Thoracic Outlet Syndrome (TOS) - Part I

What is it?

The thoracic outlet syndrome (TOS) is the upper aperture of the chest, between the collar bone and the first rib. It refers to the symptoms that arise when the nerves (three large trunks, forming the brachial plexus) or blood vessels (subclavian vein and artery) that pass through this narrow passageway are compressed at the thoracic outlet.

The thoracic outlet is surrounded by the collar bone at the top and front, the first rib below, and two muscles, one in the front and the other in behind. These muscles, which run downwards from the spine to the first rib, are called the scalene muscles, and their function is to stabilize the first rib. [1]

Causes

TOS is a repetitive motion problem and is commonly occupationally related.  

There are three areas where compression can occur. The first area of compression is the muscle area. Enlargement of the muscles, due to muscle imbalance following a shoulder injury or operation, and repetitive movements that exercise the muscle, such as certain sports, like swimming, ball throwing (cricket), and rugby; musicians, like violinists and flautists; and certain work activities where the arms are elevated a lot, like mechanics, hairdressers, schoolteachers and assembly line workers. Incorrect weight training also can cause a muscle imbalance [2]. Heavy lifting and carrying can bulk up the scalene muscles to the point where the blood vessels and the nerves are entrapped and compressed [3]. Nerve compression can also occur due to the presence of scar tissue between the muscles, for example, a traumatic injury from a car accident. In an accident, the shoulder harness of the car of the seat belt can strain or tear the muscles. As they heal, a scar tissue can build up, thus putting pressure on the nerves and blood vessels at the thoracic outlet [3]. Congenital conditions can also be responsible for TOS, such as the presence of abnormal bands that run over the nerves or between the muscles, or an extra rib in the neck. [2] 

The second area of compression locates between the collar bone and the first rib. Clavicle fractures may predispose to later scar formation, which may compress the structures later on. Fractures of the first rib may also cause immediate damage to the brachial plexus, as it runs over the rib. If there is no immediate damage, symptoms may gradually develop later, like a growth of a scar tissue around the rib. Some people may also have a very thick rib, compressing the the structures against the collar bone [2].

The third area of compression may be further down, below the collar bone, where compression is caused by a thick pectoralis muscle where it attaches to the scapula. [2]

Other causes, such as poor posture and obesity, may aggravate the condition. It occurs classically in women with long necks and dropping shoulders, as well 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 it is longstanding. [1] The hyperextension-flexion whiplash injury of the neck [4] can cause a muscle spam, which will cause compression nerves and blood vessels, and/or stretching of the brachial plexus.

Symptoms

The symptoms presents on a TOS occur due to the pressure of the blood vessels and nerves. Symptoms of pressure of the subclavian artery consist of coldness, pallor, and fatigue of the arm with exercise. These patients often experience true claudication (muscular cramp sensation). Pressure of the subclavian vein produces swelling, edema and cyanosis (bluish color) of the arm. This happens due to reduced blood flow to the arm and hand (especially in the elevated position). [4]

The symptoms caused by the compression of the nerves are aching pains in the shoulder, neck, arm and hand. There may be a pain shooting all the way down to the fingers, and they may go numb with tingling sensation (paresthesias). Paresthesias most commonly affect the ring and small fingers.. The arm may often go numb, especially when lying on the affected side. 

The hand may feel clumsy and have difficulty with certain tasks, like opening a jar, wringing out a cloth, with tendency to drop things. Overhead activities, carrying objects and driving may also be affected. [1] Headaches may occur, and be severe and disabling, starting at the base of the skull and radiating over the top of the head. [4] 

The severity of the symptoms tends to increase after certain activities, and they are worse at the end of the day or during sleep. [2]

[1] Harris, D., G. Thoracic Outlet Syndrome (T.O.S). Joe de Beer & Associate: Orthopaedic Shoulder Surgion

[2] Franklin, G.M., Glass, L., Javaher, S.P., Kearney, R.N. (2010). Work-Related Neurogenic Thoracic Outlet Syndrome: Diagnosis and Treatment. Medical Treatment Guidelines: Washington State Department of Labor and Industries.

[3] Thoracic Outlet Syndrome. Physical Therapy in Onley and Cape Charles Virginia for Shoulder.

[4] Brantigan, C.,O., Roos, D.,B. (2004). Diagnosing thoracic outlet syndrome. Hand Clin (20): 27-36