Abstract
Background:
Anterior cruciate ligament (ACL) injuries are debilitating for athletes. While numerous motor and biomechanical deficits contribute to the inciting ACL injury mechanism, the limited knowledge about the underlying neural drivers of these deficits has impeded intervention development to reduce ACL injury rates. A prospective investigation using functional magnetic resonance imaging (fMRI) in female soccer players revealed decreased connectivity between the primary somatosensory cortex and cerebellum for athletes that went on to ACL injury athletes compared to their healthy teammates. Although information about inter-region connectivity patterns is informative, this finding does elucidate the individual, intra-region brain activity that may be further underlie ACL injury mechanisms.
Hypothesis/Purpose:
The purpose of this study was to prospectively investigate the intra-region regularity of the blood oxygen-level dependent (BOLD) signal activity in 25 knee-related regions of interests (ROI) between athletes who sustained an ACL injury and matched controls.
Methods:
Adolescent female soccer athletes were evaluated using fMRI to capture resting-state brain connectivity prior to their competitive season. Two of these athletes (16.0±0yrs, 169.0±2.8cm, 60.1±8.3kg) later experienced an ACL injury and were matched to eight uninjured teammates (15.9±0.8yrs, 164.0±4.9cm, 58.3±7.6kg). Standard fMRI data processing was used to determine resting-state BOLD signal activity in 25 knee-related ROIs. Sample entropy (SampEn) was then used to quantify the regularity of each individual ROI. A lower SampEn value indicates a ROI’s BOLD signal activity was more regular (predictable) and a higher value indicates a signal’s activity was more irregular (unpredictable). T-tests—with a Bonferroni correction for the familywise error rate (p < .002)—were used to compare SampEn values between both groups for all 25 ROIs.
Results:
ACL injured athletes (M = 0.35±0.01) exhibited higher SampEn values in the left primary motor cortex than matched, uninjured athletes (M = 0.29±0.02; t(8)=4.62, p=.0017, d=3.65).
Conclusion:
Athletes who sustained an ACL injury exhibited less regularity in BOLD signal activity of the left primary motor cortex. As the primary motor cortex serves as the final destination in the brain before efferent information is sent to the spinal cord to initiate movement, decreased BOLD signal regularity in this region may alter such cortical-spinal transmission. Considering ACL injuries often occur during unpredictable environments, irregular activity of motor cortex activity may dampen an athlete’s ability to sustain a safe knee position. These findings may help to guide development of brain-driven biofeedback training to promote adaptive neuroplasticity that ‘pushes’ the motor cortex towards more regular activity.
Shown above is the location of the left primary motor cortex (indicated by the black circle to the left). In Panel A, a BOLD signal from an athlete who went on to injure her ACL is presented. In Panel B, a BOLD signal from an athlete who did not injure her ACL is shown.