Anastomosis between median nerve and ulnar nerve in the forearm

Anastomosis between the median nerve and ulnar nerve can occur in the forearm region. It consists in crosses of axons which may produce changes in innervation of the upper limb muscles, mainly motor part of intrinsic muscles in the hand. Anastomosis in the forearm can be classified in two types: Martin Gruber anastomosis and Marinacci anastomosis. This study has as purpose to report the incidence, type, topography of anastomosis found and assess the length of this anastomosis. Material and Methods: For this study, 30 forearms were dissected in the Anatomy Institute of Severino Sombra University. In order to check the incidence of anastomosis and its topography, the length of the anastomotic branch was measured with a measuring tape (3M). In addition schematic drawings were executed. Results: Three (3) anatomical pieces that contained the Martin-Gruber anastomosis with an average length of 6.6 cm were found. One (1) anatomical piece with a 7.4 cm long Marinacci anastomosis was found, even though such type of anastomosis shows low incidence, and was found only in electroneuromyography studies. Conclusion: The study of anomalous communications between median and ulnar nerves in the forearm deserves great attention for its incidence and its clinical importance, mainly in the correct diagnosis of peripheral neuropathies, for example in the Carpal Tunnel Syndrome, which produces changes in the upper limb innervation. The importance of its verification and delimitation is also crucial to avoid lesions in surgical procedures.

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

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.