Communications between the median and ulnar nerves in the forearm, often known by the eponym Martin-Gruber Anastomosis, occur in approximately 15~25% of the normal population. This anomaly is asymptomatic and often goes undetected.

Martin-Gruber Anastomosis, median-ulnar crossover, can be determined during median and ulnar conduction studies for evaluation of certain pathologic processes in forearm incidentally. In presense of Martin-Gruber Anastomosis, the lesions of median and ulnar nerves in forearm, for example, in carpal tunnel syndrome or ulnar nerve transection at elbow proximal to the site of communication, reveal confusing electrodiagnostic findings as well as unusual distribution of neurological deficit clinically.

Recently we have experienced a case of complete ulnar nerve transection at elbow with Martin-Gruber Anastomosis.