A Martin-Gruber anastomosis (MGA) is a connection from the median nerve to the ulnar nerve in the forearm. An anastomosis occurs when two structures that normally are not connected have a connection. In this case the connection is a nerve. The Martin-Gruber anastomosis is most common anastomosis that occurs between these two nerves.[1] This connection carries motor axons which innervate some of the usually ulnar nerve innervated intrinsic muscles.
This inconstant pattern of connection can serve as explanation for a difficult or challenging differential diagnosis.[2] In one study,[3] the MGA was found in 22.9% of cadaver specimens, while another found the incidence at ~11%.[4] This relatively high incidence demonstrates the necessity for healthcare specialists to factor the MGA into their diagnoses.
There are six types of Martin-Gruber anastomoses.
In the setting of proximal ulnar nerve injury, a Martin-Gruber anastomosis can prevent the complete paralysis of the intrinsic muscles of the hand.