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Causes of Thoracic Outlet Syndrome

Thoracic outlet syndrome – often abbreviated as TOS – is a group of three related disorders that involve the compression of nerves (brachial plexus) or blood vessels (subclavian veins and arteries) in the thoracic outlet. 

The thoracic outlet is the space between the collarbone and the first rib. It constitutes an essential passageway for the nerves, veins, and arteries that connect the heart, spinal cord, and brain to the body’s extremities. 

While the causes of thoracic outlet syndrome are not fully understood, there are a few risk factors that may increase your chances of suffering from it. Let’s look at these below.

Physical Trauma    

Direct trauma, such as the whiplash of a car accident or repetitive injuries such as from carrying heavy weights on your shoulders, can cause structural changes to the thoracic outlet. 

Torn ligaments and tendons or fractured bones can compress the nerves and blood vessels below the collarbone and lead to TOS. The onset of symptoms of traumatic TOS can happen weeks or months after the event.

Repetitive Stress

Occupational activities that involve repetitive or forceful arm and shoulder movements can irritate and inflame the thoracic outlet, which can lead to TOS. Some activities that could increase your risk of developing thoracic outlet syndrome include baseball, golfing, swimming, volleyball, and weightlifting.

Anatomical Defects

Some anatomical defects can narrow the space between the first rib and the collarbone, which makes the compression of nerves and blood vessels more likely. Some inherited and congenital defects that cause TOS include malformations present at birth (i.e.: having an extra rib) or tight connective tissue between the spine and the rib. 


Tumors on the first rib or conditions such as fibrous dysplasia can press on nerves, veins, and arteries located in the thoracic outlet, which can lead to thoracic outlet syndrome. 

Poor Posture

Poor posture, such as dropping your shoulders or having your head forward, can restrict the passageway of nerves and blood vessels in the area below the collarbone, making TOS more likely. Additionally, over time, poor posture can shorten and tighten the muscles in the shoulder and neck, increasing the chance that the nerves exiting the spinal cord become pinched or compressed. 


During pregnancy, joints become loose and less stable, and excessive pressure is added onto the joints’ components due to the increased weight. This can cause the bones around the thoracic outlet to move and begin to press on nearby nerves and blood vessels. 


Females are 2-4 times more likely than men to develop TOS. This is because women tend to have less-developed muscles, a lower sternum, and a smaller thoracic outlet. 

These anatomic factors, coupled with a greater risk of suffering from poor posture, can change how the bones in the thoracic outlet intersect with each other, making it more likely for the nerves, veins, and arteries in the area to become compressed.

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Symptoms of Thoracic Outlet Syndrome

Depending on whether the veins, arteries, or nerves in the thoracic outlet are compressed, there are three types of thoracic outlet syndrome that may develop:

  • Neurogenic TOS: This condition accounts for over 90% of thoracic outlet syndrome cases, and occurs when the compression affects the nerves connecting the spinal cord to the shoulder, arm, and fingers. 
  • Venous TOS: Venous TOS accounts for 4% of TOS cases and happens when the compression affects the veins located under the collarbone.
  • Arterial TOS: Arterial TOS is the least-common form of thoracic outlet syndrome and only accounts for 1% of cases. This condition occurs when the compression affects the arteries under the collarbone.

The symptoms of thoracic outlet syndrome may vary depending on what component of the outlet is compressed. Let’s look at these symptoms in more detail below.

Symptoms of Neurogenic Thoracic Outlet Syndrome

The thoracic outlet houses the brachial plexus, which is a network of motor and sensory nerves that carry signals relating to movement, touch, temperature, and vibration from the spinal cord to the arm and vice versa. In neurogenic thoracic outlet syndrome, these nerves are compressed, irritated, or damaged until they are unable to transmit signals properly, which leads to symptoms like:

  • Pain in the shoulder and arm
  • Arm and hand weakness or clumsiness
  • Involuntary movements such as spasms or cramps
  • Numbness 
  • Tingling – also known as paresthesia

Symptoms of Venous Thoracic Outlet Syndrome

Venous thoracic outlet syndrome involves the compression of the subclavian veins, which are the major veins in the upper chest and lower neck. When these veins are pressed or damaged, they can lead to symptoms such as:

  • Swelling of the arm and hand, known as edema
  • Prominent veins
  • Changes of color in the hand and arms (i.e.: business or pallor)
  • Pain, tingling, or numbness in the arm or fingers. 

In severe cases, this condition can lead to blood clots and upper-body thrombosis.

Symptoms of Arterial Thoracic Outlet Syndrome

Arterial thoracic outlet syndrome occurs when the subclavian vein is compressed. This prevents the blood from flowing freely away from the heart and into the shoulder, arm, and hand. Although this is the rarest type of TOS, it is also the most serious and can cause symptoms like:

  • Changes in color in the arm and hand
  • Increased sensitivity to cold in the upper extremities
  • Severe pain and swelling 
  • Numbness in the arms, or “pins and needles” sensations

In severe cases, arterial TOS can lead to gangrene – or the death of tissue – and aneurysms (bulging) of the subclavian artery, conditions that require immediate medical care.

Regenerative Treatment Options for Thoracic Outlet Syndrome

When experiencing the first symptoms of thoracic outlet syndrome, obtaining an accurate diagnosis and choosing an adequate line of treatment are critical steps to take in order to avoid the most severe complications of this condition. 

However, this syndrome is often misdiagnosed, and patients are left to deal with symptomatic treatments that don’t do much more than just ease the pain derived from TOS. 

Thoracic outlet syndrome can last longer than six months and, in some cases, it may be a permanent condition. Because of this, it is crucial to look beyond taking pain-relieving medications or living in fear of experiencing life-threatening complications. 

Super-Concentrated PRP for Thoracic Outlet Syndrome

Platelet-rich plasma (PRP) refers to autologous blood samples that have been processed to have platelet concentrations that are 10-40 times higher than baseline levels using a laboratory setting. The use of PRP in regenerative medicine has received significant interest, due to its ability to deliver high concentrations of growth factors precisely and non-invasively to an area in need.

PRP procedures involve injecting the body’s own healing factors (platelets) into the injured tissue using image guidance with fluoroscopy and MSK ultrasound. This procedure can be used to treat a variety of orthopedic conditions, including joint instability, minor arthritis, ligament, and tendon injuries, and strains.

More than 30 randomized controlled trials have been carried out on the effectiveness of PRP to support the body’s ability to heal naturally by stimulating the cells within the targeted area.

Bone Marrow Concentrate Injections for Thoracic Outlet Syndrome

Stem cells are an essential component of the human body and play an important role in the repair of injured bones, ligaments, tendons, and other tissues. However, when we age or suffer an injury, the body may become unable to deliver enough stem cells to the area in need.

To help with this, bone marrow concentrate procedures at Orthagenex use imaging guidance to deliver concentrated bone marrow containing stem cells to the area in need. This encourages the body’s inherent ability to heal itself by replenishing cell population in the injured area.

In practice, bone marrow concentrate procedures are carried out by cannulating the bone near the pelvis with a trocar, a sharp-tipped device. This provides a narrow tunnel that can be used to collect samples of the bone marrow’s liquid component, which is rich in stem cells.

BMC procedures can assist patients in improving their spinal health and mobility without the lengthy and painful rehabilitation periods associated with surgery.


If you suffer from thoracic outlet syndrome, the chances are that the pain and numbness in your arm, coupled with the fear of experiencing severe complications, are impacting multiple aspects of your life. 

Living a life reliant on medications or undergoing invasive procedures is no longer the only option. The regenerative orthopedic treatments offered at Orthagenex can help you improve the health, mobility, and function of your upper body without surgery.

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