ACL-reconstructed and ACL-deficient individuals show differentiated trunk, hip, and knee kinematics during vertical hops more than 20 years post-injury

PURPOSE: Little is known regarding movement strategies in the long term following injury of the anterior cruciate ligament (ACL), and even less about comparisons of reconstructed and deficient knees in relation to healthy controls. The present purpose was to compare trunk, hip, and knee kinematics during a one-leg vertical hop (VH) ~20 years post-ACL injury between persons treated with surgery and physiotherapy (ACL(R)), solely physiotherapy (ACL(PT)), and controls (CTRL). Between-leg kinematic differences within groups were also investigated. METHODS: Sixty-six persons who suffered unilateral ACL injury on average 23 ± 2 years ago (32 ACL(R), 34 ACL(PT)) and 33 controls performed the VH. Peak trunk, hip, and knee angles during Take-off and Landing phases recorded with a 3D motion capture system were analysed with multivariate statistics. RESULTS: Significant group effects during both Take-off and Landing were found, with ACL(PT) differing from CTRL in Take-off with a combination of less knee flexion and knee internal rotation, and from both ACL(R) and CTRL in Landing with less hip and knee flexion, knee internal rotation, and greater hip adduction. ACL(R) also presented different kinematics to ACL(PT) and CTRL in Take-off with a combination of greater trunk flexion, hip flexion, hip internal rotation, and less knee abduction, and in Landing with greater trunk flexion and hip internal rotation. Further, different kinematics and hop height were found between legs within groups in both Take-off and Landing for both ACL groups, but not for CTRL. CONCLUSION: Different kinematics for the injured leg for both ACL groups compared to CTRL and between treatment groups, as well as between legs within treatment groups, indicate long-term consequences of injury. Compensatory mechanisms for knee protection seem to prevail over time irrespective of initial treatment, possibly increasing the risk of re-injury and triggering the development of osteoarthritis. Detailed investigation of movement strategies during the VH provides important information and a more comprehensive evaluation of knee function than merely hop height. More attention should also be given to the trunk and hip in clinics when evaluating movement strategies after ACL injury. LEVEL OF EVIDENCE: Prospective cohort study, Level II.