What is thoracic outlet syndrome?
Thoracic outlet syndrome (TOS) is a nonspecific diagnosis covering several conditions in which the neurovascular structures passing through the thoracic outlet are compressed. StatPearls describes the outlet as formed by the first rib, the scalene muscles and the clavicle. The structures at risk are the brachial plexus, the subclavian artery and the subclavian vein.
TOS was first reported by Rogers in 1949 and characterised more precisely by Rob and Standeven in 1958. One classification recognises five types: a venous variant, an arterial variant, a traumatic variant, a true neurogenic variant and a disputed neurogenic variant. Presentation is vague and nondescript, which is why the diagnosis is hard and the true prevalence is uncertain (estimated incidence ranges from 3 to 80 per 1,000).
What causes thoracic outlet syndrome?
TOS appears when pressure in the outlet rises enough to impinge on vessels or nerves. The causes fall into three groups:
- Bony anomalies — a cervical rib or other abnormal rib. In a review of 47 neurogenic-TOS operations for abnormal ribs, 85% involved cervical ribs.
- Soft-tissue causes — fibrous muscular bands, scalene muscle abnormalities, tumours or cysts in the outlet.
- Acquired causes — neck or shoulder trauma (a leading cause of symptoms), clavicle fracture, trapezius weakness causing the shoulder to droop, and repetitive overhead activity.
Athletes who repeat extreme abduction and external rotation, such as swimmers, water polo, baseball and tennis players, are classically susceptible. The textbook swimmer reports pain, tightness or numbness in the neck or shoulder as the hand enters the water.
What is a cervical rib and where does it lie?
A cervical rib (neck rib) is a congenital overdevelopment of the transverse process of a cervical vertebra; most are attached to C7. It occurs in roughly 0.5 to 1% of the population, may be unilateral or bilateral, and unilateral ribs are found more often on the left than the right. Most people never know they have one.
To count as a rib it must articulate with the transverse process. It has a head, neck and tubercle, and is attached posteriorly to the first rib by a fibrous band near the insertion of the anterior scalene. It has no physiological function. Rare ribs arise from C5 or C6, and ribs at multiple levels have been described. Embryologically, the costal element of a cervical vertebra normally atrophies; when it fails to, it ossifies into an elongated transverse process or a complete rib.
| Type | Description |
|---|---|
| Type 1 | Complete rib that articulates with the first rib or manubrium |
| Type 2 | Incomplete rib with a free distal tip |
| Type 3 | Incomplete rib with a distal fibrous band attachment |
| Type 4 | Short piece of bone extending beyond the C7 transverse process |
What are the types of thoracic outlet syndrome?
| Type | Structure | Features |
|---|---|---|
| Neurogenic (over 90%) | Brachial plexus, mainly lower trunk | Vague pain, hand weakness, sensory loss, intrinsic hand muscle atrophy |
| Venous | Subclavian vein | Arm swelling, venous distension, bluish limb, pain; may lead to upper-limb DVT |
| Arterial (rarest) | Subclavian artery | Colour change, diminished pulses, cold limb, distal embolisation, fingertip gangrene in severe cases |
Because the arm has collateral blood flow, vascular symptoms can be insidious and appear only in certain positions. Persistent venous TOS can present with an upper-extremity DVT. In arterial TOS the cervical rib is described as the most important bony predisposing factor: chronic compression injures the artery wall, producing stenosis, post-stenotic dilatation, mural thrombus and distal emboli.
What are the clinical features and bedside tests?
In neurogenic TOS the lower plexus is compressed (C8 and T1 roots). This causes weakness of hand and forearm muscles and numbness and tingling in the little and ring fingers (ulnar nerve distribution), and can lead to clawing of the middle, ring and little fingers. A late sign is the Gilliatt-Sumner hand: wasting of the abductor pollicis brevis and the hypothenar muscles.
| Test | Method | Positive result |
|---|---|---|
| Adson manoeuvre | Arm slightly abducted and extended, patient extends and turns the neck while the examiner palpates the radial pulse | Radial pulse diminishes — suggests arterial compromise |
| Roos stress test | Shoulders abducted and externally rotated, elbows at 90 degrees; patient opens and closes the hand | Fatigue or reproduction of symptoms; can detect any TOS variant |
| Spurling test | Head extended and laterally flexed with axial compression | Reproduces radicular pain — points to cervical radiculopathy, a differential |
How is TOS investigated?
The physical examination comes first. The first imaging is a plain chest or cervical spine X-ray, which can show a cervical rib or other bony anomaly. In most patients a cervical rib is simply found incidentally on such a film.
| Investigation | Role | Comment |
|---|---|---|
| Chest / cervical X-ray | First step | Shows cervical rib and other bony anatomy |
| Ultrasound | Venous TOS | Cannot visualise the whole area; one study quoted 95% sensitivity and 92% specificity for venous TOS |
| Venous Doppler | Subclavian vein compression | Patient can reproduce the provoking position during the scan |
| Angiography / CT angiography | Arterial TOS | Shows stenosis and post-stenotic dilatation; positional compression is hard to reproduce |
| Electrodiagnostic studies | Neurogenic TOS | Useful if positive, but the neurogenic form is often transient |
| MRI | Soft tissue and plexus | A 2026 case showed denervation oedema of infraspinatus and teres minor after surgery |
How is thoracic outlet syndrome treated?
Most physicians start with conservative management: posture correction, avoiding overhead arm positions during sleep, workplace splints or pads, and physical therapy to strengthen the muscles around the outlet. This remains first-line even after complications such as upper-limb DVT have been treated, followed by rehabilitation.
Surgery is controversial and is recommended mainly for severe vascular compromise or atrophy of the intrinsic hand muscles. Without credible evidence that TOS is really the culprit, surgery is not advised. In the cited data, success was about 75% for lower-plexus and 50% for upper-plexus surgery.
| Approach | Best for | Notes |
|---|---|---|
| Supraclavicular | Arterial compression | Easy access to the proximal subclavian artery; allows scalenectomy and removal of bony and myofascial abnormalities |
| Transaxillary | Venous occlusion or neurological compression | Most commonly used; less brachial plexus manipulation; less visible scar |
| Posterior | Re-operation | Rib removed behind the nerve root with the arm adducted |
Treatment of a cervical rib causing TOS is complete resection of the rib, sometimes with first rib resection and scalenectomy; a bypass graft may be needed if the subclavian artery is completely occluded. Overall prognosis is excellent: about 90% of conservatively treated patients have their symptoms resolve.
What are the differentials and common exam traps?
- Pectoralis minor syndrome — anterior chest wall, trapezius and scapular pain with possible arm paraesthesia, caused by nerve compression by the pectoralis minor muscle, not the thoracic outlet.
- Brachial plexus injuries, cervical radiculopathy, cervical spine injury, shoulder impingement, elbow or forearm overuse injuries and acromioclavicular joint injury all mimic TOS.
- To label a nerve compression as cervical rib related, carpal tunnel syndrome, ulnar nerve entrapment and cervical disc herniation must be excluded.
- A cervical rib is usually asymptomatic — finding one on an X-ray does not make the diagnosis of TOS.