Erb Palsy

Erb palsy is upper brachial plexus birth injury, with damage to the C5 and C6 roots, and the C7 root in the extended form. It is the commonest pattern of brachial plexus birth injury and gives the typical waiter's tip posture.

It accounts for about 70% of brachial plexus birth injuries, and affects about 1 in 1000 live births. Recovery is usually good: about 90% recover fully if biceps function returns within the first 2 to 3 months.

Risk factors are shoulder dystocia, macrosomia, maternal diabetes, instrumental delivery and breech delivery.

Pathophysiology.

Excess traction on the neck widens the angle between the head and shoulder, which stretches the upper roots. Injury ranges from neurapraxia to rupture, but avulsion is uncommon in pure upper palsy.

Loss of the deltoid, supraspinatus, infraspinatus, biceps and brachialis weakens shoulder abduction, external rotation and elbow flexion. Unopposed internal rotators lead to internal rotation contracture and posterior shoulder subluxation.

• Arm adducted and internally rotated, elbow extended, forearm pronated and wrist flexed (waiter's tip), with an absent Moro response on the affected side.
• Grasp is normal. Finger movement and hand function are preserved.
• Associated clavicle fracture, humeral fracture or phrenic nerve palsy.

Red flags.

• Absent hand grasp or Horner syndrome, indicating extension to lower roots.
• Failure of biceps recovery by 3 months.
• Respiratory difficulty from diaphragm paralysis.

• Clinical examination of muscle groups at birth, 1 month, 3 months and 6 months, with a record of biceps and deltoid strength against gravity.
• Chest X-ray for clavicle, humerus and diaphragm. Shoulder ultrasound or MRI at 3 to 6 months for glenohumeral joint position.
• MRI myelography or EMG if surgery is considered.

Differential diagnosis. Clavicular or proximal humeral fracture, septic arthritis or osteomyelitis of the shoulder, cervical spinal injury and cerebral palsy.

• Physiotherapy: gentle passive range of movement for the shoulder (external rotation and abduction), elbow and wrist from about 2 weeks of age, taught to parents and repeated with each nappy change, with night splinting as advised.
• Review monthly for the first 3 months. If the biceps is not antigravity by 3 months, refer to a brachial plexus surgeon for nerve reconstruction, which is done at 3 to 6 months of age.
• Botulinum toxin to internal rotators in infants with early contracture, and surgery for shoulder subluxation or fixed deformity.

Monitoring. Muscle strength, shoulder joint position by ultrasound or MRI at 3 to 6 months, and function until growth is complete.

Referral and escalation. Refer to a specialist brachial plexus clinic by 4 to 6 weeks if recovery is incomplete, and urgently if biceps shows no antigravity function by 3 months.