Thoracic outlet syndrome

Thoracic outlet syndrome

Description, Causes and Risk Factors:

Abbreviation: TOS.

The thoracic outlet is the upper aperture of the chest, between the collar bone and the first rib. This narrow passageway is crowded with blood vessels that run out of the chest to the arm, as well as the nerves that exit the spine in the neck to supply the arm. The nerves fuse to form 3 large trunks and these run through the thoracic outlet and split up again into separate nerves lower down.

Thoracic outlet syndrome refers to the symptoms that arise when the nerves or blood vessels are compressed at the thoracic outlet.

The thoracic outlet is bordered by the collar bone at the top and front, the first rib below and two muscles, one in the front, and another behind. These muscles are called scalene muscles, and their function is to stabalize the first rib. They run from the spine, higher up and run downwards, and are attached to the first rib, one in the front and the other at the back of the rib.

The brachial plexus nerves and subclavian artery pass through the trinagle formed between the first rib and scalene muscles. The subclavian vein lies in front of the first scalene muscle and behind the collar bone.

Enlargement of the muscles as well as scar tissue between them can compress the structures. The muscles may enlarge due to muscle imbalance following a shoulder injury or operation, and repetitive movements that exercise the muscle, such as certain sports, and certain work activities.

Sport activities include swimming, ball throwing, and rugby. Typical jobs that predispose to enlargement of these muscles are those where the arms are elevated a lot, such as mechanics, hairdressers, and schoolteachers.

Incorrect weight training may cause a muscle imbalance. A soft tissue injury to the muscle can cause scar tissue. Congenital condition such as abnormal bands that run over the nerves or between the muscles and an extra rib in the neck are other causes.

Another area of compression is between the collar bone and the first rib. Clavicle fractures may predipose to later scar information, which may compress the structures later on. Fractures of the first rib may cause immediate damage to the brachial plexus, as it runs over the rib, making contact with it as it goes to the arm. If there is no immediate damage, symptoms may gradually develop later, as scar tissue grows around the rib, and encases the nerves and artery.

Some people may have a very thick first rib, causing comrpession between it and the collar bone. The third area of compression may be further down, below the collar bone, where compression occurs by a thick pectoralis minor muscle where it attaches to the shoulder blade.

Poor posture and obesity may aggravate the condition. It occurs classically in females, with long necks, and drooping shoulders, as well as in stocky, muscular people. A painful shoulder following trauma or surgery may cause the arm to hang, and stretch the nerves over the rib if this is longstanding.


Symptoms include neck, shoulder, and arm pain, numbness, or impaired circulation to the extremities (causing discoloration). Often symptoms are reproduced when the arm is positioned above the shoulder or extended. Patients can have a wide spectrum of symptoms from mild and intermittent, to severe and constant. Pains can extend to the fingers and hands, causing weakness.

Pressure on the blood vessels can reduce the blood flow to the arm and hand and cause them to tire easily, feel cold, and go pale. Pressure on the vein can cause the arm or hand to swell a bit. Pressure on the nerves can cause vague, aching pains in the shoulder, neck, arm and hand. There may be a pain shooting all the way down the fingers, and they may go numb. Headaches may occur. Overhead activities, carrying objects, and driving may be affected. The arm may often go numb when lying on that side.

The hand may feel clumsy and one may struggle with certain tasks, such as opening a jar, wringing out a cloth and there may be a tendency to drop things.


Diagnosis is confirmed by the typical symptoms, physical examination, and some tests. TOS is often only diagnosed after excluding other conditions that may be present with similar symptoms, and these need to be excluded. These are shoulder problems (rotator cuff injury, neck problems), ulnar nerve entrapment at the elbow and carpal tunnel brachial plexus.

The following investigations are routinely performed:

    Evaluation by a shoulder surgeon to exclude shoulder pathology, with clinical examination, ultrasound and x-rays and possibly MRI scan of the shoulder.

  • X-rays of the cervical spine to assess for cervical ribs and check the alignment, and if indicated, MRI scan of the neck.

  • Chest x-ray to check the lung, and look for the clavicle and first rib deformities.

Other tests performed include:

    Nerve conduction tests together with neurological evaluation. These may on occasion be of value, but a negative test does not mean that TOS is not present. The test is expensive.

  • Multi-slice CT scan: This can be performed with the arms at the side and then with the arms elevated above the head, and can confirm dynamic compression of the artery. This may be helpful, but may not diagnose nerve compression.

  • A venogram may on occasion be useful if it is thought that the vein is obstructed.


For most patients, conservative treatment is recommended. Avoiding precipitating factors such as wrong exercise, and time for the condition to settle may be all that is needed. Stress avoidance, work simplification and job site modification are recommended to avoid sustained muscle contraction and repetitive or overhead work that worsens symptoms.

Physiotherapy to help strengthen the muscles around the shoulder (deltoids and rhomboids) so that they are better able to support the collar bone. Ultrasound to the scalene muscles and sometimes strapping of the shoulder may help.

Postural exercises to help you stand and sit together straighter, which lessens the pressure on the nerves and blood vessels. If you overweight, losing some weight may help.

Anti-inflammatory medication such as Voltaren or ibuprofen together with rest may help.

If the condition settles, remember that a return to the precipitating factors may cause a recurrence. The condition does tend to flare up again, from time to time, even if the aggravating factors are avoided.

Avoiding recurrence: Avoid carrying heavy bags over the shoulder, and in particular, do not ever carry a heavy backpack.

Surgical treatment is considered when conservative measures have failed, and the symptoms continue to be bad.

Surgical Options: If the cause is due to bony obstruction such as a cervical rib, or fractured rib or collarbone with malunion, then surgery will be best as the condition is unlikely to get better on its own.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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