MAN HAS NO BODY DISTINCT FROM HIS SOUL.
—WILLIAM BLAKE
THE THORACIC SPINE is a unique part of the vertebral column. It helps to create the posterior armature of the thoracic cage, serves as an attachment point for the ribs, and provides a strong protective structure for the heart and lungs.
The normal thoracic curve is convex posteriorly, the opposite of the cervical spine, and is more stable than the neck, allowing less range of movement. This is generally true in the body. As one descends the skeleton, there is less mobility but more stability; as one ascends, there is more mobility but less stability in the weight-bearing joints.
BONES
The thorax consists of the sternum, ribs, and costal cartilage anteriorly and laterally, and the thoracic spine posteriorly (Figure 5.1).
5.1 THORACIC SPINE, ANTERIOR VIEW
The mostly flat sternum, or breastbone, is made up of three bones. The most superior one is the manubrium, which has a notch at the superior border called the jugular notch. This is the place where the chin rests during Jalandhara Bandha, or chin lock, during pranayama practice. At the sides and top of the manubrium are surfaces for the articula-tion of the sternum with the clavicle and with the first rib.
5.2 THORACIC SPINE, WITH DEMIFACETS AND RIBS; POSTERIOR VIEW
Take a moment to palpate this area on yourself. Place your fingertips at the base of your throat and at the top of your sternum. Feel gently the V-shaped jugular notch. Now move your fingers to one side, and find the location where the manubrium and clavicle join. This is the sternoclavicular joint.
The next part of the sternum is the body. This is the largest and longest portion of the sternum. At the point where the manubrium and body join is the sternal angle. The second rib joins the sternum at the sternal angle. In adults, the sternum is a key site of blood cell production.
The sternum typically ends in the xiphoid process, although not all people have one. During youth it is cartilaginous but is completely ossified by the age of twenty-five. The xiphoid process serves as an attachment for the rectus abominus muscle. (See chapter 11 for more details on this muscle.) Finally, the sternum articulates on either side, not only with the clavicle but also with the cartilage of the first seven ribs.
The ribs make up another major structure of the thorax. There are twenty-four ribs, which attach posteriorly to the thoracic vertebrae, T1-T12 (Figure 5.2). Anteriorly ribs 3-7 articulate directly with the body of the sternum by costal cartilage. These are sometimes called true ribs. These ribs attach to vertebrae T1-T 7. Remember that the first rib passes under the clavicle, not above.
The rest of the five pairs are called false ribs because they are not directly connected to the sternum. Instead, cartilage attaches the first three of these pairs to cartilage, which does attach to the sternum. The final two pairs are termed floating ribs because they are only attached to the thoracic spine and not to anything on the other end. Thus ribs T8-T12 attach to the corresponding vertebrae above and below.
Each individual rib is made up of several parts, including a head. The head of the rib is enlarged and has two articular surfaces, which join with the bodies of the two adjacent vertebrae. In other words, as the rib curves anteriorly, it touches two vertebrae. This union between vertebrae and rib is called a demifacet, which is a synovial joint.
The spinous processes of the thoracic spine vary by groups of four (Figure 5.3). The first four thoracic spinous processes point posteriorly in a fairly horizontal angle. The next set of four, numbers five through eight, point almost straight down. This directional shape of the spinous processes creates greater stability at the mid-thoracic region by limiting the movement of extension. This limitation increases protection for the heart posteriorly. The final four thoracic spinous processes point slightly more distally than the first four but more horizontally that the middle ones.
Yoga students sometimes suffer from back bender’s rib. This is a rotational fault of a thoracic vertebra caused during back bending. Because the spinous processes in the mid-region are less mobile than the other thoracic vertebrae, during extension (back bending) they may not glide as easily as other thoracic vertebrae. Sometimes, when the student continues with strong extension movements, instead of the mid-thoracic vertebra extending on the one below it, it slightly rotates instead. This causes the attached ribs to rotate and creates discomfort. Often this discomfort is experienced when the student takes a deep breath. If this happens, I recommend a consultation with a health care professional.
JOINTS
The superior thoracic vertebral facets of the vertebrae face posteriorly, in an almost vertical plane; the inferior facets thus face anteriorly. The almost vertical angle of these facets allows for a great deal of movement, although less than in the cervical spine. Side bending is practically free, up to 45 degrees, and is only limited by the sternum and ribs. This free side bending is what creates the main movement of Utthita Trikonasana.
The angle of the thoracic facets also allows for 45-degree rotation. Remember that rotation can be thought of as the facets on one side of the spine moving forward and up and the facets on the other side moving down and back. Flexion is limited by the posterior ligaments and muscles; as stated before, extension is limited by the spinous processes. The site of greatest mobility is the T8-T9 joint. The superior facet surfaces of the twelfth thoracic vertebra are similar in orientation to those of all thoracic vertebrae. In other words, the superior facets of T12 face posteriorly. Thus the top portion of the T12 vertebra is thoracic in orientation. The inferior facets of T12, however, are like the rest of the lumbar facets, in that they face laterally.
Because T11 and T12 are the most like the lumbar facets, they allow the greatest amount of flexion and extension in the thoracic spine.
You will recall that the facet surfaces on the bodies of the thoracic vertebrae connect one to another. In addition there is a demifacet on the vertebral bodies, which is the site of the articulation of the ribs with the vertebrae. One of these is near the root of the pedicle on the superior portion of the vertebrae, and the other near the vertebral notch at the inferior portion of the body. These joints between the thoracic vertebral bodies and the rib are synovial joints.
5.3 THORACIC SPINE, WITH THE THREE SECTIONS OF SPINOUS PROCESSES; SAGITTAL VIEW
Finally, it should be remembered that the cervical-thoracic intersection is a unique joint. It is called a transitional segment because the superior facets of the first thoracic vertebrae are more like the cervical facets, and the inferior vertebral facets are more like the other thoracic facets. This is the site where the cervical lordosis begins to change into the thoracic kyphosis. Thus it is the site of possible strain. It is a good idea to make sure that this area is protected by attention to the upright posture. When your student maintains Tadasana in this area, she reduces strain on all the soft tissue in the area, like ligaments, tendons, discs, and other connective tissue, such as the capsule.
CONNECTIVE TISSUE
The ligaments of the thoracic spine are discussed in detail in chapter 3. In addition, however, the thorax is unique because of the existence of costal cartilage, which joins the ribs to the sternum.
The costal cartilages are made up of hyaline cartilage, which in effect makes the ribs longer. The first seven ribs are connected by costal cartilage directly to the sternum. The next three ribs are joined by cartilage to the lower border of the rib just above it. The last two pair of ribs are tipped with cartilage but float independently.
Another important structure in this area is the thoraco-lumbar fascia. This is a vast fascial complex that is most easily understood as connecting the last posterior ribs with the posterior iliac crest, the transverse abdominus muscle, and the transverse processes of the lumbar vertebrae, although it is connected more widely across the back. It is superificial to the quadratus lumborum muscle and can be felt by many students during forward bend practice along their back waist area. The sensation of stretching this fascial sheath is described by students as broad, flat, and superficial, as opposed to the sensation of stretching muscles, which is said to be narrow, deep, and specific.
NERVES
There are twelve thoracic nerves that exit the spinal column in this region. The first eleven pair are called intercostals and are located, as their name suggests, between the ribs. The last pair is called the subcostal and lies below the last rib.
All give off cutaneous and muscular branches. They run from the back to the front, just below each respective rib. The lower six pass into the abdominal wall, supplying, in part, the skin. The branches to the muscles control the intercostals, the abdominal muscles, and various muscles of the upper back.
MUSCLES
The extensor muscles of the thorax, or posterior paravertebral muscles, are presented in chapter 3. The flexors and rotators of the thorax are the abdominal muscles that are presented in chapter 11. The unique muscles of the thorax are the intercostal muscles.
The external intercostals arise from the lower border of the rib and attach on the upper border of the rib below; they are at right angles to the internal intercostals. The internal intercostals arise from the ridge on the inner surface of a rib and the costal cartilage and insert down and back into the superior border of the rib below, perpendicular to that rib.
The action of these muscles is to draw the ribs together, as well as to aid in inhalation and exhalation. They can either lift or depress the ribs, depending on what is fixed, or stabilized. If the last rib is held firm by the quadratus lumborum muscle, then the contraction of the intercostals will depress the rib cage and can aid in a forced exhalation. They also preserve the shape of the thoracic cage.
KINESIOLOGY
One of the unfortunate actions that sometimes happens in asana practice is an over-flattening of the natural kyphosis. Students are sometimes taught to lift the sternum with the intention of opening the chest, and they do so by bringing their thoracic spine into the body, thus flattening the curve. After years of practice, the spine loses some of its natural curve.
If this happens to you, try this. Stand on your nonskid mat, placed near a doorway. Then hold onto the edge of the doorway, with your arms at chest level and your hands crossed at the wrist. Now walk backward slowly, rounding the thoracic spine upward and encouraging your scapulae to part and move toward the sides. You should drop your head between your arms. The stretch will be felt between and under the scapulae. This stretch will help loosen some of the muscles necessary to maintain a normal kyphotic curve in the thorax.
Law of Side Bending and Rotation in the Thoracic Spine. The law of side bending and rotation in the thoracic spine is that side bending and rotation occur to the opposite side, except when the movements are begun in flexion; then they occur to the same side. For example, when you rotate your thoracic spine to the right, you side bend to the left.
Try this. Sitting in a chair, with your feet on the floor and your spine long, rotate to the right. This means the bodies of the vertebrae rotate to the right. According to the law, the thoracic spine side bends to the left. After the rotation, place your left hand on the left side of your ribs and feel the left side bend.
It is also true that when you side bend the thoracic spine to the right, it rotates to the left. To feel this, sit tall and then side bend to the right, while keeping your hand placed around the middle of the sides of your rib cage. Notice how your rib cage rotates away from the side bend.
In Utthita Trikonasana performed to the right, the thoracic spine and cage rotate to the left, or toward the ceiling. Thus the law of side bending and rotation enhances the natural movement we want the student to feel in the pose of turning the chest upward.
There is a different effect of the law in Parivrtta Trikonasana, however. If you start from standing and rotate first before flexing and bending down in the pose, the rotation and side bending will be to the opposite side. This means that you will be less able to drop your top ribs in the completed pose.
Remember, if you rotate right as you come into the pose, you are side bent left; this means your top or right ribs in the pose are lifted and not dropped, the way the pose is taught. However, if you turn toward the front leg first, then flex, the exception to the rule holds. This means that if you bend forward or flex over your front leg first, then rotate into the twist of Parivrtta Trikonasana, not only will you follow the law but you will practice the pose by dropping the top ribs down.
EXPERIENTIAL ANATOMY
For Practicing
5.4 TADASANA
Applied Practice: Neutral Position of the Sternum
Props: 1 nonskid mat • 1 blanket
Take Care: Remember not to reverse your thoracic curve in an attempt to lift your sternum.
TO ASCERTAIN the neutral position of the sternum, stand in Tadasana on your nonskid mat (Figure 5.4). Remember that your sternum is not a vertical bone but instead sits at an angle. The distal end of the sternum moves away from the body, while the proximal end is deeper. Try standing in Tadasana with your sternum at different angles. When the sacrum is sitting in a neutral position, your lower ribs will be in line with your anterior superior iliac spines (ASISs) and not sticking out past them, and your thoracic spine will have its neutral curve.
For Teaching
5.5 MARICHYASANA III
Applied Teaching: The Thoracic Spine in Twists
Prop: 1 nonskid mat
Take Care: To protect the lower back, make sure that students twist the pelvis with the whole spine in Marichyasana III and do not hold it stationary.
REMEMBER THAT the facets in the thoracic spine allow for a great deal of rotation. However, this rotation is maximized when initiated with the spine in a neutral position. Have your student practice Marichyasana III on a nonskid mat (Figure 5.5). Notice her thoracic spine. Most students tend to flex the thoracic spine in twists. Suggest that she think of back bending her thoracic spine in the pose, which will not only bring her back to a more neutral position but also will allow her a fuller range of motion in the twist.
LINK
A useful visual aid for studying the vertebral column is a life-size model of the spine. A good source for ordering one of the many variations of vertebral models available is the Anatomical Chart Company, www.anatomical.com.