Medial Cord of the Brachial Plexus

fasciculus medialis plexus brachialis

The medial cord is the continuation of the anterior division of the inferior trunk (C8-T1) and lies medial to the second part of the axillary artery. It gives off the medial pectoral nerve, the medial cutaneous nerves of the arm and forearm, and ends as the ulnar nerve and the medial root of the median nerve.

Anatomical Data

Course & Distribution

Origin	Anterior division of the inferior trunk (C8-T1)
Course	Lies first behind and then medial to the axillary artery, deep to pectoralis minor, and divides at the lower border of that muscle into its terminal branches
Motor	Pectoralis minor and the sternocostal part of pectoralis major (medial pectoral nerve) Flexor carpi ulnaris, the medial half of flexor digitorum profundus and most intrinsic hand muscles (ulnar nerve) Long finger flexors and thenar muscles (C8-T1 fibres in the median nerve)
Sensory	Medial arm (medial cutaneous nerve of the arm) Medial forearm (medial cutaneous nerve of the forearm) Medial hand, little finger and half of the ring finger (ulnar nerve)

Clinical Relevance

Clinical Notes

Medial cord lesions produce weakness of all the intrinsic hand muscles (ulnar and median supplied) and the long finger flexors, together with numbness of the medial arm, forearm and hand. This combination distinguishes a medial cord or lower trunk lesion from an ulnar neuropathy at the elbow, where the medial forearm skin is spared. The cord can be compressed by an axillary artery aneurysm or haematoma after arterial puncture, and injured in shoulder dislocation and axillary wounds.

Pathology

Common Injuries & Conditions

Medial Cord Compression After Axillary Puncture

A haematoma or false aneurysm after axillary artery cannulation can compress the medial cord within the tight axillary sheath, producing hand weakness and medial forearm numbness. Prompt decompression gives the best chance of recovery.

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