Posterior cord of brachial plexus

At a glance

English

Posterior cord of brachial plexus

Latin (TA2)

Fasciculus posterior plexus brachialis

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the posterior cord of brachial plexus

The brachial plexus reorganises its fibres in the lower neck and axilla. Each of its three trunks splits into an anterior and a posterior division, and the three posterior divisions then unite to form the posterior cord. Because every trunk contributes, the cord carries fibres from all the roots of the plexus, C5 to T1, although T1 adds only a little. The cord belongs to the infraclavicular part of the plexus and is named for its position behind the second part of the axillary artery, deep to pectoralis minor.

The posterior cord is the nerve supply of the back of the upper limb. Its fibres are destined for muscles that, in development, formed on the dorsal side of the limb bud: the extensors of the elbow, wrist and fingers, the supinator and the long abductor and extensors of the thumb, and the muscles of the posterior wall of the axilla and shoulder. It gives five named branches. The upper subscapular nerve (C5, C6) enters subscapularis. The thoracodorsal nerve (C6 to C8) runs down the posterior axillary wall to latissimus dorsi. The lower subscapular nerve (C5, C6) supplies the lower part of subscapularis and teres major.

Behind the lower part of the axillary artery the cord ends by dividing into its two terminal branches. The axillary nerve (C5, C6) passes backwards through the quadrangular space round the surgical neck of the humerus to deltoid and teres minor and to the skin over the lower deltoid. The radial nerve (C5 to T1), the largest branch of the plexus, continues behind the artery into the arm and on to triceps, anconeus, brachioradialis and all the extensor muscles of the forearm, as well as the skin on the back of the arm, forearm and hand.

A lesion of the posterior cord, which can follow a fracture-dislocation of the shoulder or prolonged pressure in the axilla, combines the effects of radial and axillary nerve damage: weak shoulder abduction, loss of elbow and wrist extension with wrist drop, and weaker adduction and medial rotation of the arm. Numbness affects the outer shoulder and the back of the arm, forearm and hand. Using a crutch pressed hard into the armpit is a classic cause.

Course and supply

Arises from

Formed by union of the posterior divisions of the superior, middle and inferior trunks behind the axillary artery (C5 to T1).

Ends in

Gives the upper subscapular, thoracodorsal and lower subscapular nerves, and ends by dividing into the axillary and radial nerves.

Supplies

Supplies subscapularis, teres major, latissimus dorsi, deltoid, teres minor and all extensor muscles of the arm and forearm; carries sensation from the shoulder and the back of the arm, forearm and hand.