American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Which nerve can be injured in a proximal humerus fracture?

1. Median nerve

2. Ulnar nerve

3. Axillary nerve

4. Radial nerve

The correct answer is: Axillary nerve

The axillary nerve is the nerve most commonly associated with injury in a proximal humerus fracture due to its anatomical location and proximity to the surgical neck of the humerus. The axillary nerve innervates the deltoid and teres minor muscles and provides sensory innervation to the skin overlying the lateral shoulder. When a fracture occurs in the proximal humerus, particularly near the surgical neck, the sharp edges of the fractured bone can directly damage the axillary nerve. This results in weakness of the arm abduction at the shoulder joint, particularly from 15 to 90 degrees, where the deltoid muscle is most active. Additionally, patients may experience sensory loss over the "regimental badge" area, which is the skin overlying the lateral aspect of the shoulder. Knowledge of this relationship is crucial for both the diagnosis and management of shoulder injuries in patients with proximal humeral fractures. Careful clinical examination and assessment for axillary nerve function should be part of the evaluation following such injuries.