Muscular branches of ulnar nerve

At a glance

English

Muscular branches of ulnar nerve

Latin (TA2)

Rami musculares nervi ulnaris

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the muscular branches of ulnar nerve

In the arm the ulnar nerve gives no muscular branches. Its first motor branches arise close to the elbow, as the nerve leaves the cubital tunnel behind the medial epicondyle and enters the front of the forearm between the humeral and ulnar heads of flexor carpi ulnaris. Here, within a few centimetres, it sends branches into the two forearm muscles that it supplies. The exact pattern differs from person to person: each muscle may receive one branch or several, and they can leave the nerve just above, at, or below the level of the joint.

One group enters flexor carpi ulnaris, the superficial muscle along the ulnar border of the forearm that arises from the medial epicondyle and olecranon and ends on the pisiform. The other group passes deeper, to the medial part of flexor digitorum profundus, the part whose tendons go to the ring and little fingers. The lateral part of that muscle, for the index and middle fingers, belongs to the anterior interosseous branch of the median nerve, so flexor digitorum profundus is a muscle shared by two nerves.

Through these branches the ulnar nerve controls flexion and ulnar deviation of the wrist, through flexor carpi ulnaris, and flexion of the end joints of the ring and little fingers, through flexor digitorum profundus. The fibres come mainly from C8 and T1, with some C7 for flexor carpi ulnaris.

The level of an ulnar lesion can be judged by whether these branches still work. Injury at or above the elbow, as in cubital tunnel syndrome or a fracture of the medial epicondyle, weakens wrist flexion on the ulnar side and leaves the ring and little fingers unable to bend at their tips. A lesion at the wrist spares these branches; the long flexor still pulls on the ring and little fingers, and the clawing caused by loss of the small hand muscles looks worse. This is the so-called ulnar paradox. Surgeons moving the nerve forward at the elbow must take care to keep these short branches intact.

Course and supply

Arises from

Arise from the ulnar nerve close to the elbow, as it passes between the two heads of flexor carpi ulnaris.

Ends in

End in flexor carpi ulnaris and in the medial (ulnar) half of flexor digitorum profundus.

Supplies

Motor to flexor carpi ulnaris for wrist flexion and ulnar deviation, and to the part of flexor digitorum profundus that flexes the distal joints of the ring and little fingers.