Quadrilateral space syndrome is a rare neurovascular compression syndrome characterized by posterior humeral circumflex artery (PHCA) and/or axillary nerve compression within the quadrilateral space. The compression may be due to fibrous bands, trauma, or hypertrophy of the muscular borders.

The axillary nerve leaves axilla through the quadrangular space to the upper arm and provides motor innervation to the deltoid and teres minor muscles. 

Traumatic anterior shoulder dislocations are considered the most common etiology of acute axillary nerve palsy with as a consequence atrophy +/- fatty infiltration of the deltoid and teres minor muscles supplied by the axillary nerve ¹.