Median-Ulnar Nerve Communications

Anastomosis of the median and ulnar nerves was described as a frequent 'normal' variant by Martin (1763) in Sweden and by Gruber (1870) in Leipzig. Axons descend in the median nerve, joining the ulnar nerve in the forearm before innervating intrinsic muscles of the hand. Crutchfield and Gutmann (1980) found median-ulnar communications in 28% of the general population and in 62% of family members. They proposed autosomal dominant inheritance. No male-to-male transmission was noted in a small series of families. Most often the anomalous axons innervated the first dorsal interosseous muscles and less often the hypothenar and thenar muscles. Gruber (1870) reported a frequency of 15.1% on dissection of 125 cadaver arms. Srinivasan and Rhodes (1981) found bilateral median-ulnar anastomoses in all 8 trisomy 21 fetuses studied, but no bilateral anastomoses were found in 7 trisomy 18, 1 trisomy 13, or 10 anencephaly fetuses. Awareness of the variation is important in the evaluation of median and ulnar neuropathies. A comparable anomaly has been observed in innervations of the extensor digitorum brevis muscle by the accessory deep peroneal nerve (170980).