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Anatomy
GENERAL
The three main structures impacted by TOS are nerves, arteries, and veins. Each of these has a very specific function within the body.
Nerves are pretty much the command center of the body. The body cannot perform any functions without nerves. Nerves function as the electrical system of the body. This electrical system is used to carry signals from the brain to other parts of the body instructing that part of the body to carry out a task. There are two major parts of the body’s nervous system – the central nervous system and the peripheral nervous system. The central nervous system is made up of the brain and spinal cord. The peripheral nervous system is made up of the rest of the nerves in the body. If you think of it in terms of a power grid, the central nervous system is the powerhouse and the peripheral nervous system is the cabling that provides the electricity from the powerhouse to all the surrounding cities. The peripheral nervous system is what gets impacted by TOS. More specifically, the nerves that provide sensation to and that carry out all the functions and movements of the shoulder, arm, and hand. Nerves can either be sensory and provide sensation or motor and provide movement. For instance, if you touch your hand near a hot burner, the sensory nerves allow you to feel the heat, and the motor nerves allow you to move your hand away before it gets burned.
Arteries carry blood that is rich with oxygen and nutrients from the heart to the other organs and tissues of the body. Arteries have thick tough walls to be able to withstand the amount of pressure from the blood pumping through it that is required to keep the blood constantly flowing to the organs and tissues. The artery impacted by TOS is the axillary-subclavian artery. It supplies the blood to the shoulder, arm, and hand.
Veins carry deoxygenated blood from the tissues and organs back to the heart. After the arteries deliver the oxygen rich blood, the blood needs to go back to the heart to get more oxygen and nutrients so that the arteries can distribute it again. In contrast to arteries, veins are very low pressure. The vein impacted by TOS is the axillary-subclavian vein. It takes all the deoxygenated blood from the shoulder, arm, and hand and returns it to the heart.
THORACIC OUTLET AREA
The thoracic outlet area as a whole contains the following relevant anatomy:
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Anterior scalene muscle
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Middle scalene muscle
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Collarbone
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First Rib
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Brachial plexus
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Axillary-subclavian artery
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Axillary-subclavian vein
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Costoclavicular space
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Costoclavicular ligament
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Subclavius muscle
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Pec minor muscle
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Anatomical anomalies
Anatomy that Gets Compressed
Brachial Plexus Nerves The brachial plexus is a network of nerves that includes all the motor and sensory nerves of the chest, most of the upper back, shoulder, arm, and hand. It looks a bit like a spider web. It contains the five nerve roots of C5, C6, C7, C8, and T1 which originate from the cervical and thoracic spine. On its way from the neck to the arm, it splits and merges several times sprouting off several different nerve branches which then go to the various structures in the area to provide innervation. When it finally gets to the shoulder and upper arm, it takes the form of five main nerves that travel down the arm to the hand which are the musculocutaneous, axillary, radial, median, and ulnar nerves. It is often referred to as two different parts: the upper plexus and lower plexus. The upper plexus includes the nerve roots of C5-C6. The lower plexus includes the nerve roots of C7-T1. The path which the brachial plexus nerves take through the thoracic outlet to travel from the neck to the arm is that the nerve roots exit the neck, then they travel between the anterior and middle scalene muscles then go through a small space between the collarbone and first rib, then travel across the chest behind the pec minor muscle.
Axillary-Subclavian Artery At a certain point in its course, the subclavian artery turns into the axillary artery which is why it is referred to as the axillary-subclavian artery. It provides the blood supply for the shoulder, arm, and hand. It also has several smaller arteries that branch out to provide blood supply to other structures that are near its path. The subclavian artery originates in the middle of the upper chest. The path which the axillary-subclavian artery takes through the thoracic outlet to travel from the neck to the arm is that it goes up from behind the sternum into the base of the neck, then travels between the anterior and middle scalene muscles then goes through a small space between the collarbone and first rib, then travels across the chest behind the pec minor muscle. It is an almost identical path to that of the brachial plexus as they are side by side while traveling from the neck to the arm. As soon as the subclavian artery gets past the first rib, that is when it turns into the axillary artery which is just a continuation of the same path.
Axillary-Subclavian Vein At a certain point in its course, the axillary vein turns into the subclavian vein which is why it is referred to as the axillary-subclavian vein. It takes all the deoxygenated blood from the shoulder, arm, and hand and returns it to the heart. Because its function is to return blood from the arm back to the heart, the path it takes through the thoracic outlet is the opposite of the paths that the brachial plexus and axillary-subclavian artery take. Several superficial and deep veins within the arm merge to form the axillary vein near the armpit. The path which the axillary-subclavian vein takes through the thoracic outlet to travel from the arm to the neck and eventually back to the heart is that it goes behind the pec minor muscle, then travels across the chest and goes through a small space between the collarbone and first rib (as well as having to squeeze between the subclavius muscle and the costoclavicular ligament) and then it joins other veins in the base of the neck to continue blood flow back to the heart.
Anatomy Doing the Compressing
Anterior Scalene Muscle originates at cervical spine levels C3-C6 and attaches to the first rib. It elevates the first rib during inhale breathing. It helps to rotate the neck to the opposite side, side bend the neck on the same side, and bring the head down to the chest in flexion. (NTOS, ATOS, VTOS)
Middle Scalene Muscle originates at cervical spine levels C2-C7 and attaches to the first rib. It elevates the first rib during inhale breathing. It helps to side bend the neck on the same side and bring the head down to the chest in flexion. (NTOS, ATOS)
Collarbone (Clavicle) one end connects to the sternum just above the first rib and the other end connects to the outside of the shoulder. (NTOS, ATOS, VTOS)
First Rib this is the rib at the very top of the rib cage and just below the neck. It is the shortest and most curved rib. It sits just below the collarbone. The surface of the first rib is rough, has 2 grooves for the subclavian artery and subclavian vein to pass through, and 2 insertion points for the anterior and middle scalene muscles to attach to. (NTOS, ATOS, VTOS)
Scalene Triangle the space bordered by the anterior scalene muscle, middle scalene muscle, and the first rib. (NTOS, ATOS)
Costoclavicular Space this space is the area where the collarbone and the first rib intersect. (NTOS, ATOS, VTOS)
Costoclavicular Ligament this is a very small but strong ligament which its bottom portion attaches to the cartilage of the first rib, and its top portion attaches to the under surface of the collarbone. (VTOS)
Subclavius Muscle originates at the end of the first rib that connects to the sternum and attaches to the under side of the collarbone. It helps to stabilize the collarbone, depress the collarbone, and elevates the first rib during inhale breathing. (VTOS)
Pec Minor Muscle this muscle lies just below the pec major muscle. It originates at the 3rd through 5th ribs with the muscle head fusing into a tendon where it attaches to the front of the shoulder at a point known as the coracoid process. The coracoid process is a bony process of the shoulder blade that extends through to the front of the shoulder. The pec minor helps to stabilize the shoulder blade. (NTOS, VTOS)
Scar Tissue even though scar tissue is not anatomy in the sense that we are born with it, it is a very large contributor to TOS compression. The nerves, artery, and vein become damaged from long-term compression. The body lays down scar tissue as part of the normal healing process. Then the dense scar tissue building up on the structures also becomes part of the compression issue. (NTOS, ATOS, VTOS)
Anatomical Anomalies the thoracic outlet is known for having anatomical anomalies. An anatomical anomaly is something within the anatomy or body structure that is abnormal, unusual, and deviates from what is expected. Anomalies are something a person is born with. See list of anomalies below.
Cervical Rib regular ribs connect to the thoracic spine and are known as thoracic ribs. However, some people are born with an extra rib which originates from the cervical spine at the C7 level, and this is known as a cervical rib. Cervical ribs can be complete or incomplete. A complete cervical rib connects to the first rib by a joint or by fusion. An incomplete cervical rib (short cervical rib) has a joint but is connected to the first rib only by a fibrous band. (NTOS, ATOS)
Elongated C7 Transverse Process each level of the spine has a transverse process on each side of the vertebrae. The transverse process at the C7 level can sometimes be longer than normal, and in which case it would be what is called an elongated C7 transverse process. An elongated C7 transverse process is often connected to the first rib by a fibrous band. This is very similar to the scenario seen with an incomplete cervical rib. (NTOS, ATOS)
Scalene Minimus Muscle an extra scalene muscle that usually originates from the C7 transverse process and attaches to the first rib. (NTOS, ATOS, VTOS)
Anomalous First Rib there are several different things that can make a first rib anomalous such as being wider or thicker than normal, being fused to the 2nd rib, being free floating and not attaching to the sternum, being narrower and higher than normal. (NTOS, ATOS, VTOS)
Muscle Anomalies the anterior and middle scalene muscles can be anomalous in ways such as being much larger in size than normal or being fused together. (NTOS, ATOS, VTOS)
Bands and Ligaments there are 9 different classified fibrous bands that are known to possibly be present within the thoracic outlet. These bands are classified based on location, point of origin, and point of attachment. (NTOS, ATOS, VTOS)
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