Progression of medial osteoarthritis and long term results of lateral unicompartmental arthroplasty: 10 to 18 year follow-up of 54 consecutive implants.

INTRODUCTION: The literature results of unicompartmental knee arthroplasty (UKA) for isolated lateral osteoarthritis (OA) are not as good as for isolated medial OA. In 1988 our department started using a UKA with a fixed, all polyethylene tibial component and a resurfacing femoral component. The aim of this retrospective study is to report on the progression of medial OA and the long term results of this prosthesis implanted for isolated lateral OA, at a minimum follow up of ten years.

MATERIALS AND METHODS: From January 1988 to October 2003, we performed 54 lateral UKAs in 52 patients. All patients had isolated lateral OA, which was post-traumatic in three cases. The mean age at the time of the index procedure was 72.2 ± 15.2 years. Forty-six UKAs in 44 patients were available for follow-up. The mean duration of follow-up was 14.2 years (minimum ten years; range 10.2-18 years).

RESULTS: At final follow-up, seven had undergone a second operation, three were revised to total knee arthroplasty (TKA), three had medial UKAs implanted for progression of medial disease, and one was converted to TKA for tibial tray malpositioning. No revision surgery was necessary for wear, infection or progression of patellofemoral OA. The mean Knee Society Score (KSS) knee score was 95.1 points and mean KSS function score was 82.2 points. The mean range of motion was 132.6° (range, 115-150°). Implant survival was 94.4% at ten years and 91.4% at 15 years.

CONCLUSION: The use of a UKA with a fixed, all polyethylene tibial bearing and a femoral resurfacing implant is a reliable option for the management of isolated lateral knee osteoarthritis. We have demonstrated excellent functional results and implant survival in the long term. The most significant factor leading to reoperation is progression of medial disease.