Thoracic Outlet Syndrome

Thoracic outlet syndrome (TOS) is a spectrum of disorders caused by compression of the neurovascular bundle, the brachial plexus, subclavian artery and subclavian vein, as it exits the thoracic aperture to enter the axilla. The compression typically occurs at three anatomical narrows: the interscalene triangle, the costoclavicular space and the retro-pectoralis minor space.

Bands, not muscle. Most cases of true neurogenic TOS are caused not by muscle hypertrophy but by a congenital fibrous or fibromuscular band angulating the lower trunk (C8/T1), and this anatomy is examinable. The classic lesion is a rudimentary (incomplete) cervical rib or an elongated C7 transverse process with a taut fibrous band running forward to the first rib at the scalene tubercle, with the lower trunk or C8/T1 roots stretched over it. It is exactly the lesion Gilliatt found at operation in all nine cases of his series of true neurogenic TOS (see Evidence Base).

Why the X-ray can be normal. Bands are radiographically invisible, so a normal cervical-spine film never excludes NTOS, and at surgery it is the band, not muscle bulk, that must be divided. Roos described several types of congenital bands and ligaments crossing the scalene triangle, commonly cited as around nine. A scalene minimus, a small accessory muscle passing between the anterior and middle scalene to the first rib or Sibson's fascia, and anomalous scalene insertions or interdigitations can also narrow the triangle.

Complete and incomplete ribs. A complete cervical rib may articulate with the first rib, while an incomplete rib or elongated C7 transverse process may end in the invisible band. The complete bony rib is more often the substrate of arterial TOS (post-stenotic aneurysm); the incomplete rib with a fibrous band is the more typical substrate of true neurogenic TOS.

What a cervical rib does. By narrowing the interscalene and costoclavicular spaces, a cervical rib or its fibrous band can compress the lower brachial plexus (C8/T1) and the subclavian vessels, the structural basis of much arterial and true neurogenic TOS. Most cervical ribs, however, remain asymptomatic.

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The bundle passes the three narrows in sequence, and each has its typical disease: neurogenic and arterial TOS arise mainly at the interscalene triangle, especially with a cervical rib, venous (effort) thrombosis at the costoclavicular space, and pectoralis minor syndrome at the retropectoralis space.

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The interscalene triangle. Anterior scalene forms its front, middle scalene its back and the first rib its floor. It contains the trunks of the brachial plexus and the subclavian artery, while the subclavian vein passes anterior to anterior scalene, outside the triangle. Scalene hypertrophy therefore affects the artery and nerves but spares the vein, and the C8/T1 roots are most vulnerable at the base of the triangle.

The costoclavicular space. The clavicle lies above, the first rib below and the costoclavicular ligament in front, and artery, vein and nerve all pass through it. The mechanism is a nutcracker between the clavicle and the first rib, and clavicle fracture callus or first rib anomalies narrow it further.

The subcoracoid (pectoralis minor) space. The pectoralis minor tendon lies in front, the chest wall behind and the coracoid above. Hyperabduction of the arm stretches the bundle under pectoralis minor. Compression here is rarer than scalene compression.

TOS has four recognised types.

Neurogenic TOS (NTOS). About 95% of cases. Women are affected more than men, approximately 3:1, between 20 and 50 years of age. The pathology is scarring of the scalenes, whiplash and repetitive stress. Pain in the neck, trapezius and arm comes with paraesthesia in the C8/T1 distribution of the ulnar forearm and hand, and weakness is late. The diagnosis is often clinical, supported by exclusion of other causes.

Venous TOS (VTOS). Paget-Schroetter syndrome, or effort thrombosis, is about 3-4% of cases and affects young athletic men: pitchers, swimmers, weightlifters. Compression of the vein between the clavicle and first rib, with repetitive endothelial damage, leads to DVT. The arm presents with sudden swelling, cyanosis, heaviness and dilated collateral veins (Urschel's sign), and urgent referral to vascular surgery is required.

Arterial TOS (ATOS). Rare, about 1%. It is almost always a bony abnormality, a cervical rib or anomalous first rib, causing post-stenotic dilatation that leads to aneurysm and emboli. Ischaemia, pallor, coldness and claudication are distinct from Raynaud's; look for a palpable pulsatile mass.

Disputed (nonspecific) TOS. Subjective pain without objective NCS/EMG findings. It is controversial, and many surgeons do not operate unless objective signs exist. Psychosocial factors often play a major role.

Compression in the retropectoralis minor (subcoracoid) space is now recognised as a distinct entity, pectoralis minor syndrome, separate from but frequently coexisting with classic scalene-triangle NTOS.

Mechanism. The cords of the plexus and the axillary vessels are compressed beneath a tight or hypertrophied pectoralis minor at its insertion on the coracoid, especially in hyperabduction, the position of Wright's test.

The clinical clue. Symptoms are reproduced by pressure over pectoralis minor or the coracoid and by hyperabduction, often with anterior chest-wall and axillary tenderness rather than the supraclavicular tenderness of scalene-triangle NTOS. The two commonly coexist as combined outlet and retropectoralis compression.

Block, then tenotomy. A pectoralis minor block with local anaesthetic that relieves symptoms supports the diagnosis, exactly analogous to the scalene block for NTOS. Because the compression is distal to the first rib, isolated pectoralis minor tenotomy at the coracoid can relieve symptoms without first rib resection, a lower-morbidity operation. A missed coexisting pectoralis minor component is a recognised reason for persistent symptoms after a first rib resection.

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History. The pain is a "toothache" in the trapezius and neck, worse with overhead activity such as brushing hair or hanging clothes, and present at night when the patient sleeps with the arms up. Numbness in the 4th and 5th digits reflects C8. Ask about trauma: whiplash scars the scalenes.

Inspection. Look for drooped shoulders, and for supraclavicular fullness from a cervical rib or mass. Cyanosis suggests venous TOS. Collateral veins are an objective clue to venous outflow obstruction, so compare the sides and inspect the shoulder and anterior chest, not only the hand.

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The Gilliatt-Sumner hand. This is the hand of true neurogenic TOS, and the place to look first is the lateral thenar pad. The wasting is a lower-trunk pattern but it is most marked over abductor pollicis brevis, and in the mildest cases that is the only muscle visibly wasted. Hypothenar and interossei are involved in more advanced disease, so a wasted thenar with relatively preserved hypothenar is the early picture, and global intrinsic wasting the late one.

Provocative tests.

• Roos test (elevated arm stress test, EAST): the arms are raised in abduction and external rotation and the fists opened and closed for 3 minutes. It is positive if ischaemic pain, fatigue, heaviness or numbness forces the arms down, and it is the most reliable of the four
• Adson's test: head turned towards the side, deep breath and extension. Positive if the pulse disappears and symptoms are reproduced; low specificity
• Wright's test: hyperabduction makes the pulse disappear, implicating pectoralis minor
• Elvey's test: the upper limb tension test (ULTT)

Most have high false-positive rates (Adson's, Wright's and Roos/EAST all do) in asymptomatic people, and a large proportion of normal individuals lose the radial pulse on Adson's. No single physical test is diagnostic: they support, never confirm, the diagnosis.

NTOS is a diagnosis of exclusion, the great imitator. Its symptoms overlap with C8/T1 radiculopathy and cubital tunnel syndrome, so always check the neck (Spurling's test) and the elbow (Tinel's). The exam favourite is distinguishing it from the conditions that share C8/T1 or ulnar-border symptoms, and the answer is anchored on the pattern of motor wasting and the level of sensory loss.

Look at abductor pollicis brevis. Carpal tunnel syndrome affects it and cubital tunnel spares it; lower-trunk TOS affects it through its T1 fibres, along with the interossei. Sensory loss in the medial forearm (MABC territory) lies proximal to the wrist, and it is what places the lesion above the elbow rather than at the carpal or cubital tunnel.

Neurogenic TOS: conservative first. Physiotherapy corrects posture, strengthens trapezius to elevate the shoulder girdle and stretches the scalenes and pectoralis minor, alongside gabapentin or pregabalin and NSAIDs. Surgery is reserved for refractory cases with significant disability, when conservative measures fail, typically over 3-6 months. The operation is first rib resection plus scalenectomy.

The scalene block is a test, not a treatment. Local anaesthetic injected into anterior scalene is mainly diagnostic and prognostic: a positive response is part of the SVS NTOS criteria and predicts surgical benefit. A placebo-controlled RCT (Finlayson 2011) found that scalene Botox gave no therapeutic pain benefit, so it should not be relied on as a treatment.

Venous TOS: lyse, then decompress. Catheter-directed thrombolysis is urgent, within 14 days of the clot, followed by heparin/warfarin anticoagulation for 3 months. First rib resection is mandatory to prevent recurrence and is usually done in the same admission or shortly after lysis.

Arterial TOS. Embolectomy or thrombolysis is urgent if the limb is ischaemic. Surgery is cervical rib resection with first rib resection, adding arterial bypass or graft if an aneurysm exists, and distal embolectomy may also be needed.

Algorithm

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Choosing the approach.

• Transaxillary (the Roos approach): the most common and cosmetically superior, with access to the first rib, but it is hard to see a cervical rib or reconstruct vessels through it
• Supraclavicular: best for nerve visualisation and the cervical rib, and standard for NTOS and ATOS
• Infraclavicular: good for venous TOS, where the vein must be exposed

Supraclavicular first rib resection.

1. Transverse incision 2cm above the clavicle.
2. Identify the phrenic nerve on anterior scalene; retract medially.
3. Divide anterior scalene, protecting the phrenic nerve.
4. Expose the first rib, protecting the subclavian artery behind and the vein in front.
5. Divide the rib anteriorly and posteriorly and remove the middle scalene attachment.
6. External neurolysis of the plexus.

Complete removal of the rib back to the transverse process is key.

Intraoperative. Careful anatomical dissection and nerve identification prevent most of these:

• Pneumothorax (15-30% risk): the pleura is attached to the undersurface of the first rib by Sibson's fascia, and a chest X-ray in recovery is mandatory
• Subclavian artery or vein laceration, requiring immediate vascular repair
• Brachial plexus injury from direct trauma or excessive traction during resection
• Phrenic nerve palsy and diaphragm paralysis: the nerve lies on anterior scalene and must be protected during scalenectomy
• Long thoracic nerve injury and scapular winging: avoid excessive retraction. Winging may require tendon transfer
• Thoracic duct injury and chylothorax on a left-sided approach, requiring drainage and dietary modification

Postoperative. A supraclavicular wound haematoma may require evacuation. Wound infection is rare but treated aggressively given the proximity of the vessels. Horner's syndrome (ptosis, miosis, anhidrosis) follows sympathetic chain injury.

When symptoms persist. Consider incomplete decompression or an incorrect diagnosis. Chronic pain may indicate an incorrect initial diagnosis or neuropathic pain, and some patients have persistent weakness despite decompression.

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A depressed shoulder girdle reduces the costoclavicular interval and loads the plexus. Rehabilitation therefore targets scapular elevation and control, thoracic posture and pectoralis/scalene flexibility rather than generic shoulder strengthening alone.

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Neurogenic TOS. Surgery gives 80-90% good outcomes if the diagnosis is correct and confirmed by a positive scalene block response, with poorer results in disputed TOS or workers' compensation cases. Conservative management achieves 50-70% improvement with dedicated physiotherapy.

Vascular TOS. Venous TOS does excellently with early thrombolysis and first rib resection, with greater than 90% long-term vein patency if treated within 2 weeks. Arterial TOS does well if the arterial reconstruction is patent and there are no embolic sequelae, and it may require staged procedures.

Who does well. Patient selection is critical for surgical success, and the factors that predict it are these:

Favourable factors

• Objective positive NCS/EMG findings
• Positive response to scalene block (Botox or local anaesthetic)
• Clear anatomical cause (cervical rib, first rib anomaly)
• Short duration of symptoms before surgery
• Absence of workers' compensation or litigation

Poor factors

• Disputed/nonspecific TOS without objective findings
• Long symptom duration (greater than 2 years)
• Previous failed neck or shoulder surgery
• Significant psychosocial factors or secondary gain
• Double crush syndrome (concurrent CTS or cubital tunnel)

Recurrence. Recurrence after primary surgery runs at 5-15%, from incomplete first rib resection with too long a stump, scalene muscle regrowth, or reformation of fibrous bands or scar tissue. Re-operation succeeds less often than primary surgery, in 60-70%. Meticulous surgical technique and complete rib excision minimise recurrence.

The Gilliatt-Sumner hand does not recover. Band division arrests progression and relieves pain, but established wasting did not recover even at eight years. Consent for arrest, not restoration.

Does "disputed" NTOS exist? The biggest controversy. Many patients have subjective outlet symptoms with no objective neurophysiology and no anatomical lesion. Some surgeons operate on the basis of a positive scalene block alone; others argue this group should rarely be offered surgery given high failure rates. The SVS 4-criteria standard was created largely to discipline this grey zone.

Which approach? No randomised trial settles transaxillary versus supraclavicular first rib resection. Supraclavicular favours plexus neurolysis and cervical rib excision; transaxillary favours cosmesis and direct rib access. Robotic and thoracoscopic resection are emerging but unproven against open surgery.