Structural scoliosis' are caused by an abnormally shaped vertebra, sometimes called a hemivertebra, it's a wedge shaped vertebra causing an unlevel foundation there by causing the spine to go off to the right or left and then curve back the other way, again because of the righting reflex.
Structural scoliosis' are not completely correctable because they are caused by an abnormally shaped bone. The shape of the bone cannot be corrected, however pain and disfigurement can often be improved, through adjustments, specific muscle and ligament stretching and specific muscle strengthening.
Other Abnormal Curves
Scheuermann's Disease-Hyperkyphosis of the thoracic spine(middle back), with nuclear invagination, schmorl's nodes or persistant notochord (dents in the top and/or bottom of the vertebrae). This disorder is more common in males that females, unlike scoliosis which is more common in females than males. Appearance of hunched back, if very severe may have elements of both called a kyphoscoliosis.