A median-to-ulnar nerve communication in the forearm (Martin-Gruber anastomosis. MGA) is not rare. Awareness of this anastomosis is important in the clinical and electro-diagnostic evaluation of median and ulnar nerves. According to the muscles
innervated by the crossover, three types have classified. However, there are very few detailed studies of their incidence and combinations. Thus we studied detailed electrophysiologic aspects of MGA to determine their incidence and types.
The crossing fibers were detected bilaterally with surface recording electrodes over thenar, hypothenar, and first dorsal interosseous muscles of 112 unselected subjects. 49males and 63 females. MGA was found in 37 (33%) subjects, in 52(23%)
limbs.
The
anomaly was bilateral in 15(41%) of the subjects. Type II was seen in all the MGA-detected 52 limbs (100%), type I in 24 (46%), and type III in 2(4%). From the viewpoint of MGA-detected pattern the pure form of type II was in 27 limbs(52%), the
combination of type II and I in 23(44%), the combination of type I, II and III in 1 (2%), and the combination of type II and III in 1 (2%). The mean amplitude and amplitude ratio of the anomalous response were highest at the first dorsal
interosseous
muscle, which were 3.5mV and 22%. Siuce the crossing fibers in MGA innervate most commonly the first dorsal interosseous, recordig of this muscle is essential to evaluate the contribution of MGA to median and ulnar nerve lesions.
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