BRACHIAL PLEXUS AND/OR CERVICAL
NERVE ROOT INJURIES AT
BIRTH
The maturation and myelination of peripheral nerves, including cranial nerves, is not complete at birth. Thus these axons, not yet fully protected by myelin, associated glial cells, and connective tissue, are susceptible to perinatal injury. Brachial plexus injuries in the newborn now occur much less commonly, although the incidence is still approximately 1 in 1,000 live births. The injury results from traction forces in delivering the shoulder in vertex deliveries and delivering the head in breech deliveries. The associated obstetric factors are occipitoposterior or transverse presentation, the use of oxytocin, shoulder dystocia, and large babies (weighing more than 3,500 g) with low Apgar scores.
Brachial
birth palsy is believed to be secondary to a stretching of the plexus by
traction, with the nerve roots being anchored by the spinal column and cord. In
less severe lesions, only the myelin sheath may be damaged, which is evidenced
by swelling and edema that may, in turn, damage the myelin. If only a small
segment of the axon is affected or if it is stretched but not ruptured, quick
repair and recovery are likely. However, if the axon is interrupted, repair can
take a very long time, considering that the rate of axonal growth is believed
to be 1 mm/day. If the axon is completely ruptured, recovery is unlikely.
Bilateral brachial injuries almost always indicate spinal involvement, and
avulsion of the nerve roots may be evident on magnetic resonance imaging. Upper
brachial plexus injuries involve the junction of C5 and C6 roots (Erb point),
and lower injuries involve the junction of C8 and T1 roots.
Upper
Brachial Plexus Injury (Erb Palsy). This is the most common of the
brachial plexus injuries, affecting muscles supplied by C5 and C6 and
accounting for 90% of the total incidence. An asymmetric Moro response is
usually the first indication of the injury. The upper extremity assumes the
“waiter’s tip” position: the shoulder is adducted and internally rotated; the
elbow is extended; and the forearm is pronated, with the hand in flexion. A
mild sensory loss may develop over the lateral aspect of the shoulder and arm,
but is rather difficult to distinguish. Associated fractures of the clavicle or
humerus must be ruled out, and fluoroscopic examination should be carried out
to exclude the rare diaphragmatic paralysis caused mainly by a C4 lesion.
Lower
Brachial Plexus Injury (Klumpke Palsy). A pure lower brachial plexus injury
is quite uncommon, and most cases of Klumpke palsy involve the more proximal
muscles supplied by C7 or C6. An absent grasp reflex is the most
prominent clinical feature. Involvement of sympathetic fibers from T1 causes
Horner syndrome (ptosis, miosis, anhidrosis). A significant sensory deficit is
usually present. Infants and children may sometimes traumatize their fingers
unwittingly, with occasionally severe results such as loss of a fingertip. Prognosis for full recovery in these infants is
poor. The upper extremity often remains small and distally foreshortened.
Treatment.
In
all cases of brachial plexus injury, a thorough evaluation is indicated. The
limb should be placed in its best functional position, that is, across the
chest, not abducted, and flexed. Gentle, passive, range- of-motion exercise
should be initiated within 7 to 10 days of birth, and physical or occupational
therapy should be continued throughout at least the first year
of life. Hand and wrist splints can be used as necessary. Most infants will
experience marked recovery of function in the first few months. If no recovery
is observed, electromyography, can be useful to determine the extent of the
injury. For infants with persistent severe injury and no evidence of
improvement at 4 to 6 months of age,
magnetic resonance imaging may be helpful in determining whether the infant
will benefit from a brachial plexus repair with nerve grafts. Although brachial
plexus repair does not restore normal function, it can provide carefully selected
infants with functional improvement. After the child is 5 to 6 years of age, muscle
transfers may be helpful.
