A normal spine has several front-to-back curves between the neck and the pelvis. In scoliosis, the spine curves abnormally to the side or twists. Although scoliosis seems to run in some families, most cases appear for unknown reasons in children and adolescents who previously had a straight spine. Scoliosis without a known cause is called idiopathic scoliosis. Girls and boys are affected equally by idiopathic scoliosis, but girls with this condition are more likely to develop curves that get big enough to require treatment.
In a few cases, the cause of scoliosis is known. These include:
Congenital scoliosis – This happens when the spine fails to form completely or forms improperly during development (while in the womb).
Neuromuscular scoliosis – This can happen when the spine's discs and bones break or deteriorate in adulthood. It also can happen because certain diseases, such as cerebral palsy, cause the muscles to support the spine unevenly or to pull at the spine unevenly.
Osteoporosis with fractures — The bones are prone to fracture in people with osteoporosis and the spine is a favored location for fracture. If one side of a vertebra (spine bone) compresses more than the other side after it fractures, the spine may curve as a result.
Scoliosis is a long-term (chronic) disease that can worsen over time. Sometimes a curved spine that develops during infancy or early childhood may go unnoticed and untreated until the teenage years. The abnormal position of the spine can affect the development of muscles and ligaments associated with the spinal column, causing the ribs and pelvis also to twist and rotate to the side.