Erb's Palsy

Introduction

Introduction to Erb’s Palsy

Erb’s palsy, also known as Erb–Duchenne palsy, is a paralysis of the muscles supplied by the C5 and C6 nerve roots, and occasionally C7, resulting from an injury to the upper trunk of the brachial plexus. It is the most common form of obstetric brachial plexus palsy, but also occurs in adults following high‑energy trauma such as motorcycle accidents or falls that forcibly separate the neck from the shoulder. The characteristic clinical picture—a waiter’s tip posture of the affected arm—reflects the selective weakness of shoulder abductors and external rotators, elbow flexors, and forearm supinators, with preservation of hand and wrist function.

This module covers the anatomical basis, causes, clinical features, assessment, prognostic factors, and management of Erb’s palsy.

Study

1. Anatomical Basis

The upper trunk of the brachial plexus is formed by the union of the C5 and C6 anterior rami, with occasional contribution from C4. It gives rise to the suprascapular nerve (supplying supraspinatus and infraspinatus), the nerve to subclavius, and then divides into anterior and posterior divisions. The anterior division contributes to the lateral cord, which ultimately forms the musculocutaneous nerve (biceps, brachialis, coracobrachialis) and the lateral root of the median nerve. The posterior division joins the posterior cord, which gives off the axillary nerve (deltoid, teres minor) and radial nerve (extensor muscles of the arm and forearm). Thus, an upper trunk lesion paralyses the shoulder abductors, external rotators, elbow flexors, and supinators.

Importantly, the long thoracic nerve (C5, C6, C7) and dorsal scapular nerve (C5) are branches from the roots themselves and may also be affected, causing winging of the scapula and weakness of rhomboids. The nerve to subclavius is also from the upper trunk.

2. Mechanisms of Injury

In obstetric brachial plexus palsy, Erb’s palsy results from excessive lateral traction on the head during delivery when the shoulder is impacted behind the maternal symphysis pubis (shoulder dystocia). The C5 and C6 roots are stretched or torn. Risk factors include large birth weight, maternal diabetes, forceps delivery, and prolonged second stage of labour. In adults, the injury typically occurs when the head is forced away from the ipsilateral depressed shoulder, such as in motorcycle accidents or falls. The injury can range from neuropraxia (transient conduction block) to complete root avulsion from the spinal cord.

3. Clinical Features

The classic deformity is the 'waiter’s tip' posture: the arm hangs adducted and internally rotated at the shoulder, the elbow is extended, the forearm is pronated, and the wrist and fingers are flexed. This posture results from unopposed action of the pectoralis major and latissimus dorsi (adductors and internal rotators), and the long flexors of the forearm (median and ulnar nerves, which are spared).

Specific motor deficits include loss of shoulder abduction (supraspinatus, deltoid), external rotation (infraspinatus, teres minor), elbow flexion (biceps, brachialis), and supination (biceps, supinator). The biceps reflex is absent. Sensory loss occurs over the lateral aspect of the shoulder (axillary nerve) and the lateral forearm (musculocutaneous nerve). The grasp reflex in neonates is preserved because C8, T1 hand muscles are intact. In some cases, there may be an associated phrenic nerve palsy (C3, C4, C5) causing respiratory distress, or Horner’s syndrome if the T1 root is involved (indicating a more severe injury).

4. Diagnostic Evaluation

Diagnosis is primarily clinical, based on the characteristic posture and motor deficits. Imaging, including plain radiographs to rule out clavicle or humeral fractures, and ultrasound or MRI of the brachial plexus, can help define the extent of injury. Electromyography (EMG) and nerve conduction studies are useful after 3–4 weeks to assess the severity and location of the lesion. The presence of pseudomeningoceles on MRI or CT myelography indicates root avulsion.

5. Prognosis and Management

The prognosis of Erb’s palsy depends on the severity and whether the lesion is preganglionic or postganglionic. In obstetric cases, approximately 70–90% recover spontaneously with conservative management. In adults, the prognosis is more guarded. Physiotherapy is the cornerstone of early management to maintain passive range of motion and prevent contractures. Splinting may be required to position the arm. Surgical intervention is indicated if there is no clinical or EMG evidence of recovery by 3–6 months. Options include nerve grafting (using sural nerve) or nerve transfers (e.g., spinal accessory nerve to suprascapular nerve, intercostal nerves to musculocutaneous nerve, or Oberlin transfer – ulnar nerve fascicle to biceps motor branch). Late reconstructive procedures include tendon transfers and joint arthrodesis.

Summary

Summary of Erb’s Palsy

Erb’s palsy is an upper trunk brachial plexus injury affecting C5 and C6 nerve roots, causing the classic waiter’s tip deformity with loss of shoulder abduction, external rotation, elbow flexion, and supination. It is most commonly an obstetric injury from shoulder dystocia, but also occurs in adults from traction. The hand and wrist function are preserved. Diagnosis is clinical, and management ranges from conservative physiotherapy to nerve surgery and tendon transfers. Understanding the precise anatomy of the upper trunk is essential for accurate diagnosis and targeted reconstruction.