Abstract
Thoracic outlet syndrome is a group of distinct disorders resulting from compression of the brachial plexus and/or the subclavian vessels as the structures travel from the thoracic outlet to the axilla. There are five types of thoracic outlet syndrome: arterial, venous, traumatic neurovascular, true neurogenic, and disputed. Any anatomic anomaly in the thoracic outlet has the potential to dispose a patient to thoracic outlet syndrome. Clinical presentation of thoracic outlet syndrome is highly variable; symptoms associated with thoracic outlet syndrome are usually divided into vascular and neurogenic categories, based on the underlying structures implicated. True neurogenic thoracic outlet syndrome typically involves the lower trunk of the brachial plexus. Approximately 85% of patients diagnosed with thoracic outlet syndrome are believed to have the disputed type, which usually present with inconsistent symptomatology in the absence of a consistent anatomic abnormality. Diagnosis for thoracic outlet syndrome includes a thorough history and physical examination, pertinent provocative tests, and imaging studies. Nerve conduction studies and electromyography are helpful to support neurogenic thoracic outlet syndrome, because the electrodiagnostic manifestations are essentially pathognomonic. Conservative treatment includes relative rest, nonsteroidal anti-inflammatory medications, and physiotherapy is indicated for most patients in the acute phase; surgery is reserved for patients with acute vascular insufficiency and progressive neurologic dysfunction.
Definition
Thoracic outlet syndrome is a symptom complex caused by compression of one or more neurovascular structures as they traverse the thoracic outlet. The thoracic outlet contains many structures in a confined space. The base of the thoracic outlet is formed by the first rib and the fascia of Sibson, which is attached to the transverse process of the seventh cervical vertebra, the pleura, and the first rib. The outlet is bounded superiorly by the subclavius muscle and the clavicle, anteriorly by the anterior scalene muscle, and posteriorly by the middle scalene muscle. The brachial plexus and the subclavian artery pass over the first rib between the anterior and middle scalene muscles ( Fig. 116.1 ).
Neurovascular compression occurs most frequently at three levels:
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in the superior thoracic outlet, bordered posteriorly by the spine, anteriorly by the manubrium, and laterally by the first rib;
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in the costoscalene hiatus (interscalene triangle), bordered anteriorly by the anterior scalene muscle, posteriorly by the middle scalene muscle, and caudally by the first rib; and
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in the costoclavicular passage, bordered superiorly by the clavicle, posteriorly by the anterior scalene muscle at its insertion site, and inferiorly by the first rib.
The clinical symptoms of thoracic outlet syndrome are divided into five categories according to the structures being compressed. True neurologic thoracic outlet syndrome is often caused by the distal C8-T1 roots or proximal fibers of the lower trunk of the plexus being stretched and angulated superiorly by a taut congenital band extending from the tip of a rudimentary cervical rib to the first thoracic rib. The most common form of thoracic outlet syndrome is the disputed neurologic thoracic outlet syndrome. The term disputed has been chosen because so many of the basic tenets of this syndrome are in dispute. Venous thoracic outlet syndrome is a relatively rare disorder that is associated with venous thrombosis involving the subclavian-axillary veins. It is a unilateral disorder that occurs more commonly in young patients engaged in vigorous physical activity that emphasizes upper limb and shoulder repetitive activities (such as cricket, tennis, and baseball). Arterial thoracic outlet syndrome is very rare and may be suspected if the patient presents with claudication of the arm, coldness, and ischemia of a finger or a hand; it is almost always unilateral and involves young adults. Traumatic neurovascular thoracic outlet syndrome is a rare disorder that usually follows a remote midshaft clavicle fracture. It usually involves both neural and vascular elements and is more commonly unilateral among adult men.
Congenital bands and ligaments are observed in a large majority of patients with thoracic outlet syndrome. Cervical ribs are regarded as predisposing factors, with prevalence ranges from 0.5% to 2%. The majority of individuals with cervical ribs are asymptomatic. The cervical ribs associated with true neurogenic thoracic outlet syndrome tend to be incomplete (not connecting to the manubrium), of intermediate length, and connected to the first thoracic rib via a fibrous band. In the case of the first thoracic rib, the costovertebral and costotransverse joints allow a fair amount of rotation to take place along the long axis of the rib. Moreover, this rib has attached to it the anterior and middle scalene muscles, which act either by raising the thorax or by flexing and rotating the cervical part of the spine. Consequently, this first rib bears more stress and strain than any of the other ribs, and these are greatest at the costotransverse joint. Osteoarthritic changes are found more frequently in the costotransverse joint of the first rib. The lack of a superior supporting ligament may explain why this joint of the first rib is relatively weaker than those of the other ribs.
The elevation of the ribs during inspiration increases the anteroposterior diameter of the upper thorax. The range of this motion is reduced in older people. A disturbance of the function of the upper thoracic aperture will predispose to thoracic outlet syndrome symptoms. A dysfunction of the first rib at the costotransverse joint causes a restricted movement of the first rib. In patients with true neurogenic thoracic outlet syndrome, the C8 and T1 nerve roots are most commonly affected. The fibrous band typically contacts the lower plexus at the distal anterior primary rami, and because the T1 anterior primary rami lies inferior to the C8 anterior primary rami, the T1 anterior primary rami is stretched more than the C8 anterior primary rami. These roots constitute the part of the brachial plexus closest to the costotransverse joint. The stellate ganglion is located in the immediate vicinity of the first costotransverse joint and has numerous connections to the C8 and T1 roots. Minimal trauma associated with static, repetitive work, especially in young women, can cause abnormal stress on the upper aperture, and the poorly stabilized first rib can subluxate at the costotransverse joint. A subluxation at the first costotransverse joint could irritate the nerve roots C8 and T1 emerging in front of this joint. This irritation could explain the predominantly subjective pain and sensory loss in the ulnar distribution. The weakness of the hand and the various symptoms resembling complex regional pain syndrome may be explained by the irritation of the stellate ganglion.
Symptoms
Most patients with true neurogenic thoracic outlet syndrome present with intrinsic hand muscle weakness and wasting that is most pronounced in the thenar eminence ( Fig. 116.2 ) because of the T1>C8 pattern of motor axon involvement. Other common motor complaints include progressive inability to use the hand and loss of dexterity. Sensory complaints are relatively minor; most patients have long history of intermittent aching and paresthesias in a lower plexus (particularly T1) distribution. In contrast, disputed neurogenic thoracic outlet syndrome most commonly presents with pain and paresthesias. It may involve the lower plexus or upper plexus. The associated sensorimotor abnormalities have a C8 and/or T1 distribution for the lower plexus type, and C5 and/or C6 distribution for the upper plexus type. Coldness, easy fatigability, ischemia of a finger or a hand, and pallor on elevation are considered to be symptoms of arterial origin. Swelling, discoloration, and a heavy feeling in the hand are considered to be symptoms of venous origin. Swelling, hyperesthesia, discoloration, and a feeling of alternate cold and warm could also be signs of complex regional pain syndrome.
Traumatic thoracic outlet syndrome commonly presents with pain at the trauma site, frequently radiating into the upper extremity in the medial cord distribution. Traction on the stellate ganglion has also been considered a possible cause of pain in these patients. In general, in the absence of peripheral emboli, most “vascular symptoms” or “Raynaud phenomena” probably result from irritation of the sympathetic nerves rather than from compression of the subclavian artery in the thoracic outlet. A common feature of the symptoms is their intermittence and provocation by use of the arm above shoulder level. Aggravation of the symptoms often occurs after rather than during exercise.
Physical Examination
The diagnosis of thoracic outlet syndrome is a clinical one based on a detailed history and physical examination. Many of these patients have some psychological complaints, and a thorough clinical examination including a logical explanation for the symptoms will often reduce the psychic burden.
The physical examination starts with an inspection of the neck, shoulders, and upper extremities. Color, muscle atrophy, edema, temperature, and nails are examined. This requires the patient to be examined with the shirt off. The cervical spine is then examined to exclude symptoms of cervical origin caused by a cervical disc or spondylarthrotic intervertebral foramen. A typical pain radiculation in C5 to C8 distribution indicates that a nerve root irritation is present. A local distribution of pain with neck extension indicates a facet joint problem.
A neurologic examination is performed to include sensory testing, muscle strength testing (C5-C8), and reflexes. Tinel sign is tested to exclude carpal tunnel syndrome. Palpation of the median, ulnar, and radial nerves from the axilla to the hand may reveal tenderness. Almost all clinical tests used in the examination of the patient with thoracic outlet syndrome aim to provoke the symptoms felt by the patient, presuming that the compressing structure may be provoked to irritate the neurovascular bundle in the area of the thoracic outlet during the test. These maneuvers are unreliable in general.
A clinical test in extensive use is the Adson test. With the patient sitting, hands resting on the thighs, both radial pulses are simultaneously palpated. During forced inspiration, hyperextension of the neck, and turning of the head to the affected side, the radial pulse is palpated for obliteration, and auscultation is done for supraclavicular bruit. The test has changed during the years. In 1927, when Adson described his test, the vascular changes were considered to be pathognomonic of thoracic outlet syndrome. Later, neurologic changes occurred more frequently than vascular ones, and these can be detected better when the head is rotated to the contralateral rather than the ipsilateral side, as initially described.
Radial pulse obliteration or subclavian bruit is found in 69% of normal patients. All studies clearly indicate that pulse obliteration with the arm and head in various positions is a normal finding and has no relation to thoracic outlet syndrome.
In the hyperabduction test, symptoms are reproduced by hyperabduction of the arm. However, more than 80% of normal individuals experience obliteration of the radial pulse during this test. In the exaggerated military maneuver, also called Eden test, symptoms are reproduced by pulling back the acromioclavicular joint in an exaggerated military “attention” position. The neurovascular structures could be compressed between the first rib and the clavicle, without any anatomic predisposing factors. This maneuver is also referred to as the costoclavicular test. Arterial compression is found in 60% of asymptomatic individuals by this test.
In the abduction-external rotation test, also called Roos test or elevated arm stress test (EAST), the hands are in the “stick up” position and are then repeatedly opened and closed for 3 minutes. Roos considered the symptoms to be due to both arterial and brachial plexus compression and referred to this procedure as a claudication test; he was later convinced that thoracic outlet syndrome was neurologic rather than vascular in origin but claimed that the EAST procedure was the most reliable procedure. Roos has also claimed that the EAST procedure has great specificity, with a positive result in thoracic outlet syndrome but generally negative results in carpal tunnel syndrome and cervical radiculopathy. However, in a controlled study, it was found that the EAST procedure is an excellent test for carpal tunnel syndrome; the result is positive in 92% of patients with carpal tunnel syndrome and in 74% of normal controls. Positional compression during these tests is a common phenomenon in normal subjects, and diminishing of the pulse in Adson test, the costoclavicular maneuver, and the hyperabduction test is considered to be a normal finding rather than a pathologic one. None of these tests unequivocally establishes the presence or absence of thoracic outlet syndrome. Ribbe and colleagues used a “thoracic outlet syndrome index” to establish the diagnosis of thoracic outlet syndrome. According to these authors, a patient with thoracic outlet syndrome should have at least three of the following four symptoms or signs:
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A history of aggravation of symptoms with the arm in the elevated position
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A history of paresthesia in the segments C8-T1
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Tenderness over the brachial plexus supraclavicularly
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A positive “hands-up” (abduction-external rotation) test result
Because all of these provocative maneuvers are unreliable, one should examine the function of the thoracic upper aperture. The function of the upper thoracic aperture should be analyzed with the cervical rotation-lateral flexion test. The test is carried out as follows. The neutrally positioned cervical spine is first passively and maximally rotated away from the side being examined and then, in this position, gently flexed as far as possible, moving the ear toward the chest. This is done in both directions. A restriction blocking the lateral flexion part of the movement indicates a positive test result; a free movement indicates a negative test result ( Fig. 116.3 ). This test indicates an abnormal function of the upper thoracic aperture. The test is indicative of a subluxation of the first rib at the costotransverse joint. The test has been used to identify patients who did not gain from surgery as well as in a 2-year follow-up study after conservative treatment.
