Torn anterior cruciate ligaments (ACLs) are associated with excessive hip internal rotation and valgus collapse of the knee during standing. Knee valgus is also referred to as valgus collapse and medial knee displacement. It is characterized by hip adduction and hip internal rotation, usually when in a hips-flexed position (the knee actually abducts and externally rotates). It can also be thought of as knee caving as you sink down into a squat or landing.People with this have weak hip abductors and rotators and would be less likely to muscularly control their lower extremities while participating in sports. Having weak piriformis muscles was especially correlated with increased rates of ACL tears. Fewer than 1% of strong athletes had suffered ACL injury, while 7% of athletes with weak hip muslculature tore their ACLs.
Strengthen hip rotators and abductors by doing the clam, leg press, seated knee extension, straight leg raises. Not only do these exercises reduce pain and improve function, they also reduce valgus collapse of the knee while exercising.