Anastomosis of Motor Fibers between Median and Ulnar Nerve in the Forearm: an Electrophysiological Study

ABSTRACT

OBJECTIVE: To evaluate the frequency of forearm anastomosis in healthy Korean subjects. METHOD: Healthy Korean adult subjects (70 males, 30 females) were included. Median and ulnar nerves were stimulated at wrist and elbow and recorded with the surface electrodes over abductor pollicis brevis (APB), first dorsal interossei (FDI) and abductor digiti quinti (ADQ). RESULTS: Martin-Gruber anastomosis (MGA) was found in 18 males and 8 females (26/100, 26%). MGA was found in 37 arms (18.5%). But, Marinacci anastomosis was not observed. For each type of MGA, type II was found in 36 arms (97.3%) whereas type I was found in 11 arms (29.7%), and type III was found in 1 arm (2.7%). Anastomosis was comprised 67.6% of type II, 2.7% of type III, and 29.7% of coexistence of type II and type I. Average innervation ratio of crossing fibers was the highest in FDI (16.2%). CONCLUSION: Compound muscle action potential (CMAP) comparison method using modified incremental technique is a simple and sufficient method for evaluating forearm anastomosis without stimulus spread to adjacent nerve. In evaluating MGA, the FDI is a very important muscle because of high frequency and innervation ratio.