Learning Objective:
Understand the anatomy, contents, and clinical significance of the quadrangular space, including its role as a conduit for neurovascular structures between the axilla and posterior compartment of the arm.
The quadrangular space is a rectangular anatomical region located in the posterior axilla. It serves as a passageway for key neurovascular structures, connecting the axilla to the posterior compartment of the arm.
Anatomical Boundaries
Four structures bound the quadrangular space:
| Boundary | Anatomical Structure |
|---|---|
| Superior | Inferior margin of the teres minor |
| Inferior | Superior aspect of the teres major |
| Medial | Long head of triceps brachii |
| Lateral | Surgical neck of the humerus |
Key Point: This rectangular layout forms a passageway essential for neurovascular structures traveling to the posterior arm.
Activity
Contents of the Quadrangular Space
| Structure | Function / Role |
|---|---|
| Axillary Nerve | Innervates the deltoid and teres minor muscles; provides cutaneous sensation over the deltoid region. |
| Posterior Circumflex Humeral Artery & Vein | Supplies and drains blood from the posterior upper arm. |
Note: The quadrangular space ensures safe passage of these structures from the axilla to the posterior arm.
Quadrangular Space Syndrome
Definition:
Compression of the axillary nerve and posterior circumflex humoral artery within the quadrangular space.
Causes:
- Hypertrophy of bordering muscles (teres minor, teres major, triceps)
- Formation of fibrotic bands
Clinical Features:
| Symptom | Description |
|---|---|
| Pain | Localized to the shoulder; worsens with abduction or external rotation |
| Paresthesia | Tingling or numbness over the deltoid region (axillary nerve distribution) |
| Reduced Shoulder Movement | Difficulty with abduction and external rotation |
Points to Remember
- Borders: Superior – teres minor; Inferior – teres major; Medial – long head of triceps; Lateral – surgical neck of humerus
- Contents: Axillary nerve, posterior circumflex humoral artery (and vein)
- Clinical Significance: Compression can cause pain, paresthesia, and impaired shoulder function
- Anatomical Context: Lies posteriorly, allowing communication between the axilla and the posterior compartment of the arm
