Analyses of dynamic co-contraction level in individuals with anterior cruciate ligament injury.

BACKGROUND: A complete understanding of neural mechanisms by which ligament receptors may contribute to joint stability is not well established. It has been suggested that these receptors may be involved in a neuromuscular process related to the modulation of dynamic co-contraction, as a means of guaranteeing functional joint stability. HYPOTHESIS: Individuals with ACL injury have diminished dynamic co-contraction. STUDY DESIGN: Exploratory, cross-sectional design. METHODS: Ten subjects with unilateral ACL injury treated conservatively, and ten subjects without history of injury participated in the study. The co-contraction level was assessed through EMG recordings of the vastus lateralis and biceps femoris before and after a perturbation imposed on the subjects during a walking task. RESULTS: Subjects with ACL injury presented significantly lower co-contraction level pre-perturbation (p = 0.045) and post-perturbation (p = 0.046) than those in the control group. CONCLUSIONS: The bilateral decrease in muscular co-contraction presented by individuals with ACL injury suggests that ligament and joint receptors may be responsible for a bilateral dynamic increase in muscle and joint stiffness that could result in a greater joint stability. CLINICAL RELEVANCE: This study analyzed a neuromuscular mechanism that might contribute to the functional stability of the knee joint.