Topic Overview

Radial Nerve (Musculospiral Nerve) 

Root Value

• C5, C6, C7, C8, T1

• It is the largest branch of the posterior cord of the brachial plexus.

Course

In the Axilla

• Lies posterior to the third part of the axillary artery.

• Accompanied by the subscapular and thoracodorsal nerves.

• Gives branches to:

  • Long head of triceps

  • Medial head of triceps

  • Posterior cutaneous nerve of arm

In the Arm

1. Enters the spiral (radial) groove with the profunda brachii artery.

2. Passes obliquely downward and laterally between the lateral and medial heads of triceps.

3. Gives off:

   • Muscular branches: to lateral and medial heads of triceps, and anconeus.

   • Cutaneous branches:

     • Lower lateral cutaneous nerve of arm

     • Posterior cutaneous nerve of forearm

4. Leaves the groove and pierces the lateral intermuscular septum → enters anterior compartment.

5. Descends between brachialis (medial) and brachioradialis (lateral).

6. Just above lateral epicondyle → divides into:

   • Superficial branch (sensory).

   • Deep branch (posterior interosseous nerve) → motor to extensors.

Branches in the Arm

Areas Supplied

• Motor: All extensor muscles of arm and forearm.

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

Clinical Anatomy

1. Sites of Injury

• (a) In the Axilla – “Crutch Palsy”

  • Cause: Improper use of crutches, sleeping with arm over chair back, or axillary compression.

  • Effects:

    • Paralysis of triceps, anconeus, and all extensors of wrist and fingers.

    • Complete wrist drop.

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

• (b) In the Spiral Groove – “Saturday Night Palsy”

  • Cause: Mid-shaft fracture of humerus or prolonged compression (arm hanging over chair).

  • Effects:

    • Triceps partially spared (long and lateral heads intact).

    • Paralysis of wrist and finger extensors → wrist drop.

    • Sensory loss on dorsum of hand and posterior forearm.

• (c) Near Elbow

  • Injury to deep branch (posterior interosseous nerve) → loss of finger extension but wrist extension preserved.

  • Injury to superficial branch → isolated sensory loss over dorsum of hand.

2. Wrist Drop

• Characteristic feature of radial nerve palsy.

• Wrist cannot be extended; fingers remain flexed.

• Hand hangs flaccidly due to unopposed flexors.

3. Triceps Reflex

• Tests C7–C8 spinal segments.

• Absent in high radial nerve lesion (axillary level).

4. Surgical Relevance

• Radial nerve and profunda brachii artery must be protected during fixation of mid-shaft humeral fractures or posterior surgical approaches.

5. Diagnostic Test

• Ask patient to extend wrist and fingers against resistance.

  • Inability → radial nerve lesion.

  • If wrist extension preserved but finger extension lost → deep branch (posterior interosseous) lesion.