15. Electrophysiology study of distal median to ulnar nerve transfer to restore ulnar motor function – Case report

Abstract

Introduction Traumatic lesions of ulnar nerve can be responsible for a great loss of hand motor function. Nerve suture of the anterior interosseous nerve, especially the pronator quadratus branch, with deep branch of ulnar nerve can restore ulnar motor nerve’s intrinsic function of the hand and prevent hand clawing. Electrophysiological methods help with diagnosis and guide surgery. Objectives We present a patient with recovery of the hand intrinsic functions after interposition nerve grafting. It has been well documented, step by step, by pre-operative, intra-operative and post-operative electrophysiological examinations. Methods Electromyography (EMG) was performed before and after the surgery. Ulnar nerve neurography and ulnar nerve cortical somatosensory evoked potentials (SEPs) were examined at both motor and sensory division of ulnar nerve during the surgery. Results A 10 year old boy was referred to the neurosurgeon for ulnar nerve cut on his non-dominant arm. Urgent nerve suture was performed. Repeated EMG carried out 6 and 12 months later revealed the evidence of reinnervation potentials in the flexor carpi ulnaris muscle and no recovery in the hand’s intrinsic muscles. Repeated surgical intervention – anterior interosseous to ulnar motor nerve transfer – was recommended. Intraoperative ulnar neurography confirmed complete nerve lesion with no nerve action potential. Ulnar nerve cortical SEPs were recorded to identify sensory division of the nerve and to reduce the misdirected connection of the motor fibres. Surprisingly, cortical SEPs of ulnar nerve were recorded from both motor and sensory division. We explain it by the cross-reinnervation between motor and sensory fibres after the first nerve suture. The motor division had to be identified only by anatomic signs. Post-operative EMG study showed the recovery of action potentials from ulnar intrinsic muscles by median and not by ulnar nerve stimulation. The findings confirmed reinnervation by anterior interosseous nerve. In the post-operative follow-up we detected restored muscle strength (grade IV) of intrinsic muscles, which confirmed successful functional regeneration of the nerve. Conclusion The anterior interosseous to ulnar motor nerve transfer is the unique treatment of ulnar nerve injury. Electromyography is commonly used for diagnosis, however, intraoperative electrophysiological methods we used seems to be so far underestimate in routine clinical practice.