Do sensorimotor control properties mediate sway in people with chronic balance complaints following mTBI?

Background: Up to 40% of mild traumatic brain injuries (mTBI) can result in chronic unresolved symptoms, such as balance impairment, that persist beyond three months. Sensorimotor control, the collective coordination and regulation of both sensory and motor components of the postural control system, may underlie balance deficits in chronic mTBI. The aim of this study was to determine if the relationship between severity of impairment in chronic (> 3 months) mTBI and poorer balance performance was mediated by sensorimotor integration measures. Methods: Data were collected from 61 healthy controls and 58 mTBI participants suffering persistent balance problems. Participants completed questionnaires (Dizziness Handicap Inventory (DHI), Neurobehavioral Symptom Inventory (NSI), and Sports Concussion Assessment Tool Symptom Questionnaire (SCAT2)) and performed instrumented postural sway assessments and a test of Central Sensory Motor Integration (CSMI). Exploratory Factor Analysis was used to reduce the variables used within the mediation models to constructs of impairment (Impairment Severity – based on questionnaires), balance (Sway Dispersion – based on instrumented postural sway measures), and sensorimotor control (Sensory Weighting, Motor Activation and Time Delay – based on parameters from CSMI tests). Mediation analyses used path analysis to estimate the direct effect (between impairment and balance) and indirect (mediating) effects (from sensorimotor control). Results: Two out of three sensorimotor integration factors (Motor Activation and Time Delay) mediated the relationship between Impairment Severity and Sway Dispersion, however, there was no mediating effect of Sensory Weighting. Significance: These findings have clinical implications since rehabilitation of balance commonly focuses on sensory cues. Our findings indicate the importance of Motor Activation and Time Delay, and thus a focus on strategies to improve factors related to these constructs throughout the rehabilitative process (i.e., level of muscular contractions to control joint torques; response time to stimuli/perturbations) may improve a patient's balance control.