Yogabody: Anatomy, Kinesiology, and Asana

6. The Lumbar Spine

THERE ARE CERTAIN MOMENTS WHEN, WHATEVER BE THE ATTITUDE OF THE BODY, THE SOUL IS ON ITS KNEES.

—VICTOR HUGO

PROBABLY EVERY ADULT human has experienced at least one episode of lower back pain. Most of these occurrences are not serious, but this discomfort can interfere with asana practice as well as with the activities of daily living. Understanding the structure of the lumbar spine can give you the information necessary to practice and teach healthy back habits, thus preventing future pain. Understanding the lumbar spine will also help you know what to do when your back does hurt.

The lumbar spine is designed to function best as a weight-bearing structure when the lumbar curve is in its neutral position. In neutral, the lumbar spine can bear weight on the body of the vertebrae and the facet joints in a more equal and stable way. As with a three-legged stool, when all three legs are on the floor there is stability.

Remember that the lumbar spine normally has its concavity posteriorly. Many people in our culture have lost the awareness of this curve due, in part, to sitting hours each day, and in chairs that favor flexion (the flattening of the curve). Not only does maintaining the normal lumbar curve benefit the health of the lumbar spine itself, it also effects the positioning of the sacrum, which is discussed in chapter 7.

BONES

The lumbar spine consists of five massive, kidney-shaped vertebrae. The bodies of these vertebrae are wider at the transverse diameter than at the anterior-posterior one. Their main job is to bear the weight of the trunk, including the head, as well as the cervical and thoracic vertebrae (Figures 6.1 and 6.2).

The spinous processes are horizontal, large, and blunt. The transverse processes point laterally, the L3 transverse process being the widest.

The superior facet surfaces in the lumbar spine face medially, and the inferior surfaces face laterally. Thus these facet surfaces are almost vertical in orientation and therefore lie in the sagittal plane. To facilitate your understanding of lumbar movement, study the angle of the lumbar facets in Figure 3.5 (see chapter 3) and Figure 6.3.

6.1 LUMBAR SPINE, SAGITTAL VIEW

6.2 LUMBAR SPINE, ANTERIOR VIEW

6.3 LUMBAR SPINE, POSTERIOR VIEW

JOINTS

The facet joints in the lumbar spine are similar in structure to each other, with the exception of the superior facet surfaces at the T12-L1 joint and the inferior facet surfaces at the L5-S1 joint.

A similar variation is true of the L5 vertebra (Figure 6.4). The superior facets of L5 are like the rest of the lumbar facets, in that they face medially. But the inferior facets of L5 face anteriorly so that they can catch on the posteriorly facing superior facet of S1 vertebra. This contributes more stability to the L5-S1 joint.

CONNECTIVE TISSUE

As discussed in chapter 3, the lumbar spine has three important ligaments. The first is the anterior longitudinal ligament (ALL), running from axis to sacrum along the anterior surface of the bodies (Figure 6.5). It is one of the strongest ligaments in the body. As such, it resists the weight of the lumbar spine from moving anteriorly and therefore acts as a limitation to extension. Thus, in the lumbar region, the ALL is significant in maintaining the curves not only of the lumbar as the base of the column but also essentially of the entire vertebral column.

The next is the posterior longitudinal ligament (PLL), which runs along the posterior side of the spinal canal, connecting the bodies of the vertebrae (Figure 6.5). In flexion of the column, it helps to increase pressure on the blood supply to the vertebral bodies, thus trapping fluid in the bodies and increasing their ability to bear weight. However, in the lumbar region, the PLL narrows considerably and so does not give as much support to the intervertebral discs in the lumbar as elsewhere.

The third ligament is the supraspinous ligament, which attaches the points of the spinous processes from C7 to the sacrum. It is stretched on forward bending and twists and slack on back bending. The PLL and the supraspinous ligaments give resistance to flexion and absorb the posterior movement of the nuclei of the discs.

6.4 (ABOVE) UNIQUE THORACOLUMBAR AND 5TH LUMBAR FACETS

6.5 (MIDDLE) ANTERIOR LONGITUDINAL LIGAMENT AND POSTERIOR LONGITUDINAL LIGAMENT AT L5 AND S1 AREA

6.6 (RIGHT) LUMBOSACRAL JOINT, WITH SCIATIC NERVE EXITING THE PELVIS

NERVES

As described in chapter 3, the structure of the spinal cord in the lumbar region is unique. The spinal cord ends in the lumbar region and becomes a group of nerve fibers called the cauda equina, or horse’s tail, which continues to course down the body (see Figure 3.10 in chapter 3). At the end of the cauda equina is a structure called the filum terminale, which attaches to the first segment of the coccyx.

Two major nerve plexes (groups of nerves) are involved in the lumbar region. The first is the lumbar plexus, which is formed from the L1-L4 nerve roots and from variable contribution from the T12 nerve root. This plexus sits posterior to the psoas major muscle or is intertwined with its fibers. These lumbar nerve roots control some parts of the organs of the lower abdominal wall. The L1-L4 nerves control the muscles of the anterior thigh, parts of the medial leg, and the cutaneous innervation in this area.

The second plexus is the sacral plexus. It consists of nerves from roots L4, L5, S1, S2, and S3 (Figure 6.6). These nerves join together into one large, flat nerve root, about as big around as the index finger. This structure is called the sciatic nerve, the largest and longest nerve in the body, and it leaves the pelvis through the greater sciatic notch, which is found midway between the greater trochanter and the ischial tuberosity. After passing through the notch, it continues distally, leaving the pelvis to lie under the piriformis muscle. In some cases, the nerve is intertwined with the piriformis muscle. At the back of the thigh, it lies under the long head of the biceps femoris, one of the hamstring muscles. Finally it splits above the back of the knee. One part continues directly down the back of the calf and is called the tibial nerve. The other branch is the common peroneal nerve; it winds around the fibular head, dividing as it courses down the lateral and anterior leg.

6.7 (LEFT) LUMBAR FLEXION, WITH EFFECT ON INTERVERTEBRAL DISC

6.8 (RIGHT) LUMBAR EXTENSION, WITH EFFECT ON INTERVERTEBRAL DISC

The sciatic nerve and/or its branches supply the muscles of the posterior thigh. Its branches (like the saphenous nerve) supply some or all of the cutaneous innervation of the skin below the knee as well. (Note: L4 and L5 nerves make up part of the lumbar plexus as well as part of the sacral plexus.)

MUSCLES

The flexors of the lumbar spine are the abdominal muscles as well as the short hip flexors, which are the psoas major, psoas minor, and iliacus. The abdominals are discussed in detail in chapter 11. The hip flexors are presented in chapter 8. The lumbar extensors were discussed in chapter 3. Side bending and rotation are created by the actions of the flexors and extensors; side bending and rotation are discussed in the following section.

KINESIOLOGY

The lower back is an area of discomfort for many people. To improve your yoga practice and teaching, spend some time studying how it moves based on its unique structure.

Movements Allowed in the Lumbar Spine. As discussed in chapter 3, the direction of movement in any vertebral segment is controlled by the angle of the facet joints in that region. The lumbar facets rest in the sagittal plane. Therefore the only significant movements allowed in this region are flexion and extension. In fact, flexion and extension are relatively free, limited in large part by soft tissue.

Adding up all the degrees of movement of flexion allowed in the entire vertebral column, 50 percent of that movement is created in the lumbar spine. Of that, some 75 percent is created at the L5-S1 joint. Thus 37.5 percent of all vertebral flexion occurs at one joint segment (Figure 6.7). It is no surprise then, given the vulnerable position of the fifth lumbar vertebra and the amount of flexion allowed, that this joint would be the site of frequent dysfunction. Remember that the fifth lumbar sits at an angle such that it is partially tipped forward by its connection to the angled sacrum and partially pulled in a more vertical position by its connection with L4 and the other lumbar vertebrae. Gravity is pulling L5 forward, and yet it lacks the support of a wide PLL. Add to this the extreme freedom in its range of motion in flexion, and it makes sense that the L5 disc would be subject to unusual strains.

Extension in the lumbar is basically limited by the ALL and the abdominal muscles and organs. The facets in this region actually allow for an almost complete free range of extension (Figure 6.8). However, rotation in the lumbar spine is quite limited. Although it may seem like you are rotating from your lumbar spine in a seated twist, this is not really happening because rotation is so limited in the lumbar spine.

Picture a dresser drawer: It only moves in and out; it cannot move from side to side. The lumbar spine is similar. Because of the vertical angle of the facet joints, sideways movement is minimized. There is about 12 degrees of rotation allowed at L4-L5 and the least amount of rotation in all the lumbar spine of about 6 degrees at L5-S1. The overall average of rotation in the lumbar spine is about 10 degrees.

Side bending is allowed in the lumbar spine and is about 35 degrees. It is limited by the ribs, pelvis, and soft tissue (Figure 6.9).

Law of Side Bending and Rotation in the Lumbar Spine. Here side bending and rotation occur to the opposite side, except when the movements are begun in flexion; then they occur to the same side. This means that when you twist to the right, your lumbar vertebral bodies twist right as you bend left.

Try this experiment. Sit on the edge of a chair with your vertebral column in neutral. Exhale and twist to the right. When you do so, you will notice your left side ribs bending slightly to the left. It is possible to override this movement, but if you let the twist happen naturally, you will feel the side bend. Another way to understand this law is in Utthita Trikonasana. When practicing to the right, you are side bending right. The law states that you will thus be rotating left. This is what you experience in the pose when you turn the chest upward: right side bend and left rotation. Remember that there is not much rotation allowed in the lumbar spine, but there is some.

6.9 SIDE BENDING, LIMITED IN LUMBAR REGION

SPINAL CONDITIONS

Scoliosis. Scoliosis is a lateral curvature of the spinal column. It most often begins in the thoracic region but has implications for the cervical and lumbar regions. There are two types. A structural scoliosis is created by a difference in the height of the vertebral bodies. For some unknown reason, one side of the vertebral body grows higher than the other. This is called an idiopathic scoliosis, from the Greek meaning “unknown disease.” Structural scoliosis is usually noticed during the growth spurts of the first year of life, at around six or seven years, and again at puberty. If you notice a young student with what you think is scoliosis, notify her parent immediately, so she can get proper care. In very severe cases, the lateral curvature—and thus accompanying side bending—can impinge on the healthy functioning of the lungs and other organs. Before the discovery of antibiotics, people suffering from severe scoliosis would occasionally die from pneumonia due to decreased lung capacity.

The second type of scoliosis is a lateral curvature of the vertebral column caused by the way the body is habitually used—always rotating in one direction at work, for example, or always carrying something heavy on one shoulder. This functional scoliosis is created by changes in soft tissue, like muscles, rather than by the uneven growth of bone.

There is a simple way to tell the difference between a structural and a functional scoliosis. Have your student stand in Tadasana and then bend forward. She should not try to stretch out in Uttanasana but rather just hang forward. Now stand behind her and observe her back. If she has a functional scoliosis, the stretch will result in the soft tissue releasing, and her back will look even from side to side. If she has a structural scoliosis, it will be more apparent that one side of her rib cage is higher than the other.

Understanding the law of side bending and rotation will allow you to make a very accurate guess as to which way your student’s scoliosis exists. Stand behind her and, after asking her permission, place your hands around her mid-rib cage, using the space between your thumb and index finger to lightly hold the cage.

Now notice the difference in the thickness of her cage from front to back. If she has a right thoracic scoliosis, you will feel that her rib cage is a little thicker on the right, as it has rotated backward. This means that she is rotated right. According to the law, she is therefore side bent left. Since a scoliosis is named for its convexity (in this case her right side) and the student is side bent left, this would be a right thoracic scoliosis. This is the most common form of thoracic scoliosis.

If the student has a right thoracic scoliosis, her cervical and lumbar spines will side bend in the opposite directions in order to compensate for the shift. To imagine this, stand up and side bend your thoracic spine to the left, simulating a right thoracic scoliosis. Notice how your weight shifts to your right foot and your head tilts left.

The body will compensate for this shift. In order to keep both of your feet evenly on the ground and to tilt your head so that your eyes remain parallel to the floor, your body will side bend your cervical and lumbar curves, so that they are now side bending back to the right, the opposite direction from the primary thoracic curve. This will allow both feet to touch the floor evenly and the head to be straight. These compensatory side bends in the cervical and lumbar regions are attempts by the body to stand vertically in the face of the primary scoliosis.

However, in a right thoracic scoliosis, not only will there be three side bending actions, there will be rotational ones as well. Remember that side bending and rotation occur together in the vertebral column. Therefore in a right thoracic scoliosis the following conditions will exist:

Asana for Scoliosis. Because of this complicated picture of rotations and side bending, I advise that unless you know otherwise, since a right thoracic scoliosis is the most common type, you begin as if the thoracic spine is the primary scoliosis. Suggest movements that help the thoracic scoliosis and secondarily the cervical and lumbar segments. Obviously some of the movements you choose to help the thoracic area will be counter to the cervical and lumbar areas, but proceed anyway.

Since every structural scoliosis has a functional overlay, stretching the soft tissue of the back and trunk can help a student with scoliosis, regardless of whether it is structural and functional together or just functional.

The key to helping scoliosis is to stretch the concavity, strengthen the convexity, and derotate the rotated segments. These are the principles that will help you help your student. Here are some simple stretches that you may find effective.

▶ Standing: In Tadasana, have the student stand with one foot slightly forward of the other to help derotate the spine. For example, in a right thoracic scoliosis, try having him put his left foot slightly forward to increase weight-bearing on it and thus help to reduce the side bending in that area.

▶ Sitting: Observe the student sitting. He may actually sit more evenly if he sits a little bit forward with one side of his pelvis. When he is sitting asymmetrically, check the level of the pelvic rim to make sure that it is even. Be sure to ask permission to touch him first.

▶ Hanging: Encourage the student to hang whenever possible. He can hang from his hands or knees from playground equipment or from his pelvis in a pelvic sling.

▶ Ardha Adho Mukha Svanasana and Adho Mukha Svanasana: Have the student practice Ardha Adho Mukha Svanasana with her hands on the wall and her trunk at 90 degrees to the floor. Once in the position, she can move her feet to one side and/or drop one hand a little lower until her spine evens out. When she practices Adho Mukha Svanasana on a nonskid mat, it may even out her spine if she experiments with moving either one hand forward or one foot back or both. Remember, scoliosis is an asymmetrical problem, so asymmetry is often what is needed to help it.

▶ Adho Mukha Virasana: This pose can be very helpful. After the student bends forward in Adho Mukha Virasana, have him walk his arms forward on the floor. When he has done this, have him walk his arms to the side that causes the concavity of the curve to stretch out. Hold the pose for 10 breaths.

▶ Side-Lying with Blocking: Wedging props under a part of the body when a person is lying supine is called blocking. Determine which way the student is curved. Set up a nonskid mat for her to lie on. Add a blanket on top for comfort, if desired. Then have her lie down on her side, so that the convexity is down, over a rolled towel or rolled small blanket. This will reverse the curve by reversing the side bending. Add other padding to support her head, neck, and legs, as necessary. She can lie for as long as 10 minutes.

▶ Savasana with Blocking: This is a little tricky but worth it. Have the student lie on a nonskid mat for Savasana, with no other props. Now determine by looking which shoulder is high, and support it with a rolled towel. Place another rolled towel under the back of his lower ribs on the side that is the lowest, using the towel as a wedge. You can use a towel as a wedge under the opposite buttock. After you place the towel, ask for his permission to check if the anterior superior iliac spines (ASISs) are even. If they are not, adjust the towel under the buttocks. Finally, add support to the head and neck, a large roll to the back of the knees, and a smaller one to the back of the Achilles tendon. Cover his eyes with a soft cloth and his body with a blanket, and let him rest for 20 minutes.

Sciatica. This is the irritation of the sciatic nerve. It usually has one of two causes. The first is discogenic (caused by the disc), which means that the intervertebral disc has moved out of place and is placing pressure on all or part of the nerve. When this pressure occurs, the student may feel numbness, tingling, and/or radiating pain down the leg. The more distally the symptoms are felt, the more severe the compression. If the student has neurological signs like this, she should consult a health care professional. If her symptoms include bowel or bladder problems, she should seek immediate aid. If you think that she has discogenic sciatica, refer her to a health care professional for positive diagnosis and then to a very experienced yoga teacher for help.

The second cause of sciatica may be piriformis syndrome. This form of sciatica is caused by pressure on the sciatic nerve as is passes under or between one of the external rotators in the hip, the piriformis muscle. Stretching the rotator muscles can help this problem. See the Experiential Anatomy section in chapter 8 for instructions on how to practice a stretch for the external rotators of the hip that may help lessen or prevent piriformis syndrome.

EXPERIENTIAL ANATOMY

For Practicing

6.10 VIRABHADRASANA I

Applied Practice: Virabhadrasana I

Prop: 1 nonskid mat

Take Care: To protect your front knee when it is bent, make sure the knee points over your little toe and is held at 90 degrees of flexion.

ONE OF THE MOST common beliefs many yoga students have is that the lumbar spine should be flattened or lengthened in all poses except back bends. When you practice standing poses, are you attempting to flatten your lumbar spine? Students often struggle with Virabhadrasana I and never really enjoy it because they are trying to flex the lumbar spine.

Take the starting position for Virabhadrasana I on your nonskid mat (Figure 6.10). Facing your right leg with your arms lifted overhead, bend your knee and allow your lumbar spine to arch naturally. Do not try to tuck the tailbone. In fact, do the exact opposite: allow the lumbar to arch and the tailbone to lift slightly. Encourage your breastbone to lift as well. Place your arms in front of your face, reaching up strongly with your arms and pressing your palms together. If your neck will allow, drop your head back, part your lips, and soften your eyes. Remember to keep your breath moving and soft.

Feel how arched your back is. Lean your weight backward onto your straight back leg. This pose is actually a back bend, and when practiced that way, it will feel dynamic and satisfying. Inhale as you come up, and practice to the other side.

For Teaching

6.11 MARICHYASANA III

Applied Teaching: Marichyasana III

Props: 1 chair •1 nonskid mat

Take Care: In order 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 so that the spine and pelvis move together.

TRY THIS YOURSELF first and then have the student do it. Sit on the forward edge of a stable simple chair, with your feet flat on the floor. Now let your lumbar flex, rounding out toward the back of the chair. Try to twist to the right, and note the difficulty. Now come back to facing forward once again in your sitting posture, and create a normal lordosis. Now twist in the same direction, and notice the difference.

Ask your student to sit on a nonskid mat. When he bends his right knee to his chest in preparation to practice Marichyasana III, he brings his lumbar spine into flexion, especially the side of the lumbar where the knee is bent (Figure 6.11). Remember that the lumbar has a minimal ability to rotate, due to facet direction. Trying to twist the lumbar during flexion makes rotation even more difficult.

To improve the student’s pose, have him focus on lifting upward, so his lumbar spine comes closer to the normal lumbar lordosis. He can do this by shifting his weight off his left buttock and mainly onto his right buttock. This action will help him elongate the spine upward, bringing more of a normal curve to the lumbar spine, thus improving his ability to twist.

LINKS

Awareness practice: observe the effects that different chairs have on the curve of your lumbar spine. If you spend some time at this, you will find that most chairs do not enhance the normal lumbar curve and, in fact, actually cause you to sit in too much lumbar flexion. An interesting book on this topic is The Chair: Rethinking Culture, Body, and Design by Galen Cranz (New York: W. W. Norton, 2000). For a comprehensive yoga program for back and neck pain relief, consult Back Care Basics by Mary Pullig Schatz, M.D. (Berkeley, CA: Rodmell Press, 1992).