Neuromuscular responses in individuals with anterior cruciate ligament repair.

OBJECTIVE: Knee surgery may alter the neuromuscular response to unexpected perturbations during functional, dynamic tasks. Long latency reflexes (LLR) follow a transcortical pathway and appear to be modifiable by task demands, potentially giving them a role in neuromuscular performance. We examined LLRs of the quadriceps and hamstrings in response to unexpected perturbations in individuals with a repaired anterior cruciate ligament (ACLR) during a weight-bearing task. We also investigated the anticipatory and volitional muscle activity that preceded and followed the LLR to quantify possible reflex adaptations associated with surgical repair.
METHODS: Twelve females with ACLR and 12 healthy female controls performed a single leg squat maneuver, tracking a sinusoidal target. Random perturbations at the start of the flexion phase yielded tracking errors ("overshoot errors") and triggered compensatory reflex activity.
RESULTS: ACLR subjects demonstrated greater overshoot error and knee velocity during unexpected perturbations, increased LLR responses, and reduced absolute anticipatory, short-latency reflex, and voluntary quadriceps activity.
CONCLUSIONS: ACLR subjects showed impaired response to perturbation and a distinct EMG profile during a dynamic single leg weight-bearing task. Future research will determine the cause of neural adaptations in those with ACLR. SIGNIFICANCE: Neuromuscular adaptations may be a viable target for post-ACL injury rehabilitation interventions.