Neuromuscular compensatory strategies at the trunk and lower limb are not resolved following an ACL reconstruction

Background: Following anterior cruciate ligament reconstruction (ACLR), patients present with greater trunk ipsilateral lean, which may affect knee kinetics and increase re-injury risk. However, there has been little research into neuromuscular factors controlling the trunk and their relation to the knee between healthy and ACLR subjects. This is critical to establish in order to develop more directed and effective interventions. Hypothesis: As compared to healthy control subjects, ACLR subjects will demonstrate increased erector spinae and rectus abdominis co-contraction, greater rectus abdominis force and greater hamstring force that is correlated to increased forward trunk lean. Study design: Cross-sectional study, Level of Evidence: 3. Methods: Eleven healthy and eleven ACLR subjects were matched for age, mass and height. Subjects were asked to run at a self-selected speed while instrumented gait analysis was performed. An anthropometrically scaled OpenSim model was created for each subject. Trunk and hamstring muscle forces from Static Optimization were analyzed at impact peak. Additionally, directed co-contraction ratios were calculated for the erector spinae and erector spinae/rectus abdominis combinations. Results: ACLR subjects showed more balanced erector spinae co-contraction [p < 0.01], and greater hamstring force [biceps femoris long head (p = 0.02), semimembranosus (0.01), semitendinosus (0.01)]. There was no statistical difference for any other muscle group. Conclusion: Despite release to return to sport, ACLR subjects are continuing to increase the stiffness of their trunk as well increase their hamstring force to potentially reduce anterior tibial translation.