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What is Quadrilateral Space Syndrome?

Quadrilateral space syndrome (QSS) is a rare condition characterized by compression of the axillary nerve & posterior humeral circumflex artery(PHCA) within the quadrilateral space.

Picture of Quadrilateral Space Syndrome

Anatomy Attachments of the Quadrilateral Space

The quadrilateral space is formed by the following anatomical structures:

  • Superiorly, teres minor muscle
  • Inferiorly, teres major muscle
  • Medially, long head of the triceps
  • Laterally, humeral shaft bone

Structures running through the quadrilateral space include:

  • Axillary nerve which innervates the deltoid and teres minor providing abduction & external rotation of the shoulder.
  • Posterior humeral circumflex artery which provides blood supply to the teres minor, teres major and triceps brachii muscles.

Etiology for Quadrilateral Space Syndrome

The exact or known etiology is unclear; however, the probable risk factors for QSS are as below:

  • Overhead athletes such as volley ball players, tennis players, swimmers, pitchers etc.
  • Acute trauma
  • Development of fibrous bands in the region
  • Muscular hypertrophy
  • Labral cysts
  • Axillary nerve compression
  • Fractures
  • Osteochondroma, axillary Schwannoma
  • Lipomas
  • PHCA aneurysms
  • Post-surgical complications rarely

Symptoms of Quadrilateral Space Syndrome

Common symptoms of quadrilateral space syndrome include:

  • Gradual onset of diffuse shoulder pain radiating posteriorly
  • Impaired or loss of sensation in the axillary nerve pathway
  • Difficulty in abduction & external rotation movements of the shoulder
  • Active worsening of pain during night time
  • Tingling sensation or numbness in the arm
  • Tenderness to pressure over the arm
  • Weakness or instability of the arm

Diagnosis of Quadrilateral Space Syndrome

On physical evaluation, your doctor may look for signs of atrophy in the teres minor or deltoid muscle and check for pain or weakness with external rotation of the shoulder. Diagnostic tests may also be ordered which include:

  • MRI scan to demonstrate atrophy changes causing compression
  • Angiography or Arteriogram to rule out the occlusion of the PHCA
  • EMG (electromyography) to trace altered nerve impulses
  • X ray looking for fractures & masses

Differential diagnosis of Quadrilateral Space Syndrome

The various conditions that may need to be ruled out to obtain a diagnosis of quadrilateral space syndrome include:

  • Thoracic outlet syndrome
  • Cervical radiculopathy
  • Rotator cuff pathology
  • Internal/posterior shoulder impingement
  • Glenohumeral instability
  • Suprascapular nerve injury
  • Brachial plexus injury

Management of Quadrilateral Space Syndrome

The various treatment options include:

Conservative method:

  • Adequate rest to the arm & immobilization in minor issues.
  • Non steroid anti-inflammatory drugs (NSAIDS)
  • Corticosteroids injections
  • Physical therapy


This may involve an open surgical decompression with removal of any fibrous adhesions to the axillary nerve and ensuring no anatomical structures are impinging on the nerve and posterior humeral circumflex artery.

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