The normal spine has an S-shaped curve when viewed from the side. This shape allows for an even distribution of weight and flexibility of movement. The spine curves in the following ways:

• The cervical spine curves slightly inward, sometimes described as a backward C-shape or lordotic curve
• The thoracic spine curves outward, forming a regular C-shape with the opening at the front - or a kyphotic curve
  
• The lumbar spine curves inward and, like the cervical spine, has a lordotic or backward C-shape
  

The curves of the spine can be exaggerated in any plane, leading to pain, deformity and neurological dysfunction. About five to 10 percent of the adult population can have abnormal curves, with most being painless and asymptomatic.

Some excessive and abnormal curves are amendable to surgical treatment. Excessive kyphosis or increased angulation forward can be due to trauma or other causes. Scoliosis or a lateral curvature in some cases can be corrected with surgery. There are many types of kyphosis and scoliosis, and most need nothing more than careful observation.