Divergent Dynamics: Unicompartmental Knee Arthroplasty Enables Greater Propulsive Joint Moments Than Total Knee Arthroplasty

BACKGROUND: Current evidence indicates better functional performance following unicompartmental (UKA) compared to total knee arthroplasty (TKA). This randomized controlled trial addressed the differential effects of UKA and TKA on functional joint mechanics and patient-reported outcome measures (PROMs). METHODS: A total of 38 patients were recruited, and joint moments data were available for 28 patients allocated to either UKA or TKA study arms. Instrumented gait analysis was performed before and one year after surgery. Dependent variables were patient-specific changes in peak sagittal ankle, knee, and hip moments during push-off and maximum coronal knee and hip moments. Patients completed the Oxford Knee Score and Western Ontario and McMaster University Arthritis Index before and six weeks, three months, and one year after surgery. Statistical analyses were conducted using linear mixed effects models for biomechanics and PROMs data. RESULTS: Unicompartmental knee arthroplasty patients displayed significantly larger increases in sagittal hip (β = 0.11 Nm/kg·height; 95% confidence interval (CI), 0.04 to 0.18; P = 0.003), knee (β = 0.05; 95% CI, 0.01 to 0.09; P = 0.010), and ankle (β = -0.13; 95% CI, -0.25 to -0.01; P = 0.042) moments postoperatively than TKA patients. Further, UKA patients displayed significantly smaller changes in coronal knee moments (β = -0.12; 95% CI -0.19 to -0.06; P = 0.001) than TKA patients. While surgical technique did not affect PROMs responses, both UKA and TKA patients reported significant improvements in PROMs scores (P ≤ 0.001) across all follow-up time points. CONCLUSIONS: Unicompartmental knee arthroplasty patients demonstrated greater restoration of propulsive gait mechanics and smaller coronal knee moment changes than TKA, while PROMs improved similarly following both procedures. These findings highlight the value of biomechanical assessment in complementing PROMs and provide clinically relevant context for implant choice and rehabilitation planning in appropriately selected patients following knee arthroplasty.