Topic Overview

Ulnar Nerve (C8, T1)

Root Value

• C8, T1 (from medial cord of the brachial plexus).

Course in Arm

1. Arises in axilla, medial to axillary and brachial arteries.

2. Descends along medial side of arm with superior ulnar collateral artery.

3. At mid-arm, pierces medial intermuscular septum.

4. Enters posterior compartment, lies on medial head of triceps.

5. Passes behind medial epicondyle of humerus in a groove between medial epicondyle and olecranon (superficial and unprotected).

6. Enters forearm between two heads of flexor carpi ulnaris.

Branches in Arm

• No branches in the arm.

Relations

• Proximal: medial to brachial artery.

• Distal: accompanied by superior ulnar collateral artery.

• Posterior: lies in a groove behind medial epicondyle (site of injury).

Clinical Anatomy

• Injury at elbow (posterior to medial epicondyle):

  • Causes severe pain/tingling (“funny bone” effect).

  • Weakness of flexor carpi ulnaris and medial part of flexor digitorum profundus.

  • Claw hand deformity (hyperextension at MCP, flexion at IP joints of ring & little fingers).

  • Sensory loss: medial 1½ fingers (both palmar and dorsal aspects).

• Ulnar nerve palsy signs:

  • Loss of adduction of thumb (Adductor pollicis).

  • Flattened hypothenar eminence.

  • Positive Froment’s sign.

• Compression at cubital tunnel → cubital tunnel syndrome.

Radial Nerve (C5–T1)

Root Value

• C5, C6, C7, C8, T1 (terminal branch of posterior cord of brachial plexus).

Course in Arm

1. In axilla, lies behind axillary artery (gives branches to long & medial heads of triceps).

2. Enters spiral (radial) groove of humerus with profunda brachii artery.

3. Winds obliquely around posterior aspect of humerus → between lateral & medial heads of triceps.

4. Pierces lateral intermuscular septum → enters anterior compartment.

5. Lies between brachialis and brachioradialis, just above lateral epicondyle.

6. Divides into superficial (sensory) and deep (posterior interosseous) branches in front of lateral epicondyle.

Branches in Arm

1. Muscular Branches

• To long, lateral, and medial heads of triceps.

• To anconeus (from medial head branch).

2. Cutaneous Branches

• Lower lateral cutaneous nerve of arm.

• Posterior cutaneous nerve of arm.

• Posterior cutaneous nerve of forearm.

3. Articular Branch

• To elbow joint.

Functions

• Motor: supplies all extensors of elbow, wrist, and fingers (via triceps and posterior compartment muscles).

• Sensory: posterior surface of arm, forearm, and dorsum of hand (lateral 3½ proximal phalanges).

Clinical Anatomy

• Injury in axilla (crutch palsy):

  • Loss of elbow, wrist, and finger extension → complete wrist drop.

  • Sensory loss over posterior arm, forearm, and dorsum of hand.

• Injury in spiral groove (mid-humerus fracture):

  • Triceps partly spared (long & lateral heads intact).

  • Wrist and finger drop present (posterior interosseous nerve paralysis).

  • Sensory loss on dorsum of hand and posterior forearm.

• Injury near elbow:

  • Affects deep branch → loss of finger extension but wrist extension preserved.

  • Superficial branch → isolated sensory loss on dorsum of hand.

• Testing:

  • Ask patient to extend wrist and fingers; inability indicates radial nerve lesion.