Underrecognized anomaly: proximal martin-gruber anastomosis at the elbow

A proximal Martin-Gruber anastomosis (MGA) is an underrecognized anomaly and can mimic ulnar neuropathy at the elbow on electrodiagnostic testing. Martin-Gruber anastomosis is mainly recognized as a crossover from median nerve or its branches to ulnar nerve at the forearm, but may occur at the elbow (proximal MGA). The authors report their experience with MGA at the elbow.

Using standard nerve conduction techniques, the authors prospectively detected electrodiagnostic evidence of a proximal MGA at the elbow over the course of 4 years. An accompanying ulnar neuropathy was diagnosed based on clinical findings, focal conduction slowing, and needle electromyography.

A proximal MGA involving branch of ulnar nerve was detected in 16 cases. The detection of proximal MGA to the first dorsal interosseous muscles was more sensitive than to the adductor digiti minimi muscles in their series.

A proximal MGA is an underrecognized anomaly. This study is the largest series for proximal MGA in the literature. The authors recommend considering proximal MGA in any cases of ulnar neuropathy at the elbow, especially if the apparent conduction block is not associated with slowing of conduction velocity, and a discrepancy between clinical and electrodiagnostic findings is present.