Anomalous Innervations

1. What is a Martin-Gruber anastomosis?
2. What muscles do these ulnar fibers innervate?
3. What are the findings on NCS seen with Martin-Gruber and CTS?
4. What is a Riche-Cannieu anastomosis?
5. What are the findings on NCS with Riche-Cannieu anastomosis?

Answers:
1. It is a median to ulnar nerve anastomosis. The ulnar nerve fibers travel with the AIN branch of the median nerve and crosses over in the forearm. It is present in 15-20% of the population.
2. They innervate the ADP, ADM, and most commonly the FDI.
3. NCS shows an initial positive deflection on median CMAP at the elbow, an increased increased amplitude of median CMAP at elbow compared to wrist (can occur w/wo CTS), and CV across the forearm appears artificially fast.
4. This is a connection of the deep branch of the ulnar nerve and the recurrent branch of the median nerve in the hand, resulting in an all-ulnar hand.
5. CMAP to APB muscle is absent with median nerve stimulation but present with ulnar nerve stimulation.