Co-activation during gait following anterior cruciate ligament reconstruction.

Background: Heightened co-activation of the quadriceps and hamstrings has been reported following anterior cruciate ligament reconstruction during various tasks, and may contribute to post-traumatic osteoarthritis risk. However, it is unclear if this phenomenon occurs during walking or how co-activation influences gait biomechanics linked to changes in joint health.

Methods: Co-activation and gait biomechanics were assessed in 50 individuals with ACLR and 25 healthy controls. Biomechanical outcomes included knee flexion displacement, peak vertical ground reaction force magnitude and rate, peak internal knee extension and valgus moments and rates, sagittal knee stiffness, and the heelstrike transient. Co-activation was calculated for the flexors and extensors collectively (i.e. composite), the medial musculature, and the lateral musculature.

Findings: Composite co-activation was greater in the ACLR limb compared to the contralateral limb and the control cohort during the preparatory and heelstrike phases of gait, and co-activation of the medial musculature was greater in the ACLR limb compared to the control cohort during the heelstrike phase. Greater co-activation in multiple gait phases was associated with less knee flexion displacement (r = -0.293 to -0.377), smaller peak vertical ground reaction force magnitude (r = -0.291), smaller peak internal knee extension moment (r = -0.291 to -0.328), and greater peak internal knee valgus moment (r = 0.317).

Interpretation: Individuals with ACLR displayed heightened co-activation during walking which was associated with biomechanical outcomes that have been linked to negative changes in joint health following ACLR. These data suggest that excessive co-activation may contribute to the mechanical pathogenesis of post-traumatic osteoarthritis. ClinicalTrials.gov Identifier: NCT02605876.