AnatomyUpper limbhigh-yield
Brachial plexus and the classic nerve lesions
The roots, trunks and cords of the brachial plexus and the classic palsies with their motor loss, sensory loss and deformity in one table.
6 min read · updated 2026-08-24
The scaffold: Real Texans Drink Cold Beer
Roots (C5–T1) → Trunks (upper C5-6, middle C7, lower C8-T1) → Divisions (behind clavicle) → Cords (lateral, posterior, medial — named by position relative to the axillary artery) → Branches.
- Lateral cord → musculocutaneous + lateral root of median
- Medial cord → ulnar + medial root of median
- Posterior cord → axillary + radial (the "posterior = extensors/abductor" cord)
Root avulsion lesions
| Lesion | Roots | Mechanism | Picture |
|---|---|---|---|
| Erb–Duchenne palsy | C5–C6 (upper trunk) | Shoulder pulled down (birth, fall on shoulder) | Waiter's tip / porter's tip — arm adducted, internally rotated, forearm pronated |
| Klumpke palsy | C8–T1 (lower trunk) | Arm pulled up (grabbing to break a fall) | Claw hand + often Horner syndrome (T1 sympathetics) |
Peripheral nerve palsies
| Nerve (root) | Motor loss | Sensory loss | Deformity |
|---|---|---|---|
| Axillary (C5-6) | Deltoid (abduction), teres minor | Regimental badge over deltoid | Flat shoulder, cannot abduct 15°–90° |
| Radial (C5-T1) | Wrist & finger extensors, triceps | Dorsum of 1st web space | Wrist drop |
| Median (C6-T1) | Forearm flexors, LOAF thenar muscles | Lateral 3½ fingers, palm | Ape/simian hand; "hand of benediction" on trying to make a fist (high lesion) |
| Ulnar (C8-T1) | Interossei, medial 2 lumbricals, hypothenar | Medial 1½ fingers | Ulnar claw — worse in low lesion (ulnar paradox) |
The exam traps
- Claw is worse the more DISTAL the ulnar lesion — the ulnar paradox, because in a high lesion FDP to the ring/little fingers is also paralysed, so the DIP flexion pull is lost.
- Erb's = "waiter's tip", Klumpke's = "claw + Horner" — do not swap them.
- Radial nerve in the spiral groove spares triceps (branches leave proximally) → wrist drop with triceps intact = mid-shaft humerus fracture.
- LOAF (Lateral 2 lumbricals, Opponens, Abductor pollicis brevis, Flexor pollicis brevis) = the median-supplied thenar muscles.
Anchor: Posterior cord = axillary + radial (abduct + extend). Upper trunk C5-6 = Erb's waiter's tip; lower trunk C8-T1 = Klumpke's claw with Horner's.
Sources
- Gray's Anatomy for Students, 4e
- BD Chaurasia's Human Anatomy, Volume 1 (Upper Limb & Thorax), 8e