ISOLATED PATELLOFEMORAL PROSTHESES: LONG-TERM OUTCOME

Abstract

Purpose: Among 115 cemented patellofemoral Bechtol-Blazina prostheses implanted between 1974 and 1991, we reviewed 59 knees in 41 women and nine men (nine bilateral implants). Material and methods: Mean patient age was 60 years and mean follow-up was ten years (6–16). The main indication was primary degenerative disease (82%) followed by chondrocalcinosis (6%), chondromalacia (7%) and secondary degeneration (5%). A previous procedure had been performed on 18 knees (14 patellofemoral and four femorotibial). Associated procedures were tubercle translocation (n=15), tibial osteotomy (n=2), and tension of the medial wing (n=1). The International Knee Society score was noted.

Results: According to the IKS, outcome was good or excellent in 91% of the knees and insufficient in 9% (knee score and function score). Mean ten-year survival determined with the actuarial method was 84.4%. It fell from 91.1% to 75.5% between the ninth and eleventh year due to femorotibial deterioration. There were no cases of phlebitis, infection or prosthetic loosening. Causes of failure were predominantly femorotibial (eight degradations) rather than femoropatellar (two snaps and three painful syndromes involving the lateral parapatellar area). Thirteen reoperations were necessary: tri-compartmental arthroplasty (n=8), modification of the trochlear orientation (n=1), release of the lateral patellar wing (n=3), demaquetisation (n=1). Total or nearly total pain relief was achieved for 80% of the knees. The mean flexion angle was 123° and stair climbing was considered normal in 91% of the patients. All knees were stable. Radiographically, there were six cases of polyethylene remodelling and one case of wear associated with major femorotibial deterioration. This absence of significant wear was, in our opinion, essentially due to the absence of a metal-backed patellar insert.

Discussion: The following indications can be retained on the basis of this series: the ideal indication is isolated patellofemoral osteoarthritis with dysplasia, relative indications are advanced-stage patellofemoral osteoarthritis with axial deviation having no clinical or radiographic (tangent view) impact. In this case, the patellofemoral implant allows postponing insertion of a tricompartmental prosthesis in middle-aged patients. Contraindications are patellar chondromalacia, chondrocalcinosis, low patella, and presence of associated femorotibial degradation.

Conclusion: The long-term clinical and radiographic results after patellofemoral arthroplasty make this procedure the treatment of choice for isolated and advanced-stage patellofemoral osteoarthritis on a normally axed limb when a conservative procedure cannot be performed or has failed. It provides effective pain relief and good knee stability. The operation is difficult and must use congruent implants to avoid the problem of prosthetic instability and patellar snaps.