Hip and Ankle Kinematics in Noncontact Anterior Cruciate Ligament Injury Situations Video Analysis Using Model-Based Image Matching

Background: Detailed kinematic descriptions of real anterior cruciate ligament (ACL) injury situations are limited to the knee only. Purpose: To describe hip and ankle kinematics as well as foot position relative to the center of mass (COM) in ACL injury situations through use of a model-based image-matching (MBIM) technique. The distance between the projection of the COM on the ground and the base of support (BOS) (COM_BOS) normalized to the femur length was also evaluated. Study Design: Descriptive laboratory study. Methods: Ten ACL injury video sequences from women's handball and basketball were analyzed. Hip and ankle joint kinematic values were obtained by use of MBIM. Results: The mean hip flexion angle was 51 degrees (95% CI, 41 degrees to 63 degrees) at initial contact and remained constant over the next 40 milliseconds. The hip was internally rotated 29 degrees (95% CI, 18 degrees to 39 degrees) at initial contact and remained unchanged for the next 40 milliseconds. All of the injured patients landed with a heel strike with a mean dorsiflexion angle of 2 degrees (95% CI, -9 degrees to 14 degrees), before reaching a flatfooted position 20 milliseconds later. The foot position was anterior and lateral to the COM in all cases. However, none of the results showed larger COM_BOS than 1.2, which has been suggested as a criterion for ACL injury risk. Conclusions: Hip kinematic values were consistent among the 10 ACL injury situations analyzed; the hip joint remained unchanged in a flexed and internally rotated position in the phase leading up to injury, suggesting that limited energy absorption took place at the hip. In all cases, the foot contacted the ground with the heel strike. However, relatively small COM_BOS distances were found, indicating that the anterior and lateral foot placement in ACL injury situations was not different from what can be expected in noninjury game situations.