The contact locations in the knee during high flexion.

The aim was to determine the contact locations in the knee in a simulation of a deep squatting position, for both neutral and after tibial rotation. A rig was constructed to load the knee under quadriceps action at flexion angles from 135 to 155 degrees flexion, with a mechanism for rotating the tibia internally or externally. Fiducial points on each bone were digitized in each position of the knee. After all of the tests, the entire bone surfaces were digitized, enabling computer reconstructions to be made of the multiple positions. The software then produced color maps of the contact areas. Six cadaveric knees were tested. On the patella, contact occurred over an arcuate band across the superior, lateral and medial edges, including the medial 'odd facet'. On the upper tibia, the medial contact was close to the center of the condyle, while on the lateral side, the contact was posterior. As a result, impingement occurred between the posterior tibial edge and the femoral cortex on the medial side. However, lateral impingement also occurred when the tibia was externally rotated. Due to the stiffness of the knee at these high flexion angles, the maximum tibial rotation between external and internal averaged only 16 degrees. During this rotation, there was twice as much displacement of the lateral contact than the medial contact, indicating greater stability on the medial side. In all rotations, the medial contact moved inwards to engage the intercondylar eminence which appeared to act as the pivot area. The small rotational range implied that correct foot placement was necessary for optimal mechanics during squatting activities.