Which nerve injury results in a "waiter's tip" position?

The "waiter's tip" position is characteristic of Erb's palsy, which results from an injury to the upper trunk of the brachial plexus, typically involving the C5 and C6 nerve roots. This condition leads to paralysis of the deltoid, supraspinatus, infraspinatus, and biceps muscles. Consequently, the affected arm hangs by the side and rotates medially, with the hand in a position that resembles a waiter extending their hand to receive a tip.

This specific posture arises due to the weakness of shoulder abduction and external rotation, along with the inability to flex the elbow fully. In cases where the upper trunk of the brachial plexus is damaged, as seen in Erb's palsy, patients exhibit this distinct arm position.

Other nerve injuries listed do not typically present with this characteristic posture:

• Ulnar nerve injuries usually involve the hand muscles and lead to different forms of clawing of the hand.

• Median nerve injuries can affect the ability to flex the thumb and index fingers, causing a loss of the pincer grip, but the position of the arm does not resemble the "waiter's tip".

• Musculocutaneous nerve injuries primarily impact elbow flexion