Ultrasound Evaluation of Upper Limb Sublesional Muscle Morphology in Cervical Spinal Cord Injury

Upper limb paralysis is arguably the most limiting consequence of cervical spinal cord injury (cSCI). There is limited knowledge regarding the early structural changes of muscles implicated in grasp/pinch function and upper extremity nerve transfer surgeries. We evaluated: (1) muscle size and echo intensity (EI) in subacute cSCI (2-6 months) and (2) the influence of lower motor neuron (LMN) damage on these ultrasound parameters.

Cross-sectional B-mode images were captured bilaterally in individuals with cSCI (injury duration: 3.3 ± 1.2 months; C4-C6 injury levels; American Spinal Injuries Association Impairment Scale A-C; 45.7 ± 13.7 years; 3 females, 14 males) for biceps brachii (BB), extensor carpi ulnaris, extensor indicis proprius, flexor pollicis longus (FPL), and first dorsal interosseous. Each limb was analyzed as an independent event (n = 34). Cross-sectional area (CSA), thickness (MT), and EI were compared to healthy controls (HC). BB and FPL concentric needle electromyography (EMG) data were also obtained. Abnormal LMN health was defined by the presence of pathological spontaneous activity.

Relative to HC, forearm and hand muscle size were 15%-41% lower (p < 0.05), while EI was 21%-40% higher (p < 0.05); no significant differences were observed for sublesional BB muscles (n = 16) (p > 0.05). Muscles demonstrating abnormal LMN health displayed reduced BB MT and elevated FPL EI (p < 0.05).

These results underscore the substantial changes in forearm and hand muscle morphology within the subacute period after cSCI, with preliminary evidence suggesting that these changes are influenced by LMN damage.