Quadrangular Space

spatium quadrangulare

The quadrangular space is a four-sided gap at the back of the shoulder through which the axillary nerve and posterior circumflex humeral artery leave the axilla. It is bounded by teres minor above, teres major below, the long head of triceps medially and the surgical neck of the humerus laterally.

Anatomical Data

Boundaries & Contents

Location	Posterior shoulder, below the shoulder joint.
Boundaries	Teres minor above (subscapularis seen from the front) Teres major below Long head of triceps medially Surgical neck of the humerus laterally
Contents	Axillary nerve Posterior circumflex humeral artery and vein

Biomechanics

Function & Actions

Provides a passage for the axillary nerve and posterior circumflex humeral vessels from the axilla to the deltoid region.

Clinical Relevance

Clinical Notes

Compression of the axillary nerve in this space by fibrous bands or hypertrophied muscles causes quadrilateral space syndrome, seen in overhead athletes such as throwers and volleyball players. The nerve here is also at risk in shoulder dislocation and fractures of the surgical neck of the humerus.

Pathology

Common Injuries & Conditions

Quadrilateral Space Syndrome

Entrapment of the axillary nerve or posterior circumflex humeral artery in the space, causing vague posterior shoulder pain, deltoid and teres minor weakness and sometimes numbness over the lateral shoulder.

Axillary Nerve Injury

Damage to the nerve as it passes through the space, often with dislocation or surgical neck fracture, leading to deltoid weakness and a patch of numbness on the outer upper arm.

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