Scoliosis is defined as an abnormal curving of the spine in one or more places. Affecting the alignment of the body as well as balance and hampering the body’s ability to move naturally and normally, a spine that has scoliosis will not be straight but rather curved into a letter C or S shape.

Two to three percent of people in the United States are affected by this condition, which develops most often before puberty and is more common in young females. Sometimes traced to hereditary factors, it can also develop from degenerative disc disease or osteoporosis (secondary); be present at birth (congenital); occur when the muscles around the spine are failing, such as in people suffering from cerebral palsy or muscular dystrophy (myopathic); be the result of a spinal cord injury (paralytic); come from an unknown cause (idiopathic); or from another condition or disease. For adolescents suffering from the condition, the curvature generally worsens during periods of quick growth (i.e. “growth spurts).

Newborns, children, teens and adults can all develop scoliosis for various reasons and at various points in their lives. And because of this fact, physicians and health professionals have categorized the disorder into several different classifications and subdivisions.

The most seen form of scoliosis is idiopathic (no known cause), affecting some 80 percent of all sufferers. When a child under the age of three has the condition, it’s known as infantile idiopathic scoliosis; those afflicted at three to nine years old have the juvenile idiopathic form; those ten to 18 years of age the adolescent idiopathic type; and adults over the age of 18 contract what’s called adult idiopathic scoliosis.

In addition to the idiopathic form of this condition, there is also neuromuscular scoliosis, a result of various diseases—muscular dystrophy, cerebral palsy and polio, for instance—which affect the muscles of the back. Additionally, when scoliosis is present at birth it’s known as congenital, a result of improper development of the spine and ribs that causes an abnormal curvature.

Scoliosis can also develop after surgeries on the spine (post-surgical deformity/scoliosis). And when a fully developed and grown person has the condition—either because they’ve had it since childhood or because they developed it due to stress and strain on their spine—it’s classified as adult scoliosis.

Lastly, there are the structural and nonstructural classifications of pediatric scoliosis. When the abnormal curving of the spine is fixed, the cause usually originated from some form of neuromuscular, rheumatic or metabolic disease or is the result of a birth defect, injury or tumor and is known as structural scoliosis. Conversely, nonstructural scoliosis means the condition is the result of a muscle spasm or an inflammatory problem and is temporary in nature.