Biomechanical evidence supporting a differential response to acute ACL injury

Objective. To describe movement patterns in people with complete anterior cruciate ligament rupture objectively identified as good candidates for non-operative management of the injury. Design. Involved side kinematics and kinetics were compared to the uninvolved side and to uninjured subjects. Background. High-level athletes with anterior cruciate ligament rupture and poor dynamic stability (non-copers) have movement alterations, including less knee flexion and a decreased internal knee extensor moment during loading response, that are not seen in those with excellent knee stability (copers). Our screening exam can identify people with good rehabilitation potential for non-operative management of anterior cruciate ligament injury (potential copers), but the movement strategies of these individuals are unknown. Methods. Sagittal plane kinematics and kinetics during the stance phase of walking and jogging were collected from 11 subjects who had an acute anterior cruciate ligament rupture and met the criteria of the screening exam, and were compared to 10 uninjured subjects, who we studied previously. Variables were those in which non-copers differed from uninjured subjects. Results. The potential copers flexed their involved knee less than uninjured subjects and their uninvolved side during walking. Potential copers, compared to uninjured subjects, also had a lower vertical ground reaction force during loading response, a lower knee support moment, and an increased ankle support moment during walking. In jogging, the involved knee angle at initial contact was more extended compared to uninjured subjects, and the amount of knee flexion was less than the uninvolved side. No differences in kinetics were present during jogging. Conclusions. This study provides evidence that the potential copers identified by the screening examination have movement patterns that are consistent with people who have more knee stability than non-copers.