------------------------------------------------------------ BASIC ANATOMY PART TWO ------------------------------------------------------------ Everyone has head the term ligament. We think of football or basketball players who have "torn a ligament." Likewise most of us have head the term tendon. A ligament is a tough, dense strand of gristle-like tissue which attaches one bone to another while a tendon attaches muscle to bone. The two are thus different. Ligaments pass between two bones and have some flexibility so that motion can occur, but their elasticity is low. They can usually be stretched only a short length before a tear occurs. Once torn, a ligament does not normally heal itself and is repaired surgically. If left unrepaired, the unrestrained movement of the joint can cause additional pain, damage and loss of joint function. Many ligaments connect the spinal vertebrae, sacrum and pelvis into a single structure. 1) Interspinous ligaments connect the bony transverse spinous processes together and limit motion which can happen between two vertebrae. 2) Intertransverse ligaments pass between the transverse processes on each side of the vertebra. They are largest at the lower lumbar region of the spine and prevent you from bending too far from side to side. 3) The ligamentum flavum secures the rear section of vertebrae and forms the upper encasement of the spinal canal. It protects and covers the spinal cord and is a bit more elastic than most ligaments of the spine. 4) The annullus fibrosus connects each vertebra to its neighbor via a circular band. It contains the gel-like pulp of the disc. Curiously, its fibers are oriented in a radial ply orientation much like radial ply cords of an automobile tire. While it contains the pulp of the disc, its primary function is to hold the disc in alignment with its vertebral neighbors. 5) The anterior and posterior longitudinal ligaments which extend between the top and a bottom of the vertebrae in a longitudinal path. The muscles of our spine are for the most part under our conscious control unlike muscles of the internal organs such as the intestine or stomach. This is an important distinction since certain exercises which we can perform consciously can help alleviate back pain. It is also important to understand that the muscles within your back are only PART of the entire story. Other muscles outside the back region strongly affect the shape and structure of the back, notably the abdominal and buttock muscles. Four general groups of muscles support and affect your back. 1) The all important abdominal muscles which provide frontal support and keep internal organs such as the stomach in correct alignment. 2) Extensor muscles of the spine which hold the rearmost portion of the torso in an upright position 3) Lateral muscles which provide side to side support 4) Hip muscles which affect the spine by virtue of their attachment to the pelvis. Each of these groups of muscles works in concert with the other. One or several groups may contract while the others cooperatively relax. Just like the young tree with guy wires to hold it erect in the wind, several groups of muscles function together to add stability to a less than ideal spinal design. The abdominal muscles consist of 1) The rectus abdominus 2) internal oblique 3) external oblique 4) transverse abdominus. In addition to support for internal organs, when contracted and in proper tone, these muscles control bending movements of the spine and affect proper posture. Some backaches can be relieved by strengthening this group of muscles. The extensor muscles lie along the length of the spine. They are positioned in layered bands and have detailed names which are not necessary within this brief discussion. Some of the layers are long, usually those lying close to the skin. Other extensor muscle layers are short, and are those which are much deeper below the skin. The attachment points of this set of muscles is complex, with segments connecting to spine, pelvis, ribs and the head. They are most frequently used when you arch your back, pull a heavy weight or tense your spine rigidly. The lateral muscles, are layered into the side regions of the spine. Two major groups are apparent: 1) The quadratus lumborum and 2) The psoas major. The quadratus helps in bending and is used in dancing and gymnastics. The psoas is quite large and attaches to the top of the thigh after running along the side the spine. In addition, four muscle groups of the hips, although not directly connected to the spine, can intimately affect its shape and performance. These hip group muscles are 1) the hip flexors 2) hip abductors 3) hip adductors 4) hip extensors. Groups or combinations of these muscles can affect the tilt of the pelvis and the all important lumbar lordosis or curve of the lower back. The hip muscles dramatically control posture and exercise. Proper tension and tone of these muscle groups can affect back pain. The final stop on our anatomical tour of the back is the nervous system. Although the bones, muscles, ligaments and tendons form the mechanical structure of the back, it is the nerves which transmit sensations of pain. The tolerance for pain varies from individual to individual. A laborer or professional football player can endure one level of pain. An office worker or student perhaps a different level. The fact the back pain is often more nagging, virulent and unrelenting does not necessarily make it different - just more noticeable in our modern society. It seems most folks might be able to limp through the day with a toothache or muscle ache from playing weekend baseball. But back pain SEEMS different. It can lay you low and make you want to curl up in bed for days on end. The fact the few treatments SEEM to alleviate back pain makes it seems a special breed of pain. More unrelenting, debilitating and immune from the treatments of modern medicine. To understand backaches you need to glance at the anatomy of the nervous system. In man and most vertebrates the nerves are composed of thin fibers of tissue. The largest cluster of these fibers are obviously in the brain. The second largest concentration is in the spinal cord. Two separate structures distinguish the nervous system. 1) The autonomic nervous system and 2) the somatic nervous system. The autonomic portion of the system controls involuntary actions and senses. Functions such as vascular pressure, nutrition, heartbeat and digestion fall in this area. The somatic portion of the system governs voluntary actions and senses which we can consciously control like bending, looking, opening our mouths and so forth. At each level of the spinal chord are groups of nerves which receive impulses from transmission points like the skin and muscles. These are afferent nerves. Other groups of nerves transmit impulses from the brain and spinal cord back to the skin, muscle or site of origin. These are efferent nerves or motor nerves. Approximately 30 pairs of mixed spinal nerves emerge from openings in the vertebrae along the length of the spinal cord. The small holes which permit passage of nerve tissues through the vertebrae are known as foramens. The central spinal canal within each vertebra of course houses the spinal cord itself. Curiously the main spinal cord is housed in ONLY the upper two thirds of the spinal column. The spinal cord terminates and does not travel within the spinal canal lower than the first lumbar vertebra. In an infant the spinal cord does run the length of the bony spinal structure, but differential growth allows the spine to become longer while the growth of the spinal cord lags behind and thus occupies less than the full spinal column length in a mature individual. The nerves of the spinal cord continue their downward trip towards the legs and lower pelvis OUTSIDE the bony spinal structure once they have reached the level of the first lumbar vertebra. However the lumbar nerve roots do extend downward and emerge on the sides of the lower 5 vertebrae and sacrum. These lower lumbar nerve roots are extremely important in the production of pain from the classic "slipped disc" which we will discuss in a later chapter. From a practical standpoint what does this discussion of the nervous structure have to do with back pain? In simplest terms, this vast collection of nerves MONITORS a variety of locations which can cause pain: weak muscles, torn ligaments, torn discs, fractured bones and so forth. In some cases, efferent nerves can cause a specific muscle group to become overly tense and contract into painful spasm. This may be due to a torn disc, simple fatigue or poor posture. However this secondary muscle contraction in response to an initial pain can make a bad pain seem worse. We have looked at muscles, bones, tendons and nerves, but until this point we have not tied them together with a key word: SHAPE. Held together by the overlapping forces of various muscles, the spinal column assumes a precise S shape when viewed from the side. The reason why the spine is not normally straight is that varying forces and demands are present along its length. The S shape acts as an elegant "counterbalance" to these opposing forces. In fact, it has been calculated that the spine is 15 times stronger due to its natural S curvature than if it were straight! This S-shaped curve is formed from four separate curves. Two curves bend towards the front of the body and two curves arch toward the back. The rearward bends are produced by the precise wedging of the vertebrae and are called primary spinal curves while the forward arches are produced by the wedging of the intervertebral discs and are called secondary spinal curves. The primary curves probably arose as a mechanical strengthening design during our existence as four legged quadrupeds. The two primary curves are in a sense genetically "ancient." They have been with us and all four legged quadrupeds for a long time. The secondary curves of the spine arose much later during evolution and were necessary when our upright posture was assumed. In a sense, nature had to counteract the primary curves when we began to walk in an erect position. And the only way to do this was to add rearward secondary curves. Only man has these unique secondary curves which are located in the cervical region, near the top of the spine, and the troublesome and pain-prone lumbar region in the lower spine. As we age, the lumbar curve tends to deteriorate and actually begin to reverse its curvature. In women the lumbar curve is also more acute or pronounced. The curvature becomes still more pronounced with pregnancy to offset the protruding abdomen. This effect can also occur in people of either sex who are overweight. We will talk more about this in a later chapter, but it is sufficient to understand that these curves are unique to man, crucial to proper balance of the spinal structure and somewhat adjustable depending on age, weight and sex. This ends our brief anatomical tour of the back. Obviously both structure and function have been simplified, but understanding even this basic level of anatomy sets the stage for that which comes next: what are the causes of pain and ultimately how do you treat them? This tutorial is merely a starting point! For further information on back care and back pain, be sure to register this software ($25.00) which brings by prompt postal delivery a printed, illustrated guide to back pain written by a physician plus two software disks. From the main menu select "Print Registration Form." Or from the DOS prompt type the command ORDER. Mail to Seattle Scientific Photography (Dept. BRN), PO Box 1506, Mercer Island, WA 98040. If you cannot print the order form, send $25.00 to the above address and a short letter requesting these materials. End of chapter.