Saturday night palsy is radial nerve injury at which level?

• A. Axilla
• B. Wrist
• C. Elbow
• D. Mid-humeral region

Answer: (D)

The main idea is that Saturday night palsy is a radial nerve injury at the mid-humeral level, where the nerve passes through the spiral (radial) groove. Prolonged compression here, such as sleeping with the arm draped over a chair, damages the part of the nerve that becomes the posterior interosseous nerve to the forearm extensors. That produces weakness of wrist and finger extension—wrist drop—while elbow extension is usually preserved because the triceps branches arise before this point. Sensation over the dorsum of the hand may be affected as well. Injuries higher up in the axilla would impair shoulder and deltoid function, while injuries distal to the elbow would spare elbow/upper-arm muscles, so the mid-humeral region is the characteristic site for this presentation.