Nerves of the anterior arm and forearm
|Origin:||Terminal branch of the medial cord of the brachial plexus|
|Innervation:||Elbow, flexor carpi ulnaris, flexor digitorum profundus, medial skin of the palm and dorsum of the hand, palmaris brevis, skin of the medial one and a half digits, the wrist joint, flexor digiti minimi, abductor digiti minimi, opponens digiti minimi, interossei, the two medial lumbricals, flexor pollicis brevis, adductor pollicis|
|Vertebral levels:||C8 nerve root, T1 nerve root|
|Search for Ulnar nerve in Gray's.|
The ulnar nerve is easily palpable in a groove on the posterior aspect of the medial epicondyle of the humerus.
The ulnar nerve arises from the brachial plexus medially to the axillary artery, continuing medially to the brachial artery as it passes out of the axilla. It lies on the surface of coracobrachialis until the midpoint of the upper arm where it passes posteriorly into the posterior compartment of the arm through the medial intermuscular septum with the superior ulnar collateral artery. It comes to lie beneath the medial head of triceps on the posterior surface of the medial intermuscular septum and passes posteriorly to the medial epicondyle of the humerus in a tunnel formed by a groove in the bone and a fibrous roof which may sometimes be an actual bony tunnel to lie medial to the coronoid process of the ulna.
The nerve enters the forearm between the two heads of flexor carpi ulnaris, coming to lie deep to the muscle and superficial to flexor digitorum profundus medial to the ulnar artery. It continues in this position to the wrist, where it lies lateral to the tendon of flexor carpi ulnaris. It passes superficial to the flexor retinaculum to divide into its terminal branches just distal to pisiform.
- Medial palmar and dorsal surface of the hand, the entirety of the little finger and medial half of the ring finger.
- Palmaris brevis
- Flexor digiti minimi
- Abductor digiti minimi
- Opponens digiti minimi
- The two medial lumbricals
- Flexor pollicis brevis
- Adductor pollicis
Ulnar nerve lesions may be caused by
- Ulnar nerve injury
- Rheumatoid arthritis
- Fractured humerus
- Cubital tunnel syndrome
- Compression in Guyon's canal at the wrist
An ulnar nerve lesion causes:
- Clawing of ring and little fingers
- Hyperextension of metacarpo-phalageal joints
- Flexion at DIP and PIP joints
- Wasting of hypothenar eminence and interosseus muscles
- Weak adduction at wrist
- Sensory loss
- Other signs:
- Deformed elbow
- Rheumatoid nodules
- Froment's test