The Importance of Double Crush and Postural Distortions
Nerves emanating from the neck (cervical spine) travel into the arm (shoulder, arm, forearm wrist, hand, fingers). When a patient presents with radiating symptoms (pain, tingling, numbness, etc.) into the arm, default thinking is that the patient has a neck problem. Therefore, the initial examination, imaging, and other diagnostic endeavors target the neck and the cervical spine nerves. The technical terminology for cervical nerve root problems is radiculitis and/or radiculopathy.
Not all radiating arm symptoms are radicular (attributed to the spinal nerve root). The nerves that travel down the arm must also travel through anatomical locations where these nerves may become compressed, irritated, or inflamed. These locations are collectively termed the thoracic outlet. The thoracic outlet has three locations, described below. The technical terminology for nerve problems emanating from the thoracic outlet is neuritis or neuropathy. The distinction is the prefix “radiculo,” meaning nerve root. The prefix “neuro” means peripheral nerve. Thoracic outlet nerve involvement is “neuro.”
In contrast to the cervical spine, thoracic outlet problems may, in addition to affecting the nerves, compromise blood flow through the subclavian artery and subclavian vein.
Thoracic Outlet Anatomy
There are three anatomical locations for the thoracic outlet syndrome:
- Scalene Triangle: Compression, irritation, or inflammation occurs as the brachial plexus traverses the space between the middle and anterior scalene muscles and the first rib.
- Costoclavicular Space: Compression, irritation, or inflammation occurs in the space between the clavicle and the first rib.
- Pectoralis Minor Space: Compression, irritation, or inflammation occurs in the area formed from the pectoralis minor muscle anteriorly and the rib cage posteriorly.
Denver thoracic outlet surgeon Richard Sanders, MD, defines thoracic outlet syndrome (TOS) as (1):
“TOS is neurovascular symptoms in the upper extremity due to pressure on the nerves and vessels in the thoracic outlet area. The specific structures compressed are usually the nerves of the brachial plexus and occasionally the subclavian artery or subclavian vein.”
The Double Crush Nerve Concept
In 1973, physicians Adrian Upton and Alan McComas introduced a concept suggesting that undiagnosed cervical spine problems could increase the incidence of extremity peripheral entrapment syndromes. They referred to this as the (2):
Double Crush in Nerve-Entrapment Syndromes
Drs. Upton and McComas published their initial study on this Double Crush Nerve-Entrapment Syndrome in the journal The Lancet, on August 18, 1973 (2).
Drs. Upton and McComas performed a comprehensive electromyographic study of 115 patients with carpal-tunnel syndrome and lesions of the ulnar nerve at the elbow. In 81 cases (70%) they found electrophysiological evidence, often supported by clinical symptoms, of associated neural lesions in the neck. They concluded that the association between carpel-tunnel syndromes, elbow ulnar nerve lesions, and electrophysiological abnormalities of the cervical spine were not “fortuitous, but rather the result of serial constraints of axoplasmic flow in nerve fibers.”
Upton and McComas describe these elements supporting a nerve root lesion increasing the incidence of peripheral neuropathies:
- Radiological evidence of cervical spondylosis.
- Complaints of neck pain and stiffness.
- A previous history of neck injury, commonly of the hyperextension whiplash type sustained in a rear-end motor vehicle accidents.
- “Clinical evidence of sensory abnormality corresponding to a dermatomal rather than a peripheral nerve distribution.”
- Electromyographic evidence of denervation of other muscles that are supplied by the nerve root.
Drs. Upton and McComas state:
“Most patients with carpal tunnel syndromes or ulnar neuropathies not only have compressive lesions at the wrist or elbow, but they also have evidence of damage at the level of the cervical roots.”
“Treatment, rather than being directed at a single site, should be applied to all vulnerable points along the course of the nerve—i.e., to both the neck and to the wrist or elbow, depending on the nerve involved.”
Since the original publication on Double Crush Syndrome in 1973, many studies have continued to support its validity (3, 4, 5, 6, 7, 8, 9, 10, 11).
There is evidence for a Double Crush component to thoracic outlet syndrome (2, 3, 4). Consequently, appropriate management of cervical spine mechanical problems is essential in the overall management of thoracic outlet syndrome. Studies (3) indicate that the primary Double Crush component of thoracic outlet syndrome is discogenic. Conservative treatment duration for patients with traumatic neurogenic thoracic outlet syndrome can exceed 4 months, and even exceed 1 year if the cervical discs are involved. Treatment of the spinal problems in such patients will improve clinical outcomes.
Types of Thoracic Outlet Syndrome
There are two primary types of thoracic outlet syndrome (1, 20):
- Neurogenic Thoracic Outlet Syndrome: Neurogenic thoracic outlet syndrome (nTOS) comprises more than 95% of cases.
- Vascular Thoracic Outlet Syndrome: Vascular thoracic outlet syndrome comprises less than 5% of cases.
There are two types of vascular TOS:
- Arterial Thoracic Outlet Syndrome (aTOS), with involvement of the subclavian artery.
- Venous Thoracic Outlet Syndrome (vTOS), with involvement of the subclavian vein.
The vascular symptoms of thoracic outlet syndrome are more often arterial than venous. Arterial thoracic outlet syndrome is compression or blockage of the of the subclavian artery. The artery can also be afflicted by aneurysm, thrombosis, or emboli. Arterial thoracic outlet syndrome accounts for a large percentage of the serious disabilities resulting from thoracic outlet syndrome. Most cases of arterial thoracic outlet syndrome are associated with a bony abnormality, usually a complete cervical rib. Also, incomplete cervical ribs are usually attached to the first rib by a dense fibrous band that can exert pressure against an arterial wall similar to that imposed by a cervical rib.
Arterial thoracic outlet syndrome symptoms include coldness, pallor, Raynauld’s phenomenon (color changes), claudication, and gangrene of fingertips (from emboli).
The incidence of venous obstruction in all thoracic outlet syndrome patients is very small. Venous thoracic outlet syndrome symptoms include swelling, cyanosis, and aching.
In 2022, an article was published in the Journal of Osteopathic Medicine, titled (20):
Thoracic Outlet Syndrome: A Review for the Primary Care Provider
The authors state:
“All patients presenting with signs and symptoms of either arterial or venous compression should be evaluated urgently to prevent limb ischemia and/or other complications from developing.”
“MR and CT angiography are the preferred modalities to identify the area of compression and guide surgical treatment in vascular forms of TOS.”
Importantly, the authors state that vascular thoracic outlet syndrome patients may require urgent anti-coagulation therapy and/or surgery to prevent long-term complications and disabilities.
Incidences of Thoracic Outlet Syndrome
- A 2020 study of male high school baseball players found that 33% ha symptomatic TOS (15).
- 95% of TOS is neurogenic (nTOS).
- 3% of TOS is venous vascular (vTOS).
- 1% of TOS is arterial vascular (aTOS).
Etiologies of Thoracic Outlet Syndrome
- Congenital: cervical or first rib which may be coupled with fibrous bands.
- Traumatic: whiplash injuries, motor vehicle accidents, sports injuries, etc.
- Functional: the most encountered, from vigorous, repetitive upper-extremity activity.
Symptoms of Thoracic Outlet Syndrome
“The most common symptoms are pain and paresthesias of the head, neck, and upper extremities” (20). Typically, symptoms are distributed as follows:
- Paresthesias – 98% (58% involve all five fingers, 26% involve the fourth and fifth fingers, 14% involve the first to third fingers)
- Trapezius pain – 92%
- Supraclavicular pain – 76%
- Chest pain – 72%
- Shoulder and arm pain – 88%
- Occipital headaches – 76%
- Upper-extremity pain – 99%
- Exacerbation of symptoms by arm elevation – 97%
- Localized supraclavicular or subcoracoid tenderness on palpation – 96%
- Upper-extremity and/or hand paresthesias – 94%
Mechanisms of Thoracic Outlet Syndrome
Scalene muscle injury, secondary to cervical spine trauma, is the most common etiology of thoracic outlet syndrome. In some studies, trauma was the cause of TOS in 86% of patients, and automobile accidents were the most common type of injury (1).
Risk factors for the development of post-traumatic thoracic outlet syndrome include a longer neck, cervical kyphotic malalignment, and sloping shoulders (13). An assessment of the biomechanics of cervical risk factors can be done radiographically.
Pathology of Thoracic Outlet Syndrome
Anything that causes swelling and/or fibrosis of the scalene muscles can elicit symptoms of thoracic outlet syndrome (1, 14, 16). Since 1990, histochemical studies have demonstrated fiber changes as well as scar tissue in both anterior and middle scalene muscles of thoracic outlet syndrome patients. Histological studies show increased connective tissue in the scalenes of most thoracic outlet syndrome patients. Trauma caused inflammation, fibrosis, and contracture of the anterior scalene muscle, which compresses the brachial plexus and subclavian artery to produce thoracic outlet syndrome symptoms.
Diagnosis of Thoracic Outlet Syndrome
Dr. Sanders notes that the history is more important than the physical examination in making a diagnosis of thoracic outlet syndrome (1). Yet, in 2016, the Journal of Vascular Surgery stated that arriving at a diagnosis of nTOS is best achieved through the use of the Upper Limb Tension Test (ULTT) and the Elevated Arm Stress Test (EAST).
Elevated Arm Stress Test = EAST
- Sit at attention
- Arms abducted 90°, parallel to horizon
- Elbows flexed 90°, the surrender position
- Fingers are slowly opened and closed for 3 minutes
Upper Limb Tension Test = ULTT
Brachial Plexus Tension Test = BPTT
There are a number of variations of the BPTT test. It can be done either supine or seated. These steps are done in sequence, progressively increasing nerve tension:
- Arm abducted 90°
- Elbow flexed 90°
- Wrist and fingers extended
- Forearm supinated
- Elbow extended
- Contralateral lateral flexion of neck
Posture and Thoracic Outlet Syndrome
Postural distortions will create chronic muscle contractions. Postural distortions of the head-neck-shoulder regions will influence the scalene muscles and the pectoralis minor muscles, contributing to thoracic outlet syndrome (20).
- A common TOS postural distortion is an anterior-inferior shoulder, “which shortens the sternocleidomastoid and the scalene and pectoral muscles, and elevates the upper ribs, narrowing the costoclavicular space.”
- “Muscle imbalance, such as hypertrophied pectoralis minor or hypertrophied scalene and sternocleidomastoid muscles, can directly contribute to the entrapment of the brachial plexus, subclavian artery, and vein.”
- “Pelvic alignment affects posture, including head, neck, and upper thoracic spine alignment, thus indirectly contributing to the function of the thoracic outlet.”
- “An anterior pelvic tilt due to tight hip flexors may cause an increased lordosis of the lumbar spine and a compensatory kyphosis of the thoracic spine. This may contribute to the shoulders being rolled forward with shortening of the pectoralis minor muscles and tightening of the cervical muscles, ultimately entrapping the cervical brachial plexus and vasculature.”
- “Evaluating and treating overall posture and addressing muscle imbalances may help minimize entrapment and ease the symptoms of TOS.”
Traditional Chiropractic Connections
The scalene and the pectoralis minor muscles are innervated by cervical nerve roots:
Anterior Scalene C5-C8
Middle Scalene C3-C8
Posterior Scalene C6-C8
Pectoralis Minor C8-T1
Cervical spine nerve root problems will affect these muscles, contributing to thoracic outlet syndrome.
- “Cervical spine somatic dysfunctions can create facilitation of the nerve roots and affect the tone of the cervicobrachial musculature” (20).
- “Extension somatic dysfunctions of the upper thoracic spine are often associated with TOS symptoms of upper-extremity numbness” (20).
The Sympathetic Nervous System
Local increased sympathetic tone reduces blood flow through the subclavian artery, leading to thoracic outlet symptoms. It has been shown that chiropractic spinal adjusting will improve mechanical function and result in decreased sympathetic tone, improving blood flow (18, 19). The following statements review the importance of chiropractic spinal adjusting in an effort to inhibit aberrant sympathetic tone (20):
“Thoracic vertebral somatic dysfunctions can create facilitation of the sympathetic innervation of the upper extremities, leading to increased muscular tone and vasoconstriction.”
“Raynaud’s in the setting of nTOS is thought to be caused by an overactive sympathetic nervous system response triggered by irritation of sympathetic nerve fibers that run along the nerve roots of C8 and/or T1 and the lower trunk of the brachial plexus.”
“This anatomical relationship provides an opportunity for the use of manipulative treatment modalities that aim to decrease sympathetic tone to the upper limb.”
Tissue texture changes and restrictions in the cervical spine from C2-C7, T1, 1st rib, thoracic inlet, clavicle, and scalene muscles should be evaluated. The initial treatment for neurogenic TOS is always conservative. Surgery for nTOS is considered only if improvement fails to occur.
The best conservative approach to nTOS is a combination of spinal manipulation, other manual modalities, and a home exercise regimen. These approaches may also be utilized:
- “Evaluating the whole body and treating individual somatic dysfunctions that may be directly or indirectly contributing to the neurovascular compression helps alleviate nTOS symptoms” (20).
- Daily stretching of the TOS muscles, including the pectoralis minor, scalenes, and other muscles of the neck and shoulder.
- Postural correction through spinal adjusting, blocking, traction, stretching, and exercise.
- “Techniques such as high-velocity/low-amplitude, muscle energy, counter-strain, myofascial release… can all correct dysfunctions that are present and contributing to the TOS symptoms” (20).
- Trigger point injections may offer relief to some patients.
- Acupuncture may help to alleviate pain of nTOS.
Surgery for thoracic outlet syndrome should not be performed until the patient has failed to improve while on conservative management for at least a few months. Dr. Richard Sanders states (1):
“Surgery is a last resort; conservative treatment should be tried first.”
“If symptoms do not improve with several months of conservative management, the patient regards the symptoms as disabling, and all other treatable conditions have been excluded, the patient must either live with the symptoms or undergo surgery. With surgery not an ideal solution, if there is persistent nerve compression, surgery is the only alternative.”
“Recurrent symptoms develop in 15-20% of patients who have received operations for thoracic outlet syndrome.”
“The almost constant finding at reoperations for thoracic outlet syndrome is the presence of scar tissue around the nerves of the plexus.”
“Scar tissue lies not only around the entire neurovascular bundle, but also around the individual nerves comprising the plexus. Presumably it is the maturation and contraction of this scar tissue that produces brachial plexus compression.”
The late James Cyriax, MD, from the Department of Orthopedic Medicine, St. Thomas’s Hospital in London, and Professor of Orthopaedic Medicine, University of Rochester Medical School, notes in his 1983 text Illustrated Manual of Orthopaedic Medicine, the value of transverse friction in the treatment of post-traumatic muscle fibrosis (21).
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- Cavanna AC, Giovanis A, Daley A, Feminella R, Chipman R, Onyeukwu V; Thoracic Outlet Syndrome: A Review for the Primary Care Provider; Journal of Osteopathic Medicine; August 29, 2022; Vol. 122; No. 11; pp. 587–599.
- Cyriax J, Cyriax P; Illustrated Manual of Orthopaedic Medicine; Butterworths; 1983.
“Authored by Dan Murphy, D.C.. Published by ChiroTrust® – This publication is not meant to offer treatment advice or protocols. Cited material is not necessarily the opinion of the author or publisher.”