The term thoracic outlet syndrome (TOS) describes a condition arising from compression of the subclavian artery, the subclavian vein, and the brachial plexus between the scalene muscles and the first rib (Fig. 142-1). There exists a wide spectrum of patient symptoms, which include vascular and/or neurologic signs. Neurogenic TOS accounts for most cases, whereas venous (2%–3%) and arterial TOS (1%) are relatively rare. Objective vascular studies such as venograms and arteriograms may identify signs of vascular compromise to aid in the diagnosis of arterial or venous TOS, but neurologic findings are more varied, and there is no single specific test to diagnose neurogenic TOS.

The neurologic signs and symptoms of neurogenic TOS can range from mild paresthesias and numbness to intrinsic hand muscle atrophy. There is little controversy in this latter group of patients regarding diagnosis or treatment. However, the diagnosis of TOS is controversial in patients with the neurologic-type complaints of paresthesias, numbness, and pain but with no positive objective test to identify the cause. This chapter focuses on the management and surgical therapy of neurogenic TOS.

Many surgeons are highly skeptical of the merits of surgical intervention for patients with TOS because of the high incidence of major complications and the variable reports of successful outcome. Exceptions to this rule include uncommon cases involving vascular compromise and even rarer cases involving severe neurologic muscle atrophy in the hand.¹ Patients with intrinsic hand muscle atrophy that localizes to the level of the brachial plexus with no distal sites of nerve compression are likely to have a cervical rib or anomalous ligamentous band(s) that compresses the lower trunk of the brachial plexus. Compression of the artery may lead to poststenotic dilatation and subsequent thrombosis and embolization. Patients with symptomatic arterial TOS may present with signs and symptoms of microembolization in the digits on the affected side. Venous compression, which usually occurs at the junction of the clavicle and first rib, leads to occlusion and thrombosis. Patients characteristically become symptomatic with evidence of venous congestion after a precipitating physical activity (Paget–Schroetter syndrome).

The clinical syndrome (TOS) derives from three anatomic areas in which compression of the neurovascular structures may occur: the scalene triangle, the costoclavicular space, and the subcoracoid space (Fig. 142-2). The scalene triangle is the region bordered by the anterior scalene muscle, the middle scalene muscle, and the first rib. The brachial plexus and subclavian artery pass over the first rib between the scalene muscles, and the subclavian vein also passes over the first rib but external to the scalene triangle. The costoclavicular space is bordered by the clavicle and the first rib, with the costoclavicular ligament located anteriorly and the edge of the middle scalene muscle posteriorly. This space contains the brachial plexus, the subclavian artery and vein, and the subclavius muscle. The subcoracoid space is beneath the pectoralis muscle, the coracoid process, and the ribs posteriorly. The brachial plexus courses through this space and can become tethered with arm elevation, abduction, or abnormal depression of the coracoid. Anomalous cervical ribs are found in fewer than 1% of the population. They may compress the neurovascular structures in this region. The most common sites of compression in patients with TOS are the scalene triangle and the subcoracoid space, although it is clinically difficult to determine the exact location of the compression.

There is no single test or examination finding that establishes the diagnosis of neurogenic TOS. Rather, the clinical diagnosis is based on the history, physical examination findings, and objective tests, such as electrodiagnostic studies of the peripheral nerves, that are used to rule out other more distal compression neuropathies. Chest and neck x-rays are obtained routinely to look for cervical ribs or other bony abnormalities. Paresthesias in the upper extremity may be the result of either compression at the brachial plexus or compression more distally. The pain associated with TOS usually results from a muscle imbalance in the cervical, thoracic, and scapular regions.² Patients with TOS-related pain often assume an abnormal posture with forward position of the head and neck, thoracic kyphosis, and scapulae abduction (Fig. 142-3). This posture results from a weakness of the lower scapular stabilizers (i.e., middle and lower trapezius and serratus anterior) that leads to overuse and hypertrophy of other muscle groups (e.g., levator scapulae, upper rhomboids and trapezius, and scalene muscles). Upper extremity activities (e.g., arm abduction or elevation) often exacerbate the symptoms. The onset of symptoms is usually insidious without a defined traumatic event.

Chronic nerve compression is associated with a continuum of symptoms. Initially, the patient may complain of aching in the muscles innervated by the compressed nerve. Later, the patient complains of muscle weakness and, finally, muscle atrophy. With sensory nerve compression, patients complain first of intermittent paresthesias, then persistent paresthesias, and eventually numbness. Clinical sensory testing follows a similar continuum; therefore, not all sensory tests are equally effective for detecting nerve compression at all stages of TOS. Initially, patients may have symptoms only with positional changes or provocative maneuvers. Sensory testing in a resting position will be normal, only becoming abnormal when the patient is tested in positions of provocation (e.g., with the arms elevated). With continued nerve compression, axonal involvement, and wallerian degeneration, the innervation density of the sensory receptors decreases, and sensory testing with two-point discrimination is abnormal.

It has been hypothesized that proximal compression of a nerve increases its susceptibility to compression injury more distally. Thus, in treating upper extremity neuropathic symptoms, it is important to identify and treat all sites of compression.³ Distal sites of nerve entrapment, for example, the elbow, forearm, and wrist, should be evaluated carefully and managed conservatively. Clinical evaluation using pressure and positional provocative testing is key to making the diagnosis because electrodiagnostic studies usually do not detect these dynamic sites of nerve compression.⁴ Conservative treatment often effectively relieves these distal symptoms, but when surgical intervention is required, surgery at the carpal or cubital tunnel levels is usually more effective than surgical decompression of the thoracic outlet for complete relief of hand paresthesias and numbness. Overlapping symptoms from the cervical disc level or the shoulder are common.

Loss of radial pulse with arm movement on physical examination forms the basis of several clinical tests designed to detect vascular insufficiency, although not effective for the evaluation of neurogenic TOS. In Adson test, the patient is asked to turn his or her head toward the affected side, extend the neck, and inspire deeply. Obliteration of the radial pulse suggests compression. In Roos test, the subject elevates his or her arm to 90 degrees of shoulder abduction and then rotates the arm externally and flexes the elbow for 3 minutes. The patient then is asked to rapidly open and close the hand. A positive test will reproduce the patient’s symptoms.

The physical examination of patients with TOS should include documentation of pinch and grip and two-point discrimination, as well as examination of the upper extremity for other compression issues. The cervical spine and rotator cuff are examined as well as the muscles of the parascapular area. Standard tests performed at the wrist are used to assess carpal tunnel syndrome, including Tinel sign, the pressure provocative test, and Phalen test. Care is taken to keep the forearm in a neutral position during testing because extreme supination of the forearm will cause median nerve compression at the pronator teres and lead to a false-positive result. The elbows also must remain extended so as not to provoke signs of cubital tunnel syndrome. One test for median nerve compression in the proximal forearm is to maximally supinate the forearm with pressure applied just proximal to the pronator teres while keeping the wrist in neutral position. If this maneuver produces paresthesias in the distribution of the median nerve, it suggests median nerve compression in the proximal forearm. The radial sensory nerve is provoked by extreme forearm pronation and wrist ulnar deviation. A Tinel sign between the tendons of the extensor carpi radialis longus and the brachioradialis indicates radial sensory nerve compression in the forearm.

The evaluation for cubital tunnel syndrome or ulnar nerve compression at the elbow involves elbow flexion and pressure over the ulnar nerve at the cubital tunnel. The wrist and the forearm are kept in neutral position so as not to provoke median nerve symptoms. Brachial plexus compression in the region of the thoracic outlet is tested by elevating the arms over the head while keeping the wrist neutral, the elbows extended, and the forearms neutral. The examiner evaluates for change in pulse and color while the patient reports any new or increased sensory disturbance in the upper extremity.

Patients with neurogenic TOS typically have an associated muscle imbalance in the cervical scapular area. To evaluate these muscles, the examiner stands behind the patient while the patient slowly elevates the arms above the head. Elbows are kept extended, and the shoulders are forward flexed. The arms then are lowered to the sides from this forward-flexed, elevated position while the examiner observes for winging of the scapula. Winging of the scapula suggests weakness of the serratus anterior muscle. Middle and lower trapezius muscle function is tested by abducting the shoulders with the extremities extended while the arms are elevated above the head from an abducted position. Once again, the arms are lowered slowly to the side. Winging of the scapula suggests a weakness of the middle and lower trapezius muscles. Patients with muscle imbalance in the scapular areas typically have abducted scapulae. Instead of rotating normally with movement of the arms, the scapulae tend to move “up and down” on the back because of overuse of the upper trapezius muscle.