Mechanisms of Anterior Cruciate Ligament Injury

TLDR

Quadriceps forces during knee extension and reduced hamstring protection in highly flexible athletes may predispose to ACL injury. This study examined the mechanisms of anterior cruciate ligament (ACL) injury. The authors used a questionnaire of 89 athletes and video review of 27 ACL disruptions to classify noncontact injuries as sudden deceleration or landing with the knee near full extension, and contact injuries as valgus collapse. Noncontact mechanisms accounted for 72% of injuries, occurring mainly at footstrike with the knee near full extension, and injured athletes showed greater hamstring laxity than matched controls.

Abstract

ABSTRACT This study examined the mechanisms of anterior cruciate ligament (ACL) injury. In the first part of the study, using a comprehensive, standardized questionnaire, 89 athletes (100 knees) were interviewed about the events surrounding their ACL injury. A noncontact mechanism was reported in 71 (72%) knees 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 the knee close to full extension. Noncontact mechanisms were classified as sudden deceleration prior to a change of direction or landing motion, while contact injuries occurred as a result of valgus collapse of the knee. Hamstring flexibility parameters revealed a statistically higher level 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 knee close to extension during a sharp deceleration or landing maneuver. Because the knee is in a position to allow the extensor mechanism to strain the ACL and maximum, eccentric muscle force conditions usually apply, the quadriceps may play an important role in ACL disruption. Passive protection of the ACL by the hamstring muscles may be reduced in patients with above-average flexibility.