Which muscles are innervated by the posterior cord of the brachial plexus (Brachial Plexus)?

From the Guidelines

The posterior cord of the brachial plexus innervates several important muscles in the upper limb, including the teres major, latissimus dorsi, and all three heads of the triceps brachii, as well as the deltoid and teres minor muscles through the axillary nerve, and the muscles of the posterior compartment of the forearm through the radial nerve. The muscles innervated by the posterior cord can be broken down into several groups, including:

• The muscles of the upper arm, such as the teres major, latissimus dorsi, and triceps brachii, which are involved in movements such as extension, adduction, and rotation of the shoulder and elbow joints.
• The muscles of the shoulder, such as the deltoid and teres minor, which are involved in movements such as abduction, flexion, and rotation of the shoulder joint.
• The muscles of the posterior compartment of the forearm, such as the supinator, anconeus, brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis, which are involved in movements such as extension and supination of the wrist and fingers. The posterior cord is formed from the posterior divisions of the upper, middle, and lower trunks of the brachial plexus, and it primarily supplies muscles that are involved in extension movements at the shoulder, elbow, wrist, and fingers, reflecting its embryological origin from the dorsal (posterior) aspect of the limb bud, as described in the study on plexopathy 1.

From the Research

Muscles Innervated by the Posterior Cord

The posterior cord of the brachial plexus innervates several muscles, including:

• Deltoid muscle 2
• Triceps brachii muscle 2
• Extensor muscles of the wrist, thumb, and fingers 2
• Teres minor muscle 3
• Teres major muscle 3
• Latissimus dorsi muscle 3

Nerves Originating from the Posterior Cord

The nerves that originate from the posterior cord include:

• Axillary nerve 4, 3
• Thoracodorsal nerve 4, 3
• Radial nerve (not directly mentioned, but implied through the mention of radial palsy) 2
• Inferior subscapular nerve 3
• Superior subscapular nerve (not directly originating from the posterior cord, but related to the muscles innervated by the posterior cord) 3

Anatomical Variations

There are anatomical variations in the formation and branching pattern of the posterior cord, including:

• The posterior cord may be formed by the union of the posterior division of C5 and C6 roots with the posterior division of the middle and lower trunk 4
• The axillary nerve may take origin from the posterior division of the upper trunk 4
• The thoracodorsal nerve may arise from the axillary nerve 4