Muscle co-contraction after anterior cruciate ligament reconstruction: Influence of functional level

Abstract Background ACL reconstruction is recommended to improve function in subjects with ligament injuries. However, after surgery, some individuals are not able to return to their pre-injury functional level. The mechanisms related to this incapacity are not well understood. Study design Cross-sectional study. Methods Co-contraction levels were assessed in individuals who returned to their pre-injury functional level and in 10 individuals who were not able to return to full activity after unilateral ACL reconstruction. Electromyography of the vastus lateralis and biceps femoris muscles before and after sudden perturbations applied during the stance phase of walking was used to calculate co-contraction. Results The involved limb had lower co-contraction pre-perturbation than the non-involved limb in both groups ( p = 0.049). The co-contraction level post-perturbation was significantly higher in the limited return group than in the full return group ( p = 0.03). Conclusion Decreased co-contraction in the involved limb before perturbation may be caused by sensorial changes resulting from surgery or injury. Increased co-contraction levels observed in the limited return group after perturbation may be a compensatory mechanism to make up for possible decreased intrinsic stability of the knee joint. Clinical relevance Increased co-contraction after perturbation does not contribute to knee stability.