Scoliosis is a three-dimensional deformity of the spine and trunk which includes lateral deviation, rotation, and a disturbance of the sagittal profile.

It is of two types: non-structural (transient) and structural (permanent). In structural scoliosis, the vertebrae, in addition to sideways tilt, are rotated along their long axis; in non-structural scoliosis they are not.
Non-structural scoliosis: This is a mobile or transient scoliosis. It has three subtypes, they are: Postural scoliosis: It is the most common overall type, often seen in adolescent girls. The curve is mild and convex, usually to the left. The main diagnostic feature is that the curve straightens completely when the patient bends forwards. Compensatory scoliosis: In this type, scoliosis is a compensatory phenomenon, occurring in order to compensate for the tilt of the pelvis. The scoliosis disappears when the patient is examined in a sitting position or when the causative factor is removed. Sciatic scoliosis: This is as a result of unilateral painful spasm of the paraspinal muscles, as may occur in a case of prolapsed intervertebral disc.

Adolescent idiopathic scoliosis (AIS) is the most common type of scoliosis affecting 2%-4% of adolescents, mainly involving children between 10 and 18 years of age. Adolescent idiopathic scoliosis has both congenital and developmental components, with the former being studied from the perspective of genetic variation. Using comparative genetic methodologies, such as genome-wide association studies (GWAS), several genomic linkages have been shown to be associated with this spine pathology. Thus, it can be determined that Adolescent idiopathic scoliosis is polygenic or a quantitative trait locus, which can vary due to several different genetic loci. The etiology is not limited to genetic predispositions but has been studied in association with physiological, anatomical, and hormonal disruptions.
The main pathology is lateral curvature of a part of the spine. This is called the primary curve. The spine above or below the primary curve undergoes compensatory curvature in the opposite direction. These are called the compensatory or secondary curves. The lateral curvature is associated with rotation of the vertebrae. In curves of the thoracic spine, rotation of the vertebrae leads to prominence of the rib cage on the convex side, giving rise to a rib hump.

Any part of the thoraco-lumbar spine may be affected. The pattern of the curve and its natural evolution are fairly constant for each site.
In most cases, visible deformity is the only symptom. Pain is occasionally a feature in adults with a long-standing deformity. In exceptional cases of severe long-standing scoliosis, sharp angulation of the spinal cord over the apex of the curve may result in interference with cord functions, leading to a neurological deficit.

For proper assessment of scoliosis, a full antero-posterior X-ray of the spine in supine and erect positions, plus a lateral view are necessary. Severity of the curve is measured by Cobb's angle - an angle between the lines passing through the margins of the vertebrae at the ends of the curve. Radiological assessment regarding the likelihood of progress of the curve can be made by looking at the iliac apophysis. It fuses with the iliac bone at maturity and indicates the completion of growth, and thus no possibility of the curve worsening. This is called Reisser's sign.
Rotation of a vertebra can be appreciated by looking at the position of the spinous processes and pedicles on AP view. Normally, a spinous process is in the centre of the vertebral body. In a case where there is a rotation of a vertebra, the spinous process is shifted to one side. Also, there will be asymmetry in the position of the pedicles on the two sides.

The aim of treatment is to assess the prognosis of the curve in terms of the visible deformity it is likely to produce. Congenital curves progress at variable rates depending upon the type of vertebral malformation, but overall they grow faster than idiopathic curves. Neurofibromatotic curves progress faster. In general, the younger the patient, the worse the prognosis. Thoracic curves produce the worst deformities.
As soon as it is realised that a curve is likely to progress and result in an ugly deformity, the affected part of the spine is fused. The basic guiding principle is that a straight, stiff spine is better than a curved, flexible one. Treatment of postural curves is non-operative. Proper training and exercises form the mainstay of treatment. Structural curves of less than 30°, and well-balanced double- curves can also be successfully treated by non-operative methods. For all other curves, the patient is started on a non-operative regimen consisting of exercises and a brace. The progress of the curve is monitored clinically and radiologically every 6 months.

Operative methods comprise fusion of the spine. In congenital scoliosis, simple fusion is sufficient. In idiopathic scoliosis, the spine is fused after achieving some correction by stretching the spine. Stretching could be done pre-operatively by traction, localiser cast, or halo-pelvic distraction system. It could be achieved per-operatively by Harrington's distraction system, Dwyer's compression assembly and Luque-Hartshill systems.