Quadrilateral Space Syndrome

What is Quadrilateral Space Syndrome

Quadrilateral space syndrome is a rare condition in which a nerve in the shoulder (axillary nerve) is squeezed (compressed). A blood vessel called the posterior circumflex humeral artery (PCHA) may also become compressed. This condition causes pain and numbness in the shoulder.

Compression happens where the axillary nerve and the PCHA pass through the quadrilateral space. This is a space that is created by your upper arm bone (humerus) and three of your shoulder muscles. The three shoulder muscles are the teres major, the teres minor, and the triceps.

Quadrilateral space syndrome is an uncommon cause of shoulder and posterior upper arm pain first described by Cahill and Palmer in 1983. It is now being encountered more frequently in clinical practice because magnetic resonance imaging (MRI) makes confirmation of the clinical diagnosis much easier than the previously required arteriography of the shoulder and upper extremity.

Quadrilateral space syndrome is caused by compression of the axillary nerve as it passes through the quadrilateral space.

The onset of quadrilateral space syndrome is usually insidious, with the patient often not reporting any obvious antecedent trauma.

A patient suffering from quadrilateral space syndrome complains of ill-defined pain in the shoulder and paresthesias radiating into the posterior upper arm and lateral shoulder. This pain and associated paresthesias frequently are worsened with abduction and external rotation of the affected upper extremity.

As the syndrome progresses, the patient may note increasing weakness of the affected arm and difficulty with abduction and external rotation. Most cases of quadrilateral space syndrome have occurred in young athletes in their early second to third decade who are involved in throwing activities.

The syndrome may be seen occasionally in older patients as a result of other causes of compression of the axillary nerve as it travels through the quadrilateral space, such as glenolabral cysts or tumor. Mild cases of quadrilateral space syndrome resolve over time, but more severe cases, if left untreated, result in permanent atrophy of the deltoid and teres minor muscles

What are the causes?

This condition is caused when pressure is placed on the axillary nerve and the PCHA. This pressure is caused by the quadrilateral space becoming narrow. This narrowing can happen from:

  • Overgrowth of the muscles in the quadrilateral space.
  • Formation of fibrous bands of tissue between muscles in the quadrilateral space.
  • Swelling from injury that is caused by overuse of the shoulder. Usually, overuse injury is caused by overhead arm movements.
  • Injury from using crutches incorrectly.
  • A growth on a nerve, muscle, or bone in the quadrilateral space.
  • A dislocated shoulder injury.
  • Scar tissue from shoulder surgery.

What increases the risk?

This condition is more likely to develop in people:

  • Who play contact sports.
  • Who often raise their arms or do overhead arm movements, such as throwing or doing swimming strokes.
  • Who have poor strength and flexibility.

What are the symptoms?

The main symptom of this condition is pain in the back of the shoulder or the side of the shoulder. You may also feel pain in the back of your upper arm. Pain may get worse when you stretch (extend) your arm outward or raise it above your head. Other symptoms may include:

  • Heaviness or tiredness (fatigue) of the arm.
  • Tingling, numbness, or a burning feeling in the back of the shoulder or arm.
  • Weakness and shrinking of the shoulder muscles.

The most important finding in patients with quadrilateral space syndrome is weakness of the supraspinatus and infraspinatus muscles. This manifests as weakness of abduction and external rotation of the ipsilateral shoulder.

With significant compromise of the axillary nerve, atrophy of the deltoid and teres minor muscle is apparent on physical examination.

The pain of quadrilateral space syndrome can be exacerbated by abducting and externally rotating the ipsilateral upper extremity. Tenderness to palpation of the quadrilateral space often is present.

How is this diagnosed?

This condition may be diagnosed based on your symptoms, your medical history, and a physical exam. During the exam, your health care provider may press on your quadrilateral space to check if you feel pain. You may also have tests, including:

  • Ultrasound. This creates images of your injured area using sound waves.
  • MRI.
  • Arteriogram. This is a test in which dye is injected into your PCHA and an X-ray is done.
  • Injection of a numbing medicine into your quadrilateral space to see whether this relieves your symptoms.

Electromyography may help identify entrapment of the axillary nerve, although the test may be normal in mild cases even though significant neurapraxia is present. Electromyography helps distinguish cervical radiculopathy and Parsonage-Turner syndrome from quadrilateral space syndrome.

Plain radiographs are indicated in all patients who present with quadrilateral space syndrome to rule out occult bony pathological processes.

Based on the patient’s clinical presentation, additional testing, including complete blood cell count, uric acid level, erythrocyte sedimentation rate, and antinuclear antibody testing, may be indicated.

MRI and ultrasound imaging of the shoulder is indicated in all patients thought to have quadrilateral space syndrome because this test is highly specific for this disorder. In the rare patient in whom MRI is nondiagnostic, subclavian arteriography to show occlusion of the posterior humeral circumflex artery may be considered because this finding is highly suggestive of a diagnosis of quadrilateral space syndrome

How is this treated?

Treatment varies depending on the severity of your condition. Treatment usually includes resting and icing the injured area, and stopping any activities that make your condition worse. Treatment may also include:

  • NSAIDs to help reduce pain and inflammation.
  • Injecting medicines that help to reduce inflammation (steroids).
  • Physical therapy exercises to strengthen and stretch your shoulder.
  • Ultrasound therapy. This uses sound waves to help your injured area to heal.
  • Performing surgery to cut soft tissue that is compressing your nerve. This is usually done only if other treatment methods are ineffective.

Nonsteroidal antiinflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors represent a reasonable first step in the treatment of mild, self-limited quadrilateral space syndrome.

The use of tricyclic antidepressants, such as nortriptyline, at a single bedtime dose of 25 mg, titrating upward as side effects allow, also is useful, especially if sleep disturbance is present. Gabapentin or carbamazepine also can be considered. Avoidance of repetitive trauma thought to be contributing to this entrapment neuropathy also is important, especially in professional athletes.

If these maneuvers fail to produce rapid symptomatic relief, surgical exploration and release of the axillary nerve are indicated.

Follow these instructions at home:

  • Take over-the-counter and prescription medicines only as told by your health care provider.
  • If directed, apply ice to the injured area:
    • Put ice in a plastic bag.
    • Place a towel between your skin and the bag.
    • Leave the ice on for 20 minutes, 2–3 times per day.
  • Return to your normal activities as told by your health care provider. Ask your health care provider what activities are safe for you.
  • If physical therapy was prescribed, do exercises as told by your health care provider.
  • Keep all follow-up visits as told by your health care provider. This is important.

Differential Diagnosis

Quadrilateral space syndrome is often initially misdiagnosed as bursitis, tendinitis, or arthritis of the shoulder. Cervical radiculopathy of the lower nerve roots also may mimic the clinical presentation of quadrilateral space syndrome.

Parsonage-Turner syndrome, or idiopathic brachial neuritis, also may manifest as sudden onset of shoulder pain and can be confused with quadrilateral space syndrome.

Tumor involving this anatomical region also should be considered in the differential diagnosis of quadrilateral space syndrome, as should occult fractures of the proximal humerus and other mass lesions, such as cysts and lipomas, which may compress the axillary nerve as it traverses the quadrilateral space.

How is this prevented?

  • Make sure that you are healthy and in good physical shape before you start any new physical activity that involves your shoulder.
  • Continue to do shoulder exercises as told by your health care provider, if this applies.
  • Do not overtrain for sports that involve shoulder motions, if this applies.
  • Stop any activity that causes pain or numbness in your shoulder.

Contact a health care provider if:

  • You have symptoms that get worse or do not improve after 2 weeks of treatment.

Get help right away if:

  • You have severe pain.


Failure to diagnose quadrilateral space syndrome correctly puts the patient at risk for the missed diagnosis of other syndromes that may result in ongoing damage to the shoulder or lead to overlooked pathological processes in this anatomical region that may harm the patient, such as Pancoast tumor or primary or metastatic tumors of the shoulder.

MRI and ultrasound imaging are indicated in all patients thought to have quadrilateral space syndrome, and aggressive treatment of surgically correctable causes is generally indicated sooner rather than later to avoid ongoing irreversible shoulder damage.

Clinical Pearls

Avoidance techniques of the repetitive movements responsible for quadrilateral space syndrome often are forgotten in the rush to treatment. Mild cases of quadrilateral space syndrome are usually self-limited, but more severe cases require urgent surgical intervention. As with other uncommon pain syndromes, quadrilateral space syndrome should be considered a diagnosis of exclusion and the clinician should ensure that no potentially harmful occult space-occupying lesions are present before attributing symptoms to other benign causes.


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