Thoracic outlet syndrome (TOS) is a diagnosis of exclusion based on the patient’s history and symptoms. This syndrome can cause pain in the shoulders, neck and numbness in the fingers as the arm is moved (Figure 1).
Structures may be compressed in the thoracic outlet by the cervical rib, and there may be anomalies of the scalenus muscles (Figure 2).
It is a neurovascular compression neuropathy of the brachial plexus in the thoracic outlet in the retroclavicular region with either a neurogenic or vascular etiology (Figure 3). This condition occurs more in females.
What is the thoracic outlet space?
The thoracic outlet space is created by the clavicle, first rib, subclavius muscle, costoclavicular ligament, and anterior scalene muscle. This space also contains the subclavian vessels, thoracic duct and the lower trunk of the brachial plexus (C8, T1) (Figure 4).
There are two types of thoracic outlet syndrome; neurogenic and vascular. The neurogenic type is caused by compression of the neurovascular bundle as it passes over the first rib or through the scalene muscle.
What are the causes of compression?
The causes of compression are cervical rib, elongated vertebral transverse process (C7), anomalies of the scalene muscle insertions, first rib malunion, abnormal fibrous band on or near the two scalenous muscles, repetitive shoulder movement, extreme arm positions, abnormal pectoralis minor muscle. Weight lifting, rowing and swimming may be causes in athletes!
A vascular entity can be caused by a compressed subclavian vessel or by an aneurysm (Figure 5).
Where is the site of compression?
The site of compression is located where the brachial plexus passes over the first rib. It is usually at the site of the scalene triangle (anterior scalene anteriorly, middle scalene posteriorly and the edge of the first rib inferiorly), and the roots and trunks of the brachial plexus which lie between the scalenus anterior and medius muscles (Figure 6). The brachial plexus and the subclavian artery pass through the triangle (subclavian vein does not pass through the triangle).
The site of compression is also under the clavicle by the subclavius tendon.
The third site of compression is underneath the conjoined tendon, inserting into the coracoid process (Figure 7).
The symptoms are usually vague. There will be pain in the shoulder and neck that usually radiates to the forearm and hand (paresthesia radiating along the arm). The patient may also have a loss of sensation in the little and ring fingers. There may be some vascular symptoms such as arterial ischemia, venous congestion, Raynaud’s phenomenon (changing colors of the hands or chronically reduced pulse).
The physician will look for ulnar nerve sensory changes and intrinsic weakness. They will also look to see if the patient has intolerance to cold (Raynaud’s phenomenon). Sometimes the patient will have a forward dropping shoulder posture.
C8 radiculopathy or ulnar nerve compression at the elbow may be differential diagnoses (Figure 8). It is a combination of weakness involving the median and ulnar nerve innervated muscles that may confirm a more proximal injury to the brachial plexus. If there is no neck or radicular pain, but there is C8-T1 sensory and motor changes, this may exclude a C8 nerve injury.
The physician will need to rule out double crush syndrome with carpal tunnel syndrome and thoracic outlet syndrome (Figure 9).
Compression of the medial antebrachial cutaneous nerve could occur with compression of the thoracic outlet (Figure 10). Sensory loss occurs on the medial aspect of the forearm and the medial third of the hand, which is the ulnar and medial antebrachial cutaneous nerve (both come from the medial cord).
There are three provocative tests; Adson’s test, Wright test, and Roos Test (elevated arm stress test or EAST). Provocative tests have a high rate of false positives and are of limited clinical value when used alone.
For the Adson’s test, the physician will abduct, extend and externally rotate the arm while feeling the radial pulse. The patient will rotate their head towards the arm being tested and may also extend the neck (Figure 11). There may be a decreased interscalene space by tensing of the middle and anterior scalenus muscles. This test is positive if the pulse disappears with the reproduction of the symptoms. Radial pulse obstruction is not specific.
The Wright test is performed by abduction, external rotation of the arm with the neck rotated away that will lead to the loss of the pulses and reproduction of symptoms (Figure 12).
The Roos test (EAST) is performed by the patient raising both arms up and holding that position for one minute (Figure 13). The fingers will then be opened and closed for three minutes, while holding them overhead. The test is positive if there is a reproduction of pain and numbness of the shoulders as well as fatigue.
The cervical spine may show a cervical rib. A chest x-ray may show a Pancoast tumor (apical lung tumor) that could put pressure on the brachial plexus causing ulnar nerve symptoms (Figure 14).
EMG and nerve study results are usually not very helpful.
Vascular studies may identify a vascular form of thoracic outlet syndrome.
Treatment is initially conservative and involves physical therapy to strengthen the shoulder girdle muscles. Physical therapy is usually the first form of treatment. The patient is to maintain proper posture and modify activities as needed. A correction of the postural imbalances will be needed.
A decompression is indicated in cases of intractable pain, neurological deficit, or persistent vascular insufficiency in addition to the failure of non-operative treatment. Resection of the first rib or cervical rib if present. A release or excision of the anterior and middle scalene muscles is needed. Lastly any abnormal structures will be excised. Surgery can be done through a transaxillary or supraclavicular approach. There is a 90% of good-excellent results with a transaxillary first rib resection. Vascular procedures may be done in cases of vascular causes of this syndrome.
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