Mobile-Bearing Unicompartmental Knee Arthroplasty Enhances Patellofemoral Function and Preserves Contralateral Knee Health Versus Fixed-Bearing.

Abstract

Unicompartmental knee arthroplasty (UKA) effectively treats unicompartmental osteoarthritis (OA), but longterm outcomes are often compromised by disease progression in other compartments. Distinct impacts of fixed-bearing (FB) and mobile-bearing (MB) UKA on patellofemoral joint (PFJ) kinematics and soft tissue mechanics remain unclear. Our study aims to analyze effects of FB and MB UKA on PFJ kinematics and patellar tendon (PT) elongation and assess UKA's impact on UKA and contralateral side. A total of 24 patients (13 FB UKA, 11 MB UKA) were recruited, all with varying knee dysfunction. PFJ six-degrees-of-freedom motion, patellar lever arm and PT elongation were assessed during functional maneuvers using dual fluoroscopic imaging and virtual ligament analysis. Differences between parameters were analyzed using paired t-tests, while correlations between parameters and functional scores were assessed using Spearman correlation, with false discovery rate correction applied. We found that FB UKA resulted in a more distal and medial patellar position and increased flexion with posterior shift correlating with worse KSS scores (p < 0.05). MB UKA showed greater patellar extension and better lateral patellar positioning and better KSS scores (p < 0.05). Patellar lever arm was longer after MB UKA during single-leg lunge, whereas FB UKA differed during early sit-to-stand. Both groups experienced PT elongation on UKA side and correlated with OKS and FJS (p < 0.05). In conclusion, FB UKA offers greater knee stability but may restrict rotation and increase patellofemoral stress, requiring focused rehabilitation on alignment and quadriceps function. MB UKA better restores natural kinematics, making it preferable for active patients.