Abductor hallucis for monitoring lower-limb recovery after spinal cord injury in man

Study design: Electromyogram (EMG) study on patients with acute spinal cord injury (SCI). Objectives: We hypothesized that subjects with mild to moderate acute SCI would have a higher probability of recovering function in intrinsic muscles of the foot compared to more proximal lower-limb muscles, based on the relative density of corticospinal tract innervation to these different motoneuron pools. Setting: Miami and Syracuse, USA. Methods: We conducted repeated measures of EMG during voluntary contractions from lower-limb muscles in subjects with acute traumatic SCI. For this study, analysis was restricted to those subjects who had either no recruitment (ie 'motor-complete') or limited recruitment (ie 'motor-incomplete') in any lower-limb muscle of either leg during the initial evaluation, and all of whom had converted to a motor-incomplete status in one or both legs at the time of final evaluation. Recruitment of the abductor hallucis (AbH) muscle during contraction attempts was judged as being either 'present' or 'absent', based upon the presence or absence of EMG-based volitional motor unit recruitment. Results: A total of 70 subjects were included in this study. Of these, 58 had motor-incomplete injury at or rostral to the T10 vertebral level, and another 12 had injury caudal to T10. In the former group, the AbH muscle showed a recovery probability that was considerably higher than that of other lower-limb muscles. Quite the opposite pattern was seen in persons with injury caudal to T10. In these subjects, recruitment was more common in proximal muscles of the thigh (psoas and quadriceps), and least common in the AbH muscle. Discussion: For persons with SCI at or rostral to the T10 vertebral level, the AbH muscle proved to be an earlier and more sensitive indicator of lower-limb contraction recovery following acute SCI compared to other lower-limb muscles. Including this intrinsic muscle of the foot as part of a neurologic assessment of muscle function after SCI should increase the test's sensitivity to preserved (or restored) supraspinal motor influence over lower-limb motoneuron pools, and is recommended.