Thoracic Outlet Syndrome
Thoracic outlet syndrome (TOS) is a misnomer for the constellation of symptoms caused by compression of the brachial plexus or subclavian vessels as they pass through the thoracic inlet, the narrow passageways leading from the base of the neck to the axilla and arm. There is considerable disagreement about its diagnosis and treatment, particularly the neurogenic form. Practice guidelines are not currently possible due to the low level of evidence, and it remains a controversial condition.
The thoracic outlet is actually the diaphragm and is a misnomer. What we are actually referring to is the thoracic inlet which consists of the first rib and adjacent structures. The upper thoracic aperture is bordered by:
- Posteriorly - spine
- Anteriorly - manubrium
- Laterally - 1st rib
The pectoralis minor muscle arises from the anterior surfaces of ribs 2, 3, 4, and 5 and inserts onto the coracoid process of the scapula. Deep to the pectoralis minor is the axillary artery, axillary vein, and brachial plexus. Deep to the plexus are latissimus dorsi and subscapularis.
The anterior and middle scalene muscles originate at the transverse processes of the cervical spine and insert onto the first rib. The interscalene triangle is located between the anterior and middle scalene muscles.
The brachial plexus arises from nerve roots C5 through T1. The five nerve roots and the lower, middle, and upper trunks lie in the scalene triangle. The anterior and posterior divisions and cords form at the level of the costoclavicular space. They extend to the pectoral space and at this point the cords and branches have formed.
The stellate ganglion sits posterior to the subclavian artery. It is anterior to the 1st rib, transverse process of C7, and the anterior primary rami of C8 and T1. It receives white rami communicantes from C8 and T1 (afferent sympathetic fibres from the brachial plexus and upper intercostal nerves). It sends grey rami communicantes to C8 and T1 (efferent sympathetic fibres to brachial plexus and intercostal nerves)
Thoracic outlet syndrome is caused by an enlargement or change of the tissues in or near the thoracic outlet leading to neurovascular compression.
NTOS: Neurovascular compression in TOS can occur at three different anatomic levels
- Interscalene triangle (between the scalene muscles) - most common.
- Costoclavicular space (between the first rib and clavicle)
- Pectoralis minor space (under the pectoralis minor)
Double crush can also occur, most commonly at both the interscalene triangle and the pectoralis minor space.
VTOS: Venous compression occurs most commonly at the costoclavicular space, but can occasionally occur at the pectoralis minor space.
ATOS: Arterial compression occurs most commonly at the scalene triangle typically by an anomalous bone or ligamentous structure.
Various structural causes and physiological processes have been proposed.
Structural causes include:
- Anomalous scalene bands. fibrous band may extend from the tip of the abnormal transverse process to the first rib.
- Anomaly or fracture of 1st rib. Anomalous first ribs occur in <1% of people.
- Cervical rib. These arise from the transverse process of C7 an occur in <1% of people.
- Fracture clavicle
- Stellate ganglion irritation causing autonomic symptoms/signs.
- Repetitive trauma
- Muscle of albinus (scalenus minimus)
- Sibson's fascia crossing the T1 nerve root
- Pre- or postfixed brachial plexus
- Intraplexus anomalous connections
- Proximal junction of T1 to C8
- Fibrous edges of scalene muscles
- Extra origins of scalene muscles
- Elevated position of subclavian artery
- Anomalous vessels crossing the brachial plexus
Loss of motor control. Following trauma to the cervical spine and/or thoracic outlet there is a control imbalance involving spinal and shoulder girdle muscular instability. There is excessive activation of the accessory muscles of respiration instead of the diaphragm. Tonic stabilising muscles become underactive and phasic moving muscles become hyperactive resulting in a muscle imbalance.
- Inhibition of tonic muscles: There is inhibition of the deep flexors of one of the ulnar innervated thumb flexors, deep neck flexors, lower fibres of trapezius, serratus anterior, and the abdominal corset.
- Hyperactivity of phasic muscles: There is excessive activation of the movers of the neck, ribs 1 through 5, the three scalene muscles, subclavius, pectoralis minor, upper trapezius, and levator scapulae.
1st rib dysfunction. Subluxation cranially at the costotransverse joint leading to irritation of the nerve roots C8 and T1 as well as the stellate ganglion.
Breathing dysfunction: There is a link between breathing difficulties and back pain. Trunk muscles perform both postural and breathing functions. It is thought that disruption to one function can negatively affect the other. Many patients have excessive activation of the accessory muscles of respiration instead of diaphragm. The plexus can bowstring in a cephalad direction over the first rib with first rib elevation during inspiration.
Myofascial dysfunction and pain (scalenes, pectoralis minor, infraspinatus, teres minor). Restriction of internal rotation can be seen, this may be due to the fact that the axillary nerve C5/6 comes off the posterior cord (teres minor and deltoid)
Central sensitisation. A proposed increase in the excitability of central nociceptive afferent pathways and impaired descending inhibition.
Often there is no direct cause.
Note that anomalies of the thoracic outlet are also common in asymptomatic individuals. In a study of 50 cadavers only 10% had a bilaterally normal anatomy.
Thoracic outlet syndrome is divided into:
- Neurogenic Thoracic Outlet Syndrome (NTOS): Caused by compression of the inferior trunk of the brachial plexus due to a cervical rib, band, or enlarged scalenus muscles. This is the most common form representing 85-95% of patients.
- NPMS: Neurogenic pectoralis minor syndrome is a subgroup with compression at the pectoralis minor space. If limited to the scalene triangle it is called NTOS. It combined then it is called NTOS/NPMS.
- Arterial Thoracic Outlet Syndrome (ATOS): Objective abnormality of the subclavian artery caused by extrinsic compression and subsequent damage by an anomalous first rib or analogous abnormal structure such as a cervical rib or band at the base of the scalene triangle.
- Venous Thoracic Outlet Syndrome (VTOS): Caused by compression of the subclavian vein at the costoclavicular junction, or occasionally at the pectoralis minor space.
- Paget-Schroetter syndrome: thrombotic occlusion at the costoclavicular junction, also called effort thrombosis
- McCleeery syndrome: intermittent positional obstruction in the absence of thrombosis
- VPMS: subgroup where the compression is limited to the pectoralis minor space. If limited to the costoclavicular junction it is called VTOS. If combined it is called VTOS/VPMS.
- Persistent TOS: Of any type, means that it hasn't improved after treatment
- Recurrent TOS: Symptoms have recurred after an initial three month period of improvement.
- Secondary TOS: Symptoms of a different type have occurred after treatment of a different problem.
The following terms should not be used: True, disputed, or nonspecific NTOS, vascular TOS, mixed TOS, Roos classification.
The condition is more common in women. The onset of symptoms usually occurs between 20 and 50 years of age
Adolescents present much more often with venous or arterial TOS. This is because they are more likely to be athletic (VTOS), and because congenital problems will present earlier in life (ATOS).
NTOS: The patient may have pain, numbness, tingling, and weakness. Symptoms are worse when working with the arm above horizontal.
The pain is dull and aching in nature. It can occur in the shoulder, upper arm, chest, axilla, neck, head, and distal extremity (figure 3). Pain can occur at night. Head and neck pain is more common with entrapment related to the scalene triangle (NTOS) over entrapment related to pectoralis minor (NPMS). In isolated pectoralis minor entrapment, neck pain is usually absent or less intense. Overall patients with NTOS or combined NPMS/NTOS are more disabled than those with isolated NMPS.
Ask about occupation and any potentially relevant aggravating factors such as sporting activities, driving, prolonged typing, etc. Ask about arm dominance.
Numbness and paraesthesias of the arm usually the medial arm and hand (4th and 5th fingers). There may be weakness in the shoulders, arm, and hands.
Arterial signs and symptoms can be present in patients with NTOS. However ATOS is not diagnosis unless there is proven symptomatic ischaemia. VTOS is less commonly seen in conjunction with NTOS.
VTOS: Presents as acute or chronic upper extremity deep venous thrombosis (Paget-Schroetter syndrome, effort thrombosis), or positional swelling (McCleery syndrome). The patient has arm swelling, usually with discolouration or heaviness. This may be entirely positional only occurring with the arms overhead which suggests nonthrombotic VTOS. Alternatively if present at rest then this suggests a fixed lesion i.e. subclavian vein thrombosis.
ATOS: Presents as either symptomatic ischaemia with arm elevation or fixed arterial injury (stenosis, occlusion, or aneurysm).
NTOS: There may be tenderness in the scalene triangle (NTOS), pectoralis minor insertion site (NPMS), and axilla. Pressure over the scalene triangle or pectoralis minor insertion site may reproduce symptoms (figure 4). There are fewer physical findings in patients with isolated entrapment at pectoralis minor compared to the scalene triangle.
Weakness and/or paraesthesias can occur with arm elevation, pallor of the palm with arm elevation and fingers pointing to the ceiling, and weakness of the 5th finger. In severe cases the patient may have the Gilliat-Sumner hand (figure 5) in which there is severe wasting in the fleshy base of the thumb. Atrophy of abductor pollicis brevis may mimic Carpal Tunnel Syndrome. If weakness is detected it is usually only in the intrinsic muscles of the hand (abductor pollicis brevis, abductor digiti minimi, interossei, finger flexors, and finger extensors) and not the forearm muscles.
CRPS like signs can occur with stellate ganglion compression such as swelling of the extremities and fingers.
The first rib should be examined. The patient is seated as for examination of the cervical spine. Lateral flexion is tested bilaterally. With the head in lateral flexion, the supraclavicular area on the side of flexion is palpated. The first rib is located medially in the supraclavicular area. The patient is asked to breathe in, and the first rib rises against the pressure of the examining finger. Pain may be elicited locally. Paraesthesiae in the C8 or T1 areas may be reported.
Examine the shoulder. There may be restricted abduction and internal rotation of the ipsilateral shoulder.
Examine for Tinel signs along the radial, ulnar, and median nerves.
Also assess for signs of hypermobility.
VTOS: Examine for visible swelling at rest or with exertion, discolouration, and venous collaterals over shoulder, upper arm, or chest.
ATOS: The patient has symptoms of acute or chronic ischaemia. There is rest pain along with ischaemia with extreme exertion or arms overhead. There is paraesthesias in the arm and head. There is loss of dexterity in the hand and clumsiness of the arm. Coldness occurs with temperature sensitivity. There may be isolated finger pain or ulceration.
There are a variety of special tests (Table 1). The validity and reliability are hampered by the lack of a gold standard for diagnosis. The reporting standards published by Illig and colleagues recommend the following two tests for NTOS:
Elevation arm stress test (EAST): Also called Roos test. This test is used to assess for narrowing of the scalene triangle. (figure 6)
- The shoulders are abducted to 90 degrees and extended, and the elbows flexed to 90 degrees.
- The hands are rapidly opened and closed for up to three minutes.
- A positive test is reproduction of local or distal pain and neurologic symptoms.
Record the time to onset of symptoms and what symptoms occurred. Symptoms at 1 minute has a lower false positive rate than symptoms at 3 minutes. A modified version can be done where the head is placed in contralateral rotation. The Roos test was originally described to evaluate for a reduced radial pulse, but it can also be used to test for reproduction of neurogenic symptoms.
Upper limb tension test (ULTT): This is comparable to the straight leg raise of the lower limbs and looks to recreate the dysaesthesia that the patient usually feels (Figure 7). It can be tested with one arm at a time or both arms at the same time to allow for easier comparison. There are three sequences, each progressively increasing tension on the brachial plexus (except the last bullet point).
- The arms are abducted to 90 degrees with the elbows extended and palms facing down.
- The wrists are dorsiflexed.
- The head is laterally flexed away from the symptomatic side.
- The elbow can then be flexed. If symptoms come on at this point then cubital tunnel syndrome shoulder be considered.
Figure 6. Elevation Arm Stress Test (EAST). From Virtaj Singh.
Figure 7. Upper Limb Tension Test (ULTT). From Virtaj Singh.
|Thoracic Outlet Syndrome Tests|
|Cervical Rotation Lateral Flexion Test||0.92||0.90||9.2||0.09||1.0|
|Both Adson + Wright (pulse) positive||0.54||0.94||9.0||0.5|
|Both Adson + hyperabduction (sx) positive||0.72||0.88||6||0.3|
|Hyperabduction (pulse abolition)||0.52||0.90||5.2||0.5|
|Both Adson + Roos positive||0.72||0.82||4||0.3|
|Both Adson + Wright (sx) positive||0.79||0.76||3.3||0.3|
|Both Adson + Roos positive||0.72||0.82||4||0.3|
|Both Wright (pulse) + hyperabduction (sx) positive||0.63||0.69||2.0||0.5|
|Both Wright (sx) + hyperabduction (sx) positive||0.83||0.50||1.7||0.3|
|Both Wright (sx) + Roos positive||0.83||0.47||1.6||0.4|
|Wright test (pulse abolition)||0.70||0.53||1.5||0.6|
|Hyperabduction (sx reproduction)||0.84||0.40||1.4||0.4|
|Wright test (sx reproduction)||0.90||0.29||1.3||0.3|
|Elevated Arm Stress Test/Roos (EAST)||0.84||0.30||1.2||0.5|
Plain films: Chest and cervical spine xrays should be requested to assess for cervical rib or elongated C7 transverse process.
Other: Venous and arterial anatomy can be assessed by catheter angiography, doppler, or MR angiography and venography. MRI and CT has not been shown to affect decision making or improve outcomes.
Electrophysiological tests: Electrodiagnostic studies cannot identify compression at the thoracic inlet because this site is too close to the spinal nerve roots, chest wall thickness variation invalidates amplitude measurements, and because of the inability to measure distance variables. The H wave is also not reliable - this wave travels from the finger to the spinal cord and back and there are multiple potential sites of entrapment along this path.
The one form of thoracic outlet syndrome that can be tested using electrophysiology is with compression of the lower trunk - that formed by the C8 and T1 nerve roots. In this setting, abnormal findings are as follows:
- Low compound muscle action potential in the thenar and intrinsic muscles (both median nerve and ulnar nerve mediated muscles) - abductor digiti minimi, first dorsal interosseous, opponens pollicis, abductor pollicis brevis
- Abnormal sensory nerve conduction in the ulnar nerve
- Prolonged F-wave latency in the ulnar nerve
- Normal sensory amplitude of the index finger
- Abnormal medial antebrachial cutaneous sensory nerve conduction
TOS Muscle Test Block
The most modern version of this test targets the terminal branches of the intramuscular nerves of the anterior scalene, subclavius, and pectoralis minor. The test has evolved over the years increasing the diagnostic validity. Older techniques only targeted the anterior scalene which resulted in high rates of false negatives due to failure to block more distal sites of potential compression.
A positive test temporarily improves symptoms due to muscle relaxation leading to reduced tension on the neurovascular structures between the muscles in the interscalene triangle and dropping of the first rib. If the symptoms are temporarily reversed with selective blockade then surgical decompression is more likely to be successful.
The gold standard test block for NTOS is a single multi site injection that includes controls for placebo effects and examiner bias. Live combined ultrasound and EMG guidance is performed to ensure accurate placement of the injection and to confirm small volumes of injectant to the motor innervation within the muscle, while avoiding spread across tissue planes. When done the following way at an experienced centre the true-positive rate is 96% with the gold standard being a good outcome from botulinum chemodenervation or thoracic outlet decompression (879 cases). The false negative rate is 27%. Failure to double blind increases the risk of poor outcome from decompression.
Occasionally weeks or months of therapeutic benefit may result from the test injection, but the primary purpose is for diagnosis.
Pre-procedure: The patient is instructed about the need for double blinding and that either a short or long acting anaesthetic will be injected into the targeted muscles including the anterior scalene, subclavius, and pectoralis minor. In some cases it may be appropriate to perform sequential, staged blocks where blocks of isolated muscles are done at different dates.
They are shown how to keep an hourly pain diary for measurement of pain, numbness, and weakness at rest and with stress manoeuvres including the one minute EAST test every hour while awake and the following morning. They are also asked to perform any activities that usually bring about symptoms. They are coached to focus on either a 1 hour or 5 hour response. The anaesthetic used is determined by a coin flip by someone other than the doctor and placed in a sealed envelope.
Patient Position: The patient is in a semi rotated supine position with the upper body elevated to 30 degrees and the shoulder rotated off the table with a wedge.
Monitoring: Combined EMG and live ultrasound is performed throughout. EMG is a critical addition in two circumstances. Firstly it confirms the ultrasound appearance with seeing the needle tip in the muscle. Without EMG the doctor does not know if the muscle is simply being invaginated and not penetrated. The second benefit is that it allows monitoring of intramuscular location when the tip of the needle is obscured by the clavicle during injection of the subclavius muscle.
Approach: For the anterior scalene approach from lateral to medial to reduce the risk of vascular injury. Angle to the muscle at approximately 45 degrees.
For pectoralis minor introduce the needle at 45 degrees cephalad to avoid entering the pleural cavity, with the point of injection 3cm below the clavicle and into the point of maximum tenderness..
Active Target: The target muscles are anterior scalene, subclavius, and pectoralis minor. The muscles of interest are targeted in the mid belly region with a 25 gauge Teflon coated hypodermic EMG and injection needle.
EMG recording confirms high frequency motor unit activity at rest that is consistent with clinically observed dystonia. Motor thresholds are applied and a twitch on ultrasound is observed at approximaly 1 mA.
The patient is asked to respond upon feeling the effects of EMG stimulation. Pain intensity and concordance with typical pain patterns are recorded. The recording nurse is blinded to the muscle being injected.
The anterior scalene, subclavius, and pectoralis minor are sequentially subjected to the above targeting procedure and injected with 1mL of anaesthetic and 1mg of dexamethasone or 2mL of anaesthetic. Live ultrasound observes injectant flow along the targeted muscle and not into the plexus.
Controls: Control muscles are similarly injected with saline, such as the trapezius and sternocleidomastoid.
Interpretation: The pain diaries are returned the following day and interpreted prior to revealing the identify of the injectant. A valid response is 50% or greater reduction in the pain scale at rest and with provocation for a time that is concordant with the expected duration of the anaesthetic. Provocation testing should reveal concordant pain responses from the scalene, subclavius, or pectoralis muscles and not from control muscles. Unexpectedly long or short responses can be interpreted as placebo or non specific effects.
A negative response is a lack of improvement in symptoms. This can occur due to incorrect diagnosis, technical issues, or a fixed plexus compression by bony or soft tissue anomalies such as extensive scalene or pectoralis muscle fibrosis. Therefore a negative result can't fully exclude NTOS but lowers the chance of a successful outcome with treatment.
- Rotator Cuff Tendinopathy
- Cervical disc disorders
- C7 or C8 nerve root compression
- Ulnar neuropathy
- Carpal Tunnel Syndrome
- Myofascial Pain
- Multiple Sclerosis
- Raynauds Syndorme
- Cervical dystonia
- Neuralgic Amyotrophy or other brachial plexus injury
- Acromioclavicular Joint Pain
- Pancoast tumour
Thoracic outlet syndrome is a "fuzzy" diagnosis. It is a valid entity but it difficult to diagnose, and it can overlap with multiple other problems.
NTOS: The diagnosis of NTOS can be made when three of the following four criteria are present:
- LOCAL FINDINGS:
- History: Symptoms consistent with irritation or inflammation at the site of compression (scalene triangle for NTOS, and pectoralis insertion for NPMS), plus symptoms due to referred pain. Patients may have pain in the chest, axilla, upper back, shoulder, trapezius, neck, or head.
- Examination: Tenderness of the affected area.
- PERIPHERAL FINDINGS:
- History: Arm or hand symptoms consistent with proximal nerve compression. Symptoms include numbness, pain, paraesthesias, vasomotor changes, and weakness. Muscle wasting can occur in extreme cases. Symptoms are exacerbated by movements that either narrow the thoracic outlet (lifting arms overhead) or stretch the brachial plexus (dangling, driving, walking/running).
- Examination: Reproduction of peripheral symptoms with palpation of the affected area (scalene triangle or pectoralis minor insertion site). The EAST or ULTT test may provoke symptoms.
- ABSENT FINDINGS:
- Cervical disc disease, shoulder disease, carpal tunnel syndrome, chronic regional pain syndrome, brachial neuritis.
- Response to a properly performed test injection
VTOS: As many as possible of the following are required.
- HISTORY: Swelling, discoloration, heaviness, pain. Worse with arms overhead, driving, or exercising. Dilated veins in shoulder or chest.
- EXAMINATION: Swelling and discoloration at rest and with arms elevated
- IMAGING: Consistent imaging findings
- TOS Disability scale
ATOS: As many as possible of the following are required
- HISTORY: classic symptoms or acute or chronic ischaemia
- EXAMINATION: objective findings of ischaemia. Note that loss of pulse or discolouration with provocative manoeuvres in those with NTOS is not sufficient to diagnosis ATOS.
- IMAGING: Objective imaging findings of subclavian artery compression along with the presence or absence of a cervical rib, elongated transverse process, or anomalous first rib.
- TOS Disability scale.
Malfunction of the first rib: isometric contraction of scalenus anterior and medius results in elevation of the first rib anteriorly, and reduces posterior subluxation. The therapist places their hand over the lateral head with the patient in a seated position. The patient contracts against the therapists hand. Gentle mobilisations are done over 20 seconds.
Postural dysfunction: Spinal postural stability; release tight pectoralis minor (pec minor may be tight without 1st rib dysfunction with arm elevation), scalene and shoulder girdle muscles (e.g. infraspinatus and teres minor); maintain cervicothoracic mobility; strengthen scapula muscles, lower and middle trapezius, and serratus anterior; strengthen rotator cuff; address ergonomic factors; address work behaviour factors.
ENVEST Protocol: ENVEST stands for Edgelow Neuro Vascular Entrapment Syndrome Treatment which has been tested in thousands of patients with pain arising from the thoracic outlet. It involves learning to Activate the stabilisers of the neck and low back, diaphragm Breathing to allow relaxation of the scalene and pectoralis minor muscles, and Cardiovascular conditioning See video lecture on method here, which is part of channel with multiple other related videos.
General: Ergonomic modifications at workplace and home.
Medication: TCAs and anticonvulsants can be considered.
Injections: Botulinum chemodenervation
The aim is decompression of the thoracic outlet. Options include the following which can be done as individual procedures or combined. In properly selected patients at a specialised centre, surgery is successful in 80-90% of cases of NTOS.
- Pectoralis minor tenotomy. This can be a good treatment options in suitable patients and can be performed as an outpatient in 30 minutes.
- Supraclavicular decompression with scalenectomy
- First rib resection. This is usually unnecessary when scalenectomy is performed.
- Brachial plexus neurolysis.
The prognosis is better in younger patients. If surgery is performed it is very important that it is done by a centre and surgeon that is used to doing it. In this setting the prognosis is good with relatively short hospital stay, low risk of complications, and low chance of recurrence. Such a highly experienced centre may not exist in New Zealand.
Poor prognostic factors are fibromyalgia, opioid hyperalgesia, and CRPS. Having any one of these factors predicts a very high chance of failure of NTOS targeted intervention. These conditions are not uncommon in patients with NTOS.
In Musculoskeletal Medicine the controversies for neurogenic thoracic outlet syndrome are around:
- Whether there is a more proximal cause leading to the tight scalene or pectoralis minor muscle, such as a painful cervical disc or zygapophysial joint.
- The lack of an agreed upon gold standard diagnostic criteria
- Reporting standards are by Illig et al. 
- Book by above group.
- Review article (closed access) on ultrasound guided scalene muscle injection.
- 2014 cochrane review on treatment.
- Article on neuropathic pain.
- Illig et al.. Reporting standards of the Society for Vascular Surgery for thoracic outlet syndrome. Journal of vascular surgery 2016. 64:e23-35. PMID: 27565607. DOI.
- Illig, Karl A. Physical Therapy for NTOS In: Thoracic outlet syndrome. London New York: Springer, 2013.
- Juvonen T, Satta J, Laitala P, Luukkonen K, Nissinen J. Anomalies at the thoracic outlet are frequent in the general population. Am J Surg. 1995 Jul;170(1):33-7. doi: 10.1016/s0002-9610(99)80248-7. PMID: 7793491.
- Chang K, Graf E, Davis K, Demos J, Roethle T, Freischlag JA. Spectrum of thoracic outlet syndrome presentation in adolescents. Arch Surg. 2011 Dec;146(12):1383-7. doi: 10.1001/archsurg.2011.739. PMID: 22184299.
- Singh Virtaj et al. Thoracic Outlet Syndrome (Neurogenic) In: Peripheral nerve entrapments : clinical diagnosis and management. Switzerland: Springer, 2016.
- Illig, Karl A. Surgical Techniques:Pectoralis Minor Tenotomy for NTOS In: Thoracic outlet syndrome. London New York: Springer, 2013.
- Gillard et al.. Diagnosing thoracic outlet syndrome: contribution of provocative tests, ultrasonography, electrophysiology, and helical computed tomography in 48 patients. Joint bone spine 2001. 68:416-24. PMID: 11707008. DOI.
- Lindgren KA, Leino E, Manninen H. Cervical rotation lateral flexion test in brachialgia. Arch Phys Med Rehabil. 1992 Aug;73(8):735-7. PMID: 1642524.
- A Lee Dellon. Thoracic Outlet Syndrome In: Encyclopedia of Pain 2013.
- Illig, Karl A. Scalene Test Blocks and Interventional Techniques in Patients with TOS In: Thoracic outlet syndrome. London New York: Springer, 2013.
- Illig KA. Thoracic outlet syndrome in adolescents is real: comment on "Spectrum of thoracic outlet syndrome presentation in adolescents". Arch Surg. 2011 Dec;146(12):1388. doi: 10.1001/archsurg.2011.1026. PMID: 22184300.
- Torriani, Martin; Gupta, Rajiv; Donahue, Dean M. (2009-11). "Sonographically guided anesthetic injection of anterior scalene muscle for investigation of neurogenic thoracic outlet syndrome". Skeletal Radiology. 38 (11): 1083–1087. doi:10.1007/s00256-009-0714-x. ISSN 1432-2161. PMID 19440705. Check date values in:
- Povlsen B, Hansson T, Povlsen SD. Treatment for thoracic outlet syndrome. Cochrane Database Syst Rev. 2014 Nov 26;(11):CD007218. doi: 10.1002/14651858.CD007218.pub3. PMID: 25427003.
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