Quadrilateral space syndrome

Overview

Quadrilateral space syndrome (QSS) is a rare neurovascular condition that affects the posterior shoulder region. It occurs when the axillary nerve and the posterior circumflex humeral artery become compressed within the quadrilateral space, an anatomical interval bordered by the teres minor, teres major, long head of the triceps brachii, and the surgical neck of the humerus. This syndrome is typically seen in athletes who perform repetitive overhead movements, such as baseball pitchers or volleyball players. QSS can lead to shoulder pain, weakness, and sensory disturbances in the lateral arm.

Causes

The primary cause of quadrilateral space syndrome is compression of the axillary nerve and/or posterior circumflex humeral artery within the quadrilateral space. Factors that can contribute to this compression include:

• Repetitive overhead or throwing motions

• Muscle hypertrophy, particularly of the surrounding shoulder muscles

• Fibrous bands or scar tissue formation

• Space-occupying lesions such as cysts or tumors

• Trauma to the shoulder region

Athletes, especially those in overhead sports, are at higher risk due to repeated microtrauma and muscular overuse in the shoulder girdle.

Symptoms

The symptoms of quadrilateral space syndrome can range from mild to disabling and usually affect the posterior and lateral shoulder. Common clinical features include:

• Dull, aching pain in the posterior shoulder

• Radiating pain to the lateral upper arm

• Paresthesia (tingling or numbness) over the deltoid area

• Weakness of the deltoid and teres minor muscles

• Muscle atrophy, particularly in chronic cases

• Aggravation of symptoms during overhead activity

Diagnosis

Diagnosis of quadrilateral space syndrome is based on a combination of clinical evaluation and imaging studies. Steps in the diagnostic process may include:

• Detailed physical examination, including palpation and provocative maneuvers

• Magnetic resonance imaging (MRI) to detect muscle atrophy or compression

• MR angiography to assess vascular involvement

• Electromyography (EMG) and nerve conduction studies to evaluate axillary nerve function

• Ultrasound to assess dynamic impingement or vascular changes

Proper differentiation from other causes of shoulder pain, such as rotator cuff injuries or cervical radiculopathy, is essential.

Treatment

Treatment of quadrilateral space syndrome typically starts with conservative measures. Surgical intervention is considered only if symptoms persist. Treatment options include:

• Rest and activity modification, especially avoiding overhead movements

• Physical therapy focusing on shoulder strengthening and mobility

• Nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief

• Corticosteroid injections to reduce inflammation

• Surgical decompression to release the axillary nerve and restore blood flow, in refractory cases

Prognosis

The prognosis for quadrilateral space syndrome varies depending on the severity of nerve compression and response to treatment. Many patients improve with non-surgical therapy, particularly when the condition is diagnosed early. However, chronic cases with significant nerve damage may result in persistent muscle atrophy and functional limitations. Surgical outcomes are generally favorable when performed appropriately, with many individuals returning to full activity after recovery.