Scoliosis. Coloured X-ray of the abdomen of an adolescent girl with scoliosis. The spine is at centre, the blue blocks are the vertebrae of the spine. The pelvis is at bottom. Scoliosis is a lateral (sideways) curvature of the spine. This condition usually starts in infancy or adolescence, and is most often seen in girls. Its cause is not known, although occasionally it may be due to a congenital abnormality of the vertebrae, polio or an injury. Treatment depends on the severity of the curvature. In mild cases none is needed, but others may require immobilisation of the spine or surgery to pin the vertebrae in a straight line.