The incidence of brachial plexus injury is 1 to 4 per 1000 live births per year, or 10 times more common than spinal-cord injuries. The mechanism of injury is generally from shoulder dystocia during delivery. Other risk factors include high birth weight, breech presentation, primiparous mother and assisted delivery. Three general patterns of injury are recognized (see also Chapter 3). The majority of injuries are upper brachial plexus injuries involving the C5 and C6 nerve roots; signs include weakness in shoulder adduction, elbow extension and wrist flexion. This syndrome complex is also known as Erb's palsy. A lower plexus injury affects the C7, C8 and T1 nerve roots, resulting in weakness of the intrinsic muscles of the hand, wrist and elbow extension. This type of injury is also known as Klumpke's palsy. If the entire arm is affected, global weakness and loss of function results.
Upper brachial plexus injuries are attributed to stretching of the brachial plexus by an increase in the angle made by the head and shoulder in the delivery process. Lower brachial plexus injuries usually result from an upward traction of the arm relative to the head. Other rare causes include upper limb compression by the umbilical cord, amniotic band, or a bicornuate uterus. Clavicular and humeral fractures should be excluded before the diagnosis of a plexus injury can be confirmed.
Injuries can also be subclassified by severity of injury into three general groups: neuropraxia, neuroma in continuity and nerve-root avulsion. Neuropraxia is defined as a physiological disruption without anatomic injury, and spontaneous recovery is the rule. A neuroma in continuity implies a loss of nerve fiber integrity with the overall nerve remaining intact. A neuroma implies disordered regeneration with loss of normal conduction across the site of injury. Spontaneous recovery can occur, although it is often partial. Nerve-root avulsions, as is implied, involves separation of the nerve roots from the spinal cord, and regeneration and spontaneous recovery do not occur. Because most brachial plexus injuries recover spontaneously, expectant management for 6 to 9 months is the preferred option. Outcome can be inferred if recovery occurs rapidly. Failure of any recovery by 6 months suggests a more severe injury. Early surgery for more severe injuries is advocated by some authors because of the limited additional recovery after 6 months and the presence of irreversible neuropathic muscle degeneration if reinnervation does not occur by 12 months. In general, patients undergoing neurolysis and nerve grafting have more favorable outcomes compared to those who undergo neurotization.
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