PT Tip of the Month Archive

Thoracic Outlet Syndrome (TOS)

What is Thoracic Outlet Syndrome (TOS)?

Thoracic outlet syndrome (TOS) refers to a group of syndromes where the blood vessels or nerves in the space between your collarbone and your first rib (aka, thoracic outlet) become compressed. These disorders manifest themselves with pain in the shoulder and neck which spreads into the arm, sensory deficits, weakness, swelling, and decreased blood supply to the affected arm. One syndrome involves compression of the brachial plexus (and/or C8 or T1 nerve roots), which is a collection of nerves in the area of the neck and armpit (neurogenic form), and manifests itself with signs and symptoms of numbness/tingling in the fingers, pain in the shoulder and neck, an ache in the arm or hand, and a weak grip. A second syndrome involves compression of the subclavian artery or vein, which are the major blood vessels of the upper chest (vascular form). Signs and symptoms of vascular TOS include: a bluish discoloration in the hand, arm pain/swelling, a throbbing lump near the collarbone, lack of color in the fingers or hand, or black spots on the fingers. The third syndrome is non-specific or disrupted TOS, in which case the specific cause of pain can't be determined. This last syndrome makes up the majority of cases of TOS. Prevalence of symptomatic TOS has been estimated to be about 10 out of every 100,000 people.

Currently, there is a lack of accepted standards in diagnosing TOS. After other conditions that can cause one-sided symptoms of arm pain, weakness, or loss of sensation are ruled out, the diagnosis of TOS is often made. X-rays, MRIs or EMGs may also be used to help diagnose TOS.


The thoracic outlet refers to the upper/front quarter of the body, from the mid-neck to the upper chest and tip of the shoulder. The nerves that originate from behind the neck at the top of the spinal cord course through three narrow passageways down into the arm. One of the passageways, called the interscalene triangle, is formed by the anterior and middle scalene muscles and the first rib. This space is already small at rest, but can become smaller with certain provocation tests (to test for TOS) or from the anatomical anomalies mentioned below. The bundle of nerves that pass through this area are referred to as the brachial plexus. The subclavian artery is a major artery that supplies blood to the head and arm, and the subclavian vein is a major vein that returns blood from the upper extremities back to the heart. All of these structures are located below the clavicle and can become compressed, giving way to signs and symptoms of TOS.


TOS may result from various anatomical abnormalities, such as an extra rib in the neck (cervical rib syndrome), anomalies in the shape of the vertebrae, abnormal fascial bands of tissue under the skin that connect the spine to the rib, or variation in muscle attachment of the different neck muscles, including the anterior/middle scalenes and pectoralis minor muscles. Often, TOS is associated with a history of trauma, such as car accidents or repetitive injuries from work or sports.

Other causes associated with TOS are poor posture, such as a forward head posture or drooping shoulders, which can cause the thoracic outlet structures to become compressed, or from pressure on the joints, such as in obesity or from carrying heavy loads on the shoulder.


The physical therapy exam includes ruling out other possible causes that may produce similar symptoms, and then applying provocation tests used to diagnose TOS. If diagnosis of TOS is made, conservative treatment may include stretching, shoulder strengthening, postural retraining, joint and soft tissue mobilizations, and the use of modalities. If you feel that you are experiencing signs or symptoms of thoracic outlet syndrome, and you would like to schedule an evaluation, call 617-232-PAIN for our Brookline office, and 617-325-PAIN for our West Roxbury office.


  1. Abdul-Jabar H, Rashid A, Lam F. Thoracic outlet syndrome. Orthop Trauma. 2008;23(1);69-73.
  2. Povlsen B, Belzberg A, Hansson T, Dorsi, M. Treatment for thoracic outlet syndrome. Cochrane Database of Systematic Reviews. 2010;1:1-20. doi: 10.1002/14651858.CD007218.pub2.
  3. Watson LA, Pizzari T, Balster S. Thoracic outlet syndrome part 1: clinical manifestations, differentiation, and treatment pathways. Man Ther. 2009;14:586-595.
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