This tutorial is an attempt at offering you an introduction and outline to understand some of the basic concepts of spinal function and disease processes that affect the spine. Perhaps this tutorial will help you understand this difficult subject better, for what is mysterious and often frightening about the spine, is the unknown.
The back in everyday language has a connotation of “physical strength.” Expressions such as “back bone” refer to courage, determination, and firmness. In our culture, the back is symbolic of our strength and thus anything which happens to our back becomes threatening to our strength, triggering a host of fears. Conversely seemingly unrelated physical or emotional troubles can translate into back symptoms.
The back, which in medical terms is called the spine, is a master-piece of architecture. Due to a highly advanced spinal column, the human can stand and run on rear limbs (the legs). This product of mammalian evolution is a tremendously complex structure which functions as a protection to the spinal cord and nerves, a support for the trunk and upper extremities (arms), a positioning system for balance, and bears spring-like properties that permit absorption of tremendous forces. Understanding such a complex structure is not a simple task. When disease or injury affects the spine, determining the ideal treatment may thus be quite challenging.
The back bone, or spine, is a dynamic structure not only in the terms of motion and displacement but also in terms of change over time. The contour, or structure, of the spine is determined by the bones of the spine (vertebrae), the discs between these bones, the ligaments and the muscles. This structure changes from the earliest fetal stages to the end of life. In the womb and until an infant reaches the standing position the spine is extremely flexible and rounded in a “C ” shape inside which the spinal cord (the nerve connections from the brain to the rest of the body) is protected. Both the spinal cord and spinal column grow together during the transition period form an infant to toddler. During this growth the shape of the spine changes significantly, becoming less “c” shaped and developing into a balanced upright structure. The growth of the spinal column continues until the end of puberty which in girls corresponds roughly to 18 months after the first menstrual period and around the age of 18 for boys.
When a healthy spine has completed its growth, it assumes a certain set of normal curvatures which lets us refer to the term “in good balance.” This means that at rest in a standing position the head is well centered above the pelvis. The spine when we look at the back of a standing individual is straight from the head to the pelvis yet when seen from the side it shows a set of natural curves that balance each other to maintain the head above the pelvis. In the cervical area (neck) there is a forward curvature, (lordosis) in the upper back (thoracic spine) there is a backward curvature or hunching, and in the lower back (lumbar spine) there is again a forward curvature (lordosis). Each of these curves is essential to sustain the load of the body part above it. There are 4 anatomic zones in the spine:
Neck or Cervical spine: 7 vertebral bones in lordosis (convex to the front) Upper back or Thoracic spine: 12 vertebrae in Kyphosis (convex to the back) Lower back or Lumbar spine: 5 vertebrae in lordosis (convex to the front) Buttock area or Sacral spine: 5 vertebrae grouped together in kyphosis
Each of the above zones in the spinal column, except for the sacrum, is flexible (cervical and lumbar are the most flexible). This mobility along the spine is due to what is referred to as the mobile segment. A mobile segment consists of two vertebral bones bound by a disc in between and supported by ligaments, the facet joints and muscles. It is important to understand the individual structures of the spine, and their function to understand diseases and conditions which disrupt the normal function of the spine.
As mentioned above, the balance of the spine is essential to normal functioning. The evaluation of this balance may be done on a patient who is standing or sitting by using a plumb line. In simplest terms a plumb line is a small weight attached to a string that can be suspended next to a patient or against an X-ray of the spine in order to measure where the head of a patient falls in respect to the pelvis. Frontal balance (the spine seen from the front) is determined by holding the plumb line from a point in the middle of the back of the head to assess if it falls between the buttocks. Sagittal balance (the spine seen from the side) can be evaluated by a plumb line held at the level of the ear and assessing where it falls in relation to the pelvis and ankles in a standing person (or from X-rays).
When the normal balance of the spine becomes disrupted, a number of problems may arise. At first, when an imbalance develops, the body may be able to compensate for this by the use of muscles in order to force the trunk into better balance. Additionally, some of the flexible portions of the spine may develop abnormal curvatures in an attempt to correct a deformity of one portion of the spinal column. When corrective mechanisms fail to adequately correct a significant imbalance of the spine, walking, standing and even sitting may become difficult without support or assistance. A person affected with spinal imbalance may thus experience symptoms ranging from fatigue and back pain to stumbling, walking difficulty and possibly severe disability.
Diseases and conditions affecting the spine can occur due to problems of an individual structure (such as a disc, joint, ligament or muscle), or more generally due to dysfunction of an entire portion of the spine such as is seen in deformities like scoliosis. In some cases a spinal condition may be an interaction of local and global problems. This section will not address the separate category of injuries which can affect spine or such processes such as tumors, metabolic diseases or infections.
Spinal problems by age group
At birth the spine may be affected by congenital malformations which are nowadays sometimes diagnosed “in utero” by a sonogram. Congenital abnormalities can alter the development of the individual vertebrae thereby leading to deformities such as scoliosis. Many of these deformities can become quite severe requiring early surgical intervention.
In addition to congenital spinal deformity, idiopathic deformity may affect the spine. Infantile scoliosis is diagnosed before the age of walking and commonly resolves spontaneously for unknown reason. Idiopathic scoliosis which develops after the age of three is called Juvenile scoliosis or early onset scoliosis. Given the significant growth remaining in young children, and the fact that many scoliosis curves progress with remaining growth, these deformities can become quite severe and difficult to treat. The outcome of juvenile and early onset scoliosis is rarely excellent and it requires permanent medical skilled attention often necessitating several surgical procedures to treat.
Childhood and Adolescence
As in the juvenile age group, scoliosis remains a significant problem in the adolescent age group. However, as skeletal maturity advances, the risks of marked scoliosis progression are generally diminished. Aside from scoliotic deformity, kyphotic deformity may also develop in this age group due to abnormal development or growth of the vertebrae. Postural round back and Scheuermann’s disease are certainly the most common although they rarely require aggressive intervention.
In addition to overall balance and development of the spinal column as a whole, stability of an individual segment of the spine may become abnormal in the growing spine. A common condition affects the lowest level of the spine, at the junction of the last lumbar vertebra and the sacrum. Spondylolisthesis can result from an accident but most often appears to result from dysplasia (abnormal formation) of the L5-S1 area of the spine. In most of the cases this is more a condition than a true problem and if it becomes a problem it may be due to stress and overuse of this area like in gymnastics, football, or weightlifting.
Young adult years
Once the spine has stopped growing, spinal deformities are usually the result of injuries, degeneration, tumors or gradual progression of a childhood problem. Scoliosis which appears during the young adult years is thus very rare. On the other hand, degenerative problems (often referred to as wear and tear) begin to appear even in young adults.
One of the most common areas of spinal problems in the young adults involved the intervertebral disc. This disc, which acts as stabilizer between vertebra of the spine, and shock absorber, can begin to collapse, herniated (or bulge), tear or fragment.
With aging, a number of changes occur in the spinal column. On the one hand the soft tissues (discs, ligaments, muscles) lose their elasticity, and stabilizing ability. On the other hand the bones themselves begin to lose minerals and thereby become fragile (ex. Osteoporosis) placing them at risk for collapse and fracture.
Scoliosis can be present in the elderly due to a number of causes. The most common types of adult scoliosis are due to either gradual instability of the spine leading to loss of normal vertebral alignment or progression of a scoliosis that was already present during adolescence. Aside from scoliosis, which represents a global loss of alignment in the spine, focal problems can arise in the aging spine. Discs and ligaments begin to degenerate at around 30 to 35 years of age, and depending upon mechanical and genetic factors, this process can be more or less pronounced in any particular individual. When the discs lose their water content (or sponginess) with aging, the spine at that level is at risk of becoming unstable. This means that instead of controlled limited motion between the vertebrae, abnormal and increased motion may develop leading to problems such as spondylolisthesis. Abnormal motion due to disc failure will also lead to facet joint arthritis that can cause pain or lead to spinal stenosis.
If the degenerative process proceeds gradually and without marked instability or stenosis, then a normal shortening and forward settling (kyphosis) of the spine will occur as will a gradual stiffening. Eventually, the spine may lose all its flexibility due to advanced disc collapse. This in turn can cause the facet joints to gradually fuse together, or lock into place (cartilage in the joint is destroyed and the joint no longer permits motion). This process is called ankylosis and may have a protective effect to prevent more deterioration or instability of the spine which houses the spinal cord and nerves.