What is Erb's palsy?
Erb's palsy (Erb–Duchenne palsy) is a lesion of the upper trunk of the brachial plexus, formed by the C5 and C6 roots. StatPearls describes it as most commonly an upper brachial plexus birth injury, with occasional extension to C7, causing flaccid weakness of the affected arm. When C7 is also involved the pattern is called extended Erb's palsy; Chater and colleagues report C7 involvement in about half of cases.
It is the commonest pattern of neonatal brachial plexus palsy (NBPP) — the preferred modern term, which covers upper (Erb), lower (Klumpke) and total plexus injuries. Erb's palsy accounts for roughly 90% of NBPP, and upper plexus injuries are about 20 times more frequent than lower ones (Adams and Victor). The global incidence of NBPP is 0.38–5.1 per 1,000 live births.
What causes Erb's palsy?
The classic mechanism is excessive lateral traction that pulls the fetal head and shoulder in opposite directions, forcibly increasing the angle between the neck and shoulder and stretching the upper roots, which take the strain first. The nerve can be stretched (neurapraxia), partly disrupted (axonotmesis), ruptured, or avulsed from the spinal cord in the worst cases.
| Strength of association | Risk factors |
|---|---|
| Strong | Humeral fracture, shoulder dystocia, clavicular fracture |
| Moderate | Pre-existing maternal diabetes, forceps or vacuum delivery, episiotomy, fetal or birth asphyxia, macrosomia (> 4.5 kg), large for gestational age |
Shoulder dystocia is the textbook association, but not every case follows obvious traction — the Canadian review notes that injury can be sustained in utero and during descent as well as at expulsion. Breech deliveries typically produce the upper (C5–C6) pattern (Williams Obstetrics).
Erb's palsy is not only an obstetric injury. In older children and adults the same neck–shoulder distraction occurs with falls onto the shoulder, motorcycle and road accidents, contact-sport tackles, prolonged heavy backpack use and stretch during surgical positioning (StatPearls). Schwartz's Surgery also links C5–C6 injury to glenohumeral dislocation.
Which muscles are paralysed and why does the arm take the waiter's tip position?
The C5–C6 fibres supply the shoulder abductors and lateral rotators and the elbow flexors and supinators. Their loss — and the unopposed pull of the intact muscles — produces the posture.
| Muscle | Nerve (from upper trunk fibres) | Action lost | Resulting position |
|---|---|---|---|
| Deltoid | Axillary | Shoulder abduction | Arm adducted, hangs by the side |
| Supraspinatus | Suprascapular | Initiation of abduction | Arm adducted |
| Infraspinatus (± teres minor) | Suprascapular (teres minor: axillary) | Lateral (external) rotation | Arm medially rotated |
| Biceps brachii (± brachialis) | Musculocutaneous | Elbow flexion, supination | Elbow extended, forearm pronated |
| Brachioradialis (supinator longus) | Radial | Elbow flexion (mid-prone) | Elbow extended |
The result is the 'waiter's tip' (or 'porter's/bellhop's tip') position: the arm hangs adducted and medially rotated at the shoulder, the elbow is extended, the forearm pronated, and the wrist and fingers are often flexed — like a waiter discreetly holding out a palm for a tip. Nelson describes the infant as unable to abduct the arm at the shoulder, externally rotate it or supinate the forearm, with painless adduction, internal rotation and pronation.
Which reflexes and sensations are lost in Erb's palsy?
- Moro reflex — absent (asymmetric) on the affected side, because the arm cannot abduct and extend.
- Grasp reflex — present, because the hand (C8–T1) is spared. An absent grasp points to a lower or total plexus lesion.
- Biceps and brachioradialis reflexes (C5–C6) — absent or reduced.
- Sensation — sometimes reduced over the lateral aspect of the proximal arm (C5 dermatome, over the deltoid); sensory loss is often hard to demonstrate in a newborn.
- Phrenic nerve (C3–C5) can be injured alongside, causing diaphragmatic paralysis with respiratory distress; an elevated hemidiaphragm on chest X-ray is the clue.
What is Erb's point and how is the brachial plexus organised?
Erb's point is where the C5 and C6 roots join to form the upper trunk. As a surface landmark it lies about 2–3 cm above the clavicle at the posterior border of the sternocleidomastoid. It is the first point at which the plexus is tethered proximally yet free to be stretched distally, which is why traction concentrates here — and why a direct blow above the clavicle (a tackle, for example) can injure it.
| Level | Components | Location | Key branches at this level |
|---|---|---|---|
| Roots | Ventral rami of C5, C6, C7, C8, T1 | Interscalene triangle (between anterior and middle scalenes), with the 3rd part of the subclavian artery | Dorsal scapular (C5, rhomboids); long thoracic (C5–C7, serratus anterior) |
| Trunks | Upper (C5+C6), middle (C7), lower (C8+T1) | Root of the neck, above the clavicle (Erb's point on the upper trunk) | From the upper trunk: suprascapular nerve and nerve to subclavius |
| Divisions | Each trunk splits into anterior (flexor) and posterior (extensor) divisions | Behind the middle of the clavicle | None |
| Cords | Lateral (anterior divisions of upper + middle), medial (anterior division of lower), posterior (all three posterior divisions) | Axilla — named by their relation to the 2nd part of the axillary artery | Lateral: musculocutaneous, lateral root of median. Medial: ulnar, medial root of median. Posterior: axillary, radial, subscapular and thoracodorsal nerves |
Localising tip: the dorsal scapular and long thoracic nerves leave the roots, before Erb's point. If an Erb-pattern weakness also involves the rhomboids (or serratus anterior), the lesion is very proximal — at root level, raising the possibility of avulsion (Adams and Victor).
How does Erb's palsy differ from Klumpke's palsy?
Klumpke's palsy is an isolated lower trunk (C8, T1) injury, sometimes with C7. It follows hyper-abduction / upward traction of the arm — for example upward force on the arm during delivery, or a hyper-abduction injury in an adult — and compression by an apical (Pancoast) lung tumour can produce the same picture in adults. It is much rarer than Erb's palsy.
| Feature | Erb's (Erb–Duchenne) | Klumpke's |
|---|---|---|
| Roots / trunk | C5–C6, upper trunk (± C7) | C8–T1, lower trunk |
| Mechanism | Head and shoulder forced apart (neck–shoulder angle widened) | Arm hyper-abducted / pulled upward; Pancoast tumour |
| Muscles | Deltoid, supraspinatus, infraspinatus, biceps, brachioradialis | Intrinsic hand muscles (lumbricals, interossei, thenar, hypothenar), long finger flexors |
| Deformity | Waiter's tip — adducted, medially rotated, elbow extended, forearm pronated | Claw hand — MCP joints extended, IP joints flexed |
| Newborn reflexes | Moro absent on that side; grasp present | Grasp absent (hand paralysed) |
| Sensory loss | Lateral upper arm (C5) | Medial forearm and hand (C8–T1) |
| Horner syndrome | No | Possible — ipsilateral (T1 sympathetic outflow) |
| Prognosis | Good — most recover | Worse when Horner signals root avulsion |
The Horner syndrome of Klumpke's palsy — ptosis, miosis and anhidrosis on the same side — appears because the preganglionic sympathetic fibres to the face leave the cord with the T1 root. See Horner syndrome for the three-neuron pathway. In any brachial plexus birth injury, Horner syndrome implies sympathetic chain involvement and root avulsion, and therefore a poor prognosis for spontaneous recovery.
How is neonatal brachial plexus palsy classified and what is the prognosis?
| Group | Roots | Clinical picture |
|---|---|---|
| I | C5–C6 | Absent shoulder abduction, external rotation and elbow flexion — classic Erb's |
| II | C5–C7 | Group I plus absent wrist and digital extension — extended Erb's |
| III | C5–T1 | Complete flaccid paralysis — flail arm |
| IV | C5–T1 + sympathetic chain | Flail arm with Horner syndrome |
Prognosis is good for the upper pattern. Reported recovery in Erb's palsy ranges from 69% to 95% (Shah et al.), and Chater and colleagues quote complete resolution within the first year in 80–96%. In contrast, almost 80% of children with global C5–T1 injuries still have deficits at 18 months. Radiopaedia notes that about 70% of cases are transient and recover with physiotherapy alone. Poor prognostic signs are a total (flail) plexus lesion and Horner syndrome, which signals root avulsion; recovery that is still incomplete at 1 month warrants specialist referral.
How is Erb's palsy managed?
- Examine and exclude mimics — clavicle or humerus fracture (pseudoparalysis), and check the diaphragm (chest X-ray) and eye (Horner).
- Early physiotherapy — gentle passive and active range-of-motion exercises and positioning from the first weeks to prevent shoulder internal-rotation and elbow contractures while the nerve recovers.
- Refer early — the Canadian Paediatric Society advises referral to a multidisciplinary brachial plexus team if recovery is incomplete by 1 month of age (for example, no active elbow extension at 1 month).
- Nerve surgery — for infants who do not recover, evidence supports nerve repair (grafting or nerve transfer) from as early as 3 months, with low complication rates.
- Secondary procedures — later muscle-rebalancing procedures around the shoulder for residual weakness or glenohumeral deformity (Schwartz).
- How it's asked: image of the waiter's tip posture → name the roots (C5–C6) or the trunk (upper).
- Muscle questions: which muscle is spared in Erb's palsy? (intrinsic hand muscles / long finger flexors).
- Reflex questions: asymmetric Moro with intact grasp.
- Erb's point — the junction of C5 and C6 forming the upper trunk.
- Klumpke + Horner pairing, and claw hand = C8–T1.
Practise previous papers at NEET PG Anatomy PYQs and NEET PG Pediatrics PYQs, and see the most repeated topics.