[Electrodiagnosis in Martin-Gruber anastomosis]

An anomalous median-ulnar nerve communication in the forearm (Martin-Gruber anastomosis) is not rare. Knowledge of this crossover is of crucial importance in the clinical evaluation of nerve injuries of median and ulnar nerves as well as in accurate interpretation of nerve conduction velocity of these nerves especially in association with carpal tunnel syndrome. The aim of this study was to describe a simple electrophysiological method to detect the anomalous communication innervating hypothenar and thenar muscles. A crossover was detected in 83 (14%) of 600 unselected subjects or 116 (9.7%) of 1,200 limbs. The anomaly was bilateral in 33 (40%) of the subjects and unilateral in 50 (60%), thirty-three on the right and seventeen on the left. Since the crossing fibers are likely to supply primarily the 1st dorsal interosseus muscle, recording of this muscle is essential to disclose the anomaly in addition to routine median and ulnar motor studies of hypothenar and thenar muscles. The anomaly may represent a phylogenetic variant.