Five large nerves leave the spinal cord from positions between the cervical vertebrae (bones in the neck) and come together to form the brachial plexus at the side of the neck. Nerves positioned slightly higher in the plexus branch out to innervate the shoulder, while nerves in the lower parts of the plexus pass behind the collarbone and down into the arm, with the lowest travelling the length of the arm to innervate the hand and fingers.

The most common brachial nerves affected during birth are the upper nerves. The damage to one or more of the nerves results in a loss of movement in the shoulder, the extent of which will depend on how many nerves have been injured and the severity of the injury. If lower nerves are also stretched the loss of movement will extend further down the arm.

The injury can range from a relatively mild neuropraxia that stretches but does not tear the nerve, to a complete avulsion where the nerve has been torn away from the spinal cord. The degree of recovery from Erb’s palsy depends largely on the severity of the original injury.

Causes:
A difficult delivery is the usual cause for Erb’s palsy in an infant. Several situations can result in brachial nerves being stretched, for example, a breech presentation, extended labor, or a complication during delivery that requires the baby to be delivered swiftly from the birth canal. Any circumstance that causes the neck to be stretched may damage the brachial nerves.

Other situations where the brachial plexus can be damaged are:

• A trauma to the side of the neck, for instance a motor vehicle accident, fall or heavy blow
• A stretch injury sustained while participating in a sport
• An attempt to reduce a dislocated shoulder

Symptoms:

• Typically an infant will have one arm that hangs down by the side, with the elbow pointing out, the forearm rotated in towards the chest, and the hand turned backwards (a position sometimes described as ‘waiter’s tip’)
• Partial or total lack of muscle control in the shoulder and perhaps the arm
• Weakness in the arm
• Numbness in the arm
• Atrophy of the arm muscles
• Possible drooping of the eyelid on the affected side
• Pain, possibly severe, at the time of injury, typically described as burning, crushing or pins and needles

Diagnosis:
If the patient is a baby, the pediatrician is likely to make the diagnosis. He or she will examine the baby’s neck, shoulder, and arm and evaluate the degree of weakness. X-rays may be taken to view the structures of the neck and shoulder. MRI (magnetic resonance imaging) or CT (computed tomography) scans can be used to assess the amount of damage to the nerves. Nerve function tests, which may include EMG (electromyogram) or NCS (nerve conduction study), are normally only performed after a three month period of observation.

Treatment:
Most cases of Erb’s palsy in newborns resolve successfully on their own, with time and dedicated physical therapy. Regular check-ups with the doctor would be required to monitor the recovery. Physical therapy, which is critical to recovery, would consist of massage, range of motion exercises, performed several times a day to prevent permanent stiffness in the shoulder, arm, and wrist, and strengthening exercises. Therapy might also include sensory stimulation as Erb’s palsy can result in a loss of sensation in the arm. Exercises should be done only under instruction from the doctor or physical therapist.

Older patients are generally also treated with a period of observation for the first three months. Some recovery of function often occurs spontaneously. Any pain would be treated, and physical therapy undertaken.

If, after the observation period, no improvement in the condition was evident, exploratory surgery might be considered. Further surgery that might improve function could be considered at a later date. Surgical options include nerve transplants or muscle adaptions. As with all surgery, there are both risks and benefits to be carefully evaluated before a decision should be made. A successful outcome after surgery is not guaranteed and it can take several months for nerves, repaired in the neck, to finally reach the lowest affected parts of the arm. Nerve regeneration takes place at a rate of about one inch every month.

Prognosis:
Recovery depends on the extent of the original injury and, to a large degree, on the age of the patient. Neuropraxia is relatively mild and most cases spontaneously recover full function of the arm. In more serious cases of Erb’s palsy, where nerves have been ruptured or avulsed, regaining full use of the arm is less certain. Generally, the recovery of range of motion in children under one year old is likely. Older children will usually have some lasting functional loss and permanent arm weakness. Stiffness in the shoulder may restrict the child’s ability to raise the arm above shoulder height.

Nerves have a certain affect on growth, so a child with a lasting disability may have one arm smaller and weaker than the other, with a degree of muscle atrophy. The arm will continue to grow, but at a slower rate than the unaffected arm. He or she may also suffer from a reduced ability to heal in the affected arm, so care must be taken to keep any scratches or cuts clean. Damage to the circulatory system also means that the arm cannot adequately regulate its temperature. Again, care must be taken to make sure that the arm does not become too cold during the winter months.