Upper Extremity Muscle Recovery Profiles with Functional Electrical Stimulation Therapy in Chronic Spinal Cord Injury

BackgroundSpinal cord injuries (SCI) can affect muscle control, often resulting in significant functional impairments. Damage to sensorimotor pathways in the spinal cord can lead to muscle weakness, which may gradually recover during the first year post-injury. Functional electrical stimulation therapy (FEST) aims to enhance muscle strength, particularly when natural recovery diminishes. However, the recovery profiles of individual muscles treated with FEST during the chronic phase are still not well understood. The primary objective of this study was to characterize the timing and magnitude of gains in individual muscle strength during FEST. The secondary objective was to identify factors predictive of the response. MethodsIn this cohort study, we examined the strength recovery profiles of 136 muscles treated with FEST, from 17 participants with cervical SCI at the chronic phase of the injury. Electrophysiology was conducted at baseline to assess corticospinal tract (CST) integrity and the excitability of the lower motor neuron pools using surface electromyography (sEMG). ResultsOur findings reveal that 69 muscles did not respond to the treatment, while 67 muscles showed a median strength increase of one muscle motor score (MMS). Among responder muscles, achieving a 1 MMS increase required approximately 59 days (19.2 FEST sessions). A prediction model highlighted key predictors of responsiveness to FEST, including baseline MMS, characteristics of lesion location/severity, and neurophysiological indicators of CST integrity. ConclusionOur findings underscore the need for refined guidelines in rehabilitation medicine, particularly for FEST in cervical SCI. The data demonstrates that achieving a 1-point increase in muscle strength requires {approx}59 days and 19 FEST sessions. Further evidence also suggest that CST integrity and the responsiveness of lower motor neuron pools may influence FEST outcomes. These insights will enable more personalized and effective rehabilitation strategies, optimizing outcomes and resource allocation for individuals living with cervical SCI.