technique for the treatment of isolated PFJ arthritis. However, the survivorship of this procedure is inconsistent. This study aimed to evaluate survival rates of PFJ replacement, assess postoperative functional outcomes, and identify predictors and primary modes of failure in a single institution. We retrospectively studied a consecutive cohort of 34 patients (36 knees) who underwent PFJ replacement in our centre. We included all patients who had PFJ replacement for isolated PFJ pathology and complained of specific anterior knee pain. Mean age was 60 (SD 12) years, and mean BMI was 30 (SD 7) kg/m2. There were 25 female patients, and mean follow-up period was 5.2 (3 to 9) years. We used the Oxford Knee Score (OKS) and Short Form 12-item Health Survey version 2 (SF-12v2) as functional outcome measurements. All postoperative immediate X-rays were reviewed and compared with the most recent images. All postoperative complications were registered. We performed Kaplan-Meier curves to analyze survival rates, using conversion to total knee arthroplasty (TKA) as the endpoint. Cox proportional hazards regression analysis was used to evaluate potential risk factors for implant failure. The patient-reported outcome measures showed a mean OKS of 34.87 (SD 9.67), and mean SF-12v2 were 36.98 and 52.60 for physical and mental components, respectively. No radiographic failures were recorded at the latest follow-up. The cumulative survival rate was 83.3% at five years of follow-up, with 6 (16.7%) implant failures. All patients were converted to TKA due to unexplained anterior knee pain that persisted even after revision, except for one patient. All revisions were in patients with the patella resurfaced as part of the initial procedure, and none of the unsurfaced native patella were revised. Cox proportional hazards regression analysis revealed that the patient's age, sex, and previous surgeries had no effect on converting PFJ replacement to TKA. Finally, higher BMI was not associated with implant failure and conversion to TKA. This study has shown that PFJ replacements had an 83% survival rate and good functional outcomes at 5-year follow-up in our institution. The most common cause of failure was ongoing and unexplained anterior knee pain, and we did not find any association between age, sex, previous surgeries, and revision surgery.