The thoracic outlet is a narrow space between your collarbone (clavicle) and your first rib. Nerves and blood vessels pass from your chest to your arm through this area. The nerves and blood vessels include:

• A bundle of nerves that serve your shoulder, arm, and hand

• A large and important vein (subclavian vein)

• A very large important artery (subclavian artery)

Your shoulder muscles normally keep your clavicle raised and in place. But with thoracic outlet syndrome, the upper rib and clavicle are closer. This makes the thoracic outlet smaller. Nerves and blood vessels going through the area can be compressed. Conditions that can cause thoracic outlet syndrome include:

• Having an extra rib at birth

• An abnormality in the neck muscles at birth

• Neck injury

• Injury to the first rib or collarbone

• Repetitive overhead arm movements that may cause inflammatory changes

Poor posture and obesity may raise your risk for thoracic outlet syndrome. People who do repetitive overhead arm movements, such as swimmers or pitchers, may also have a higher risk.

Your symptoms may come and go. This may be partly based on your activity level. Overhead activities may make your symptoms worse. You most likely have symptoms on only 1 side. In some cases thoracic outlet syndrome can cause symptoms on both sides of the body.

Symptoms can include:

• Aching in your neck, shoulder, arm, or hand

• Pain, numbness, or tingling of your forearm or fingers

• Hand weakness

• Limited range of motion of your arm

• A depression in your shoulder

• Pain in your neck muscles

• Swelling and redness of your arm

• Pale and cool arm and hand

Thoracic outlet syndrome is often more difficult to diagnose than other shoulder problems. Your healthcare provider will ask about your health history and your symptoms. You will also have a physical exam. Your healthcare provider may move your hand and arm in different positions.

A specific test may be done to help diagnose thoracic outlet syndrome. Your healthcare provider may have you raise your arms and then open and close your fist for a few minutes. This often brings on symptoms.

You may have other tests, such as:

• Nerve conduction tests. This is done to see how your nerves are affected.

• Doppler ultrasound. This looks at blood flow through your arm and hand.

• Chest X-ray. This is done to check for abnormal bone such as an extra rib.

• CT scan. This may be done if your healthcare provider needs to see more detail.

• CT angiography. This is done to get more information about blood flow through your arm.