Upper limbs | Musculoskeletal system | Anatomy

Brachial plexus and lesions

The brachial plexus is formed by the anterior or ventral rami of spinal segments C5 to T1. It supplies the upper limb. The roots are ventral rami of spinal nerves which carry both motor and sensory input. The roots join to form three trunks - upper, middle and lower. Upper or superior trunk is formed by the joining of ventral rami of C5 and C6; middle trunk is only ventral ramus of C7 while lower or inferior trunk is formed from ventral rami of C8 and T1. The trunks are found in the posterior triangle of the neck between the anterior and middle scalene muscles. The trunks divide into anterior and posterior divisions which form cords. Anterior divisions supply flexors while posterior divisions supply extensors. The three posterior divisions join to form the posterior cord ((C5 -T1) ); the anterior divisions of the superior and middle trunks form the lateral cord (C5,6,7) while the anterior division of the inferior trunk continues as the medial cord ( (C8-T1). The cords are named based on their relation to the axillary artery. They pass over the first rib, close to the apex of the lung and continue under the clavicle posterior to the subclavian artery.

Table showing brachial plexus branches, their origin and distribution

Branch	Origin	Distribution
Median Nerve	C6-T1, from medial and lateral cords	Motor to forearm flexors and thenar muscles including pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, lateral 2 lumbricals, opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis Sensory innervation to lateral 3.5 digits on the palmar surface and also including fingertips on the dorsal side of the thumb, index finger, middle finger and lateral half of ring finger. It’s branch anterior interosseous nerve supplies flexor pollicis longus, pronator quadratus and lateral half of flexor digitorum profundus.
Ulnar Nerve	C8-T1, medial cord only	Forearm muscles medial half of the flexor digitorum profundus, flexor carpi ulnaris. Superficial branch supplies palmaris brevis and sensory to medial 1.5 fingers on palmar and dorsal surfaces including the fingertips. Deep branch supplies hypothenar muscles abductor digiti minimi, flexor and opponens digiti minimi; adductor pollicis; deep head of the flexor pollicis brevis; 3rd and 4th lumbricals and all palmar and dorsal interossei muscles.
Musculocutaneous Nerve	C5-7, lateral cord only	Motor to biceps brachii, coracobrachialis, brachialis; continues as the lateral antebrachial cutaneous nerve to supply the skin of lateral upper forearm.
Radial Nerve	C5-T1; posterior cord only	All extensor muscles of the arm and forearm; above the elbow it supplies the triceps, anconeus, brachioradialis and extensor carpi radialis longus; sensory innervation to parts of posterior arm and forearm: at the elbow it divides into superficial and deep branches- superficial supplies dorsal aspect of lateral 3.5 fingers including continuous dorsal hand and also a small area on the palmar aspect of the base of the thumb ; deep supplies supinator and extensor carpi radialis brevis. As the posterior interosseous nerve, it supplies the extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus and brevis and extensor indicis.
Axillary Nerve	C5,6; posterior cord only	Motor to deltoid and teres minor muscles. Sensory supply to shoulder joint and skin over the lateral and posterior part of the deltoid muscle.
Dorsal Scapular Nerve	Direct branch from C5 root	Motor to rhomboids major and minor and levator scapulae.
Long Thoracic Nerve	Direct branch from roots C5,6 and 7	Serratus anterior
Suprascapular Nerve	Branch from upper trunk, C5,6	Supraspinatus and infraspinatus muscles, sensory to shoulder joint
Lateral Pectoral Nerve	Branch from lateral cord, C5,6 and 7	Pectoralis major muscle
Medial Pectoral Nerve	Branch from the medial cord, C8, T1	Pectoralis minor muscle and major
Medial Brachial Cutaneous Nerve	Branch from the medial cord, C8, T1	Sensory to lower, medial arm
Medial Antebrachial Cutaneous Nerve	Branch from the medial cord, C8, T1	Sensory to medial forearm
Nerve to Subclavius	Branch from the upper trunk, C5,6	Subclavius muscle
Phrenic Nerve	Direct from C3,4 and 5 roots (connected to both cervical and brachial plexuses)	Supplies the diaphragm and mediastinal pleura and pericardium
Upper Subscapular Nerve	Branch from posterior cord, C5,6	Subscapularis muscle
Lower Subscapular Nerve	Branch from posterior cord, C5,6	Subscapularis and Teres major muscles
Middle Subscapular or Thoracodorsal Nerve	Branch from posterior cord, C6,7,8	Latissimus dorsi

Brachial plexus lesions

Erb Duchenne palsy

It is due to damage to the superior trunk (C 5 and 6) of the brachial plexus. It may result from birth injuries when the head and shoulder are forcibly separated, disc herniation and traffic accidents. Axillary, suprascapular and musculocutaneous nerves are affected. Waiter’s tip deformity is seen where arm is medially rotated and adducted at the shoulder. Sensory loss in musculocutaneous distribution on lateral forearm.

Klumpke’s palsy

Damage is to the Inferior trunk ( C8 and T1) of the brachial plexus. It may result from birth injuries, when upper limb is forcefully abducted above the head like while grabbing an object while falling, thoracic outlet syndrome. It presents with ulnar nerve palsy, weakness of intrinsic muscles of the hand, loss of sensation on medial forearm and medial 1.5 digits with an ulnar claw hand affecting medial 1.5 digits. Ape hand deformity is seen. Ape hand is an inability to abduct the thumb. It is seen in median nerve lesions with the paralysis of opponens pollicis muscle. Patients may have Horner’s Syndrome.