Human Anatomy Vol 1

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UPPER LIMB

Dorsum of base

of distal phalanx

Dorsum of base

of middle phalanx

Extensor expansion

Third dorsal

interosseous

Tendon of

extensor

digitorum

Fig.9.59: The dorsal digital expansion of right middle finger.

Note the insertions of the lumbricals and interossei into it

DISSECTION

Deep terminal branch of radial nerve posterior

interosseous nerve and posterior interosseous artery:

ldentify the posterior interosseous nerve at the distal

border of exposed supinator muscle. Trace its branches

to the various muscles.

Look for the radial nerve in the lower lateral part of

front of arm between the brachioradialis, extensor carpi

radialis longus laterally and brachialis muscle medially.

Trace the two divisions of this nerve in the lateral part

of the cubital fossa. The deep branch (posterior intero-

sseous nerve) traverses between the two planes of

supinator muscle and reaches the back of the forearm

where it is already identified.

The nerve runs amongst the muscles of the back of

the forearm, and ends at the level of the wrist in a

pseudoganglion (Fig. 9.60).

This nerve is accompanied by posterior interosseous

artery distal to the supinator muscle. This artery is

supplemented by anterior interosseous artery in lower

onejourlh of the forearm.

Feotures

It is the chief nerve of the back of the forearrn. It is a branch

of the radial nerve given off in the cubital fossa, just

below the level of the lateral epicondyle of the humerus.

Course

It begins in cubital fossa. Passes through supinator

muscle to reach back of forearm, where it descends

downwards. It ends in a pseudoganglion in the 4th

compartment of extensor retinaculum.

Relotions

L Posterior interosseous nerve leaves the cubital fossa

and enters the back of the forearm by passing

between the two planes of fibres of the supinator.

Within the muscle it winds backwards round the

lateral side of the radius (Fi9.9.60).

2 It emerges from the supinator on the back of the

forearm. Here it lies between the superficial and deep

muscles. At the lower border of the extensor pollicis

brevis, it passes deep to the extensor pollicis longus.

It then runs on the posterior surface of the

interosseous membrane up to the wrist where it

enlarges into apseudoganglion and ends by supplying

the wrist and intercarpal joints.

Bronches

Posterior interosseous nerve gives muscular and

articular branches (Fig. 9.61).

A. Muscular branches

a. Before piercing the supinator, branches are given

to the extensor carpi radialis brevis and to the

supinator.

b. While passing through the supinator, another

branch is given to the supinator.

Posterior

interosseous nerve

Common

interosseous artery

Oblique cord

Anterior

interosseous artery

Abductor

pollicis longus

Extensor

pollicis brevis

Superficial

muscfes of

back of forearm

Supinator

Posterior

interosseous

artery

Extensor pollicis

longus

lnterosseous

membrane

Fig. 9.60: Course and relations of the posterior interosseous

nerve and the interosseous afierres