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

The "waiter's tip" position is characteristic of Erb's palsy, which occurs due to an injury to the upper trunk of the brachial plexus (primarily involving the C5 and C6 nerve roots). This type of injury often happens during childbirth when excessive lateral traction is applied to the infant's head. In this condition, the affected arm is adducted, extended, and rotated medially, resembling a posture as if the individual is requesting a tip or offering a hand in greeting, hence the name "waiter's tip."

In Erb's palsy, the muscles that are affected include those responsible for shoulder abduction and external rotation, predominantly innervated by the affected nerve roots. The deltoid, supraspinatus, and infraspinatus muscles are particularly impacted, leading to this characteristic arm position.

In contrast, the ulnar nerve injury typically affects the hand's intrinsic muscles, resulting in an inability to properly function with the fifth finger and the ulnar side of the fourth finger. A median nerve injury primarily affects the thenar muscles and leads to "ape hand," where the opposition of the thumb is compromised. Lastly, a musculocutaneous nerve injury impacts the flexion