Natural History

The Natural History of a Curvature of the Spine

The natural history of a curvature refers to the course of events in spinal maturation without any intervention.

Two factors are of paramount importance in the natural history of a curvature: the magnitude of the curvature and the degree of skeletal maturity. The angle of the curvature is measured from the X-ray. The degree of skeletal maturity is determined by looking at the top of the pelvis to examine the appearance of a small piece of bone called the apophysis. The appearance of the apophysis is divided into stages known as the Risser signs. Growth centers on the vertebral body can often be identified as well, indicating continuing spinal growth. Skeletal maturation is closely linked to the hormonal changes in puberty, which produce the more visible changes of adolescence. These changes also provide clues as to the state of skeletal maturity.

It is important to recognize that our information about the natural history of curves is incomplete. Nevertheless, we do know a great deal from studying large groups of patients. From such studies, for example, we know that in the patient who is relatively immature skeletally — that is, a Risser 0 or 1 — and who has a curve of less than 20 degrees, there is about a 25 percent chance that a curve will progress. However, in patients with a similar state of skeletal maturity with a curvature greater than 20 degrees, the chance of progression is about 70 percent. When the child gets older and reaches a greater level of maturity — that is, a Risser 2, 3, or 4 — the chance of the small curves (20 degrees or less) progressing is extremely small (about 2 percent). However, larger curves, at the same level of maturity, have about a 25 percent chance of progression. These studies point to a trend: the less mature the skeleton, and the larger the curve, the more likely the curve is to progress.

Other information and trends from natural history are also important in determining treatment.

Boys and girls have small curves in almost equal numbers, but girls are far more likely to progress than are boys. Therefore, more girls need treatment than boys. Curves progress most during periods of rapid growth. Most curves that progress do so at a little less than 1 degree per month, or about 10-12 degrees per year. Curves can progress after growth is finished. Although this is not common, it can happen and depends on how large the curvature is at the end of growth. While studies tell us what the probabilities are for large groups, they do not tell us what will happen for each particular patient. That is why observation is so important in the treatment of smaller curvatures.