Which nerve is most commonly compressed when a humerus is dislocated?

The axillary nerve is the nerve most commonly compressed when a humerus is dislocated, particularly in the context of anterior shoulder dislocations. This is due to the anatomical proximity of the axillary nerve to the shoulder joint and the humerus. The axillary nerve innervates the deltoid and teres minor muscles, and it also provides sensation to the lateral aspect of the shoulder through the superior lateral cutaneous nerve of the arm.

When a dislocation occurs, especially if the humerus moves forward (anterior dislocation), there is a significant risk of stretching or compressing the axillary nerve as it passes closely around the surgical neck of the humerus. This compression can lead to motor deficits in abduction of the arm at the shoulder, as well as sensory loss in the region innervated by the nerve.

In contrast, while the other nerves listed can be involved in other injuries or dislocations, they are less commonly associated with a standard anterior dislocation of the shoulder. Understanding the anatomical relationships and the typical mechanisms of nerve injury can help you appreciate why the axillary nerve is the most affected in these scenarios.