The mechanisms of ACL injury in female athletes include high knee valgus torques and lateral trunk motion, with most of the body’s weight shifted over the injured limb and the foot placed lateral to the body’s center of mass. An unanticipated disturbance often contributes to the injury mechanism. A strong association exists between increased lateral trunk motion and coronal plane abduction valgus torques on the knee. Neuromuscular control deficits at the hip and trunk may contribute to decreased active neuromuscular control of the lower extremity that may increase knee abduction valgus torques and strain on the knee ligaments.
Trunk motion may result in increased knee abduction by increasing the magnitude or distance of the ground reaction force vector to the knee center or reactive hip adductor torque or by both knee loading mechanisms. These associations provide a strong, evidence-based rationale for the development of effective trunk or “core-based” interventions to decrease ACL injury risk in high-risk female athletes.
The combination of the greater susceptibility and a 10-fold increase in the female sports population since the inception of Title IX has resulted in a dramatic increase in the number of ACL injuries in females. In the United States, 100,000 to 300,000 total ACL injuries occur each year. The treatment costs exceed $1 billion annually in female varsity athletics alone and do not end with the ACL reconstruction and rehabilitation. A strong association exists between ACL injury and development of posttraumatic knee osteoarthritis at a relatively young age, which also occurs with much greater incidence in females than males.