Plexus is formed in the neck by the union of the anterior rami of C5 through
C8 and the greater part of T1. The plexus is divided into roots, trunks, divisions,
cords, and branches.
Injury to the superior trunk of the plexus (C5, C6) results in the characteristic "waiter's tip position" in which the limb hangs from an adducted shoulder, medially rotated arm, and extended elbow. Various terms describe this syndrome (Erb palsy, Erb-Duchenne palsy, upper radicular syndrome). Injury to the inferior trunk of the plexus (C8, T1) affects the intrinsic muscles of the hand resulting in clawhand.