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

Background: Spinal cord injuries (SCIs) often cause significant functional impairments. Functional electrical stimulation therapy (FEST) aims to enhance muscle strength, particularly when natural recovery decreases. However, the recovery profiles of individual muscles treated with FEST during the chronic phase are 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.

Materials and methods: This cohort study evaluated the strength recovery profiles of 136 muscles treated with FEST, from 17 participants with chronic cervical SCI. Electrophysiology was conducted at baseline to assess corticospinal tract (CST) integrity and the excitability of the lower motor neuron pools using surface electromyography.

Results: Overall, 69 muscles did not respond to the treatment whereas 67 muscles showed a median strength increase of one muscle motor score (MMS). Among responder muscles, achieving a one-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 neurophysiologic indicators of CST integrity.

Conclusions: Our findings can inform rehabilitation medicine guidelines for FEST in cervical SCI. The data indicate that achieving a one-point increase in muscle strength requires approximately 59 days and 19 FEST sessions. 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.

Clinical trial registration: The Clinicaltrials.gov registration number for the study is NCT05462925.