Lateral crookedness of the spine, often associated with convex crookedness (kyphosis). In cases with one curve it is known as simple scoliosis; if there are more than one, it is termed multiple scoliosis. Usually the vertebrae are also twisted, displacing the ribs on the side of the curvature to form a so-called humpback. Scoliosis can occur at any age, often without recognizable cause; in other cases deformity of the vertebrae is caused by injury, rickets, osteomalacia, osteoporosis or metastasized tumours. Diseases of the spinal column associated with kyphosis can also cause scoliosis. Other causes are disorders or paralysis of the back muscles and pelvic deformities, in which scoliosis serves to correct the position of the lower spine. Reasonable treatment of scoliosis is possible only while the patient is growing, and is naturally dependent on the cause. Generally treatment is by strengthening the back muscles, exercise therapy to correct posture and possibly a lengthy period in bed to allow stretching of the spine, using a device which is supported by the pelvis and pushes the head upwards. In serious cases where growth has stopped the position of the spine can be altered by bone implantation.