- Anatomy:
    - formed by:
           - humerus
           - teres major
           - teres minor
           - long head of triceps
    - contents:
           - axillary nerve & posterior humeral circumflex artery pass posteriorly thru the quadrangular space;

- Quadrilateral Space Syndrome:
    - caused transient blockage of the posterior humeral circumflex artery (and axillary nerve);
    - typically occurs when the arm lies in a position of abduction, extension, and external rotation;
    - patients note shoulder pain and paresthesias down the arm, esp with overhead activity;
    - MRI findings may include atropy of the teres minor muscle as seen on saggital oblique MRI views

Quadrilateral space syndrome. 

Surgical Decompression of the Quadrilateral Space in Overhead Athletes

Quadrilateral Space Syndrome: Incidence of Imaging Findings in a Population Referred for MRI of the Shoulder