Design-dependent associations between quadriceps strength and sagittal knee biomechanics after posterior-stabilized total knee arthroplasty: A 3D motion analysis study

Purpose: Single-radius (SR) and multi-radius (MR) femoral components are widely used in posterior-stabilized total knee arthroplasty (TKA). While previous studies have compared these designs primarily using clinical outcomes or basic kinematics, the relationship between quadriceps strength and dynamic sagittal-plane knee biomechanics remains insufficiently understood. Methods: This prospective exploratory cohort study included 31 posterior-stabilized TKAs (SR: 16 knees; MR: 15 knees). Patients were evaluated at 6 months and 1 year postoperatively. Knee extension strength was measured using a handheld dynamometer. Sagittal-plane biomechanics during level walking, stair ascent, and stair descent were assessed using three-dimensional motion capture. External knee flexion moment (KFM) and KFM impulse were calculated. Associations between quadriceps strength and sagittal-plane biomechanical variables were analyzed using Spearman correlation coefficients. Results: No significant between-group differences were observed in demographics or clinical activity levels. In the SR group, no significant associations were identified between quadriceps strength and sagittal-plane biomechanical variables at any postoperative time point. In contrast, the MR group demonstrated a moderate positive correlation between knee extensor strength and stair-descent knee flexion moment (KFM) impulse at 6 months postoperatively (r = 0.498, p < 0.05), which was not observed at 1 year postoperatively. During stair ascent, a significant positive correlation between knee extensor strength and the first peak KFM was observed in the MR group at 1 year (r = 0.606, p < 0.05). Conclusions: This exploratory study demonstrated design-dependent associations between quadriceps strength and sagittal-plane knee biomechanics after posterior-stabilized TKA. While no significant between-group differences were observed in clinical or absolute biomechanical outcomes, task- and time-dependent strength-biomechanics associations were identified in the MR group, whereas no such associations were observed in the SR group, suggesting potential clinical relevance in patients with delayed quadriceps recovery.