Ulnar

Question 1

Spinal roots:

Answer 1

C8-T1

Question 2

Motor functions:

Answer 2

Innervates the muscles of the hand (apart from the thenar muscles and two lateral lumbricals), flexor carpi ulnaris and medial half of flexor digitorum profundus.

Question 3

Sensory functions:

Answer 3

Innervates the anterior and posterior surfaces of the medial one and half fingers, and the associated palm area

Question 4

Anatomical Course

Answer 4

The ulnar nerve is derived from the brachial plexus. It is a continuation of the medial cord, containing fibres from spinal roots C8 and T1.

After arising from the brachial plexus, the ulnar nerve descends down the medial side of the upper arm. At the elbow, it passes posterior to the medial epicondyle, entering the forearm. At the medial epicodyle, the nerve is easily palpable and vulnerable to injury.

In the forearm, the ulnar nerve pierces the two heads of the flexor carpi ulnaris, and travels alongside the ulna. Three branches arise in the forearm:

Muscular branch: innervates some muscles in the anterior compartment of the forearm.
Palmar cutaneous branch: innervates the skin of the medial half of the palm.
Dorsal cutaneous branch: innervates the skin of the medial 1 and 1/2 fingers, and the associated palm area.

At the wrist, the ulnar nerve travels superficially to the flexor retinaculum. It enters the hand via the ulnar canal (or Guyon’s canal). In the hand the nerve terminates by giving rise to superficial and deep branches.

Question 5

Motor Functions

Answer 5

The ulnar nerve innervates muscles in the anterior compartment of the forearm, and in the hand.

The Anterior Forearm

In the anterior forearm, the muscular branch of the ulnar nerve supplies two muscles:

Flexor carpi ulnaris – Flexes and adducts the hand at the wrist.
Flexor digitorum profundus (medial half ) – Flexes the fingers.
The remaining muscles in the anterior forearm are innervated by the median nerve.

The Hand

The majority of the intrinsic hand muscles are innervated by the deep branch of the ulnar nerve.

The hypothenar muscles (a group of muscles associated with the little finger) are innervated by the ulnar nerve. It also innervates some other muscles of the hand:

Medial two lumbricals
Adductor pollicis
Interossei of the hand
The other muscles in the hand (such as the thenar eminence) are innervated by the median nerve.

Question 6

Sensory Functions

Answer 6

There are three branches of the ulnar nerve that are responsible for its cutaneous innervation.

Two of these branches arise in the forearm, and travel into the hand:

Palmar cutaneous branch: Innervates the skin of the medial half of the palm.
Dorsal cutaneous branch: Innervates the skin of the medial one and a half fingers, and the associated palm area.
The last branch arises in the hand itself:

Superficial branch – Innervates the palmar surface of the medial one and a half fingers.

Question 7

Clinical significance

Answer 7

At the elbow

Common mechanisms of injury: Cubital tunnel syndrome, fracture of the medial epicondyle (causing cubitus valgus with tardy ulnar nerve palsy)
Motor deficit:
Weakness in flexion of the hand at the wrist, loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand. (Note: Motor deficit is absent or very minor in cubital tunnel syndrome as the ulnar nerve is compressed in the cubital tunnel, rather than transected.)
Presence of a claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the metacarpophalangeal joints, and flexion at the interphalangeal joints.
Sensory deficit: Loss of sensation or paresthesiae in ulnar half of the palm and dorsum of hand, and the medial 1½ digits on both palmar and dorsal aspects of the hand
At the wrist

Common mechanism: penetrating wounds, Guyon canal cyst
Motor deficit:
Loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand.
Presence of a claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the metacarpophalangeal joints, and flexion at the interphalangeal joints.
The claw hand deformity is more prominent with injury at the wrist as opposed to a lesion higher up in the arm, for instance, at the elbow, as the ulnar half of the flexor digitorum profundus is not affected. This pulls the distal interphalangeal joints of the 4th and 5th digit into a more flexed position, producing a more deformed ‘claw’. This is known as the ulnar paradox.
Sensory deficit: Loss of sensation or paresthesiae in ulnar half of the palm, and the medial 1½ digits on the palmar aspect of the hand, with dorsal sparing. The dorsal aspect of the hand is unaffected as the posterior cutaneous branch of the ulnar nerve is given off higher up in the forearm and does not reach the wrist.
In severe cases, surgery may be performed to relocate or “release” the nerve to prevent further injury.