Martin-Gruber anastomosis and unusual sensory innervation of the fingers: report of a case.

We report the electrophysiological study of a patient with carpal tunnel syndrome who, besides the features of median nerve entrapment at the wrist, showed an aberrant motor innervation of Martin-Gruber type and an unusual distribution of the sensory innervation of the fingers. Studies based on collision between sensory volleys showed that the fibers supplying the anomalous innervation did not follow the same path as the aberrant motor fibers. This finding is consistent with the hypothesis that Martin-Gruber anastomosis is made up of motor axons only, and supports the idea that other abnormalities of innervation may be found in patients with Martin-Gruber anastomosis.