Knee rotation during a weightbearing activity: influence of turning

Kinematic studies, in which mobile- and fixed-bearing total knee arthroplasty (TKA) were compared, showed controversial results with respect to axial femorotibial rotation. However, all studies focused only on straight ahead tasks, which may underestimate possible differences in freedom of rotation. The purpose of this study was to investigate the influence of turning on normal axial knee rotation. If large differences across tasks were to be found, this would support the use of this task in the evaluation of in-vivo TKA kinematics. In 15 healthy persons, crossover and sidestep turns were added to a standardized chair rise. Three-dimensional knee angles were recorded using an optoelectronic motion analysis system, and a noninvasive epicondylar frame was developed to track the femur. Compared to knee rotation during the straight ahead task, average peak tibial internal rotation increased during a crossover turn (p<0.001), as did peak external tibia rotation during a sidestep turn (p<0.001). The combined range of axial rotation for both turning tasks together was 20.9 degrees , versus 13.5 degrees for the straight ahead task (p<0.001). The turning maneuvers in this study induced a large range of axial knee rotation, so they could be important in studies comparing freedom of rotation in mobile- and fixed-bearing TKA.