Martin-Gruber communicating branch: anatomical and histological study.

We dissected 72 upper limbs of fresh cadavers and found 17 cases with a Martin-Gruber communicating branch (23.6%). These were classified into 4 types: type I (n = 5, 29.4%): communicating branch between the anterior interosseous and ulnar nn, type II (n = 3, 17.6%): Communicating branch between the median and ulnar nn., type III (n = 3, 17.6%): Communicating branch between the muscular branches to the flexor digitorum profundus m., type IV (n = 6, 35.3%): combination of type I or II and type III. At histologic examination the number and size of the nerve bundles each communicating branch contained proved to be very different. In one case of type II only a single nerve bundle was found. We suggest that the different numbers of nerve bundles innervate different amounts of the intrinsic hand musculature. The communicating branch with a single nerve bundle probably innervated only the first dorsal interosseous muscle.