Neuromuscular responses in individuals with anterior cruciate ligament repair

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.

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.

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.

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.

Neuromuscular adaptations may be a viable target for post-ACL injury rehabilitation interventions.