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