Anteroposterior tibiofemoral displacements during isometric extension efforts. The roles of external load and knee flexion angle.

Rehabilitation of knee extensors is a major consideration in patients with cruciate injuries and repairs. Extension exercises, however, can produce undesirable loads on the injured or replaced anterior cruciate ligament (ACL) resulting in permanent stretch of this restraint. Our study measures the tibiofemoral displacements associated with proximal, middle, and distal locations of the external resisting force and knee flexion angles of 30 degrees, 60 degrees, and 90 degrees. Our results show that tibiofemoral displacements are dependent on both location of the external resisting force and knee flexion angle, with anterior displacements being associated with distal displacement of the resistance pad. The results suggest that patients with ACL injuries or repairs conduct extension exercises with a proximal position of the resistance pad to minimize loads and prevent stretching of this constraint.