Ulnar nerve

At a glance

English

Ulnar nerve

Latin (TA2)

Nervus ulnaris

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the ulnar nerve

The ulnar nerve is the largest branch of the plexus's medial cord, with fibres from C8 and T1 and sometimes some C7 by way of the lateral cord. In the upper arm it runs on the medial side of the brachial artery. About halfway down it passes through the medial intermuscular septum with the superior ulnar collateral artery and descends on the medial head of triceps to the back of the medial epicondyle. Here, in the cubital tunnel, only skin and fascia cover it, so a knock to the funny bone jolts the little finger. It gives no branches in the arm.

The nerve reaches the forearm by passing between the humeral and ulnar heads of flexor carpi ulnaris, then runs on flexor digitorum profundus under cover of flexor carpi ulnaris, with the ulnar artery joining its lateral side lower down. Near the elbow it supplies flexor carpi ulnaris and the ulnar half of flexor digitorum profundus. Lower in the forearm it gives a palmar branch to the hypothenar skin and a dorsal branch that winds round the ulna to the back of the hand. It crosses the wrist superficial to the flexor retinaculum, beside the pisiform, in the ulnar canal.

In the hand it divides into superficial and deep branches. The superficial branch supplies palmaris brevis and the palmar skin of the little finger and half the ring finger. The deep branch runs with the ulnar artery's deep branch between the hypothenar muscles, round the hook of the hamate and across the palm. It supplies the three hypothenar muscles, all the interossei, the third and fourth lumbricals, adductor pollicis and the deep head of flexor pollicis brevis.

The nerve is most often damaged at the elbow, by cubital tunnel compression or a fracture of the medial epicondyle, and at the wrist by cuts or cysts in the ulnar canal. Signs include numbness of the little and half the ring finger, wasting between the metacarpals, inability to spread or cross the fingers, a weak pinch in which the thumb tip bends to compensate (Froment's sign), and clawing of the ring and little fingers. Clawing is worse with a wrist lesion, because the profundus branch is spared: the ulnar paradox.

Course and supply

Arises from

Medial cord of the plexus (C8, T1, sometimes C7), in the axilla.

Ends in

Ends in the hand by dividing, at the ulnar canal, into the superficial and deep branches.

Supplies

Motor to flexor carpi ulnaris, the ulnar half of flexor digitorum profundus, the hypothenar muscles, all interossei, the third and fourth lumbricals, adductor pollicis and the deep head of flexor pollicis brevis; sensory to the ulnar side of the hand and the little and ulnar half of the ring finger.