Abstract
Loss of hand function after cervical spinal cord injury (SCI) impacts heavily on independence. Multiple nerve transfer surgery has been applied successfully after cervical SCI to restore critical arm and hand functions, and the outcome depends on nerve integrity. Nerve integrity is assessed indirectly using muscle strength testing and intramuscular electromyography, but these measures cannot show the manifestation that SCI has on the peripheral nerves. We directly assessed the morphology of nerves biopsied at the time of surgery, from three patients within 18 months post injury. Our objective was to document their morphologic features. Donor nerves included teres minor, posterior axillary, brachialis, extensor carpi radialis brevis and supinator. Recipient nerves included triceps, posterior interosseus (PIN) and anterior interosseus nerves (AIN). They were fixed in glutaraldehyde, processed and embedded in Araldite Epon for light microscopy. Eighty percent of nerves showed abnormalities. Most common were myelin thickening and folding, demyelination, inflammation and a reduction of large myelinated axon density. Others were a thickened perineurium, oedematous endoneurium and Renaut bodies. Significantly, very thinly myelinated axons and groups of unmyelinated axons were observed indicating regenerative efforts. Abnormalities exist in both donor and recipient nerves and they differ in appearance and aetiology. The abnormalities observed may be preventable or reversible.
Highlights
Nerve transfers are increasingly being used to restore volitional control to arm and hand muscles in patients with a cervical spinal cord injury (SCI) [1,2]
With respect to the donor nerves examined in this study, the most unexpected finding was that of marked abnormalities in all specimens of the posterior axillary nerve and the nerve to the teres minor muscle
In SCI, the ventral horn motor neurons and axons below the injury are at risk of degeneration even though they are outside the injury zone
Summary
Nerve transfers are increasingly being used to restore volitional control to arm and hand muscles in patients with a cervical spinal cord injury (SCI) [1,2]. Brain Sci. 2016, 6, 42 branch to the anterior interosseous nerve (AIN) for extrinsic thumb flexion and reanimation of flexor digitorum profundus to the index and middle finger [6,7]. Selection of candidates for nerve transfer surgery is based on the availability of supralesional donor nerves that are uninjured, redundant and have intact upper motor neuron (UMN) and lower motor neuron (LMN) pools; and of infralesional recipient nerves that are intact and innervate muscles that are responsive to electrical stimulation [1]. Connectivity of donor nerves to the motor cortex is ascertained by measuring action potentials following transcranial electrical stimulation, and recipient nerve/muscle function is assessed by visualisation of muscle contraction and nerve conduction measurement following direct stimulation [7]
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