Conversion of Patello-femoral Arthroplasty to Total Knee Arthroplasty: Survivorship, Function, and Predictors of Patellar Revision.

Abstract

Patello-femoral arthroplasty (PFA) is used to treat isolated patello-femoral osteoarthritis, but progression of tibio-femoral disease or implant failure may require conversion to total knee arthroplasty (TKA). Data describing outcomes after conversion and factors associated with patellar component management at conversion are limited. We evaluated survivorship, radiographic outcomes, and clinical outcomes after conversion of PFA to TKA and assessed whether pre-conversion patellar alignment was associated with patellar component revision at conversion. We retrospectively identified 37 patients who underwent conversion of PFA to TKA (2000 to 2022) at a single tertiary referral center. There were 33 onlay PFAs and four inlay designs. The primary indication for conversion was progression of tibio-femoral osteoarthritis (78%). The median time from PFA to conversion was seven years, and the median follow-up after conversion was six years. The five-year survivorship free of revision was 89.2%, and the five-year survivorship free of reoperation was 83.9%. The most common indications for revision were aseptic loosening (n = 2) and periprosthetic joint infection (n = 1); two additional patients underwent non-revision reoperation. Patients who had pre-conversion lateral patellar tilt of ≥ 10° had increased odds of patellar component revision at conversion compared with those with tilt of less than 10° (odds ratio, 10; P = 0.009). The Knee Society Function score improved from 59 to 80 at two years (P = 0.04). Conversion of PFA to TKA was associated with improved function and modest survivorship. Pre-conversion lateral patellar tilt of ≥ 10° was associated with patellar component revision at conversion and may aid surgical planning and patient counseling.