It's only when these curves become too large that they present a potential problem. When the backward curve in the upper spine is too great, the condition is called thoracic hyper-kyphosis, round back, Scheurmann's disease, or sometimes simply kyphosis. When there is not enough backward curve in the upper spine, the condition is called hypo-kyphosis. When the inward curve in the lower back is too great, the condition is called hyper-lordosis or swayback. Although the spine does curve from front to back it should not curve sideways very much.
Scoliosis is more than just a curve to the side.
The scoliotic spine is also rotated or twisted, like the stripes on a barber pole. You may have noticed that one of your shoulders is higher than the other or that your clothes hang unevenly at the waist because one hip is higher than the other. To better understand this, compare the drawings of the normal spine and the scoliotic spine. Many people with scoliosis also have hypo-kyphosis. Because of all the possible combinations of curvatures, scoliosis can be very different in different people.