Gait Biomechanics and Quadriceps Muscle Function Across ACL Reconstruction Chronicity

Background: Following anterior cruciate ligament reconstruction (ACLR) surgery, patients often experience chronic knee disability characterized by self-reported chronic knee dysfunction and an elevated risk for developing early onset knee joint degeneration. Post-traumatic adaptations in musculoskeletal function, including abnormal lower-extremity gait biomechanics, impairments in quadriceps muscle function, and underlying neural adaptations is proprioception, may contribute towards the development of chronic knee disability. Timely detection of potential deleterious adaptations in musculoskeletal function may allow clinicians the opportunity to intervene and potentially slow the adverse effects on knee joint function; however, there is currently limited understanding of when adaptations in muscle function actually develop over the course of time post-surgery. The overall purpose of these projects were to examine gait biomechanics, submaximal quadriceps muscle control, and the effects of vibration on muscle function in individuals with a history of ACLR at sequential time-frames post-surgery. Methods: ACLR participants were stratified into groups based on time post-surgery, Early (<2 years), Mid (2-5 years), Late (5-15 years), and healthy individuals participated as healthy controls. Walking and jogging knee and hip kinetics and kinematics were collected using three-dimensional motion capture analysis and inter-limb differences were evaluated with in group. Submaximal quadriceps force control was measured during isometric, concentric, and eccentric force-matching tasks at 25% of maximum contraction and force variability and error were calculated. Quadriceps strength was measured at baseline and following a 20-minute patellar tendon vibration intervention and the change in quadriceps strength was calculated. Results: The Early group demonstrated the inter-limb differences in frontal and sagittal plane knee and hip kinetics and kinematics, the Late group demonstrated inter-limb differences in frontal plane knee and hip kinetics, and the Mid groups and controls had no significant differences between limbs for any gait variables. Knee adduction moment was lower in the Early group but higher in the Late group. ACLR knees demonstrated lower force variability and error during concentric contractions than controls. Lower variability and error were correlated with lower physical activity levels in ACLR knees but not time post-surgery. Vibration increased quadriceps strength in ACLR knees and controls. Effect sizes for raw-change indicated ACLR knee experienced an attenuated increased in quadriceps strength post-vibration than controls. Earlier time post-surgery was correlated with an attenuated response to vibration. Conclusions: We observed altered gait biomechanics, submaximal quadriceps force control, and response to tendon vibration in ACLR groups compared to controls. Time post-surgery may play a role in the presentation of post-traumatic adaptations in muscle function. Our most interesting findings suggest that there may be a pattern in knee adduction moments during gait from a reduced moment early after surgery to an increased knee adduction moment later after surgery.