Motor Planning and Sensory Neuroplasticity after ACL Reconstruction

Abstract

Anterior cruciate ligament (ACL) injury and reconstruction may induce brain motor control adaptations that influence function and injury risk. Traditional neuromuscular control assessment and therapy may not adequately address this neuroplasticity. fMRI (functional magnetic resonance imaging) provides a detailed method to asses brain function to bridge this gap in knowledge. PURPOSE: To investigate the degree of unilateral sensory-motor brain activation during knee extension-flexion between a group with knee ACL reconstruction (ACLR) and a healthy matched control group. METHODS: Participants were matched on height, mass, extremity dominance, education level, history and current physical activity level. Six left ACLR (25.5±1.37 years, 1.70±0.13 m, 75.6±19.2 kg, Tegner activity level 6.0 ± 1.5, 23±18 months post-surgery) and 6 matched healthy controls (23.6±3.14 years, 1.75±0.05 m, 73.5±12.24 kg, Tegner activity level 6.0 ± 1.5) participated. The brain fMRI was collected during a unilateral knee motor task consisting of repeated cycles of extension and flexion while lying supine in the MRI scanner. The differences between the ACLR activation and contralateral side were contrasted followed by comparison with the control group with a general linear model fixed-effects analysis a priori threshold at p <.01 corrected. RESULTS: Patients with ACLR had increased activation in the supplementary motor region (z=3.29±1.063, p<.001) and somatosensory cortex (z=4.72±1.576, p<.001) when compared to their contralateral healthy extremity and the matched controls. CONCLUSIONS:The ACLR side had greater sensory and motor planning specific brain activation compared to the contralateral knee and control group. The increased sensory cortex activation may be due to the disrupted afferent signals from the ACLR. The motor planning increase may be in response to the adapted sensory integration and feed-forward compensation to sustain motor output. The relatively stable motor cortex activation across side and group indicates that the task requires the same amount of motor drive regardless of side or group, but ACLR status influences the level of motor cortex input from sensory and planning areas to generate the same output.