RADIAL NERVE - ANATOMY

DR.Murali.M.S;M.B.A Prof. of Surgery D Y Patil Medical

College Mauritius.

Objectives

Origin Course & Relations Branches Distribution Applied Anatomy

Radial Nerve

Originates as the terminal branch of the posterior cord of the brachial plexus

Roots from C5, 6, 7, 8, & T1.

Largest branch of brachial plexus

It is primarily a motor nerve

Course – RN – Ant.view

It commences its decent into the arm by passing anterior to the latissimus insertion and dives into the triceps to lie on the posterior surface of the humerus

Post view Ant view

Course of Radial Nerve

Largest terminal branch of posterior cord

Enters posterior aspect of humerus through lower triangular interval Teres major (superior) Long head triceps

(medial) Humerus (lateral)

Gives posterior cutaneous nerve of arm in axilla

Course of Radial Nerve

It lies on the surface of the medial head of the triceps, rather than the bony surface – of the humerus and does not do so until it crosses to the lateral aspect of the humerus along the spiral groove

Course of R N

Comes to lie in distal part of spiral groove with profundi brachii artery Beneath lateral head of

triceps and proximal to origin of medial head

Gives branches to triceps, anconeus and inferior lateral cutaneous nerve of arm

Course of Radial Nerve

The lower portion of the radial nerve crosses the midline at an average of 15 cm from the distal articular surface and pierces the lateral intermuscular septum at approximately 8-12cm from the lateral epicondyle

Course of Radial Nerve

Enters the forearm anterior to lateral epicondyle More specifically

over articulation between capitulum and radial head

At some point 1-3cm above & distal - LE & deep to BR divides into: Superficial radial PIN

Course of Radial Nerve

In anterior compartment of arm lies between brachialis and brachioradialis

At its division – closely related to radial recurrent artery

Course of Superficial R.Nerve Runs down the

forearm along the lat.border of BR with radial artery on its ulnar side in the middle 1/3 of forearm

Passes posteriorly through tendon of BR proximal to radial styloid.

Course of Superficial R.Nerve Passes over

tendons of snuffbox

Terminates as cutaneous branches to dorsum of hand and lateral 3 1/2 digits short of nailbeds

Course – P I N

The PIN continues down the forearm diving between the heads of supinator and then emerging to split into several branches that supply the extensors of the wrist and hand

Posterior Interosseous Nerve After exiting the

supinator divides into deep and superficial muscular branches

Superficial EDC, ECU, EDM

Deep APL, EPL, EPB, EI

APPLIED ANATOMY

Lesions

Level I – Axilla

Level II – Spiral groove

Level III – Elbow

Level IV – Forearm

Axilla

Lesions in the axilla Involves the posteriorcord /

high axillary lesions.

* Etiology: Crutches /

shoulder dislocation

Position

• Hand hangs in flexion(wrist drop)

• Wasting of dorsal arm (triceps)& muscle mass on the posterior surface of the forearm

• Paraesthesias & sensory loss on the entire extensor surface of the arm & forearm & on the back of the hand & dorsum of the first 4 fingers.

Spiral Groove

Etiologies

Humeral factures/Compressive

lesions / Saturday night palsy

Entrapment by tendinous arch

of lateral head of triceps

muscle/damaged after arm

excercise .

Soldiers developing palsies at

the lateral border of humerus

after military shooting training

Sensibility on the extensor aspect of arm is spared .

Sensibility on the extensor aspect of forearm may or may not be spared.

Wrist drop + / No loss of elbow extension

Elbow – Radial Tunnel Syn.

• Involvement of the PIN.

• Etiologies A constricting

band at the radiohumeral joint capsule.

Lacerations ,gunshot wounds,closed injuries(fracture of proximal radius),chronic repeated trauma related to stressful supination & pronation in swimmers, frisbee players,tennis players,violinist .

Position

Atrophy & paresis of the ECU,ED,Extensor digiti minimi APL,EPL,EPB & extensor indices.

Extensor carpi radialis is intact.

• Drop finger deformity

Difficulty in extending the MCP of all five fingers

Partial wrist drop No sensory loss The wrist deviates

radially,when the patient makes a fist.

Cheiralgia Paresthetica

• The superficial cutaneous branch of the radial nerve → pure sensory syndrome that affects the radial part of the dorsum of the hand & dorsal aspect of the first 3 ½ fingers.

• Etiology:Crushing/twisting injuries of the

wrist/forearm ( “Hand-cuff / Wrist watch neuropathy” )Repetitive pronation & supination.

Summary

Radial nerve arises from posterior cord of the brachial plexus

It passes posterior to the axillary artery between long and medial heads of triceps muscle, to lie in the spiral groove between medial & lateral heads of triceps muscle.

Here it is accompanied by the profunda brachii artery before it pierces lateral intermuscular septum of the lower third humerus to run between brachialis & brachioradialis

At the lateral of epicondyle humerus, it gives rises to PIN & superficial radial nerve

Radial nerve supply all the extensor muscles of forearm & arm. However it also supply brachioradialis, which is flexor of elbow when forearm pronated.

Damage to the nerve in the spiral groove causes

wrist drop but no loss of elbow extension, as fibres of

triceps remain intact proximal to this site. Only damage in the axilla will causes loss of

elbow extension & wrist drop Damage to posterior interosseus nerve

(PIN) does not cause wrist drop because extensor carpi radialis longus receives its innervation from the main radial nerve

Pin only causes inability to extend metacarpophalangeal joint finger drop.

Clinical case presentation