Proximal Martin-Gruber anastomosis mimicking ulnar neuropathy at the elbow.

We present a case of Martin-Gruber anastomosis (MGA) mimicking conduction block between the above- and below-elbow sites of ulnar nerve stimulation. We review the anatomical and electrophysiological literature on this subject and discuss its clinical implications. The potential for a MGA to occur very proximally in the forearm and thus mimic ulnar neuropathy at the elbow is underrecognized. We recommend that a check for MGA be performed on all patients with an apparent conduction block at the elbow, and suggest that 3 cm distal to the medial epicondyle may be an optimal below-elbow ulnar nerve stimulation site.