Brachial plexus injury

The brachial plexus is a network of nerves that conducts signals from the spinal cord, which is housed in the spinal canal of the vertebral column (or spine), to the shoulder, arm and hand. These nerves originate in the fifth, sixth, seventh, and eighth cervical (C5-C8), and first two thoracic (T1-T2) spinal nerves, and innervate the muscles and skin of the chest, shoulder, arm and hand. Brachial plexus injuries, or lesions, are caused by damage to those nerves.

Brachial plexus injuries, or lesions, can occur as a result of shoulder trauma, tumours, or inflammation. The rare Parsonage-Turner Syndrome causes brachial plexus inflammation without obvious injury, but with nevertheless disabling symptoms. But in general, brachial plexus lesions can be classified as either traumatic or obstetric.

Obstetric injuries may occur from mechanical injury involving shoulder dystocia during difficult childbirth.  Traumatic injury may arise from several causes. "The brachial plexus may be injured by falls from a height on to the side of the head and shoulder, whereby the nerves of the plexus are violently stretched....The brachial plexus may also be injured by direct violence or gunshot wounds, by violent traction on the arm, or by efforts at reducing a dislocation of the shoulder joint."

Causes of brachial plexus injury

In most cases the nerve roots are stretched or torn from their origin, since the meningeal coverings of the nerve roots are thinner than the sheaths enclosing the peripheral nerves. The epineurium of the peripheral nerve is contiguous with the dural mater, providing extra support to the peripheral nerves.

Brachial plexus lesions typically result from excessive stretching; from rupture injury where the nerve is torn but not at the spinal cord; or from avulsion injuries, where the nerve is torn from its attachment at the spinal cord. A build-up of scar tissue around a brachial plexus injury site can also put pressure on the injured nerve, disrupting innervation of the muscles.

Although injuries can occur at any time, many brachial plexus injuries happen during birth: the baby's shoulders may become impacted during the birth process causing the brachial plexus nerves to stretch or tear.

Obstetric injuries may occur from mechanical injury involving shoulder dystocia during difficult childbirth, the most common of which result from injurious stretching of the child's brachial plexus during birth, mostly vaginal, but occasionally Caesarean section. The excessive stretch results in incomplete sensory and/or motor function of the injured nerve.

Traumatic brachial plexus injuries brachial plexus injury may arise from several causes, including sports, high-velocity motor vehicle accidents, especially in motorcyclists, but also all-terrain-vehicle (ATV) accidents. Injury from a direct blow to the lateral side of the scapula is also possible. The severity of nerve injuries may vary from a mild stretch to the nerve root tearing away from the spinal cord (avulsion).

Brachial plexus lesions can be divided into two types: 

1. An upper brachial plexus lesion, which occurs from excessive lateral neck flexion away from the shoulder. Most commonly, forceps delivery or falling on the neck at an angle causes upper plexus lesions leading to Erb's palsy. This type of injury produces a very characteristic sign called Waiter's tip deformity due to loss of the lateral rotators of the shoulder, arm flexors, and hand extensor muscles. 
2. Much less frequently, sudden upward pulling on an abducted arm (as when someone breaks a fall by grasping a tree branch) produces a lower brachial plexus lesion, in which the eighth cervical (C8) and first thoracic (T1) nerves are injured "either before or after they have joined to form the lower trunk. The subsequent paralysis affects, principally, the intrinsic muscles of the hand and the flexors of the wrist and fingers". This results in a form of paralysis known as Klumpke's paralysis. 

Brachial Plexus Injury Classification  

The severity of brachial plexus injury is determined by the type of nerve damage. There are several different classification systems for grading the severity of peripheral nerve and brachial plexus injuries. Most systems attempt to correlate the degree of injury with symptoms, pathology and prognosis. Seddon's classification, continues to be used, and is based on three main types of nerve fiber injury, and whether there is continuity of the nerve.

Signs and Symptoms of Brachial Plexus Injury

Signs and Symptoms may include a limp or paralyzed arm, lack of muscle control in the arm, hand, or wrist, and lack of feeling or sensation in the arm or hand.

Although several mechanisms account for brachial plexus injuries, the most common is nerve compression or stretch. Infants, in particular, may suffer brachial plexus injuries during delivery and these present with typical patterns of weakness, depending on which portion of the brachial plexus is involved.

The most severe form of injury is nerve root avulsion, which results in complete weakness in corresponding muscles. This usually accompanies high-velocity impacts that occurs during motor vehicle or bicycle accidents.

The cardinal signs of brachial plexus injury then, are weakness in the arm, diminished reflexes, and corresponding sensory deficits.

Diagnosis of Brachial Plexus Injury

The diagnosis may be confirmed by an EMG examination in 5 to 7 days. The evidence of denervation will be evident. If there is no nerve conduction 72 hours after the injury, then avulsion is most likely.

Treatment of Brahcial Plexus Injury

Treatment for brachial plexus injuries includes occupational or physical therapy and, in some cases, surgery. Some brachial plexus injuries may heal without treatment.

Many infants improve or recover within 6 months, but those that do not have a very poor outlook and will need further surgery to try to compensate for the nerve deficits. The ability to bend the elbow (biceps function) by the third month of life is considered an indicator of probable recovery, with additional upward movement of the wrist, as well as straightening of thumb and fingers an even stronger indicator of excellent spontaneous improvement.

Gentle range of motion exercises performed by parents, accompanied by repeated examinations by a physician, may be all that is necessary for patients with strong indicators of recovery.

The site and type of brachial plexus injury determine the prognosis. Avulsion and rupture injuries require timely surgical intervention for any chance of recovery.

For milder injuries involving build-up of scar tissue and for neurapraxia, the potential for improvement varies, but there is a fair prognosis for spontaneous.