Erb palsy, or Erb-Duchenne paralysis, is one of most common neurological birth injuries. It is caused by injury to brachial plexus which form of C5, C6, C7, C8, and T1. These nerves network from the spine and pass through the cervicoaxillary canal in the neck and the ribs and emerge into the axilla. Brachial plexus is a musculocutaneous nerve that innervates all muscles of the upper limb except the trapezius muscle which is supplied by accessory nerve CN XI.
Erb palsy relates to an injury of C5 and C6. Traction of the shoulder can injure the brachial plexus (particularly C5 and C6) during delivery. It usually occurs in macrosomia infants who needed to be pulled from the birth canal. This maneuver causes stretching of the brachial plexus which may injure it. Other causes that lead to forced pulling of the shoulder include breech delivery, multipara mother, maternal obesity, maternal diabetes, or vacuum and forceps delivery. Erb palsy also may occur in cesarean section.
It is a common birth injury with estimated prevalence ranges of 0.2 to 2.0 of every 1000 births. It causes significant arm weakness that affects 0.4 to 5 in 10,000 births.
C5 and C6 of the brachial plexus join to form the upper trunk. Each trunk later is divided into anterior and posterior divisions which further divided to create the cords then branches to supply the muscle of the upper limb. Injuries to the brachial plexus range from mild to severe. The degree of severity can be defined as neuropraxic, axonotometric, or neurometric. A neuropraxic injury is the least severe. It is reversible and heals without any complication. Axonometric lesions involve disruption of axon and myelin sheath. Recovery of axonometric lesions depend on the level of lesion, and it may take months to heal with proper treatment including physiotherapy. Neurometric is the worst prognosis, as the lesion causes irreversible damage affecting the axon, myelin sheath as well as the supporting structures through the nerve. The proximal end of nerve tries to regenerate by forming a neuroma.
Erb palsy presents with a history of birth injury. The neonate presents with adduction at the shoulder, internal rotation of the upper arm, pronation of the forearm, an outward direction of the palm, giving the appearance of "waiter's tip posture." Moro reflex is absent. Meanwhile, the grasp reflex is present which differentiates it from another brachial nerve palsy, Klumpke palsy (C7, C8, and T1). The neonate may have impaired sensation on the outer side of the arm and/or phrenic nerve palsy (C3, C4, and C5a).
Erb palsy is a disorder of clinical diagnosis, but some interventions can confirm it. An X-ray of the baby's shoulder can exclude any fractured bone or problems with the shoulder or elbow joints. Electromyography (EMG) results can estimate and record the electrical activity of the muscle. Nerve conduction studies (NCS) can measure the time required for the electrical stimulus to move through a particular nerve. An MRI can exclude any cancer or tumor that may affect the brachial plexus. CT myelography works by injecting the contrast material to give detail of neonate spinal cord and nerve root.
Hydrotherapy is a form of physical therapy used because of the anti-gravity environment. It minimized the stress on the musculoskeletal frame, allowing the neonate to move with less pain and at the same time strengthening muscles and reducing spasms. Paralyzed muscles relax in the opposite position of the waiter's tip posture by abduction at the shoulder, external rotation of the arm, and supination of the forearm. Physiotherapy begins after two weeks. Surgical intervention, nerve graft, or nerve decompression is the next step if there is no response after 3 to 6 months.
Erb palsy should be differentiated from other brachial plexus injuries such as Klumpke injury due to birth. In case of Klumpke injury, there is paralysis of the forearm and hand muscle due to injury in C7, C8, and T1. The neonate presents with "claw hand" due to injury to the flexor muscles of the wrist, fingers, and forearm pronator. It also affects the intrinsic muscles. The neonate injury also may be associated with Horner syndrome due to the affection of T1 which will affect the dilators of iris and elevators of the eyelid.
Denervated muscle changes begin at the moment of injury, and without reinnervation, becomes irreversible at 18 to 24 months. These time-sensitive, irreversible changes are the scientific basis for early management recommendations
Neglected cases may lead to 20% to 30% permanent deficit of the nerve function.
The timing of rehabilitation is controversial. The effectiveness of rehabilitation timing to the functional outcomes of the patient can be evaluated using Modified Mallet Scale (MMS). Rehabilitation is the best choice of treatment before surgical procedures in mild to a moderate degree regardless of age.
Several paradigms may bring disadvantage to the neonate including “all neonatal brachial plexus palsy recovers,” “wait a year to see if recovery occurs," and "do not move the arm." These approaches by far lead to 20% to 30% deficit of total function of the nerves affected. Thus early recognition and interference are necessary beginning with proper diagnosis and including rehabilitation and, in certain cases, surgical intervention.
Erb palsy requires multidisciplinary care involving the parents, primary care physicians, nerve surgeons, physiatrists, and occupational and physical therapists.
About 10% of infants with neonatal brachial plexus palsy fail to gain functional recovery. An intervention for this group is needed and includes the resection of neuroma-in-continuity (NIC) and surgical nerve reconstruction to solve the problem. Formation of NIC inhibits functional recovery of neonatal brachial plexus palsy. A series of NIC tissue samples are obtained and analyzed using an array of immunohistochemical techniques. It is discovered that NIC contained multiple focal globular areas with markedly diminished myelination. This focal area, focal myelin deficits (FMDs), includes Schwann cells that wrap axons in normal configuration but do not form the myelin sheath. Axon segments in FMDs also had disturbed nodes of Ranvier. The axon in FMDs may be a pathobiological basis for explaining conduction blocks in neonatal brachial plexus that leads to failure of functional recovery. Otherwise, this mechanism needs further studies.