Which features are characteristic of Erb's palsy?

Erb's palsy is a condition resulting from an injury to the upper trunk of the brachial plexus, typically occurring during birth when excessive lateral traction is applied to the head. The characteristic features of this condition are closely associated with the affected nerves which supply the shoulder and arm.

The correct answer highlights the loss of shoulder abduction, external rotation, elbow flexion, and forearm supination, all of which are governed by the C5 and C6 nerve roots. Muscles such as the deltoid and supraspinatus, responsible for shoulder abduction, are affected, resulting in the inability to lift the arm. The infraspinatus contributes to external rotation, and the biceps brachii and brachialis govern elbow flexion. Additionally, the supinator muscle, responsible for forearm supination, is also impacted. As a result, the arm typically presents with a characteristic "waiter's tip" posture, emphasizing these functional losses.

In contrast, the other options do not accurately reflect the classic presentation of Erb's palsy. The first option mentions only elbow flexion and forearm pronation, which does not encompass the broader implications of a C5-C6 injury. Claw hand and