Scoliosis means abnormal curvature of the spine. The curvature takes place in three dimensions. The normal spine is straight when looking at a person from the front or back. When looking at a person from the side, the spine is curved. There is a gentle bending forward of the spine in the chest and a bending backward, called lordosis, of the spine between the chest and the pelvis.

In scoliosis, the spine becomes S-shaped when looking from the front or back. When looking from the side, the normally curved spine typically straightens out. In addition, the spine twists on its axis, pushing the ribs and flanks backward and forward to produce a prominence, or hump.