Shorts # 208: The Nerve Secret in Animation: Martin-Gruber Anastomosis"

[00:00:00]Learning hand surgery one point at a time. A patient has had an ulnar nerve injury but still has preserved intrinsic muscle function. How is that possible?

[00:00:10]That could be possible due to the Martin Gruber anastomosis. This represents the median nerve, the motor fibers of the nerve, the anterior interosseous nerve, and the sensory fibers. This represents the ulnar nerve, the motor fibers, and the sensory fibers. An abnormal connection of motor fibers alone between the median and ulnar nerves in the middle of the forearm is known as the Martin Gruber anastomosis. This was described by Martin in 1763 and confirmed by Gruber in 1870. The occurrence of this anastomosis is not so rare. It has an incidence of 5 to 40% with an average of 17%. It is bilateral in 10 to 40% and when unilateral, it usually involves the right side. The crossing axons can innervate intrinsic muscles supplied by the ulnar nerve, the median nerve, or both. The presence of this anastomosis could have clinical significance or electrophysiological significance. When the median nerve is involved at the elbow, normally we would expect features of median nerve palsy in the hand. But when features of paralysis of the ulnar nerve innervated muscles are also present, it could point to the presence of Martin Gruber anastomosis.

[00:01:23]Likewise, in a lesion of the ulnar nerve at the elbow, if a Martin Gruber anastomosis is present, there would be features of ulnar nerve palsy in the hand with sparing of some ulnar innervated muscles also. When there is involvement of the median nerve in the wrist, there would be features of median nerve palsy with sparing of some median nerve innervated muscles if the Martin Gruber anastomosis is present in the forearm. If the MGA is present in the forearm, a lesion of the ulnar nerve at the wrist will show features of ulnar nerve palsy and paralysis of some median nerve innervated muscles also. of some median nerve innovated muscles also.