Q1 LONG ANSWER 10M ★ High-yield

Describe the formation, parts and branches of the brachial plexus. Add a note on its injuries.

Anatomy · 1st Professional — Pre-Clinical

The brachial plexus is a network of nerves formed by the ventral rami of C5, C6, C7, C8 and T1, supplying the upper limb.

Prefixed plexus — contribution from C4; postfixed — contribution from T2
Arranged in five stages: Roots, Trunks, Divisions, Cords, Branches
Mnemonic — "Read That Damn Cadaver Book"

Stage	Location
Roots and trunks	Posterior triangle of the neck, between scalenus anterior and medius
Divisions	Behind the clavicle
Cords and branches	Axilla

Cord	Formed by	Root value
Lateral	Anterior divisions of upper and middle trunks	C5, C6, C7
Medial	Anterior division of the lower trunk	C8, T1
Posterior	Posterior divisions of all three trunks	C5–T1

Cord	Branches
Lateral	Lateral pectoral; musculocutaneous; lateral root of median
Medial	Medial pectoral; medial cutaneous nerve of arm; medial cutaneous nerve of forearm; ulnar; medial root of median
Posterior	Upper subscapular; Thoracodorsal (nerve to latissimus dorsi); Lower subscapular; axillary; radial

Mnemonic for the posterior cord — "ultra": Upper subscapular, Lower subscapular, Thoracodorsal, Radial, Axillary
Mnemonic for the lateral cord — "LML"; for the medial cord — "MMMUM"

The plexus enters the axilla through the cervico-axillary canal
In the neck it lies in the interscalene groove, between scalenus anterior and scalenus medius, with the subclavian artery
The subclavian vein lies anterior to scalenus anterior, separated from the plexus — the anatomical basis of the supraclavicular approach
The cords are named by their relation to the second part of the axillary artery

C5 and C6 roots, at Erb's point where they unite
Cause — undue increase in the angle between the neck and shoulder: birth injury with shoulder dystocia, a fall on the shoulder, or traction on the arm
Muscles paralysed — deltoid, supraspinatus, infraspinatus, biceps, brachialis, brachioradialis, supinator
Deformity — the "policeman's tip" or "waiter's tip" hand:Arm adducted (deltoid, supraspinatus paralysed)
Medially rotated (infraspinatus, teres minor paralysed)
Elbow extended (biceps, brachialis paralysed)
Forearm pronated (supinator, biceps paralysed)
Sensory loss over the lateral side of the arm and forearm

C8 and T1 roots
Cause — undue abduction of the arm: a breech delivery with the arm extended, clutching at something when falling, or a cervical rib
Muscles paralysed — all the small muscles of the hand, and the long flexors
Deformity — claw hand: hyperextension at the metacarpophalangeal joints with flexion at the interphalangeal joints
HORNER syndrome may accompany it — ptosis, miosis, anhidrosis and enophthalmos — because the T1 sympathetic contribution is damaged
Sensory loss along the medial side of the forearm and hand

Winging of the scapula — injury to the long thoracic nerve (serratus anterior), classically after axillary surgery or radical mastectomy; the medial border of the scapula projects when pushing against a wall
Brachial plexus block — performed by the interscalene, supraclavicular, infraclavicular or axillary route for upper limb surgery
Cervical rib compresses the lower trunk and the subclavian artery → thoracic outlet syndrome, with wasting of the small hand muscles and vascular signs
Erb palsy has a better prognosis than Klumpke, and most birth injuries recover with physiotherapy
The posterior cord supplies all the extensors and the lateral and medial cords the flexors — a consequence of the limb bud rotating during development

All questions in Upper Limb