Brachial Plexus Birth Injuries: Erb's vs. Klumpke's
Nerve Injuries · 10 min read · 2025-10-04
Introduction
Brachial plexus birth injury (BPBI) refers to a spectrum of conditions resulting from trauma to the brachial plexus during delivery. These injuries, though relatively rare, can lead to significant functional impairment in the affected limb. The most common forms are Erb's palsy and Klumpke's palsy, each affecting distinct parts of the brachial plexus and presenting with characteristic clinical signs. As clinical anatomists, understanding the precise anatomical segments involved is paramount for accurate diagnosis, prognosis, and guiding rehabilitation strategies.
The brachial plexus is a complex network of nerves formed by the anterior rami of spinal nerves C5-T1, responsible for innervating the entire upper limb. Its intricate arrangement of roots, trunks, divisions, cords, and terminal branches makes it vulnerable to stretch and compression injuries during difficult deliveries, particularly those involving shoulder dystocia. Differential diagnosis between Erb's and Klumpke's palsy hinges on identifying which nerve roots have been damaged.
Erb's Palsy vs. Klumpke's Palsy: A Clinical Comparison
### Erb's Palsy (C5-C6/C7 Injury)
Erb's palsy, also known as Erb-Duchenne palsy, is the most common form of BPBI, accounting for approximately 90% of cases. It results from damage to the upper trunk of the brachial plexus, primarily involving the C5 and C6 nerve roots. Less commonly, C7 may also be involved.
The mechanism of injury typically involves excessive lateral traction on the neonate's head and neck during delivery while the shoulder is fixed, such as in cases of shoulder dystocia. This stretches or tears the superior trunk where C5 and C6 unite.
Clinical Manifestations:
The classic presentation is the "waiter's tip" hand:
* Shoulder: Adducted and internally rotated (due to paralysis of deltoid, supraspinatus, infraspinatus).
* Elbow: Extended (due to paralysis of biceps and brachialis).
* Forearm: Pronated (due to paralysis of supinator muscles, unopposed pronators).
* Wrist: Often flexed (though wrist extensors may be spared in pure C5-C6).
Muscles affected include the deltoid, supraspinatus, infraspinatus, biceps brachii, brachialis, and brachioradialis. This leads to weakness in shoulder abduction, external rotation, and elbow flexion. Sensory loss is typically along the lateral aspect of the arm, forearm, thumb, and index finger. Phrenic nerve (C3-C5) involvement leading to diaphragmatic paralysis is a possible complication but is less common with pure Erb's.
### Klumpke's Palsy (C8-T1 Injury)
Klumpke's palsy, or Klumpke-Dejerine palsy, is rarer than Erb's, affecting the lower trunk of the brachial plexus (C8 and T1 nerve roots). C7 may also be involved in some cases.
The usual mechanism involves hyperabduction of the arm, often seen when the arm is pulled over the infant's head during a breech delivery or if the arm is extended forcefully during a cephalic delivery. This stretches or avulses the inferior trunk.
Clinical Manifestations:
The hallmark of Klumpke's palsy is the "claw hand" deformity:
* Metacarpophalangeal (MCP) joints: Hyperextended.
* Interphalangeal (IP) joints: Flexed.
This deformity results from paralysis of the intrinsic hand muscles (interossei and lumbricals) and weakness of the long extensors of the digits due to unopposed long flexors. Muscles affected include the intrinsic hand muscles (median and ulnar nerve components from C8-T1), as well as the flexor carpi ulnaris and medial half of the flexor digitorum profundus. Patients will exhibit weakness in wrist and finger flexion, thumb adduction, and opposition. Sensory loss is typically along the medial aspect of the arm, forearm, ring finger, and little finger.
A critical association with Klumpke's palsy is Horner's syndrome. This occurs when the T1 ventral root is avulsed, leading to damage to the sympathetic fibers that join the sympathetic trunk from T1. Symptoms include ipsilateral ptosis (drooping eyelid), miosis (constricted pupil), and anhidrosis (absence of sweating) on the affected side of the face. The presence of Horner's syndrome indicates a more severe injury (preganglionic) and generally carries a poorer prognosis.
Common Pitfall
A common pitfall in diagnosing BPBI is failing to fully assess the sensory component and to miss associated signs like Horner's syndrome. An isolated motor deficit, while indicating a peripheral nerve injury, can be misleading without a complete neurological exam. Forgetting to check for the Moro reflex, asymmetric arm movements, and the presence of a grasp reflex can delay accurate diagnosis. Furthermore, distinguishing between root avulsions (preganglionic, worse prognosis) and ruptures (postganglionic, better prognosis) requires careful electrophysiological studies and imaging, which shouldn't be overlooked in persistent cases.
Summary
Differentiating between Erb's and Klumpke's palsy relies on a thorough understanding of brachial plexus anatomy and associated motor and sensory deficits. Erb's palsy (C5-C6/C7) typically presents with the "waiter's tip" posture affecting shoulder and elbow movements due to upper trunk involvement. Klumpke's palsy (C8-T1), conversely, manifests as a "claw hand" deformity with intrinsic hand muscle weakness and is often associated with Horner's syndrome due to lower trunk involvement. Early and accurate diagnosis is critical for initiating appropriate physical therapy, monitoring recovery, and determining the need for surgical intervention. Clinical anatomists play a vital role in educating practitioners on these distinctions to optimize patient outcomes. Each condition arises from distinct mechanisms of injury and affects specific myotomes and dermatomes, guiding the clinician to the exact level of neural compromise within the intricate network of the brachial plexus.