Electrophysiological evaluation of the incidence of martin-gruber anastomosis in healthy subjects.

The Martin-Gruber Anastomosis (MGA) is probably the most well known of the anastomotic anomalies that occur at various levels between the median and ulnar nerves. It is formed by motor axons from the median nerve or its branch anterior interosseous nerve that cross in the upper forearm to join the ulnar nerve. The purpose of this study was to establish the frequency of MGA in healthy subjects and to draw the attention of clinicians working in the neurophysiological laboratory to the presence of this anastomosis, and thus to avoid possible misinterpretations of data from needle electromyography (EMG) and nerve conduction studies. 100 volunteers (60 women and 40 men) were selected for the study. Surface recording electrodes were placed on the right hand thenar, hypothenar and on the first dorsal interosseous (FDI) muscles. The median and ulnar nerves were stimulated supramaximally at the wrist and at the elbow and compound muscle action potentials (CMAPs) were recorded and their amplitudes evaluated. MGA was found in 27 of the 100 subjects. The type of anastomosis most frequently seen was type II, which was observed in 21 subjects. Type I anastomosis was observed in three, type I + type II in two and type III anastomosis in one subject. It can thus be concluded that MGA is frequently encountered and it should be borne in mind that abnormal innervation models may influence the electrophysiological findings and thus give rise to faulty interpretations, especially in the case of median and ulnar nerve lesions.