Do ACL-injured copers exhibit differences in knee kinematics?: An MRI study

Kinematic changes after anterior cruciate ligament (ACL) injury may play a role in the long-term development of osteoarthritis (OA). Some ACL-injured patients (copers) successfully return to demanding activities without the reconstructive surgery usually recommended for functionally unstable patients (noncopers). We determined whether copers exhibit less disruption to kinematics than noncopers, perhaps because of lower impairment of muscular control as observed in earlier studies. We used dynamic magnetic resonance imaging and model-based tracking to investigate anteroposterior (AP) and internal-external tibial positioning in copers, presurgical noncopers, and uninjured control subjects during dynamic nonloaded knee extension. Copers and control subjects showed similar levels of side-to-side differences in AP tibial positioning (1.1 +/- 4.9 mm and 1.4 +/- 2.7 mm, respectively), whereas noncopers exhibited anterior tibial positioning in their injured knees (2.6 +/- 3 mm) that differed from control subjects. Copers were the most variable of the three groups, and contrary to our hypothesis, tibial positioning in copers was not different from that of noncopers. Differences in tibial positioning did not correlate with side-to-side differences in AP laxity in any of the groups, and we identified no changes to tibial axial rotation patterns associated with ACL deficiency.