Flexion moments, knee joints

On the stance side, the hip joint extends, accompanied by muscular contraction that prevents dropping of the pelvis toward the swing side. The knee joint is in slight flexion at the moment of foot contact, or heel strike, after which the knee is extended. 

A sequential cutting study was performed on 8 fresh-frozen human knees. The femoral attachment of the ACL was divided into a central area of dense fibers which directly inserted into the femur and into the anterior and posterior fanlike extension areas (Fig. 1.4). The ACL fibers were cut sequentially from the bone in 2, 4, and 2 stages in the posterior fanlike area, the central dense area, and the anterior fanlike area, respectively. Each knee was mounted in a robotic joint testing system at 0-90 of flexion tibial anteroposterior 6 mm translations and 10 or 15 of internal rotation were applied. The reduction in restraining force or moment was measured after each cut. 

---