Does mobile-bearing knee arthroplasty motion change with activity?

BACKGROUND The purpose of this study was to evaluate the effect of mobile-bearing implant design and activity on knee arthroplasty kinematics during three activities of daily living. METHODS In vivo kinematics were analyzed using 3D model registration from fluoroscopic images of non-weightbearing knee flexion-extension, weight-bearing squatting and stair activities in 20 knees in 10 patients with bilateral total knee arthroplasty. Each patient had one rotating-platform and one meniscal-bearing variant of the same prosthesis design. RESULTS Anteroposterior translations in meniscal-bearing knees were larger than those in rotating-platform knees for the different dynamic conditions. Meniscal-bearing knees showed more posterior femoral locations with activities that increased demand on the quadriceps. Condylar translations changed little in rotating-platform knees with different activities. CONCLUSIONS Activity dynamics can have a significant influence on knee kinematics, and have a greater effect on the kinematics of unconstrained meniscal-bearing prostheses than rotating-platform knee prostheses. LEVEL OF EVIDENCE Level II.