Patella-Femoral Joint Revision Surgery Following a Rare and Interesting Case of Implant Failure: A Case Report and Retrospective Analysis of Our Hospitals Implant Data

According to the national joint registry, patello-femoral joint (PFJ) replacement accounts for 1% of all knee arthroplasty procedures in the UK, 1014 of which were performed in 2018. The femoro-patella vialla (FPV) implant by MicroPort orthopaedics has a high reported rate of revision, more than four times that of other knee replacements. The mechanisms of failure are usually loss of fixation at the bone-implant interface. We observe a rare and unusual case form of patella component failure whereby the facets of the implant remain imbedded within the patella as a result of shear force, leaving a loose patella button within the knee. A literature review was conducted of reported modes of failure of the FPV implant and retrospective analysis of our units' results looking into rate of revision, modes of failure, and assessment of a single surgeon's patient outcome measure (Knee Society Scores). Retrospective analysis of our hospital's data revealed that 11% of FPV implants were revised in our unit, a large percentage of which were due to pain and progressive osteoarthritis. We observed revision rates of 5.84% at 3 years, 10.21% at 5 years, and 13.13% at 10 years, which is favourable to national joint registry revision estimates of 6.99%, 10.13%, and 19.10%, respectively. Knee Society Scores reveal a mean improvement of 39.65 (-38 to 100) at follow-up following FPV unicompartmental knee arthroplasty surgery. Our unit demonstrated better results from patient outcome measures when compared to literature and a lower rate of revision when compared to national figures.