Martin-Gruber Anastomosis

Martin-Gruber Anastomosis is median to ulner anastomosis in the forearm. It occurs through a communicating nerve branch between the median nerve and the ulnar nerve in the forearm. This connection carries motor nerve fibers. It can be confusing clinically and also on an EMG. It has a clinical significance for understanding the median nerve lesions and carpal tunnel syndrome. The axons will leave the median nerve or the anterior interosseous nerve crossing through the forearm to join the main trunk of the ulnar nerve, innervating the intrinsic muscles of the hand. The lesion above the communicating branch will affect the median nerve muscles. A lesion below the anastomosis (connecting branch) will not affect the median nerve muscles, it will spare the thenar motor intrinsic muscles of the hand. An isolated ulnar nerve lesion at the elbow will produce an unusual pattern for intrinsic muscle paralysis. Martin-Gruber Anastomosis is the most common anastomosis anomaly between the two nerves. In cases of nerve lesions of the median or ulnar nerve, this anastomosis serves as a conduit or an alternative innervation of parts of the hand and the forearm (it is really a detour). This can be a good explanation of difficult challenges, especially in the differential diagnosis. Incidence is high (about 15%). The physician should factor Martin-Gruber anastomosis into the differential diagnosis and the diagnosis.

If the communicating nerve arises from the anterior interosseous nerve, then a patient with anterior interosseous nerve palsy may present with hand intrinsic weakness, normally supplied by the ulnar nerve. Damage of the ulnar nerve at the wrist will lead to severe deficit of the intrinsic hand function greater than expected. There are other anastomoses available and reported as well as many variations that are possible.

There are three common anastomoses:

1. Ulnar to median anastomosis in the forearm-reverse of Martin-Gruber (Marinacci anastomosis)
2. Ulnar to median anastomosis in the hand (Riche-Cannieu anastomosis)
   1. Connection between the deep branch of the ulnar nerve and the recurrent branch of the median nerve
   2. It carries motor fibers and this anastomosis usually occurs in the region of the thenar and adductor pollicis muscles.
3. Berrettini Anastomosis
   1. Communication between the digital nerves (sensory nerves) arising from the ulnar and median nerves in the hand
   2. Most common nerve anastomosis pattern

When the examination does not make sense and it is confusing, you can consider Martin-Gruber anastomosis.