Mechanisms of anterior cruciate ligament injury

This study examined the mechanisms of anterior cruciate ligament (ACL) inju ry. In the first part of the study, using a comprehensive, standardized que stionnaire, 89 athletes (100 knees) were interviewed about the events surro unding their ACL injury. A noncontact mechanism was reported in 71 (72%) kn ees and a contact injury in 28 (28%) knees; one patient was unsure if there was any contact. Most of the injuries were sustained at footstrike with th e knee close to full extension. Noncontact mechanisms were classified as su dden deceleration prior to a change of direction or landing motion, while c ontact injuries occurred as a result of valgus collapse of the knee. Hamstr ing flexibility parameters revealed a statistically higher revel of laxity in the injured athletes compared with a matched group of 28 controls. In the second part of the study, videotapes of 27 separate ACL disruptions were reviewed and confirmed that most noncontact injuries occur with the kn ee close to extension during a sharp deceleration or landing maneuver. Beca use the knee is in a position to allow the extensor mechanism to strain the ACL and maximum, eccentric muscle force conditions usually apply, the quad riceps may play an important role in ACL disruption. Passive protection of the ACL by the hamstring muscles may be reduced in patients with above-aver age flexibility.