Quadrilateral space

The quadrangular space (or quadrilateral space [of Velpeau] or Foramen Humerotricipitale) is an axillary space in the arm. This is a clinically important anatomic space in the arm. In the quadrangular space, the axillary nerve and posterior circumflex humeral artery can be compressed or damaged due to space-occupying lesions or disruption in the anatomy due to trauma. Symptoms include axillary nerve related weakness of the deltoid muscle in the case of any significant mass lesions in the quadrangular space. Boundaries

It is bounded by:

above/superior: the subscapularis and teres minor. Some sources exclude the teres minor.

below/inferior: the teres major

medially: the long head of the triceps brachii

laterally: the surgical neck of the humerus