American Society for Peripheral Nerve

Back to 2018 ePosters

Saved by Martin-Gruber: Anastomosis Restores Full Function after Complete Ulnar Nerve Injury
Madhawi Mitwalli, MD1; Arvin Raj Wali, BA2; Justin Brown, MD2; Ross Mandeville, MD2
1University of Alabama at Birmingham, Birmingham, AL, 2University of California, San Diego, La Jolla, CA


Communication can occur between median and ulnar nerves resulting in distal muscles receiving mixed innervation comprising some axons that left the brachial plexus via the median nerve and some via the ulnar nerve. This anastomosis most frequently occurs in the forearm, approximately 20% of the population, receiving the eponym Martin-Gruber anastomosis (MGA). Axons destined for the ordinarily ulnar-innervated thenar, hypothenar, and dorsal interosseous muscles are involved, travelling most of their course in the median nerve instead. The most common muscle to receive anastomotic fibers is the first dorsal interosseous (FDI), and of the numerous variations of MGA, the most common originate from the anterior interosseous nerve to communicate with the ulnar nerve in the forearm.

Case Report:

A 36-year-old male sustained a gunshot to his left arm. The entry point was the medial arm, exiting posterior medial, 2 inches proximal to the medial epicondyle. Initial trauma exam not only demonstrated no ulnar-innervated activation, but also significant weakness in median-innervated muscles including MRC 3 flexor policis longus, MRC 4 flexor digitorum superficialis and wrist flexion, and no thenar muscle activation. Sensation was reduced predominantly in an ulnar distribution. Six months post-injury, exam showed MRC 4 in all ulnar-innervated muscles and full strength elsewhere. Electromyography at that time showed borderline compound motor action potential amplitudes in the adductor digiti minimi and FDI, with their entire innervation coming from an MGA. Nine months' post-injury, he had essentially full strength in all hand and forearm muscles with no wasting. Decreased sensation remained in the ulnar distribution, about 20% of his unaffected contralateral hand. There was a positive Tinel's sign along the ulnar nerve in the proximal forearm.


In this interesting and fortunate patient, the MGA acted as a natural median to ulnar nerve transfer, and enough anastomotic axons were present to restore completely normal strength and function after collateral reinnervation, and without need for functional rehabilitation as no axons were repurposed. Further points of interest include: if ulnar grafting were pursued, the fate of regrown native ulnar axons on finding their muscle fibers occupied by collateral sprouts is unclear but could be evaluated through motor unit number estimate or size index quantitative neurophysiologic techniques. These techniques could also be used to inform on the critical number of anastomotic axons required to restore adequate function and thereby the possibility for early intervention and improved outcomes.

Back to 2018 ePosters