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Updated: Jun 4 2021

Quadrilateral Space Syndrome

Images atrophy.jpg space.jpg
  • summary
    • Quadilateral space syndrome is a rare source of posterolateral shoulder pain caused by the compression of the axillary nerve and posterior humeral circumflex artery in the quadrilateral space.
    • Diagnosis is clinical with point tenderness over the quadrilateral space and possible presence of teres minor atrophy. MRI studies may show axillary nerve compression. 
    • Treatment involves a course of NSAIDs, activity modification and physical therapy with surgical decompression indicated in refectory cases. 
  • Epidemiology
    • Incidence
      • rare and often misdiagnosed as subacromial impingement
    • Demographics
      • 20-40 years old
    • Anatomic location
      • most commonly affects the dominant shoulder
    • Risk factors
      • overhead movement athletes (e.g. basketball)
      • contact or throwing sports
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • compression and reduction of quadrangular space due to
          • iatrogenic (tight fibrous bands, muscular hypertrophy)
          • paralabral cysts (most commonly inferior labral tears)
          • trauma (scapular fracture, shoulder dislocation)
          • benign or malignant masses
      • pathomechanics
        • greatest amount of compression occurs when the arm is positioned in the late cocking phase of throwing (abduction and external rotation)
  • Anatomy
    • Quadrangular space
      • location
        • lateral to triangular space and medial to triangular interval
      • boundaries
        • superior - teres minor
        • inferior - teres major
        • medial - long head of triceps brachii
        • lateral - surgical neck of the humerus
      • contents
        • axillary nerve (C5 nerve root, posterior cord)
        • posterior circumflex humeral artery
  • Presentation
    • Symptoms
      • poorly localized pain of the posterior/lateral shoulder
        • often worse at night
        • worse with overhead activity or late cocking/acceleration phase of throwing
      • non-dermatomal distribution of paraesthesia along the lateral shoulder and arm
      • shoulder external rotation weakness
    • Physical examination
      • inspection
        • may see atrophy of the teres minor and deltoid
      • palpation
        • point tenderness over the quadrangular space
      • motion and strength
        • external rotation weakness with the arm abducted in throwing position
        • pain exacerbated by active and resisted abduction and external rotation of the arm
      • neurological examination
        • usually normal
        • have mild sensory changes in the axillary nerve distribution
  • Imaging
    • Radiographs
      • recommended views
        • shoulder series (AP, lateral, axillary views)
      • findings
        • usually normal
        • used to rule out pathologic entities
    • MRI
      • indications
        • often used to rule out rotator cuff pathology
      • findings
        • may show atrophy of teres minor (axillary innervation)
        • may show compression of the quadrilateral space
        • may show inferior paralabral cyst associated with labral tear
    • Arteriogram
      • may shows lesion in posterior humeral circumflex artery
    • EMG
      • indications
        • used to confirm diagnosis
      • findings
        • will show axillary nerve involvement
  • Treatment
    • Nonoperative
      • NSAIDS, activity restriction, physiotherapy
        • indications
          • first line of treatment
        • techniques
          • glenohumeral joint mobilization and strengthening
          • posterior capsule stretching
          • massage
        • outcomes
          • most people improve with 3-6 months of nonoperative treatment
      • diagnostic lidocaine block
        • indications
          • will help to confirm diagnosis
        • technique
          • inject plain lidocaine directly into the quadrilateral space
          • starting point is 2 to 3 cm inferior to the standard posterior shoulder arthroscopy portal
        • outcomes
          • positive if no point tenderness or pain with full ROM of the shoulder following injection
    • Operative
      • nerve decompression
        • indications
          • failure of nonoperative management
          • significant weakness and functional disability
          • decompression of space-occupying lesion
        • techniques
          • open release of quadrilateral space +/- arthroscopic repair of labral tear
  • Techniques
    • Open Quadrilateral Space Decompression
      • approach
        • lateral decubitus position
        • 3 - 4 cm incision over the quadrilateral space
        • identify posterior border of deltoid and reflect superolateral
        • expose fat in quadrilateral space between teres minor and teres major
      • technique
        • identify the axillary nerve by using the humeral neck as reference
        • avoid cutting the posterior circumflex artery
        • free any fibrous lesions adhering to the nerve
        • ensure the nerve is completely free of compression by moving the arm into abduction and external rotation
      • postoperative care
        • immediate sling for comfort
        • early pendulum exercises to avoid new adhesions
        • progress to full active ROM with supervised physiotherapy
  • Prognosis
    • Long-standing cases often causes atrophy/weakness of teres minor and deltoid
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