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.
|Origin:||Posterior cord of the brachial plexus|
|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.|
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.
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.
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
- Distal radioulnar joint
- Intercarpal joints
- Carpometacarpal joints
- Metacarpophalangeal joints
- PIP joints
Supplied from branches:
- Extensor carpi radialis brevis
- Extensor digitorum
- Extensor digiti minimi
- Extensor carpi ulnaris
- Abductor pollicis longus
- Extensor pollicis brevis
- Extensor pollicis longus
- Extensor indicis
- Posterior cutaneous nerve of the arm
- Lower lateral cutaneous nerve of the arm
- Posterior cutaneous nerve of the forearm
- "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
- "Anatomical snuffbox" - dorsum of first web space hand
- Loss of brachioradialis
- Triceps preserved if nerve injured below mid-shaft of humerus