Thoracic Outlet Syndrome (TOS) is characterized by symptoms attributable to compression of the neural or vascular anatomic structures that pass through the thoracic outlet.
The other names used for TOS are based on descriptions of the potential sources for its compression. These names include:
- cervical rib syndrome,
- scalenus anticus syndrome,
- hyperabduction syndrome,
- costoclavicular syndrome,
- pectoralis minor syndrome,
- first thoracic rib syndrome.
See Also: Clavicle Fractures
Thoracic Outlet Syndrome was first noted in 1743 when an association was made between the cervical rib and Thoracic Outlet Syndrome, although it was not until 1818, that the medical management of Thoracic Outlet Syndrome was discussed. In the early twentieth century, Adson stressed the role of the scalene muscles in neurovascular compromise, and Wright showed that shoulder hyperabduction could produce thoracic outlet obstruction. It was Peet who coined the term Thoracic Outlet Syndrome in 1956. Then, in the early 1960s, Roos emphasized the importance of the first rib and its muscular and ligamentous attachments in causing thoracic outlet obstruction.
The thoracic outlet is the anatomic space bordered by the first thoracic rib, the clavicle, and the superior border of the scapula, through which the great vessels and nerves of the upper extremity pass.
The bony boundaries of the outlet include the clavicle, first rib, and scapula, and the outlet passage is further defined by the interscalene interval, a triangle with its apex directed superiorly. This triangle is bordered anteriorly by the anterior scalene muscle, posteriorly by the middle scalene muscle, and inferiorly by the first rib.
See Also: Brachial Plexus Anatomy
Thoracic Outlet Syndrome Causes:
Traumatic: Twenty-one percent to 75% of Thoracic Outlet Syndrome patients have an association with trauma. This may involve macro-trauma, as in the case of an MVA, or microtrauma, as in the case of a muscle strain of the scapular stabilizers, resulting from repetitive overhead activities.
Developmental: During the normal growth of children and adolescents, the scapulae gradually descend upon the posterior thorax, with the descent being slightly greater in women than in men. A strain injury to the scapular suspensory muscles, which lengthen in conjunction with scapular descent during normal development, is known to be associated with Thoracic Outlet Syndrome. These facts help to explain the rarity of symptomatic Thoracic Outlet Syndrome until after puberty, and the increased prevalence in women.
The lowest trunk of the brachial plexus, which is made up of rami from the C8 and T1 nerve roots, is the most commonly compressed neural structure in Thoracic Outlet Syndrome. These nerve roots provide sensation to the fourth and fifth fingers of the hand and motor innervation to the hand intrinsic muscles.
The subclavian artery and the lower trunk of the plexus pass behind the clavicle, and into the costoclavicular space. From there they pass over the first rib, between the insertions of the anterior and middle scalene muscles and are joined by the subclavian vein.
See Also: Clavicle Anatomy
Thus, the course of the neurovascular bundle can be subdivided into three different sections, based on the areas of potential entrapment:
- As the brachial plexus and subclavian artery pass through the interscalene triangle, interscalene triangle compression can result from injury of the scalene or scapular suspensory muscles. In some cases, fibromuscular bands can develop between the anterior and middle scalenes, or between the long transverse processes of the lower cervical vertebrae, producing entrapment. The subclavian vein is not involved, because it usually passes anterior to the anterior scalene muscle. Entrapment at this site may also result from cervical ribs, which are present in 0.2% of the population and occur bilaterally in 80% of those affected. However, the presence of a cervical rib does not necessarily precipitate signs and symptoms, with fewer than 10% of individuals with cervical ribs ever experiencing .
- As it passes the first rib, clavicle, and subclavius: the costoclavicular space. Entrapment in this space between the ribcage and the posterior aspect of the clavicle may occur with clavicle depression, rib elevation caused by scalene hypertonicity, repetitive shoulder abduction, or a first rib-clavicular deformity. A postfracture callus formation of the first rib or clavicle can also increase the potential for entrapment.
- As it passes the coracoid process, pectoralis minor, and clavipectoral fascia to enter the axillary fossa. At this point, the subclavian artery and vein become the axillary artery and vein. At this third site, the neurovascular bundle can be compromised with arm abduction or elevation, especially if external rotation is superimposed on the motion. Pectoralis minor tendon compression is associated with shoulder hyperabduction. During hyperabduction, the tendon insertion and the coracoid act as a fulcrum, about which the neurovascular structures are forced to change direction. Hypertrophy of the pectoralis minor tendon has also been noted as a cause of outlet compression.
There may be multiple points of compression of the peripheral nerves between the cervical spine and hand, in addition to the thoracic outlet. When there are multiple compression sites, less pressure is required at each site to produce symptoms. Thus, a patient may have concomitant Thoracic Outlet Syndrome, ulnar nerve compression at the elbow, and carpal tunnel syndrome. This phenomenon has been called the multiple crush syndrome.
Symptoms vary from mild-to-limb threatening and often mimic common but difficult to treat conditions such as tension headache or fatigue syndromes.
The chief complaint is usually one of diffuse arm and shoulder pain, especially when the arm is elevated beyond 90 degrees.
Potential symptoms include:
- pain localized in the neck, face, head, upper extremity, chest, shoulder, or axilla;
- upper extremity paresthesias, numbness, weakness, heaviness, fatigability, swelling, discoloration, ulceration, or Raynaud phenomenon.
Neural compression symptoms occur more commonly than vascular symptoms.
Karas described five symptom patterns of Thoracic Outlet Syndrome, characterized by the primary structures compressed:
- The lower trunk pattern reflects lower plexus compression and manifests with pain in the supraclavicular and
infraclavicular fossa, back of the neck, rhomboid area, axilla, and medial arm and may radiate into the hand and
fourth and fifth fingers. The history includes reports of feelings of coldness, or electric shock sensations in the
C8–T1 or ulnar nerve distributions.
- The upper trunk pattern results from upper plexus compression and is distinguished by pain in the
anterolateral neck, shoulder, mandible, and ear, and paresthesia that radiate into the upper chest and lateral
arm in the C5–7 dermatomes.
- With venous involvement, the signs and symptoms can include swelling of the entire limb, nonpitting edema, bluish
discoloration, and venous collateralization across the superior chest and shoulder.
- Arterial involvement produces coolness, ischemic episodes, and exertional fatigue.
- The mixed pattern consists of a combination of vascular and neurologic symptoms.
Thoracic Outlet Syndrome Diagnosis
Thoracic Outlet Syndrome is a clinical diagnosis, made almost entirely on the basis of the history and physical examination.
To help rule out other conditions that can mimic Thoracic Outlet Syndrome, the physical examination should include the following:
- A careful inspection of the spine, thorax, shoulder girdles, and upper extremities for postural abnormalities, shoulder
asymmetry, muscle atrophy, excessively large breasts, obesity, and drooping of the shoulder girdle.
- Palpation of the supraclavicular fossa for fibromuscular bands, percussion for brachial plexus irritability, and auscultation for vascular bruits that appear by placing the upper extremity in the position of vascular compression.
- Assessment of the neck and shoulder girdle for active and passive ranges of motion, areas of tenderness, or other signs of intrinsic disease.
- A thorough neurologic examination of the upper extremity, including a search for sensory and motor deficits and abnormalities of muscle stretch reflexes.
- Assessment of respiration to ensure patient is using correct abdominodiaphragmatic breathing.
- Assessment of the suspensory muscles: the middle and upper trapezius, levator scapulae, and SCM (thoracic outlet “openers”). These muscles typically are found to be weak.
- Assessment of the scapulothoracic muscles: the anterior and middle scalenes, subclavius, pectoralis minor and major (thoracic outlet “closers”). These muscles typically are found to be adaptively shortened.
- First rib position or presence of cervical rib.
- Clavicle position and history of prior fracture, producing abnormal callous formation or malalignment.
- Scapula position, acromioclavicular joint mobility, and sternoclavicular joint mobility.
- Neurophysiologic tests, which are useful to exclude coexistent pathologies such as peripheral nerve entrapment or cervical radiculopathy. An abnormal reflex F wave conduction and decreased sensory action potentials in the medial antebrachial cutaneous nerve may be diagnostic.
Thoracic Outlet Syndrome Tests include:
Radiology Views incude:
- Cervical spine x-ray to rule out cervical rib.
- Chest x-ray to rule out Pancoast tumor.
Angiography to assess the vascular structurs.
Conservative treatment should be attempted before surgery and should be directed toward:
- muscle relaxation,
- relief of inflammation,
- attention to posture.
This intervention approach may require a change of occupation for the patient, because Thoracic Outlet Syndrome is more common in those who stoop at work.
Aggressive physical therapy, particularly traction, may worsen symptoms.
The focus of the thoracic outlet syndrome treatment is:
- the correction of postural abnormalities of the neck and shoulder girdle,
- strengthening of the scapular suspensory muscles,
- stretching of the scapulothoracic muscles,
- mobilization of the whole shoulder complex and the first and second ribs.
Thoracic Outlet Syndrome Surgery is indicated if symptoms progress or fail to respond within 4 months.
Lower plexus thoracic outlet syndrome surgery include the first rib and (if present) cervical rib excision.
Although it has been suggested that the insured patient is more likely to have an operation, results are independent of any associated litigation.
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