Quadrangular Space

The quadrangular space is an anatomical interval located in the posterior shoulder region. It serves as a passageway for important neurovascular structures traveling from the axilla to the posterior arm, most notably the axillary nerve and the posterior circumflex humeral artery.

Boundaries

Contents

• Axillary nerve (branch of the posterior cord of the brachial plexus)
• Posterior circumflex humeral artery (branch of the axillary artery)

Relations

• Located posterior to the glenohumeral joint and deep to the deltoid muscle
• Lateral to the triangular space and superior to the triangular interval

Function / Significance

• Serves as a conduit for axillary nerve and vascular structures to reach the deltoid and surrounding posterior shoulder
• Important surgical and clinical landmark in posterior shoulder approaches

Clinical Significance

• Quadrangular Space Syndrome: Compression of the axillary nerve or posterior circumflex humeral artery within the space, causing:
  • Paresthesia over the deltoid region
  • Deltoid and teres minor weakness
  • Posterior shoulder pain aggravated by abduction and external rotation
• Shoulder Dislocation or Humeral Fracture: May injure axillary nerve as it passes through this space

Comparative Anatomy

The quadrangular space is a human-specific anatomic configuration that allows for enhanced mobility and neurovascular routing in the upper limb, supporting complex shoulder movement and upper extremity function.