What is scoliosis?

Causes and Symptoms

Of all the structures making up the human body, the spine is second only to the closely associated brain in its centrality to human characteristics. Two distinct aspects of human life are deeply involved in the correct functioning of the spine. First, the spinal column protects the spinal cord, which carries out critical message-carrying functions in the body. Second, the spinal column also holds the body erect, a distinctly primate feature. An abnormal curvature of the skeletal structure of the spinal (or vertebral) column is known as scoliosis

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The usual term for the spine, the backbone, is completely misleading. If one really had a backbone, one would be unable to bend, nod, or stretch. The normal spine consists of approximately thirty-three separate bones whose very name, vertebrae, is derived from the Latin verb “to turn.” Furthermore, it is essential to know that the normal spine takes the form of four separate curves. Each of these curves is associated with a distinct set of vertebrae. At the very top of the spine are the cervical vertebrae. In the chest area are found the thoracic vertebrae, which support the body when one leans backward and which are the sites of attachment of the twelve pairs of ribs. The largest of the vertebrae, which support the upper body weight, are called lumbar, from the Latin for “loin.” At the very base of the spine are two sets of small vertebrae called the sacrum and coccyx.

Although these curves are a vital part of a healthy spine, they are not always obvious because one usually sees people from the front or rear, so that the spine appears straight. If one looks at a person with good posture from the side, however, the gently S-shaped curve of the spine is clearly visible. Deformities involving abnormal spinal curvature toward the front or back are well known, but they are not called scoliosis. The side-to-side curvature of scoliosis is referred to as a lateral curve.

As important as the bones are, the vertebral spine is a much more complicated structure. Along its entire length is a surrounding complex of ligaments and muscles making it possible for the body to bend and straighten again. Within the vertebral column are rubbery cylinders of cartilage called disks. These disks absorb shocks, relieving the body from the countless pressures of movement. With this array of closely balanced mechanisms and associated forces, it is no wonder that the curvature of the spine is a complex subject for diagnosis and treatment.

Scoliosis can result from a number of different causes. While a birth defect, an accident, poliomyelitis, or muscular dystrophy can all result in lateral curvature, the cause is unknown in the majority of cases. Some authorities believe that 80 percent of all scoliosis cases have no known cause. The technical term for this important class of malady is “idiopathic scoliosis.” Within this general subdivision, three separate forms are recognized, based on the age of the patient at the onset of the curvature.

The adolescent form of scoliosis, which is usually recognized between ten and thirteen years of age, is by far the most common form. A brief look, however, at infantile (birth to three years) and juvenile (four to ten years) scoliosis will help to illustrate the difficulty faced by researchers in this area and the enormous problems yet to be solved. (All these age groupings refer to the age at which the deformity is first noted, not the age at which the curvature began.)

When the scoliosis is recognized in the youngest range, it is more common in males, with one study giving a 3:2 ratio. By contrast, in the far more common adolescent condition one finds a striking shift to females, who are three times more likely to be affected. While it is often observed that infantile idiopathic scoliosis corrects itself (that is, it spontaneously resolves), this natural remission is rarely observed when the diagnosis is made later. More fascinating but puzzling is the noted absence of the infantile conditions in the United States and Canada, while its occurrence is well documented in Great Britain and France. J. I. P. James, who studied scoliosis extensively at the University of Edinburgh for many years, reported this form to be as common in Europe as the adolescent variety is worldwide. At a subtler level of research, one finds that 90 percent of the curves in infants are formed to the left, whereas 90 percent of those in adolescent girls lie to the right.

It is small wonder that James’s collaborator, Ruth Wynne-Davies, called the cause of infantile scoliosis “multifactorial” and wrote, “The exact cause in each individual is likely to be different.” Wynne-Davies made important studies of the influence of heredity in producing scoliosis. She, like many others, has seen infantile idiopathic scoliosis in a different class from the adolescent variety.

The juvenile condition is likely to be related closely to adolescent scoliosis. As before, there is marked evidence of hereditary influence. In this age range, males and females share equally in the likelihood of being diagnosed. The chance of significant progression of the curvature is so variable that close watching of the patient is the single point of common agreement among specialists. There is concern among parents, patients, and practitioners alike over the excessive use of X-rays for diagnosis.

Some research suggests intriguing clues about the cause of scoliosis from unexpected sources. For example, studies at the University of Rochester suggest that in scoliosis patients there may be significant differences in the side of the brain that processes sound. In most people, the left hemisphere of the brain hears and understands phonetic sound as in language, but those people with scoliosis seem much more likely to use both sides or the right side of the brain for these functions. It may be possible that a simple listening test can determine who is at risk for spinal curvature.

A dozen different types of curves associated with scoliosis have been identified, but four major classes are of greatest frequency and concern. In the chest area, one finds the most common of all curve patterns, the right thoracic curve. It is possible for this condition to progress rapidly. Early treatment is essential. As the curve develops, the ribs on the right side shift and create a deformity that not only is unattractive but that also can squeeze the heart and lungs; this so-called rib hump can result in serious cardiopulmonary difficulties.

A similar, but gentler, curve is the thoracolumbar curve. It begins in the same region of the thoracic vertebrae and ends farther down the back, in the lumbar region. The twist may be either right or left and is generally less deforming in its appearance. A lumbar curve is found far down in that region of the back, producing a twist in the hips. In pregnant women and other adults, this twist often causes severe back pain.

The three curves described thus far are single, or C-shaped, curves. The double major curve is an S-shaped curve and is the most common of that type. Curvature begins in the thoracic or chest area and is complemented by a second curve in the opposite direction found in the lumbar region. To some extent, the two curves offset each other and the scoliosis is less deforming. The double major curve can progress and become the source of a rib hump.

These and the other less common curves demand an accurate description beyond their location. John Cobb searched for such an important tool and developed the widely used Cobb angle measurement. His suggestion was to relate the top of the first and the bottom of the last vertebrae of a curve by determining the angle formed by the intersection of lines perpendicular to them. It is not difficult, using an X-ray of the spine, to draw lines above and below the vertebrae, construct the required perpendiculars, and measure the angle of their intersection. This technique allows physicians to communicate accurately and have a useful measure with which to note the progression, remission, or stabilization of the patient’s scoliosis. In addition to degree of curvature, the complex structure of the spine shows rotation in scoliosis. The rotation causes the pedicles or indentations of the vertebrae to shift closer to the midline drawn on the X-ray. The relative shift is described as a rotation of +1, +2, and so on.

Treatment and Therapy

Scoliosis can result from many different causes, each of which demands treatment, as well as the idiopathic variety under discussion. Since there is no known cause, prevention is impossible, and since there are enormous difficulties in predicting the course of the condition, the most that can be achieved is satisfactory correction.

A diagnostic examination for scoliosis demands specific attention to accurate family history. Particularly important is information concerning the first recognition and previous treatment of the condition. Then a detailed evaluation of the nature and extent of the curvature must be made. The examining physician should make certain that the patient is standing straight with the knees unflexed. A simple plumb line is used to examine the patient’s back to determine any curvature in the spine. Then the forward bending test is conducted. This observation is considered one of the most reliable diagnostic tools. Various forms of curvature, including scoliosis, can be seen by the trained observer. When viewed at eye level from both front and back, one side of the thoracic or lumbar regions is higher. An accurate measurement of the degree of difference can be made with a level. The use of X-ray photographs also forms a vital part of the diagnostic data.

Even with the best diagnostic skill, training, and experience, the decision concerning the treatment of scoliosis is hardly straightforward. One important consideration is the patient’s bone age. Because people grow and mature at such different rates, chronological age may not correspond well to the degree of maturity of that person’s skeleton. Many clues are used to determine the bone age, including the degree of fusion observed in the individual vertebra or the bony pelvic girdle. A catalog of X-rays of hands is available and provides a useful measure of the bone age. The central concern is that curvature is more likely to progress if the growth and development of the patient’s skeleton is still incomplete.

The treatment of scoliosis varies from none at all to extensive surgical procedures. In general, treatment is undertaken for the prevention of further curvature or for the correction of the curvature already present. Some treatments, such as exercise, are of benefit to the patient in general but are seen as having no prospect of arresting or correcting the spinal curvature. Research has also suggested that copper in the diet may play a key role in scoliosis treatment. These studies were carried out with chickens, which show scoliosis very similar to that found in humans, but much remains to be learned about these and similar studies before confidence can be placed in the applicability of the data to human treatment or prevention.

Of all the methods proposed, the use of braces and casts is certainly the oldest and the most common. The many modifications of design and material used in braces over the centuries have had the central purpose of forcing the spine to become straight. The evolution of the brace has reached the point of an active or kinetic apparatus called the Milwaukee brace, developed by Walter Blount and Albert Schmidt. It is a carefully designed assembly of a molded plastic pelvic girdle and three metal bars that keep the wearer erect and allow a neck ring to be attached. The neck ring and its associated axillary sling keep the torso balanced and prevent listing to the right or left. This brace was often used to correct scoliosis in the mid-to-late twentieth century. Its use has since lessened, as there are now other specialty braces available that may better suit a patient's particular case.

In order for the Milwaukee brace (or any modified versions of it) to be effective, it must be worn day and night and until the growth period of the patient has been completed. It is also imperative that exercise be carried out on a daily basis. There are many advantages of the modern brace over older systems. For example, it can be removed for showering and swimming, and much greater activity is allowed. The one serious drawback is that a patient must not expect correction of the scoliosis. The value of the brace is that it can, with good use and exercise, maintain the already present curvature and prevent further progression.

Only in certain cases will braces be of benefit to the patient. With curves of 45 degrees or more, pain that does not respond to treatment, or the failure of the brace to stop the curve’s progression, surgery is the most reasonable approach. Surgery can offer some degree of correction, but it is important to recognize that only a partial correction is possible. Even with the safest techniques, pressure must be applied to the spine, creating a serious risk of damage to the spinal cord.

Once it is agreed that surgery is the proper route of treatment, a wide range of methods are available. The most common, and generally considered the safest, method in the mid-to-late twentieth century was the Harrington rod technique. The incision was from the back (as opposed to front or side entries), and metal hooks were inserted at the highest and lowest points in the curve. These hooks held metal rods used to straighten the spine and then to hold it in place. Small chips of bone were then taken from the hip or ribs and inserted between especially prepared vertebrae. In a period of six to eight months, solid bone would grow and fuse the vertebrae, giving a solid bone mass of a single elongated vertebra. After the surgery, the patient was usually placed in a brace or cast for four to six months.

The success of the Harrington rod technique has inspired several modifications, such as using two rods to achieve more balance and greater correction. With a patient who has unusually soft bones, a system of wires is used to hold the rods in place. This method is considered superior because the normal hooks might break off. Several variants of the wire technique are also available. Some surgeons thread the wires through the neural canal, and others drill small holes to avoid coming near to the spinal cord.

Another technique that grew in popularity in the late twentieth century avoids the use of a Harrington rod. Many small wires are attached through the neural canal and twisted around two thin rods, one on either side of the curvature. This Luque method provides greater stability, and usually there is no need to wear a cast after surgery. These advantages must be balanced, however, against a significantly greater risk of paralysis and a smaller amount of room for new bone growth in fusion.

In the late 1990s, surgeons began to replace the straight-rod technique with spinal fusion instead, rendering the Harrison rod obsolete. In this technique, which helps correct the spine in a more natural way, surgeons fuse parts of the spine together so that it can heal into a single, solid unit.

Another modern technique that has shown some success involves placing small electrodes near the spine and transmitting tiny electrical impulses to nerve endings periodically during sleep. This electronic bracing, or electrosurface stimulation, appears to stop scoliosis curves from progressing in about 80 percent of the cases studied. These devices have about the same limitations as do conventional braces—that is, curves of greater than 45 degrees, curves treated after the end of bone growth, and certain types of lumbar curves will fail to benefit from this treatment.

Perspective and Prospects

One finds the beginning of serious study of the spine in the writings of Hippocrates (c. 460–370 BCE). He described the curves of both the normal and the abnormal spine. He may not have been as clear in his description of scoliosis as with those of the clubfoot or epilepsy, but he was well aware of the difficulty of its treatment and recognized its possible relationship to pulmonary
disease. Another celebrated physician of antiquity, Galen (129-c.199 CE), first suggested the medical term for this deformity, scoliosis, in the late years of the second century. Among the complications faced by early medical science were the inadequate methods and equipment available for making subtle diagnoses. Thus it was not until the sixteenth century that Ambrose Pare carefully described the various types of spinal curves. He also noted for the first time that scoliosis is largely a condition of children.

Over the centuries, many men and women added to the array of methods and instruments as well as the store of knowledge and thoughtful speculation about scoliosis. Many possible causes were presented on the basis of observation and research. Many approaches to the treatment of these deformities were described and tested. Yet, despite all this research, scientists are just beginning to appreciate the complexity of the problem of scoliosis.

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