Scoliosis is a three-dimensional deformity of the spine and rib cage. It is a side-to-side curving of the spine, and it may develop as a single primary curve (resembling the letter C) or as two curves (a primary curve along with a compensating secondary curve that forms an S shape).
There are many causes of scoliosis, but the most common type is termed "idiopathic". This means that the actual cause is unknown. Scoliosis can begin to develop in early childhood or even in adulthood (mostly caused by degenerative conditions), but the most common time to develop a spinal curvature is during the adolescent growth spurt.
Not all the scoliosis will need surgical intervention. The purpose of corrective surgery will depend on the type of scoliosis (angulation and severity).