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Mechanism of Neonatal Brachial Plexus Injuries

Leslie Iffy

This article is based on a literary review pertaining to the etiology and pathological mechanism of brachial plexus damage sustained by neonates at birth. The study attempts to identify characteristic environmental, chronologic, epidemiologic and clinical features of arrest of the shoulders at birth in order to establish their compatibilities with two competing concepts about the cause and mechanism of Erb’s and Klumpke’s palsies in newborn infants: A) Excessive traction exerted by the professional who assists the mother during the birthing process. B) Spontaneous injury ‘in utero’ caused by myometrial activity during gestation and/or labor. Of the pertinent literary data the following ones appear to be of importance within the context of this analysis:
1. Since fluid fills the amniotic cavity during pregnancy, according to Pascal’s law of fluids no part of the fetal body can be subjected to excessive pressure as long as the membranes are intact.
2. Uterine contractions spread from the fundus towards the cervix gradually, thus creating an expulsive force. The musculature generates no traction force; the mechanism responsible for evulsion and rupture injuries that manifest clinically as Erb’s and Klumpke’s palsies.
3. Because almost one-third of all births occur by cesarean section in contemporary practice, brachial plexus palsy should be frequent following abdominal deliveries if the spontaneous in utero damage hypothesis was correct. However, Erb’s and Klumpke’s palsies after cesarean section are extremely rare.
4. Forceps and ventouse deliveries increase the risk of brachial plexus damage up to 10-fold. This could not be the case if a high proportion of these injuries were unrelated to vaginal birth.
5. Shoulder dystocia and its associated injuries are 5 to 15-times more frequent in the USA than in England, Italy, Ireland, Israel or Hongkong (China). Because the reproductive process is largely identical among all races, a difference of such magnitude is unlikely to be caused by a factor which is intrinsic to human pregnancies.
6. During the last 50 years the rate of arrest of the shoulders and the typical injuries associated with it increased 5–10-fold in America. Such a sudden change is unlikely to be attributable to some inherited predisposition in a stable population.
7. Before 1975 non-interference with the birthing process was standard requirement in the USA. Then the policy changed and physicians were advised to extract the child promptly after the delivery of the head. Increase of rate of shoulder dystocia shortly after the introduction of the new policy suggests a cause-effect relationship between the two events.
8. Non-interference with the birthing process has been the recommended routine in Great Britain since the early 20th Century. The rates of shoulder dystocia in the USA and Great Britain were equally low before the 1970’s. Its occurrence has remained stable in the Britain but increased steeply in this country after obstetricians had changed the method of delivery from conservative to active. The above summarized observations have practical implications in obstetrics. These are discussed with emphasis upon the fact that some of the new developments in perinatology, perceived as part of the progress initially, have proved counterproductive in the long run.