What characterizes Erb's Palsy?

Erb's Palsy is characterized by an upper trunk injury of the brachial plexus, which typically occurs during childbirth due to excessive pulling on the infant's head or shoulders. This type of injury affects the C5 and C6 nerve roots, leading to weakness and paralysis in the affected arm. The "waiter's tip" position is a hallmark sign of this condition, where the affected arm hangs at the side, in internal rotation and adduction, with the wrist and fingers extended and unable to grasp effectively.

This description highlights how the loss of function is related to specific muscle innervation that is compromised due to the injury. The upper trunk's damage impacts muscles primarily responsible for shoulder abduction and external rotation, as well as elbow flexion.

The other options reflect different conditions or findings not directly related to the defining characteristics of Erb's Palsy. Absent grasp and poor wrist flexion could be indicative of various neurological or muscular conditions, and absent deep tendon reflexes might suggest a different type of neurological involvement or injury. Damage to the lower trunk, while also concerning, refers more to Klumpke's Palsy, which affects different nerve roots and results in a different set of symptoms.