Description

Cervical ribs are an anomaly that arise from the lowest cervical vertebrae but their relationship to thoracic outlet syndrome (TOS) is not so constant that the two conditions should be seen as synonymous. Perhaps no more than 10% of people who have cervical ribs develop TOS and the syndrome may well occur in the absence of ribs.^[1] Diagnosis may be difficult as a fibrous band that acts like a rib but is not calcified does not show on X-rays. There is also considerable controversy in the literature as to whether the condition actually exists. Some authors claim that it is under-diagnosed^[2] whilst others say that it is over-diagnosed.^[3]

The syndrome involves irritation or compression of the neurovascular bundles in the lower neck (usually the lower trunk or medial cord of the brachial plexus).^[4] The subclavian artery or vein may also be compressed.

Epidemiology

With so much uncertainty and dispute over the diagnosis, it is not possible to give a meaningful figure for incidence but the true neurological type probably affects no more than 1 person in 1 million.^[4] The overall incidence is given as between 3 and 80 per 1,000. Onset is from the 2nd to 8th decade with a peak in the 4th decade. It is more common in women than in men, with an excess of between 3- and 9-fold.
Analysis of 1,352 chest radiographs in London suggested the prevalence was 0.74% with a higher rate in females compared with males.^[5]

History^[4]

• There is often a history of trauma. This may be whiplash from a road traffic accident. It occurs in sportsmen, especially swimmers^[6] and throwers.^[7]
• The interval between trauma and symptoms may be hours to weeks.
• There may be pain, numbness or tingling of the upper limb. Symptoms are often vague and general and may affect the whole arm. There may be a painful neck and headache too.
• Autonomic features, such as cold hands, swelling or blanching, can occur. Stellate ganglion involvement may be possible.

Examination

A careful neurological and musculoskeletal examination is required. Neurological examination is discussed elsewhere - see separate article Neurological Examination of the Upper Limbs. Disease of the neck and arm must be excluded. Stress tests or provocative manoeuvres form the basis of examination. They have very low specificity, sensitivity and predictive value.^[8]

• The most common tests are Adson's manoeuvres.^[4] The head is extended and bent to one side and the patient takes a deep breath and holds it, followed by rotation to stretch or tether the brachial plexus and/or artery between the anterior and middle scalenes. The position is held for 15 to 30 seconds while the examiner checks for the onset of symptoms and obliteration of the pulse.
• Symptoms have been reported both to the side of bending and, more commonly, to the opposite side. If the symptoms occur on the side of bending, this is consistent with Spurling's sign for the diagnosis of cervical radiculopathy. This sign is described further in the separate article Cervical Disc Protrusion and Lesions. Some clinicians ask the patient to pull the head forward while maintaining the test position, causing the anterior scalene to contract against the plexus to enhance the stress effect.
• Hyperabduction of the arm can also be used as a test to stress the outlet. This often causes symptoms and loss of pulse even in normal people and may be misleading.
• Costo-clavicular bracing reduces the space between the clavicle and first rib and may reproduce symptoms.
• Focal stress tests involve direct application of pressure to the anterior scalene or upper segment of the pectoralis minor. A positive result is if symptoms are reproduced within 15 to 30 seconds. Some people use Tinel's sign, where percussing over the plexus reproduces symptoms.
• The elevated arm stress test is sensitive. The upper extremity is held in the 'hands-up' position with the arms abducted and elbows flexed at 90° for 3 minutes, while the patient vigorously flexes and extends the fingers. A positive sign is if the patient cannot complete the full 3 minutes. This test is demanding even for those without neurovascular symptoms and so its practical application is limited.
• The upper chest wall may be asymmetrical after a previous fracture of a clavicle. A non-tender, hard mass over the middle third of the clavicle is typical. A fracture that failed to unite or has excessive callus can cause direct compression of the plexus. Pressure on the clavicle can produce or aggravate symptoms, especially an ununited fracture. Motion can be felt between the fragments.

Aetiology

Causes of TOS:

• Cervical ribs or fibrous bands are just one feature that predisposes to narrowing and compression at the outlet.
• Poor posture can produce mechanical problems. Sometimes people who are depressed or just have a bad habit with regard to posture let the head drop forward, shoulders droop, and this allows the thoracic outlet to narrow and compress the neurovascular structures.
• Large breasts can pull the chest wall forward and cause symptoms. Reduction mammoplasty may have a beneficial effect. Sometimes the cause may be excessively large breasts that are not natural but have been surgically augmented.^[9]
• Trauma can move structures in the shoulder and chest wall. Fracture of the clavicle can cause compression by bone fragments, excessive callus, haematoma or pseudoaneurysm.
• Some of the typical precursors of myofascial pain can cause this syndrome too: sleep disorder, oestrogen or thyroid deficiency, inflammatory disease including rheumatoid arthritis, fibromyalgia and disorders of posture such as kyphosis and scoliosis.
• It is necessary to exclude thrombosis, embolism and nerve entrapment in other places. This includes Pancoast's syndrome, where lung cancer infiltrates the brachial plexus. Paget-Schrötter syndrome is thrombosis of the subclavian vein following heavy exercise of the upper limb.^[10]

Investigation

• The value of blood tests is to exclude other conditions.
• CXR with apical lordotic views and cervical spine should be obtained. An X-ray may show cervical ribs, which may be the cause, or have fibrous bands with them. It may also show elevated first ribs, caused by tight anterior or middle scalene muscles. Displaced fractures of clavicle, non-union and excessive callus may be apparent. Cervical spine degenerative changes may be causing neck or shoulder pain or impingement of the spinal nerve roots. Exclude a malignant lesion in the chest.
• MRI scan of the cervical spine and supraclavicular or brachial plexus area is useful to find other causes. A CT scan of the area of the brachial plexus and apex of lung may be indicated. MRI and CT can distinguish cervical root injury from degenerative spurs, herniated discs or other causes.
• Doppler and plethysmography studies can show impediment of blood flow. A near-complete cut-off of flow during the stress manoeuvre with reproduction of the symptoms would be most impressive. Occlusion can occur in normal subjects but is unusual and is not related to age.^[11]
• Angiography and venography can show blockage of the vessels from thrombi or emboli. Angiography can demonstrate aneurysms that may be compressing the plexus and causing neurological features.
• Asymmetry of temperature suggests interference with blood flow from obstruction of autonomic dysfunction. It should improve with successful treatment. The technique is controversial as the sensitivity is high but the specificity is low.
• An anterior scalene block is sometimes used as a diagnostic test but it is both difficult and dangerous, as the needle may damage the nerve. However, if it does give positive results, then there is a good chance of successful surgical decompression.
• Musculoskeletal sonography may be useful in children.^[12]

Treatment

The diffuse and uncertain nature of this condition makes the application of RCTs very difficult.

• Unless there is clear evidence of a lesion impinging on a nerve or vessel, surgery should be a last resort.^[13]
• Physical therapies include ultrasound, electrical stimulation, superficial heat, stretching exercises, postural correction exercises and strength and endurance exercises.^[14]
• Mobilisation and manipulation may be performed by a physiotherapist, osteopath^[15] or chiropractor. The aim is to release tight contracted or restricted vertebral segments and soft tissue.
• Occupational therapy may help with back protection techniques and better working practices.
• Injection of trigger points and associated muscles may be necessary. An injection of deep muscular structures, as in a scalene block, is dangerously close to the brachial plexus.
• Non-steroidal anti-inflammatory drugs (NSAIDs) have a good analgesic as well as anti-inflammatory action and it may be the former that is rather more important.
• Some people recommend muscle relaxants such as methocarbamol but they cause sedation and the benefit is unclear.
• Calcium channel blocking agents may possibly be of value where there is vascular instability.
• Surgical intervention may help where there is an obvious physical lesion but, in many cases where this is not the case, it not only fails to improve matters but may lead to deterioration.^[16] Damage to the long thoracic nerve or the brachial plexus are possibilities. Patients need careful appraisal before neurosurgery.^[17]
• Paget-Schrötter syndrome requires thrombolysis followed by surgical decompression of the subclavian vein. This gives rather better results than more conservative practices such as anticoagulation.^[9]
• Some surgeons resect the first rib and others remove the scalene muscles too.^[18] Cervical ribs and fibrous bands should be removed if they are tethering the plexus.
• Where the clavicle has been fractured, the removal of excessive callus may be required. Fixation of a fracture that has failed to unite may be required.
• As mentioned earlier, reduction of very large breasts may be beneficial.

Complications and prognosis

Generally prognosis is good, unless the condition is severe enough to merit surgery, and spontaneous recovery will occur. However, sometimes complications occur:

• Chronic pain
• Loss of function
• Depression
• Neurological complications
• Thrombosis, ischaemia or pseudoaneurysm
• Post-thrombotic syndrome of the lower limb following deep vein thrombosis is well recognised but problems may also follow thrombosis of the upper limb, although they have been less well documented.^[19]