Radial nerve

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The radial nerve is a terminal branch of the posterior cord of the brachial plexus. It is the largest branch of the plexus, suppling the majority of the posterior and extensor components of the forearm.

Radial nerve
Radial nerve.gif
System:
Function:
Origin: Posterior cord of the brachial plexus
Branches:
Insertion:
Arterial supply:
Venous drainage:
Lymphatic drainage:
Innervation: Triceps, anconeus, brachialis, brachioradialis, extensor carpi radialis longus, elbow
Vertebral levels: C5 nerve root, C6 nerve root, C7 nerve root, C8 nerve root, T1 nerve root
Search for Radial nerve in Gray's.


Contents

Roots

Surface anatomy

The course of the radial nerve in the upper arm can be represented by a line which starts posteriorly from the origin of the brachial artery and continues distally to a point at the junction of the upper and middle thirds of the line joining the deltoid tuberosity and the lateral epicondyle. From there it moves anteriorly to the lateral epicondyle itself.

Anatomical Course

The nerve arises as a continuation of the posterior cord of the brachial plexus. Initially it descends posterior to the third part of the axillary artery and the upper brachial artery, anterior to subscapularis and passing posteroinferiorly to the tendons of teres major and latissimus dorsi.

It inclines dorsally with the profunda brachii and later its radial recurrent branch, passing through the triangular space between triceps and the humerus to enter the posterior compartment of the arm. Once there, it bends obliquely across the posterior surface of the humerus, spiralling along its surface in the radial groove.

On reaching the lateral humerus it pierces the lateral intermuscular septum, entering the anterior compartment of the arm. It then descends in a depression between brachialis and brachioradialis proximally, extensor carpi radialis longus distally, lying on supinator. At the level of the lateral epicondyle it splits into its terminal branches.

Sensory Supply

The sensory supply of the radial nerve is entirely through its branches. Skin supply:

  • Posterior aspect of arm and forearm
  • Lower lateral arm
  • Dorsal aspect of lateral three and a half digits

Joint supply:

Motor Supply

Supplied from branches:

Branches

Terminal branches

Clinical Relevance

Causes

  • "Saturday night Palsy"
    • Compression of radial nerve in axilla by falling asleep with arm over back of chair
    • Similar mechanism of injury has led to use of elbow crutches
  • Mid-shaft fracture of humerus
    • Damages radial nerve in spiral groove
    • Branches to triceps already given off

Examination

  • Sensation
  • Weakness
    • Extensors wrist / fingers
      • Supinator
      • Extensor carpi radialis
        • → wrist drop
      • Abductor pollicis longus
        • but thumb abduction preserved by abductor pollicis brevis (median nerve)
  • Reflexes
    • Loss of brachioradialis
    • Triceps preserved if nerve injured below mid-shaft of humerus