THE SELF-CENTERING FEMOROPATELLAR PROSTHESIS: RESULTS AT MEAN 6-YEAR FOLLOW-UP IN 57 CASES

Abstract

Purpose of the study: The aim of this retrospective study was to analyze the results obtained with the femoropa-tellar self-centering prosthesis and to confirm its usefulness and limitations for the treatment of femoropatellar osteoarthritis.

Material and methods: This continuous series of 57 patients, mean age 65.6 years underwent surgery fro 1986 to 2003 for implantation of a self-centering prosthesis. Most (60%) presented osteoarthritis on a dysplasic knee; others presented primary osteoarthritis (31%) or trauma sequelae (9%). Mean follow-up was 74.5 months (range 12–180 months). Functional outcome was assessed with the IKS and activity daily living (ADL) scales. The radiographic study enabled 3D analysis of the implant position.

Results: At last follow-up, the mean IKS score was 157.3/200. The mean ADL score was 73.8 (range 48.8–96.3). The IKS score gave 66.7% good and the ADL score, which takes into consideration all daily life functions, 57% very good outcome. Outcome was best in patients with trochlear dysplasia. The eleven knees requiring revision for a total knee arthroplasty (24%) had initially a narrower trochlear angle (p=0.02) and a thicker patella (p=0.02). In these patients, the initial prosthesis protruded more anteriorly (p=0.004) and the horizontal axis was greater (p=0.02).

Discussion: The results of this series are less satisfactory than in the literature, but assessments may depend on the scores used since there was a 10% difference between the ADL and IKS scores. The results were better in the group of patients undergoing surgery for osteoarthritis due to dysplasia, in agreement with De Cloedt and Argenson. Analysis of the radiological parameters enabled identification of technical errors leading to failure. A successful femoropatellar prosthesis depends basically on two factors: technical precision and patient selection.

Conclusion: These results led us to avoid widening indications for femoropatellar prostheses, which are already in our experience rather limited (2%). For us, patients aged 50–70 years with advanced-stage femo-ropatellar osteoarthritis due to dysplasia and no other anomaly and who have not responded to conservative treatment would be the population of choice. The lack of any technical problem for revision total knee arthroplasty is an argument in favor of the femoropatellar prosthesis.