In-vivo kinematics of high-flex posterior-stabilized total knee prosthesis designed for Asian populations

The purpose of this study was to determine in-vivo kinematics of our developed posterior-stabilized (PS) total knee prosthesis for Asian populations in comparison with a popular high-flexion PS prosthesis. We analyzed 62 osteoarthritic knees: 31 knees with the new PS prosthesis (group A) and 31 knees with a popular high-flexion PS prosthesis (group B). Radiographic knee images were taken during standing, lunge, and kneeling activities. The three-dimensional position and orientation of the implant components were determined using model-based shape matching techniques. Group A showed slightly greater implant flexion angles compared with knees with conventional prosthesis at maximum lunge (average: 119 vs. 110A degrees, p = 0.001), and at maximum kneeling (121 vs. 114A degrees, p = 0.004), although the range of motion was not significantly different. The femoral centre positions were more posterior in group A at standing, at 90A degrees lunge, at maximum lunge (-9 and -7 mm, p = 0.004), at 90A degrees kneeling, and at maximum kneeling (-9 vs. -7 mm, p = 0.016), and posterior translations of the femoral center were greater at 90A degrees knee flexion postures. The femoral centre positions had a strong negative correlation with implant flexion angles at maximum lunge in group B (r = -0.893, p < 0.001), but not in group A (p = 0.242). The new PS prosthesis designed for Asian knee morphology achieved flexion angles and range of motion at least comparable to that of conventional high-flexion PS prosthesis. The femoral roll-back pattern, however, is different from a conventional knee, reflecting the post/cam design.