Obstetric lesions of the brachial plexus

Abstract

The few studies on prognosis of obstetric lesions of the brachial plexus that are not hampered by selection bias or a short follow-up suggest that functional impairment persists in 20-25% of cases, more than commonly thought. Electromyography (EMG), potentially useful for prognosis, is often considered of little value. Denervation in the first week of life has been interpreted as evidence of an antenatal lesion, but is the logical result of the short axonal length affected. EMG performed at close to the time of possible intervention (3 months) usually shows a discrepancy: motor unit potentials are seen in clinically paralyzed muscles. This can be explained in five ways: an overly pessimistic clinical examination; overestimation of EMG recruitment due to small muscle fibers; persistent fetal innervation; developmental apraxia; or misdirection, in which axons reach inappropriate muscles. Further research into the pathophysiology of obstetric lesions of the brachial plexus is needed to improve prognostication.

High birthweight and shoulder dystocia: the strongest risk factors for obstetrical brachial plexus palsy in a Swedish population‐based study

“…The incidence of OBPP is between 0.5% and 5 ‰ in countries with well developed obstetric services (6)(7)(8)(9)(10)(11)(12). Reduction in incidence from 1.56 per 1000 live births in 1938 to 0.28 per 1000 in 1962 was reported in New York.…”

Extensive motor axonal misrouting after conservative treatment of obstetric brachial plexus lesions

“…3,4 Functional recovery following OBPL is dependent not only on the number of outgrowing motor axons that reinnervate muscle fibres but also on the extent of misrouting. [5][6][7] There are indications that misrouting occurs more often in children than in adults. 5 Misrouting occurs when a regenerating axonal sprout grows into a distal basal lamina tube that is not the original one.…”

“…[5][6][7] There are indications that misrouting occurs more often in children than in adults. 5 Misrouting occurs when a regenerating axonal sprout grows into a distal basal lamina tube that is not the original one. 8 In misrouting, an outgrowing axon reinnervates muscle fibres in areas other than where they are intended.…”

“…6,13,14 Co-contraction in OBPL might also be due to disturbed central motor programming, owing to factors such as deafferentation, 15 misrouting, and the fact that the lesion occurs before motor programmes have been developed fully. 5,6,16 Peripheral factors may, therefore, be involved in co-contraction in addition to central factors. 5 The aim of this study was to assess how often motor misrouting occurred in patients with conservatively treated OBPL, to link its occurrence to the site of the lesion, and to probe its clinical significance by comparing it with clinical motor function.…”

Neonatal Magnetic Resonance Imaging Without Sedation Correlates With Injury Severity in Brachial Plexus Birth Palsy

“…12 Various explanations have been given for this, including different innervation patterns of the infants' musculature. 13,14 Computed tomography (CT) myelography, which involves general anesthesia, a lumbar puncture, and radiation, has been shown to have high specificity for nerve root avulsion when pseudomeningoceles are seen. 15 A recent evaluation of magnetic resonance myelography found that it had a similar specificity for avulsed nerve roots as for CT myelography.…”