An Obstetrical Brachial Plexus Injury, sometimes referred to as a Brachial Plexus Birth Palsy, most typically occurs during the delivery process.  There is, however, tremendous controversy as to the exact cause.  Frequently there is a shoulder dystocia as the baby’s shoulder gets stuck behind the mother’s pubic bone.  Traction occurs as the head is delivered through the birth canal and the shoulder is impacted behind the symphysis pubis.  This traction, or stretching, results in damage to the brachial plexus.  There are approximately 1 to 2 injuries to the brachial plexus for every 1,000 births. Roughly 60% of these injuries will resolve themselves to near-complete recovery within the first two weeks of life. About 10-15% of children injured at birth will eventually need primary surgical intervention. Of those children that recover well enough in the 3-6 month window to avoid primary surgery, around 60% of them may eventually need secondary surgery.

     The brachial plexus is a complex bundle of nerves that originates from the spinal cord and travels through the neck and under the clavicle to innervate the muscles of the fingers, hand, arm, shoulder and upper back.  The roots from the spinal cord consist of the C5, C6, C7, C8 and T1 spinal nerves.  These roots combine to form three main trunks. C5 and C6 form the upper trunk, C7 forms the middle trunk and C8 and T1 form the lower trunk.  The most common type of brachial plexus injury (Erb’s Palsy) affects the upper trunk.       

Patterns of Brachial Plexus Injuries

     The extent of the damage to the nerves is a result of the amount of traction or stretching that occurred across the injured nerve segment(s).  The nerves may be damaged in several ways:

1. The nerve may be stretched.  Stretched nerves usually heal, to varying degrees of success, over time.  This is the “best case” scenario and the outlook for children with this degree of injury is typically good.
2. There may a neuroma.  This is when scar tissue builds up around the injured part of the nerve as it tries to repair itself.  This disrupts the nerve’s signal to its respective muscle group.
3. The nerve may be ruptured.  This is when the nerve is torn somewhere along its path to the muscles, but not where it attaches to the spine.  Primary surgery involving nerve grafts or transfers is often recommended in these cases.
4. The nerve may be avulsed.  This is when the nerve root is torn from the spinal cord.  Primary surgery is strongly recommended.  This is the most serious type of nerve injury.

                  The resulting damage to the arm depends on the number of nerves injured and the extent of the injury.  A slight stretching of the nerves results in the most favorable outcome and total rupture and avulsion have the least favorable outcome.  The child may be left with partial or total paralysis of some combination of the shoulder, elbow, hands and fingers.  Unfortunately in nearly all cases of complete rupture and avulsion (and some will argue even those cases when recovery is delayed beyond 2 months of age), the child will have some permanent physical and/or functional deficit in the affected arm. 

Injuries to the brachial plexus typically result in muscle weakness, muscle imbalances and muscle contractures.  These conditions are extremely detrimental to the development of bones and joints in a rapidly developing newborn baby, especially to the formation of the glenohumeral (shoulder) joint.