Brachial plexus lesion

Brachial plexus lesions are classified as traumatic or obstetric.

Causes
These typically result from excessive stretching and avulsion injury. Traumatic injuries are often caused by high-velocity motor vehicle accidents, especially in motorcyclists. Injury from a direct blow to the lateral side of the scapula is also possible.

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.

Much less frequently, sudden upward pulling on an abducted arm (as when someone breaks a fall by grasping a tree branch) produces a lower plexus injury. This results in the sign known as clawed hand due to loss of function of the ulnar nerve and the intrinsic muscles of the hand it supplies.

Signs
The cardinal signs of brachial plexus avulsion are:
 * a weakness in the arm
 * diminished reflexes
 * corresponding sensory deficits

Presentation
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. In cases where the nerve roots have been torn, recovery is unlikely without invasive experimental surgical techniques.

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