Obstretrical Brachial Plexus Injury
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Birth related brachial plexus injuries occur in approximately 1-2/1000 live births. The majority of these recover with conservative care and only 10-15% require surgical correction. Although other mechanisms for birth brachial plexus injury exists, the accepted cause is extreme traction on the neck causing a stretch injury. It occurs during delivery of a neonate with shoulder dystocia. It is more commonly observed in multiparous mothers, prolonged labor, increased birth weight, shoulder dystocia and with the use of forceps. Bilateral injuries occur in breech presentation.
Clinical Injury Types
A child with an birth related brachial plexus may present with a C5C6 deficit, a classic Erb's Palsy, a complete plexus injury or a Klumpke's Palsy. Injury to C5C6 results in weakness of the bicep and deltoid. Erb's Palsy involves the roots of C5,C6 and C7. There is weakness of the deltoid, biceps, coracobrachialis and brachioradialis. The shoulder is abducted and internally rotated. The elbow is extended and the forearm is pronated with flexion of the wrist and fingers. It is also called the "waiter's tip" arm. A complete injury leaves a flaccid arm. Klumpke's Palsy injuries are demonstrated by loss of function at C8 and T1 to include loss of flexion at the elbow, extension of wrist and a claw hand. Further information can be gathered. The elevation of a diaphragm on radiographs indicates damage to the phrenic nerve (C3-C5). Horner's syndrome will usually accompany the injuries to the lower roots. Upper trunk injuries will involve the suprascapular nerve. Root injury or avulsion can be assumed with weakness in the anterior serratius (long thoracic) or rhomboid (dorsal scapular) nerves as they divide prior to the trunks.
There are four types of injury that the nerve may sustain after a stretch injury. The child should be examined at birth and every month afterwards. The mildest is a neuropraxic injury. In this injury the axon and its covering remains intact. Recovery from this injury is quick and complete within 4-6 weeks. Axonotemesis is disruption of the axon with an intact covering. As a nerve grows 1mm per day, this injury can take 4-6 months to recover. Neuronotemesis involves the complete disruption of the axon and its sheath. A neuroma may form after a neuronotemesis injury. A neuroma is a mass of tangled, misdirected growing nerve stumps. There is no improvement from this injury. Initially the arm may be flaccid. Motor strength should be assessed using the scale of 0-5. The Mallet Score will discern any improvement in functional use of the arm and shoulder. Sensory findings may be difficult. Additional on exam should include a chest radiograph to evaluate the diaphragm, presence or absence of Horner's findings and previous history of fractures to the clavicle, superior ribs or humerus.
Most children sustain a neuropraxic injury. The motor function returns within 2 weeks of birth and is almost normal by the end of the first year. If the child lacks 3/5 strength in shoulder and particularly, elbow flexion by 4-5 months, surgical management should be undertaken at 6 months. No motor or functional improvement at 2 months mandates early surgery.
There is no standard method for pre-operative work-up of a surgical patients. Some centers commonly exam electromyography to determine the extent of the injury and the extent of recovery. MRI may demonstrate pseuodmeningocele formation consistent with nerve root avulsion or nerve root injury.