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  • Writer's pictureDaniel Selin

Thoracic outlet syndrome

Thoracic outlet syndrome, TOS, TOS symptoms, Upper thoracic outlet compression syndrome, shoulder girdle, shoulder girdle compression, subclavian artery compression, subclavian vein compression, upper limb pain, radiating pain, pain, numbness, weakness, fatigue, neck pain, neck and facial pain, upper back pain, shoulder pain, chest pain

Thoracic outlet syndrome (TOS) describes a situation where nerves and/or blood vessels in the upper thoracic outlet area are compressed or irritated by adjacent structures. The thoracic outlet is formed by the anterior and middle scalene muscles, along with the first rib, creating a triangle. Other possible compression sites include the space between the clavicle and the first rib, as well as the space between the pectoralis minor muscle and the chest wall. TOS symptoms are often attributed to compression or irritation of neurovascular structures in one or more of these areas.

Thoracic outlet syndrome has long been a controversial topic and there are still no universally accepted precise diagnostic criteria for it. Diagnosis relies on medical history, clinical examination and the exclusion of other conditions that could explain the patients symptoms.

Patients with TOS often experience pain or numbness in the upper limb, radiating pain in the shoulder and scapular region. Additionally, migraines, headaches, facial pain and other symptoms have been reported. These varied symptoms can pose challenges in diagnosis, and patients may be misunderstood, leading to delays in placing the correct diagnosis.

In arterial TOS, symptoms may include coldness and ischemia in the upper limb, while in venous TOS, symptoms may include swelling and hyperesthesia in the thoracic outlet and upper limb region. Symptoms may also trigger a sympathetic nervous system reaction, resembling of CRPS.

Improper strain, poor ergonomic postures during work, deviations in shoulder posture and especially working with arms raised can exacerbate symptoms. Nocturnal symptoms are also possible, especially if sleeping positions contribute to compression of the shoulder girdle or associated vascular structures.


The Brachial plexus

The brachial plexus is a complex network of nerves that extend from the cervical spine all the way to the armpit, playing a crucial role in sensory and motor functions throughout the entire upper limb.

It consists of nerve roots forming the front branches of the four lower cervical vertebrae (C5-C8) and the first thoracic vertebra (T1). The course of the nerve plexus is accompanied by major blood vessels leading to the upper limb. The brachial plexus is responsible for the majority of the sensory and motor innervation of the entire upper limb.

The brachial plexus is divided into five main components: roots, trunks, divisions, cords, and terminal branches. When viewed from top to bottom, the anterior branches of the nerve roots (C5–T1) converge and form the upper (C5–6), middle (C7) and lower (C8–T1) nerve trunks. Each trunk divides into anterior and posterior divisions, forming six divisions in total. The divisions merge again to form three cords, which then further divide to create three main nerve branches to the upper limb, as well as the musculocutaneus nerve and skin and the axillary nerve. Therefore, the five terminal nerves of the brachial plexus are the ulnar nerve, median nerve, radial nerve, the musculocutaneus nerve and axillary nerve.

Together, these nerves are responsible for the sensory and motor innervation of the entire upper limb, with two exceptions: the trapezius muscle receives its motor innervation via the accessory nerve (cranial nerve XI) and its sensory innervation from the anterior branches of the C3 & C4 nerve roots. Additionally, the skin of the axillary region is innervated by the intercostobrachial nerve.

Peripheral nerve branches also extend from the brachial plexus to the neck, scapula, shoulder and upper chest area.


Anatomical compression sites predisposing to TOS symptoms

Listed from top to bottom, typical compression sites underlying TOS symptoms include the Scalene triangle, the costoclavicular space and the space beneath the pectoralis minor muscle, also known as the subcoracoid space.

Typical compression sites of neurovascular structures in thoracic outlet syndrome (TOS):

A) the scalene triangle B) the costoclavicular space C) the space beneath the pectoralis minor muscle

The Scalene triangle is formed by the anterior and middle scalene muscles and the first (uppermost) rib, creating a space through which the brachial plexus and subclavian artery pass. Entrapment of the brachial plexus or the subclavian artery in the Scalene triangle may result from a dysfunction of the first rib, the existence of a cervical rib or hypertrophy or overuse of the scalene muscles.

The costoclavicular space is formed by the middle third of the clavicle, the first rib, and the upper border of the scapula. The brachial plexus, subclavian artery and subclavian vein traverse through the costoclavicular space before continuing their course beneath the coracoid process. Entrapment of the brachial plexus or subclavian vessels in the costoclavicular space may result from congenital deformities, trauma to the first rib or clavicle or because of structural changes in the subclavius muscle or the costocoracoid ligament.

The space beneath the pectoralis minor muscle (subcoracoid space) is located below the coracoid process, just beneath the tendon of the pectoralis minor muscle. The coracoid process forms the ceiling, the pectoralis minor forms the anterior wall and ribs 2-4 form the posterior wall of this space. Particularly, tightening or tension in the large pectoral muscle can lead to narrowing of this space and consequently compression of neurovascular structures during abduction of the arm.

Certain anatomical anomalies can also narrow the thoracic outlet, posing additional challenges to the passage of the brachial plexus and vascular structures. Examples include cervical ribs (extra ribs originating from the lowest cervical vertebra), elongated transverse processes of the cervical vertebrae, congenital soft tissue changes or restricted movement of the clavicle. Additionally, functionally acquired anatomical changes in the area can cause compression and irritate the neurovascular structures.


Epidemiology and Etiology

TOS symptoms occur in approximately 8% of the population, with the syndrome being 3-4 times more common in women than in men. Initial symptoms often begin between the ages of 30-40 and are rarely seen in children. The majority of TOS symptoms (up to 95%) are attributed to compression and irritation of the brachial plexus, with only a small percentage (~5%) resulting from vascular compression.

The etiological factors of TOS can be broadly divided into two groups, where the underlying causes are either functional or structural. Functional factors are more common than structural factors but these are also more controversial.

The most common functional cause of TOS symptoms is constriction of the Scalene triangle due to the elevated position of the upper limb. Additionally, forward or downward positioning of the head and shoulders combined with abduction or flexion of the arm beyond 90 degrees can narrow the costoclavicular space or the space beneath the pectoralis minor muscle. It is believed that women experience TOS symptoms more frequently than men partly because women have less developed shoulder and scapular muscles, leading to tendencies for rounded and protruding shoulders. Additionally, the weight of the breasts can pull the shoulders forward and downward, increasing the prevalence of potential compression areas.

Structural reasons include acquired or congenital bone and soft tissue abnormalities, such as rib deformities or extra ribs. For instance, hypertrophy of the scalene muscles or abnormal attachment points to the first rib may structurally constrict the Scalene triangle. Hypertrophy of the scalene muscles often results from upper chest breathing.

Previously, cervical ribs were thought to be a common cause of TOS, but considering that cervical ribs occur in only about 0.5-0.6% of the population, of which only 10-20% seem to cause symptoms, this does not appear to be very likely.

Functional changes such as postural deviations, muscle shortening or tension, poor working postures or inadequate sleep ergonomics, as well as thickening of connective tissues, appear to explain a larger portion of TOS symptoms. However, below are listed a few structural and functional reasons underlying TOS symptoms.

Structural or congenital reasons:

  • Cervical rib

  • Elongated transverse processes in cervical vertebrae

  • Abnormal muscle anatomy

  • Thickening and abnormalities in connective tissues

  • Abnormalities in the attachment of the scalene muscles

  • Exostosis of the first rib

  • Cervical scoliosis

  • Congenital elevated or bilaterally elevated scapula

  • Abnormal course of the subclavian artery or vein

Functional or acquired reasons:

  • Changes in posture; drooping and protruding shoulders, forward head posture

  • Poor work posture, with emphasis on the brachial plexus or surrounding vessels

  • Heavy breasts

  • Stiff or elevated first rib

  • Trauma; fractures of the clavicle or ribs

  • Whiplash injuries

  • Repetitive use of a heavy or poorly fitting backpack

  • Repetitive strain injuries (such as prolonged sitting at a keyboard)

  • Working or sleeping with hands above shoulder level

  • Hypertrophy of the scalene muscles (often resulting from weakened diaphragmatic breathing)



The presentation of TOS symptoms varies widely, ranging from mild pain and sensory disturbances to severe complications that threaten the function of the entire limb.

TOS patients commonly experience pain and sensory changes in the upper limb, shoulder, chest area, upper back, neck, throat, face or skull base. Pain is often accompanied by numbness, tingling or an electric shock-like sensation. Pain may be constant or occur only in specific situations or positions. A feeling of weakness or rapid muscle fatigue is also a common concern among TOS patients. Changes in skin colour and temperature are also possible.

Symptoms typically worsen when the upper limb is raised or when working postures are static and prolonged. Typical situations where TOS symptoms occur include:

  • Hanging curtains or changing a light bulb

  • Repeated overhead throwing motions, such as throwing a ball over the head

  • Serving in tennis

  • Driving a car

  • Sleeping with hands above the head

  • Writing or working on a computer

The symptom profile varies slightly depending on which part of the brachial plexus is involved. When the upper part of the brachial plexus (C5, C6, C7) is affected, pain often occurs on the side of the neck, radiating to the ear and face on the same side. Pain often radiates backward from the ear towards the skull base and then downward towards the shoulder blades. Pain and abnormal sensation may also be felt in the area around the collarbone and chest muscles. Severe headaches or migraines are also possible when there is damage or irritation to the upper plexus. In this case, headaches are usually felt in the back of the head but may also radiate to the facial area.

In injuries or irritation to the lower part of the brachial plexus (C8, T1), symptoms are typically present in the front and back of the shoulder, radiating along the outer edge of the forearm to the hand.

Coldness in the upper limb, ischemia of the hand or fingers and paleness of the upper limb when raised may be signs of arterial TOS, whereas swelling, bluish discoloration of the skin, hyperesthesia and alternating sensations of cold and warmth are considered venous symptoms.

TOS can be broadly categorized into three main types based on the presumed neurovascular structure involved, but classification is difficult and the topic is controversial. Furthermore, there may be overlaps between subtypes, and it is entirely possible for TOS symptoms to be explained by multiple subtypes simultaneously. It is important to remember that the diagnosis of TOS is primarily an exclusion diagnosis, where other possible causes of symptoms are ruled out and there is no clear diagnostic criterion for TOS itself.

The subtypes of TOS are classified according to which structure is presumed to be compressed. Collectively accepted subtypes of TOS include Arterial TOS, Venous TOS, and Neurogenic (or Neurological) TOS, with Neurogenic TOS further subclassified into either "true Neurogenic TOS" or "Controversial Neurogenic TOS" (sometimes also referred to as Symptomatic TOS). Neurogenic TOS is significantly more common than either arterial or venous TOS, which occur only rarely.

Additionally, there are other ways to classify TOS and a common consensus is not always easy to find. However, this text focuses on the above classification and thus discusses their characteristics.

Arterial TOS is the rarest of all TOS types and may result from compression at any point along the brachial plexus pathway. Symptoms of arterial TOS may include numbness and tingling in the upper limb or shoulder. Pain is often felt in the upper limb area, and a decrease in cold tolerance, claudication, or paleness of the skin may occur. Symptoms often start suddenly, and the condition is often seen in young adults who perform intense or prolonged manual labor.

Venous TOS results from either structural or functional narrowing of the costoclavicular or subpectoral spaces. Typical symptoms of venous TOS include bluish discoloration of the hands or forearms, numbness and fatigue in the upper limb. Swelling and numbness of the fingers and hands is common. A feeling of heaviness in the upper limb, especially with prolonged use, is also common. Venous TOS typically worsens in situations where the upper limb is repeatedly or continuously stressed. Venous TOS can also cause a blood clot in the axillary or subclavian vein, so this possibility should always be considered when examining the patient.

"True neurogenic TOS" occurs when the lower parts of the brachial plexus (C8-T1) are compressed due to either structural or functional factors. Symptoms often include pain, numbness, tingling and/or weakness in the areas innervated by the C8 and T1 nerve roots. The thenar muscle of the hand may also atrophy and might for this reason be misdiagnosed as carpal tunnel syndrome. Fine motor skills in the hands and fingers may deteriorate along with a decrease in cold tolerance. Symptoms typically occur both during the day and at night, but daytime symptoms are often more severe than nighttime symptoms. A head or neck injury may also be involved, but symptoms may also occur without a history of trauma. It often affects younger individuals with either hypertrophy of the scalene muscles or structural changes in the ribs.

"Controversial neurogenic TOS" occurs when there is compression or irritation of the upper part of the brachial plexus (C5-C6) due to structural or functional factors. Symptoms may include shoulder pain, which radiates to the neck and head on the same side. Additionally, pain in the chest and shoulder blade area is common. Possible sensory or motor symptoms generally follow the areas innervated by the C5 or C6 nerve roots. Headaches located in the back of the head or migraines that may radiate to the facial area are also possible. Symptoms worsen when the upper limbs are stressed for prolonged periods or held in an elevated position for too long. Hands often become numb at night, disrupting sleep, but this is thought to be due to the release of compression, leading to restoration of nerve blood flow in the brachial plexus. This is considered a positive response. The sensation is somewhat comparable to the numbness or tingling felt in the foot or toes, when removing a tight shoe or ice skate.



The primary treatment approach for TOS is conservative, combining both pharmacological and non-pharmacological pain management methods along with physiotherapy.

The goal of conservative treatment is to alleviate pain and improve function and work capacity. This is achieved through a combination of education and advice, a precise and progressive exercise program and manual therapy. Pain medication, including potential anti-inflammatory medication, should also be considered to achieve the best possible treatment outcome. Pushing through severe pain often only complicates recovery and can, in the worst case, lead to chronic pain.

Medication therapy commonly involves a combination of pain relievers and anti-inflammatory drugs and possible inflammation and swelling can also be treated with cold therapy. For more severe pain management, opioids or medications that increase pain threshold may be considered.

Surgical treatment may be considered if the patient has TOS that significantly impairs daily life and does not respond to long-term and properly implemented conservative treatment or if the patient has a significant neurological finding caused by TOS. In such cases, one of three surgical options may be considered:

  1. Scalene release, which involves releasing nerves and blood vessels from the soft tissue compression above the clavicle.

  2. First rib resection, which is a partial removal either through the armpit or via thoracoscopic surgery.

  3. Combined scalene release and first rib resection.

Among these, first rib resection seems to have slightly more convincing evidence compared to scalene release alone. There is limited research on factors affecting the prognosis of TOS surgery, but short-term response is generally good. Factors that may worsen surgical outcomes include vague neurological symptoms, inadequate first rib removal, surgical complications and previous TOS surgery. Smoking, a history of injury preceding the onset of symptoms and prolonged duration of symptoms also worsen surgical response.

Surgical intervention should only be considered if desired results are not achieved with appropriate conservative treatment over several months or if symptoms worsen continuously.



The content of physiotherapy varies based on the symptomatology, background factors, structures under compression and clinical findings. Therefore, physiotherapy always begins with a thorough assessment of background factors and a clinical examination, allowing for the development of an individualized and effective rehabilitation program.

Self-care guidance is a central part of treatment, providing patients with a better understanding of TOS and teaching methods to manage their symptoms.

In general, physiotherapy for TOS often includes a combination of the following methods:

  1. Manual therapy: Soft tissue manipulation and joint mobilizations are used to reduce muscle tension, promote fluid and blood circulation, and improve joint function and mobility.

  2. Movement and posture therapy aim to promote the passage of neurovascular structures and reduce potential compression or pinching.

  3. Activating exercises aim to improve fluid circulation and muscle function.

  4. Pain management techniques may include heat or cold therapy, manual therapy, acupuncture or supportive positions.

  5. Biomechanical assessment and treatment aim to reduce increased load on nerve and vascular structures by changing prevailing movement patterns and postures.

  6. Assessment of sleep ergonomics and necessary guidance.

  7. Diaphragmatic breathing guidance if unfamiliar.

Here are a few specific physiotherapy interventions and their main goals in the treatment of Thoracic outlet syndrome:

Progressive exercises and load modification aim to:

  • Give nerve structures time to regenerate and recover from excessive strain.

  • Manage overall load.

  • Reduce compression and stretching load on irritated nerve tissues.

  • Increase fluid and blood circulation in irritated tissues.

  • Alleviate pain.

  • Improve the sliding properties of irritated nerves, for example, with exercises that mobilize neural tissues.

Manual therapy aims to:

  • Alleviate pain and activate descending pain pathways.

  • Reduce friction and compression load on irritated nerves.

  • Reduce muscle tension.

  • Improve muscle and joint performance.

  • Reduce cortisol secretion in tissues.

  • Improve blood circulation in treated tissues.

  • Improve mobility.

  • Reduce the bothersomeness of pain.

Guidance and counseling aim to:

  • Provide sufficient information about the nature of the condition, its background factors, and rehabilitation, alleviating the patient's concern and improving their self-efficacy. Additionally, knowledge of the healing process and prognosis often increases motivation for self-rehabilitation. Factors influencing the treatment prognosis and schedule can also be addressed, reducing patient uncertainty and concern, thereby making it easier to live with pain.


Self care

If you suspect you have symptoms related to TOS, I recommend contacting a healthcare professional before initiating any treatment. However, you can still start self-care with the following advice, provided that these actions do not exacerbate your symptoms:

  1. Posture correction: Maintain good posture and avoid letting your shoulders slump too low or forward. You can also strengthen the muscles needed to maintain proper posture by practicing an "improved" posture while exercising your upper extremities, such as during weightlifting.

  2. Stretching: Perform gentle dynamic stretches, avoiding intense or symptom-aggravating exercises. You can lightly stretch the pectoralis minor, chest muscles and the upper trapezius muscle.

  3. Muscle strength exercises: Try strength training for the shoulders, neck and upper back muscles. Start with light resistance and listen to any symptoms that may arise. Avoid exercises that cause pain if the situation hasn't been thoroughly assessed.

  4. Resting positions: Experiment with resting positions that reduce compression on the thoracic outlet area. Sit or lie down with your shoulders supported in an elevated position using a pillow or blanket, maintaining this position for about thirty minutes.

  5. Ergonomics: Ensure that your workspace is ergonomically set up to reduce strain on the thoracic outlet area. Avoid excessively low work surfaces that cause your shoulders to hang.

  6. Take breaks: Avoid prolonged static positions. Remember to take breaks from your work and move around during your breaks.

  7. Pain management: Use pain relievers such as ibuprofen or acetaminophen to alleviate symptoms following recommended dosage guidelines. Discuss long-term pain management strategies with a healthcare professional.

  8. Relaxation techniques: Practice stress-reducing techniques such as deep breathing, meditation or yoga.

  9. Sleep ergonomics: Try different sleeping positions to find one that minimizes pressure on your neck and shoulders. Avoid sleeping positions where you keep your arms above your head.

  10. Rest: Ensure you get enough rest and sleep. Sufficient sleep improves recovery and tissue healing.

  11. Consult a healthcare professional: Discuss your symptoms with a doctor or physical therapist to receive personalized guidance and a tailored treatment plan.

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