Evidence-based indications for mobile-bearing unicompartmental knee replacement in a consecutive cohort of 1000 knees.

Background The indications for unicompartmental knee replacement (UKR) remain controversial. Previously recommended contra-indications include: age under 60years, weight 180lb (82kg) or over, patients undertaking heavy labour, chondrocalcinosis, and exposed bone in the patellofemoral joint. This study explores whether these contra-indications are valid in mobile-bearing UKR. Methods Using a prospective series of 1000 consecutive medial UKR in which the reported contra-indications were not applied, the functional outcome and survival in patients with or without contra-indications were compared. Results Of the 1000 consecutive UKR (818 patients) 68% (678 knees) would be considered contra-indicated based on published contra-indications. At a mean follow-up of ten-years (5 to 17) there was no difference in American Knee Society Objective Scores (AKSS-O) (p=0.05) or Oxford Knee Score (OKS) (p=0.08) between groups. However, knees with contra-indications had significantly (p=0.02) fewer poor outcomes and significantly better AKS Functional Scores (AKSS-F) (p<0.001) and Tegner Activity Scores (p<0.001). At fifteen-years no difference in implant survival (p=0.33) was observed. The 3% of UKR performed in young males (age<60) weighing 180lb or over with high activity levels, who have been reported to have poor outcomes after fixed-bearing UKR, had significantly better AKSS-F (p<0.001), OKS (p=0.01) and Tegner Activity Score (p<0.001) at ten-years. No difference in AKSS-O (p=0.54) at ten-years or implant survival at fifteen-years (p=0.75) was seen. Conclusion This large case series provides evidence that patients with the previously reported contra-indications do as well as, or even better than, those without contra-indications. Therefore these contra-indications should not apply to mobile-bearing UKR.