Thoracic Outlet Syndrome (TOS)

Thoracic outlet syndrome (TOS) refers to a group of conditions that occur when blood vessels o

Julie Cai

November 15, 2022

Thoracic outlet syndrome (TOS) refers to a group of conditions that occur when blood vessels or nerves that run from the neck to the armpit are compressed. It only describes a group of conditions because the signs and symptoms of this condition vary from patient to patient, depending on the structures involved.

So.. what is the thoracic outlet?

The thoracic outlet is the space above the collarbone that is bounded by the collarbone, first rib, pectoralis minor and scalene muscles as seen above. Important arteries, veins and nerves (i.e. the subclavian vessels & brachial plexus) that run down the arm have to pass through this area of the thoracic outlet. Because of their proximity to one another, they are susceptible to compression, which results in the following symptoms.

Signs & Symptoms of Thoracic Outlet Syndrome

Individuals with TOS most likely present with pain in the neck or shoulder, or numbness or tingling involving either the entire upper limb or the forearm and hand. The arm may also feel weak, or easily fatigued and also have reduced grip strength. The involved arm may also feel colder, discoloured or blotchy skin, a throbbing lump near the collarbone or have a weak pulse.  

These symptoms typically worsen when the head is held in a forward position, when the shoulders are drooped, raising the arm overhead or back, or sleeping on the affected shoulder. This is because any sort of movement that compresses the space in the thoracic outlet will lead to a worsening of the symptoms.

It also commonly occurs in:

  • Overhead sports people (1)

→Due to the repetitive compression of the thoracic outlet

  • People with poor posture with drooping shoulders

→ The change in scapular positioning can decrease the diameter of the cervicoaxillary canal

  • People with chronically poor scapular control

→These people typically have a tight pectoralis minor, scalanes, and upper trapezius muscles, with a weak serratus anterior and lower trapezius muscles; this causes excessive anterior tilt and protection of the scapula

TOS can also be caused by a traumatic event such as a car accident where there is a crush injury of the upper thorax, fractures of the clavicle (collarbone and/or first rib) or clavicle callus formation. It can also be caused by congenital anatomical abnormalities.


Physio & Chiro treatment of Thoracic Outlet Syndrome is aimed at reducing compromised structures in the thoracic outlet through correcting posture. Depending on the body mechanics, treatment usually involves soft tissue release of the pectoral and scalene muscles, mobilisation of the first rib and adjustments as indicated. Forward head posture, neuromobility, and scapulothoracic mobility and control on the thoracic cage can also be corrected with a mixture of manual therapy and therapeutic exercise.

If you have any further questions about how we can help with Thoracic Outlet Syndrome, head over to our Contact Us page, or book in now to make an appointment.

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