A diagram showing thoracic outlet syndrome

Thoracic Outlet Syndrome

In Thoracic Outlet Syndrome, the brachial plexus (a bundle of nerves) and far less often, the subclavian nerve or artery can become compressed by surrounding structures. These structures are:

  • The first rib
  • The clavicle (collar bone)
  • The scalenus anterior muscle
  • The scalenus medius muscle


Symptoms of TOS may include arm numbness, pain, pins and needles, coldness or heaviness of the arm. The ulnar nerve is the most commonly compressed and this supplies the inside of the elbow, the little finger and the ring finger so symptoms are often felt but not confined to these area. Sometimes TOS may affect the whole hand, arm, neck and even the side of the face. Symptoms are often aggravated by overhead activities (such as hanging out washing or sleeping with the arm overhead) put traction on the brachial plexus.

Causes and Types

Structural Thoracic Outlet Syndrome is a rare condition, which involves bony restriction of the space through which the nerves and blood vessels pass. This may be due to an abnormality present from birth, such as an extra rib attaching to the lower cervical spine or may be the consequence of injury. Investigations such as a CT scan or MRI can help with diagnosis. Physiotherapy may still be indicated, however consultation with a specialist medical practitioner may be advisable. In some cases it requires surgery.

Functional Thoracic Outlet Syndrome (also known as Physiological Thoracic Outlet Syndrome) is very common condition in which prolonged postures (such as sitting at a computer with shoulders hunched forwards and down) may result in compression of the nerves of the brachial plexus. Excessive tension or hypertrophy of the adjacent muscles may cause direct compression. Muscle imbalances can also alter the position of both the first rib and the clavicle contributing to nerve compression, pain and numbness in the arm. Physiotherapy plays a vital role in this form of the condition.

Muscle imbalances, posture, breathing and TOS

Muscle imbalances occur when particular muscles may become short and tight due to overuse of poor posture. These include the scalenus anterior and medius and the pectoralis major and minor and the subclavius. The opposing muscles are usually weak (rhomboid major and minor and trapezius). The result of this imbalance (or perhaps the cause of it) is poor posture. When the shoulders and clavicle pulled forward and down for prolonged periods, this may result in a reduced space in the thoracic outlet. In addition an upper chest breathing pattern will tend to pull the first rib upwards, further reducing the size of the thoracic outlet, with the potential to cause TOS.

Scalene Muscle Tightness

There are three scalene muscles and the two at the front, scalenus anterior and medius, connect the side of the neck to the first rib. The brachial plexus passes in between them and may become compressed. Painful trigger pains in the scalenes may also refer pain to an area just behind the scapula (shoulder blade) the upper arm, forearm and thumb side of the hand. Tight scalenes can also cause neck pain. If you breathe with an ‘upper chest’ breathing pattern the scalenes can pull the first rib up towards the neck and Clavicle, further reducing the size of the thoracic outlet and putting pressure on the brachial plexus.

Pectoralis Minor Tightness

The pectoralis minor connects the front of the shoulder to the front of the chest wall. It pulls the shoulder forwards and downwards and when the shoulder is in this position for prolonged periods, it becomes tight, short and sometimes painful. Trigger points in this muscle may refer pain to the front of the shoulder and chest and the inside of the arm, little finger and ring finger. ‘Pectoralis Minor Syndrome’ occurs when this muscle compresses the brachial plexus as it passes between the muscle and the chest wall. Pectoralis minor can also affect the thoracic outlet by pulling the clavicle down, reducing the functional size of the thoracic outlet.

Pectoralis Major and Subclavius tightness

The pectoralis major and subclavius muscle pull the shoulder forward and so tightness will accentuate the aggravating posture. In addition subclavius can pull the first rib upwards in a person who has an upper chest breathing pattern.

Rhomboids and Trapezius Weakness

Weakness in the middle trapezius and rhomboids muscles can result in the ‘shoulders down and forward’ position that predisposes to Thoracic Outlet Syndrome. Strengthening these muscles and correcting posture can help to reduce pressure on the structures which pass through the thoracic outlet.

thoracic outlet syndrome

Above: brachial plexus passing under the pectoralis minor and in between the scalenes

Physiotherapy Programme for overcoming Thoracic Outlet

  • Stretch the relevant tight muscles (usually scalenes, pectorals and subclavius)
  • Massage the affected muscles and treat trigger points with acupressure or acupuncture
  • Mobilise the first rib in a downwards direction
  • Improve breathing pattern by teaching relaxed diaphragmatic breathing where relevant
  • Strengthen the opposing muscle groups (usually trapezius and rhomboids)
  • Improve posture and muscle use – taping may be helpful
  • Teach brachial plexus nerve glides for radial, median and ulnar nerves as relevant.