Responsiveness to transcutaneous spinal stimulation for upper extremity recovery following spinal cord injury: A case series exploration of midsagittal tissue bridges.

CONTEXT: Transcutaneous spinal stimulation (TSS), applied to the cervical spine, is able to improve voluntary upper extremity strength and function in individuals with cervical spinal cord injury (SCI). While most respond and improve in the presence of TSS, others do not respond as favorably. Midsagittal tissue bridges, adjacent to the lesion, can be observed and measured using T2-weighted magnetic resonance imaging (MRI), and both ventral and dorsal tissue bridges are associated with recovery following SCI. Tissue bridges may also be important for responding to neuromodulation such as TSS. The purpose of this case series was to explore potential relationships between the presence of tissue bridges and responsiveness to TSS for recovery of upper extremity strength and function in research participants with cervical-level SCI.

METHODS: This study involved six research participants who completed a clinical trial of rehabilitation paired with TSS to improve upper extremity strength and function. Ventral and dorsal midsagittal tissue bridges were quantified using T2-weighted MRI.

RESULTS: Three participants classified as both strength and function responders showed presence of ventral tissue bridges, while the three strength-only responders did not. The same was found for dorsal tissue bridges, except for one strength-only responder that had a dorsal tissue bridge.

CONCLUSIONS: The findings of this case series shed light onto the potential importance of midsagittal tissue bridges - a proxy for spared sensorimotor tracts - for responsiveness to TSS for upper extremity recovery following SCI.