Thoracic Outlet Syndrome

Basic Facts

Thoracic outlet syndrome (TOS) is caused by a variety of conditions that narrow the thoracic outlet, the enclosed space between the base of the neck and the armpit through which nerves and blood vessels of the arm must pass.
TOS, which is more common among women than men, usually causes pain in the arm, neck, or shoulder. Symptoms of TOS are most likely to occur in individuals between the ages of 20 and 40, are highly variable, and depend primarily on whether the compression involves the nerves or the blood vessels.
Classical TOS is sometimes associated with a congenital abnormality of an extra rib or so-called cervical rib. Sometimes there is a history of neck trauma. Poor posture and obesity do not cause TOS but can aggravate it.

The thoracic outlet is a small anatomical space between the collarbone and first rib that is crowded with blood vessels, muscles, and nerves. If this space is narrowed by any one of a number of factors, pressure is placed on underlying nerves and blood vessels, causing thoracic outlet syndrome (TOS).


When compressed, the blood vessels and nerves passing through the thoracic outlet cause a variety of symptoms, including:

  • Arm swelling;
  • Hand or arm weakness;
  • Feeling of tiredness in the arm aggravated by performing overhead work;
  • Tingling or numbness, especially in the middle, ring, and little fingers;
  • Radiating pain in the shoulder, arm, or hand-commonly between the fourth and fifth fingers; and
  • Pain in the fingertips.


Causes of TOS include:

  • Presence of an extra rib (called a cervical rib);
  • Enlargement of a muscle;
  • Deformity of the collar bone (clavicle) or the first rib after fracture; and
  • Sagging of the shoulder because of aging.

TOS is most common among younger adults who are physically active and engaged in occupations that require repetitive raising of the arms, such as dental workers, truck drivers, and machinery operators.

People born with an extra rib are 10 times more likely to develop TOS than those with a normal number of ribs.


The diagnosis of TOS can be complex because several other conditions can cause the same or similar symptoms.

During a physical exam, a physician may look for:

  • Reduced pulses in the arm with certain overhead arm positions or with extreme turning of the head to one side (Adson’s maneuver);
  • Swelling in the arm or abnormally prominent arm veins;
  • Discoloration of the fingers or signs of reduced blood flow in the lower arm or hand;
  • Limited range of arm motion;
  • Reduced ability to feel pinpricks or temperatures; and
  • Abnormal blood vessel sounds through a stethoscope examination of the shoulder region.

To confirm whether or not a patient has TOS, the physician may order one of the following tests:

  • X ray;
  • Arteriography;
  • Venography;
  • Nerve conduction velocity tests;
  • Computed tomography (CT) scan; and
  • Magnetic resonance imaging (MRI).


How the doctor treats TOS will depend on the range of symptoms. If a cervical rib or vascular problems with arm artery or veins is present, the physician usually recommends treating these underlying causes first. Otherwise, the usual first treatment is a course of specific physical therapy aimed at strengthening the supporting muscles of the thoracic outlet structures. In addition, muscle relaxants, nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, moist heat, massage, analgesics, and short courses of steroids may be recommended.

In severe cases that have not improved with physical therapy, the physician may recommend surgery to relieve the source of compression or eliminate scar tissue.


Lifestyle changes that lower the risk for TOS include:

  • Maintaining correct posture while working;
  • Taking frequent stretch breaks;
  • Avoiding carrying heavy bags over the affected shoulder;
  • Losing weight; and
  • Evaluating and redesigning the workplace to make it more ergonomically sound. Occasionally, occupational change may be required.