Nerve Transfer Surgery in Tetraplegia

Abstract

Objective: Spinal cord injury leads to upper motor neuron paralysis below the level of the injury. However, emerging evidence suggests lower motor neuron denervation is evident in these paralyzed muscle groups. We aimed to study patients with chronic cervical spinal cord injuries who underwent nerve transfer surgery for evidence of lower motor neuron dysfunction in the upper limb preoperatively. Methods: Patients with cervical spine injuries who were being considered for nerve transfer surgery were examined using electromyography for evidence of spontaneous activity in the form of fibrillations. The neuromuscular units were divided into clinically functional “donors”—teres minor, brachialis, and supinator—and into clinically low-functional or nonfunctional “recipients”—flexor digitorum profundus (FDP), flexor pollicis longus (FPL), extensor digitorum communis (EDC), extensor pollicis longus (EPL), and triceps. The aim of the nerve transfer surgery was to restore pivotal upper limb functions such as elbow extension, key pinch, grasp, and release. Results: A retrospective review of the preoperative electromyography results for 25 upper limbs from 17 male patients was performed. A significant proportion of the recipient muscles showed evidence of fibrillations: FDP 96%, triceps 92%, and FPL 91%. Incidence of fibrillations for EDC and EPL was significantly lower despite also being in the recipient group. Interestingly, donor muscle groups with volitional control also showed evidence of fibrillations. Although at a much lower rate than most of the recipient groups, the incidence of fibrillations in the donor muscles were as follows: supinator 8%, brachialis 14%, and teres minor 34%. Conclusion: Patients with cervical spinal cord injury show evidence of lower motor neuron injury on electromyography. This finding has implications for the timing of nerve transfer surgery. The authors propose that, to maximize outcomes, prospective recipient muscles demonstrating denervation should be reinnervated using nerve transfers early (6-12 months post injury) before the neuromuscular endplate degeneration that follows denervation occurs. The presence of fibrillation potentials in prospective donor nerves, which are clinically normal on examination, may have implications for the outcome of nerve transfer surgery using these nerves.