Erb's palsy causation: iatrogenic or resulting from labor forces?

To determine whether there is direct evidence that Erb's palsy is caused by clinician-applied excessive lateral traction on the fetal head and neck, a literature review was performed. Both the medical literature outlining the maternal forces generated from uterine contractions and maternal pushing and limited reports on clinician-applied forces were examined. Research involving clinician-applied force measurements during actual deliveries has the potential for increasing our understanding of the mechanism of the injury. However, studies to date have involved only 29 deliveries and did not include measurement of vertical or maternally generated forces. During the past 15 years, studies have provided considerable indirect evidence that maternal propulsive forces are responsible for the injury leading to Erb's palsy.