Negative Influence of Joint Line Change on 10.8-Year Outcomes and Survival of Medial Unicompartmental Knee Arthroplasty.

Abstract

This study aimed to investigate the effect of changes in joint line height on clinical outcomes and survival rates of unicompartmental knee arthroplasty (UKA) for medial compartmental knee osteoarthritis at a mean follow-up of 10.8 years. We reviewed 205 patients who underwent medial UKA between March 2005 and December 2017 and had a minimum follow-up of five years. The mean overall follow-up duration was 10.8 years (range, 5.1 to 18.2). Patients were divided into two groups based on the degree of joint line restitution following surgery: the restored joint line group (joint line change less than two mm; n = 125) and the joint line lowering group (joint line change ≥ two mm; n = 80). Radiographic evaluations included the mechanical hip-knee-ankle angle, medial proximal tibial angle, lateral distal femoral angle, joint line convergence angle, and posterior tibial slope. Clinical outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Forgotten Joint Score (FJS). Kaplan-Meier survival analysis was performed using conversion to total knee arthroplasty as the endpoint. There were significant differences in postoperative WOMAC function score, WOMAC total score, and FJS between the restored joint line group and the joint line lowering group (all P < 0.05). During the follow-up period, 13 implant failures were identified, with aseptic loosening being the most common mode of failure, accounting for 46.2% of revisions. At a mean follow-up of 10.8 years, survival rates were significantly lower in the joint line lowering group (90.7% [95% confidence interval (CI), 80.1 to 95.8]) compared to the restored joint line group (97.5% [95% CI, 89.8 to 99.4]; P = 0.014, log-rank test). Multivariate regression analyses identified higher body mass index (hazard ratio [HR], 1.301; P = 0.046) and joint line lowering (HR, 1.562; P = 0.029) as independent risk factors for implant failure. Joint line lowering ≥ two mm was associated with worse clinical outcomes and lower survival rates following UKA at a mean follow-up of 10.8 years. These findings underscore the importance of restoring the joint line to achieve optimal outcomes and survival after UKA for medial compartmental knee osteoarthritis.