Tibiofemoral contact areas and pressures in six high flexion knees.

The tibiofemoral articulating interfaces of six high flexion knee designs were examined using a standard testing protocol developed by Harris et al. [J Biomech 32:951-958 (1999)] to investigate the polyethylene insert contact areas and pressures. A load of 3600 N was applied for 10 s at 0, 30, 60, 90, 110, 135 and 155 degrees of flexion. Contact areas and pressures at the femoral-polyethylene insert interface were measured with a I-scan 4000 system. Up to 110 degrees of flexion, the VANGUARD RP HI-FLEX showed the highest contact area and lowest pressure. At the deep flexion angles, contact area decreased and contact pressure increased significantly in all knees. The NexGen series showed a constant contact area throughout the various flexion angles. In general, all high flexion knees could result in almost point contact in an extremely high range of motion.