Medial‐pivot total knee arthroplasty enhances tibiofemoral axial rotation stability in weight‐bearing mid‐range flexion compared to posterior‐stabilised system

Purpose Total knee arthroplasty (TKA) stands as a primary intervention for severe knee ailments, yet concerns remain regarding postoperative patient satisfaction and flexion instability. This study aims to evaluate the in‐vivo kinematics of medial‐pivot (MP) and posterior‐stabilised (PS) designs during step‐up activity, in comparison to the kinematics of the nonoperated contralateral knee. Methods Sixteen patients with PS‐TKA and 14 with MP‐TKA were retrospectively examined. Clinical outcomes were assessed using patient‐completed questionnaires. Motion during step‐up was captured using a dual fluoroscopic system. Statistical analysis was applied to evaluate the in‐vivo tibiofemoral six‐degree‐of‐freedom kinematics and articular contact positions between the two groups. Results Despite being older, patients in the MP group reported higher postoperative subjective scores for weight‐bearing functional activities. The axial rotation centres of MP‐TKA located on the medial tibial plateau exhibited less variance compared to PS‐TKA and contralateral knees. Compared to the contralateral knee (contralateral to medial‐pivot [C‐MP] or contralateral to posterior‐stabilised [C‐PS]), the MP group exhibited limited range of motion in terms of anteroposterior translation (MP: 3.6 ± 1.3 mm vs. C‐MP: 7.4 ± 2.5 mm, p