The brachial plexus is a network of nerves, located in the neck, which supplies the upper limb(s) facilitating limb movement and sensation. This plexus can be injured in situations where the neck and shoulder are separated more than is usual, for example, during a difficult delivery when the shoulder is stuck within the mother’s pelvis and the head is pulled in an attempt at childbirth.
Stretching or tearing of brachial plexus nerves may occur resulting in paralysis of some upper limb muscles. The paralysed upper limb subsequently takes on a distinctive posture where it hangs limp, with the elbow straightened and the wrist bent akin to the posture a waiter’s hand assumes when asking for a tip – waiter’s tip deformity. Erb’s palsy is a synonym for the waiter’s tip deformity.
Foad LS, Mehlman CT, Ying J: The Epidemiology of Neonatal Brachial Plexus Palsy in the United States. J Bone Joint Surg Am, 2008 90(6):1258-64. Go to reference