I personally dont know this but this is what I found online
Erb's palsy is a form of brachial plexus palsy.
Erb's palsy leads to a weakness of a newborn baby's arm. It is caused by a stretch injury to the brachial plexus (BRAY-key-el PLEK-sis). The brachial plexus is a network of nerves near the neck that give rise to all the nerves of the arm. These nerves provide movement and feeling to the arm, hand, and fingers.
One or two of every 1,000 babies have this condition. Most infants with brachial plexus birth palsy will recover both movement and feeling in the affected arm. Parents must be watchful and active participants in the treatment process to ensure maximum functional recovery.
Anatomy
This infant has brachial plexus birth palsy. The arm is rotated inwardly (internal rotation) toward the body and the infant cannot move the arm effectively.
(Courtesy of Texas Scottish Rite Hospital for Children)The brachial plexus is formed as the nerves to the arm, hand, and fingers pass from the spinal cord between the bones (vertebrae) of the neck and go into the arm. Along the side of neck, these nerves merge together. From there, they branch out to form a "highway system," or "plexus," of nerves.
This system of nerves then travels below the collarbone (clavicle) and spreads out into the arm. The nerves that go to the shoulder lie higher in the neck than those that travel to the hand and fingers. Nerves that provide feeling to the hand and fingers lie lower in the neck, just above the chest.
There are many nerves in the brachial plexus. Each nerve contains many little nerve fibers with layers of "insulating" tissue.
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Cause
Brachial plexus stretch injuries in newborns usually occur during a difficult delivery, such as with a large baby, a breech presentation, or a prolonged labor. It may also happen when the person assisting the delivery must deliver the baby quickly and exert some force to pull the baby from the birth canal. If one side of the baby's neck is stretched severely, the nerves may also be stretched, causing the injury.
Most often, it is the upper nerves that are affected. This brachial plexus birth palsy is known as Erb's palsy. The infant may not be able to move the arm, but may be able to move the fingers. If both the upper and lower nerves are stretched, the condition is usually more severe than just Erb's palsy. This is called a "global," or total, brachial plexus birth palsy.
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Symptoms
In general, there are four types of nerve injuries. One infant may have one or more types of injury.
A stretch injury that "shocks," but does not tear, the nerve is the most common type. This is called a neurapraxia (new-rah-PRAK-see-ah). Normally, these injuries heal on their own, usually within three months. Neurapraxia is not limited to infants. It can happen in adults as well. For example, when it happens to football players who are injured during play, they call this '"burners and stingers.''
A stretch injury that damages some of the nerve fibers may result in scar tissue. This scar tissue presses on the remaining healthy nerve. This condition is called a "neuroma." Some, but not total, recovery usually occurs.
A stretch injury that causes the nerve to be torn apart (ruptured) will not heal on its own. A rupture happens when the nerve itself is torn.
The fourth type of injury, an "avulsion," happens when the nerve is torn from the spinal cord. Nerve ruptures and avulsions are the most serious types of nerve injury. It may be possible to repair a rupture by "splicing" a donor nerve graft from another nerve of the child. It is not possible to repair an avulsion from the spinal cord. In some cases, it may be possible to restore some function in the arm by using a nerve from another muscle as a donor.
The symptoms of a nerve injury (loss of feeling and partial or complete paralysis) are the same, regardless of the type of injury. It is the severity of the injury that affects both treatment decisions and the extent of recovery possible.
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Diagnosis
This toddler has brachial plexus birth palsy. It has caused a weakness of the right arm. The child is unable to raise the right arm overhead when reaching for an object.
(Courtesy of Texas Scottish Rite Hospital for Children)A pediatrician will usually be the one to make the diagnosis of a brachial plexus palsy injury, based on weakness of the arm and physical examination. A doctor may order an X-ray or other imaging study to learn whether there is any damage to the bones and joints of the neck and shoulder. The doctor may also do some tests to learn whether any nerve signals are present in the muscle of the upper arm. These tests may include an electromyogram (EMG) or a nerve conduction study (NCS).
Because most newborns with brachial plexus birth palsy recover on their own, the baby will be re-examined frequently to see if the nerves are recovering. It may take up to two years for complete recovery. During this time, the parent will be taught how to do exercises with the baby to protect the soft joints and to keep the baby's arm in good condition.
Sometimes, the affected arm is noticeably smaller than the unaffected arm. This occurs, in part, because the arm is not used as much. This also occurs because normal nerves do have an effect on growth. Although the size difference is permanent, the arm will still grow until the child stops growing.
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Treatment
Nonsurgical Treatment
Because a baby cannot move the affected arm alone, it is important that parents take an active part in keeping the joints limber and the functioning muscles fit. Daily physical therapy and range of motion exercises, done as often as possible during the day, begin when the baby is about three weeks old. The exercises will maintain the range of motion in the shoulder, elbow, wrist, and hand. This will prevent the joint from becoming permanently stiff, a condition called a joint contracture.
Surgical Treatment
Weakness of the left shoulder, arm, and hand persist in this young child with brachial plexus birth palsy.
(Courtesy of Texas Scottish Rite Hospital for Children)If there is no change over the first three to six months, the doctor may discuss exploratory surgery on the nerves to improve the potential outcome (prognosis). Nerve surgery will not restore normal function, and is usually not helpful for older infants. Because nerves recover very slowly, it may take several months, or even years, for nerves repaired at the neck to reach the muscles of the lower arm and hand.
Many children with brachial plexus injuries will continue to have some weakness in the shoulder, arm, or hand. There may be surgical procedures that can be performed at a later date that might improve function.
The doctor will discuss the various treatment options and make a specific recommendation based on each child's individual situation. Do not hesitate to ask questions. There is much that parents can do to help ensure a good return of function.
Children are very adaptable. Parents should be supportive and encouraging, focusing on what the child can do. This will help a child develop a healthy sense of self-esteem and compensate for any limitations in function