The Knee, Hip Joints and Spine
These are two of the most important joints for the yogi to understand, for they are central to a safe, comfortable and ever-deeper practice of the asanas.
The knee joint is the largest, most complicated joint in the body. It’s also integral to and often vulnerable in many asanas. Therefore yogis need to understand the knee’s structure in order to avoid knee injuries. Particularly risky are poses in which the knee is flexed yet carries weight, and sitting poses such as siddhasana.
Three bones meet at the knee:
the femur (thigh), tibia (shin) and fibula. Cartilage is attached to the end of each of these bones. In addition, between the femur and tibia are the medial meniscus and lateral meniscus, which are two semicircular pieces of cartilage (semilunar cartilage) that serve as shock absorbers. In the middle of the joint are the two cruciate (“crossed”) ligaments, which prevent forward and backward slippage. Around the whole joint is a tough fibrous covering called the capsule.
The knee is a hinge joint; it is designed not to bend sideways or backward (hyperextension), except to very small degrees. This is why, although it’s often recommended that one contract the quadriceps in forward-bending asanas (to stabilize the knee as well as to release the hamstrings via reciprocal inhibition), that may not be advisable for persons who have a tendency to hyperextend the knee. Be sure that all rotation (when bending the knee) takes place in the hip joint, because it is possible to rotate the knee slightly in effect, bending it sideways which can damage ligaments and/or cartilage. Most easily damaged is the meniscus, because it is fairly easy to catch this cartilage between the two bones and tear it. Torn cartilage can result in great pain, and it will need to be surgically removed. Helping guard against sideways bending are the collateral (side) ligaments medial and lateral which are on either side of the joint capsule. These ligaments are aided in this task by the ends of the hamstring muscles, which wind around the sides of the knee. This is not a “fail-safe” mechanism, however, because the collateral ligaments and cruciate ligaments can also be torn by twisting the knee. In the realm of athletics/ the terms “torn meniscus” and “torn anterior cruciate ligament” are all too familiar and dreaded.
To summarize the knee cautions for asana practice (and any other movement or position):
• Don’t hyperextend, ‘Lock” the .knee.
• Don’t twist, rotate, torque the knee. When a leg is supporting weight, keep the knee pointing in same line as toes. When entering a cross-legged position, let all rotation come from the hip joint.
• Don’t extend knee beyond ankle when leg is bent and bearing weight (e.g., virabhadrasana, lunges).
• Don’t move the knee medially or laterally when the foot is in a fixed position.
• Be careful (especially with weak or injured knees) when knees are in extreme flexion with leverage being applied (e.g., balasana, supta vajrasana).
The hip joint on the other hand, is a very deep ball-and-socket joint, meant to extend, flex and rotate. Thus, if the hip is sufficiently flexible, it will be able to rotate and flex enough to take strain off the knee joint, especially in the cross-legged sitting poses. It’s not that easy, however, for the hip has some of the strongest ligaments in the body, which prevent the femur (thigh bone) from being dislocated. The cost of this stability/however, is decreased mobility.
It takes careful, consistent practice to increase this limited range of motion, as we lengthen the muscles in the hip region and gently stretch the ligaments. This is the key to being comfortable and anatomically safe in the cross-legged sitting postures. The knee should swing out to the side and down to the floor through a lateral rotation in the hip socket. To move to half or full lotus position, in which one or both ankles come up onto the thigh(s), it is imperative that this movement take place only through further lateral rotation of the hip joint, not through twisting the knee joint.
Remember: never force the knees into a yoga posture. Move carefully and slowly with patience and concentration. Use the breath to help release the hip joints.
Although technically a part of the skeletal system, even on a physical level the spine is the center of yogic anatomy, and therefore deserves special mention. In addition to simply supporting the head, the spine is a bony, protective canal for the spinal cord, the great central trunk line of nerves that issues out from the brain toward every part of the body (It’s like the cable in “cable TV.”)
Vertebrae, Discs and Nerves
The spine is made of a series of vertebrae, which are roughly cylindrical building blocks of bone, each with a bony “cage” on its posterior to protect the spinal cord as it runs the length of the spine. The shapes of the vertebrae vary depending on where they are located in the spine: cervical region, thoracic region or lumbar region.
The most prominent features of the “cage” behind the vertebral body are a spinous process (which sticks straight out behind you; the “bumps” on your back) and two transverse processes (which stick out to the side and slightly behind). In addition to helping protect the spinal cord, the processes are important attachment points for muscles and ligaments, as we’ll soon see.
Each pair of vertebrae is separated by a small, but very important, shock-absorbing cushion called a disc. Discs are made of fibro cartilage, which means that they’re firm, but will yield with pressure. The center of each disc is filled with a gel-like substance. (Image: The soles of some running shoes are made of two layers of tough rubber, with gel in-between for shock absorption. All movement of the spine occurs at these discs and is limited by two factors:
• The degree of firmness or squishiness of the discs.
• The ligaments that span the discs, and connect each vertebra with the vertebrae above and below it.
At each disc joint, the vertebrae can bend forward, backward and sideways; they also can rotate just a little bit. The overall movement of the spine is the sum of all these little movements. Such movements cause the gel to move within the discs: backward during a Forward bend, forward during a backward bend, and to one side when bending to the opposite side.
Young discs tend to be very squashy; their centers are almost fluid. However, discs tend to get thinner as we age, and if we do not exercise the disc joints adequately, the discs will dry out and shrink into hard little plates. In this condition they limit motion severely, and they can no longer serve as shock-absorbers for the vertebrae.
In addition to the disc joints between the bodies of the vertebrae, each pair of vertebrae also touch at two other points in the bony “cage” behind the body of the vertebrae. These points are called the facet joints, and it is these that your chiropractor adjusts. The facet joints have different configurations in the cervical, thoracic and lumbar regions of the spine (see below), resulting in different movement capabilities in each section.
A pair of nerves exit the spinal column between each pair of vertebrae at the level of the disc. One nerve exits to the left and one to the right, each through a hole called a spinal foramen. The top half of the hole is formed by a “cutout” area in the top vertebra, the bottom half by a cutout area in the bottom one. These nerves are the communication channels between the brain and every cell in the body, and we’ll discuss them when we study the nervous system.
When two vertebrae are misaligned, their two spinal foramina may no longer be nice, rounded holes. The nerves may then be pinched where they exit the spinal cord. This hurts.
In fact, even just rounding the spine excessively can alter these holes and thus impinge upon the nerves. Nerves can also be impinged upon by slipped discs (i.e., discs that scoot backward and rest against a nerve), hen-dated discs (i.e., discs that abnormally bulge backward against a nerve), and ruptured discs (leaking gel;). You may sometimes hear “herniated” used to mean, “ruptured.”
The Five Regions of the Spine
The spine consists of 26 pieces, which are usually divided into five sections or regions. From top to bottom, these are:
• Cervical spine 7 vertebrae. The skull rests on the topmost vertebra, called the atlas. The atlas and the second cervical vertebra (the axis) have special modifications to support the movements of the head. These vertebrae are usually referred to as C1 (or atlas, the top vertebra), C2 (or axis, the second vertebra), and so on down to C7, which is the bump you can feel at the base of your neck.
• Thoracic spine 12 vertebrae, usually referred to as T1 (top) through T12 (bottom). These are the vertebrae to which the ribs (thoracic cage) attach.
• Lumbar spine 5 vertebrae, usually referred to as LI (top) through L5 (bottom).
• Sacral spine, or sacrum 5 vertebrae that are fused into a single unit in adults.
• Coccyx (tailbone) 3 or 4 tiny vertebrae that are fused into a single unit at the base of the spine.