Scoliosis. Back view of an adolescent girl with severe scoliosis - sideways curvature of the spine. Scoliosis usually starts in childhood or adolescence, becoming progressively worse until growth stops. In many cases another part of the spine bends in an opposite direction to compensate, resulting in an S-shape. The cause of scoliosis is often unknown (idiopathic scoliosis). If the curvature is slight the spine may be left untreated. Severe or progressive scoliosis may be treated by immobilization of the spine followed by surgery to fuse affected bones into a straight line.