The Many Faces of Thoracic Outlet Syndromes

By Whitney Lowe
[Science of Nerves]

Thoracic outlet syndrome (TOS) is both common and highly misunderstood. One reason for the confusion around this condition is that the term can refer to a number of different syndromes involving different tissues. More accurately, the variety of pathologies should be categorized in the plural as thoracic outlet syndromes and named more accurately according to the tissues involved: cervical rib compression, anterior scalene, costoclavicular, and pectoralis minor syndromes.
 In this column, we explore the details of the four variations that can be involved in thoracic outlet syndrome, the tissues that may be involved, anatomical anomalies, expected symptoms of each, and massage therapy strategies that are helpful.   
Anatomical Background
What makes this syndrome even more convoluted is that there isn’t full agreement on where the thoracic outlet is. When you speak of “thoracic outlet syndrome,” you could be discussing potential tissue pathologies that exist anywhere within the shaded region of Image 1. Anatomically, the upper opening of the rib cage is defined as the thoracic inlet (as the respiratory and digestive tracts enter the thorax). Consequently, the lower opening of the rib cage is the thoracic outlet.  
However, the lower opening of the rib cage is a long way from where the nerve and vascular compression occurs in TOS. The term thoracic outlet is more commonly applied to the superior opening of the rib cage. The use of this term in relation to the upper opening of the rib cage is likely attributed to the focus of vascular surgeons on the aorta and its exit from the upper rib cage, and, therefore, it would be more appropriately termed an outlet with that view. To fully understand the development of problems in this area, we need to dig deeper into some of the key anatomical relationships.
The brachial plexus is the group of nerves in the lower cervical and upper thoracic region that is vulnerable to compression and tension pathology in the various thoracic outlet syndromes. The brachial plexus is comprised of nerve fibers that originate at the nerve roots from the C5 to T1 level. Important anatomical relationships make portions of it more vulnerable to compression and tension pathology in this region.
Adverse nerve compression can occur when the lower portion of the brachial plexus is pressed against underlying structures. Therefore, the fibers that are contained within the inferior trunk and eventually split off into the medial cord of the brachial plexus are the ones most vulnerable (Image 2). Notice from this image that the T1 nerve root is actually lower than the first rib. As a result, its fibers are under greater tension when other obstructions like a cervical rib are present.  
In TOS, vascular structures may also be compressed in this region. The most common problems occur to the subclavian artery or vein. Both these structures follow a curved pathway over the top of the first rib. Obstructions in their path, such as a cervical rib, fibrous bands, or narrow opening between the scalene muscles, make them vulnerable to compression in this region.
The scalene muscles play a key role in thoracic outlet pathologies. However, it is only the anterior and middle scalene muscles that may potentially compress neurological or vascular structures (Image 3). Nerves and the subclavian artery course between these two muscles in what is referred to as the scalene triangle. The first rib forms the base of the triangle.  
Previously, I’ve made several references to a cervical rib. This term may seem odd because the ribs are all located in the thoracic region. However, there is an anatomical anomaly that occurs in a small percentage of the population. As the skeleton matures, lateral aspects of the C7 transverse process that are ossified are eventually reabsorbed and the transverse process assumes its normal shape. However, sometimes this does not occur and an elongated transverse process is produced. In some cases, the elongation of the transverse process extends all the way down and has fibrous connections with the first rib (Image 4, page 88). This is called a cervical rib. It is estimated that somewhere between one half and 2 percent of the population have cervical ribs, and, for some reason, they appear more frequently in women.1  
These anatomical structures all play a role in one or more of the various TOS pathologies. While TOS is generally described by the compression location, it may also be described by what type of tissue is involved. Consequently, you may see any of these different variations of TOS described:
• Arterial (A-TOS): compression of the subclavian artery or any of its distal branches in the cervical and upper thoracic region.
• Venous (V-TOS): compression of the subclavian vein or any of its distal branches in the cervical and upper thoracic region.
• True Neurogenic (TN-TOS): compression of any of the branches of the brachial plexus without arterial or venous involvement.
Numerous cases involve more than one of these at the same time. For example, you could have arterial and neurological compression but not venous (which is common). You could have arterial and venous compression that does not have a neurological component. The compression is considered neurovascular if it involves not only nerves, but at least some arterial or venous compression at the same time.

Description by Location
The most common method for classifying TOS variations is by location. There are four potential variations/regions where neurovascular compression may occur, and each is discussed below. As a general rule, the symptoms from each of these four variations can be similar with a few exceptions. The key symptoms to watch for in any one of these TOS variations include:
• Atrophy of the thenar or hypothenar muscles of the hand.
• Pain, aching, or numbness in the hand, fingers, or medial forearm (most commonly along the ulnar aspect of the hand and the C8 dermatome).
• Paresthesia, although it is not as common from TOS as with carpal tunnel syndrome.
• Loss of dexterity or grip strength.
• Coldness or color changes in the hand (often confused with Raynaud’s syndrome).
Cervical Rib Variation  
If there is an osseous extension of the transverse process or a true cervical rib, it will take up space in the thoracic outlet region. Neurological and vascular structures must course over the top of the cervical rib before making their way under the clavicle and down the arm. Because the cervical rib sits above the first rib, the neurovascular structures get bowstrung across the top of the cervical rib as they course through this region. This is especially true with the brachial plexus fibers that originate at the T1 nerve root, because they already sit below the first rib.  
Because this neurovascular compression problem is the result of a bony obstruction in the thoracic outlet region, there is very little massage can do to address this problem. Yet, learning about the presence and existence of cervical ribs is important for massage therapists because many may attempt to perform vigorous work on what appear to be very hard scalene muscles when, in effect, they are actually pressing on a cervical rib structure.  
If pathological symptoms continue to persist with a cervical rib TOS variation, surgery may be suggested. The surgical procedure usually involves removing the bony extension from the C7 transverse process. In many cases, immediate relief will be felt as the obstruction is no longer obscuring the path of the neurovascular structures.

Massage can still be helpful for addressing hypertonicity of surrounding muscles.  
Anterior Scalene Syndrome
Neurological or vascular compression may occur between the anterior and middle scalene muscles. Therefore, this TOS variation is frequently referred to as anterior scalene syndrome. Compression may impact the various fibers of the brachial plexus or the subclavian artery. Note that the subclavian vein does not pass through the scalene triangle so it is not involved in this variation (Image 5).  
Because both muscles insert on the first rib, they may pull the rib in a superior direction when hypertonic. Consequently, hypertonicity of the scalene muscles may decrease the size of the scalene triangle and increase potential neurovascular compression in this region. The space inside the scalene triangle for passage of the neurovascular structures may also be decreased from enlargement (hypertrophy) of the lower scalenes.  
Neurological compression may occur in this region even if there isn’t a decreased space in the scalene triangle. In one recent anatomical investigation, researchers found close to 45 percent of the cadaver specimens had one or more branches of the brachial plexus that were piercing directly through the scalene muscles as opposed to coursing freely through the scalene triangle.2 If that many people have nerves piercing directly through the scalenes, we should reconsider how often we use deep pressure techniques to treat these areas.  
Many of the special orthopedic tests used to identify variations of TOS focus on palpating and identifying the radial pulse. If the pulse diminishes during a positional movement, it would indicate a likely vascular (and probably also neurological) compression in that region. Yet, here is a good example of how a negative test may not truly show the presence of neurological involvement. If brachial plexus nerves are piercing directly through the scalene muscles, evaluating the pulse for potential compression in certain head or neck positions may be irrelevant because the nerves are getting compressed by tight muscles in every position, even if the vascular structures are not.  
In most cases, the anterior scalene TOS variation results from hypertonicity or problems directly in the scalene muscles. Therefore, massage and soft-tissue manipulation applied to this region can generally be helpful. However, the practitioner should be very careful about applying significant pressure in the anterior neck region as there are numerous sensitive structures in this area as well.  
The scalene muscles are superficial, and often it takes very little pressure to encourage some relaxation and decreased tightness in these muscles. Sometimes just applying a gentle traction force to the skin over the muscles can help decrease tightness and lessen symptoms. The direction of a traction force may vary from person to person, and it is perfectly fine to experiment with different directions and see which gives the greatest relief of symptoms (Image 6). Gently stretch the skin and superficial tissues in the direction of greatest symptom reduction and hold that position for a minute or so. It is also helpful to encourage some gentle and easy passive and active movement of the cervical region immediately after this to help reestablish safe and pain-free movement for the region.   

Costoclavicular Syndrome
Moving inferiorly from the scalene triangle, the next potential location for neurovascular problems is between the clavicle and first rib. In this location, the brachial plexus, as well as the subclavian vein and artery, are all susceptible to compression. The space between clavicle and first rib can vary significantly from person to person. In women, the shoulder has a lower position relative to the thorax than in men. This could be another reason this condition is far more prevalent in women than men.
Other factors, such as poor posture, wearing of backpacks or straps across the shoulders, or various occupational activities, can lead to increased compression in the costoclavicular region.3 Scalene tightness is also reported as a causative factor because when the muscles are tight, they may pull the first rib in a superior direction and decrease space between the rib and clavicle.
One method commonly used to identify costoclavicular syndrome is called the military brace test. In this procedure, the scapula are squeezed together in the back while the arms are extended posteriorly (Image 7). The position is held for about a minute to assess if neurological symptoms appear. The pulse may also be palpated to assess if the pulse dissipates in intensity while in this position.  
The role of massage in addressing costoclavicular compression is more indirect. Treating the scalene muscles may reduce tightness and mediate their role in elevating the first rib. Overall treatment of the cervical and upper thoracic region can be very beneficial in reestablishing proper neuromuscular balance and facilitating less painful and more natural movements.  
Pectoralis Minor (Hyperabduction) Syndrome
The final TOS variation is called the pectoralis minor syndrome or hyperabduction syndrome. As its name implies, the primary culprit is the pectoralis minor muscle. The brachial plexus along with the axillary artery and vein (branches from the subclavian artery and vein) all course underneath the pectoralis minor muscle in the upper thoracic region. In this variation, the structures may be compressed against the upper rib cage.  
This TOS variation may be clarified with an evaluation procedure called the Wright abduction test. The client’s arm is lifted overhead in a fully abducted position (usually with the elbow flexed) and held in this position for about 60 seconds to assess if neurological symptoms recur (Image 8). If they recur within about 30–45 seconds, this is a good indicator of potential neurovascular compression underneath the pectoralis minor. It is interesting to note that if the primary neurovascular compression is between the clavicle and first rib (costoclavicular variation) those symptoms will generally be relieved with the Wright abduction test because this movement lifts the clavicle off the rib cage.  
This variation seems to be predominantly caused by hypertonicity within the pectoralis minor muscle. Postural challenges may contribute to the problem as well. As a result, massage is generally effective for helping to address this problem. Keep in mind that the pectoralis minor lies deep to the pectoralis major muscle, so it is not easy to get pressure applied to the pectoralis minor without working through the pectoralis major first.
Many practitioners also attempt to stretch the pectoralis minor by bringing the arm into full flexion overhead. This position may cause a sensation of stretch in the anterior shoulder girdle and feel like it is really stretching the pectoralis minor. However, keep in mind that bringing the arm overhead into this position does very little to stretch the pectoralis minor because it is attached to the coracoid process of the scapula and not to the humerus, so it actually moves very little in this position.  
Most practitioners have heard of TOS, but may not realize there are different variations, which tissues are involved, and where the problem is located. Helping to effectively address this problem is greatly enhanced when you can narrow down the most prominent contributing factors.  

1. M. A. Ferrante and N. D. Ferrante, “The Thoracic Outlet Syndromes: Part 1. Overview of the Thoracic Outlet Syndromes and Review of True Neurogenic Thoracic Outlet Syndrome,” Muscle Nerve 55, no. 6 (2017): 782–93. doi:10.1002/mus.25536.
2. V. Leonhard et al., “Anatomical Variations in the Brachial Plexus Roots: Implications for Diagnosis of Neurogenic Thoracic Outlet Syndrome,” Annals of Anatomy 206 (2016): 21–6. doi:10.1016/j.aanat.2016.03.011.
3. M. Pecina, A. Markiewitz, and J. Krmpotic-Nemanic, Tunnel Syndromes: Peripheral Nerve Compression Syndromes (Boca Raton: CRC Press, 2001).
Whitney Lowe is the developer and instructor of one of the profession’s most popular orthopedic massage training programs. His texts and programs have been used by professionals and schools for almost 30 years. Learn more at