Causes

In 80% of patients, the cause of scoliosis is unknown. Such cases are called idiopathic scoliosis. (Idiopathic means without a known cause.) Idiopathic scoliosis may be due to multiple, poorly understood inherited factors, most likely from the mother's side. However, the severity often varies widely among family members who have the condition, suggesting that other factors must be present.

Researchers have not been able to identify the specific genetic abnormalities that make a young person susceptible to spinal distortion. Inherited physical abnormalities, problems in coordination, abnormalities in the central nervous system, and other inherited factors may play some role either alone or in combination with other conditions to produce scoliosis.

Physical Abnormalities. Researchers are investigating possible physical abnormalities that may cause imbalances in bones or muscles that would lead to scoliosis. Among them are the following:

• Imbalances in Muscles around the Vertebrae. Some research suggests that imbalances in the muscles around the vertebrae may make children susceptible to spinal distortions as they grow.
• High Arches. One study showed a higher incidence of abnormally high arches in the feet in people with idiopathic scoliosis, suggesting that altered balance may be a factor in certain cases.

Problems in Coordination. Some experts are looking at inherited defects in perception or coordination that may cause asymmetrical growth in the spine of some children with scoliosis.

Genetic Abnormalities in the Central Nervous System. Genetic defects that cause altered processing in the brain may play a role in producing abnormalities in the growing spine. For example, research has implicated low levels of melatonin, a hormone secreted in the pineal gland in brain. Melatonin is involved with sleep and growth. Researchers speculate that genetic factors that cause reduced blood levels of melatonin may adversely affect muscle tone and development during sleep, perhaps contributing to scoliosis.

Other Biologic Factors. Several other biologic factors are being investigated for some contribution to scoliosis:

• Abnormalities in collagen, the critical structural protein found in muscles and bones. Enzymes known as matrix metalloproteinases are involved in the repair and remodeling of collagen. Researchers have found high levels of the enzymes in the disks of patients with scoliosis, which suggests that the enzymes may contribute to curve progression. Elevated levels of the enzymes can cause abnormalities in components in the spinal disks, contributing to disk degeneration.
• A possible defective gene responsible for production of fibrillin, an important component of connective tissue, which makes up bones and muscles.
• Abnormalities in a protein called platelet calmodulin that binds to calcium. This protein acts like a tiny muscle and pulls clots together. Measuring levels of this protein may eventually help predict whether scoliosis will worsen.

Congenital Scoliosis

Congenital scoliosis is caused by inborn spinal deformities that may result in the development of absent or fused vertebrae. Kidney problems, particularly having only one kidney, often coincide with congenital scoliosis. The condition usually becomes evident at either age 2 or between ages 8 and 13 as the spine begins to grow more quickly, putting additional stress on the abnormal vertebrae. It is essential to diagnose and monitor such curvatures as early as possible, since they can progress quickly. Early surgical treatment -- before age 5 -- may be important in many of these patients to prevent serious complications.

Causes of Degenerative Lumbar Scoliosis in Adults

Adult scoliosis has two primary causes:

• Progression of childhood scoliosis.
• Degenerative lumbar scoliosis. Degenerative lumbar scoliosis is a condition that typically develops after age 50. With this condition, the lower spine is affected, usually due to disc degeneration. Osteoporosis, a serious problem in many older adults, is not a risk factor for new-onset scoliosis, but it can be a contributing factor. In most cases, however, it is not known why scoliosis occurs in adults.

Conditions That Affect the Spinal Column and Surrounding Muscles

Scoliosis may be a result of various conditions that affect bones and muscles associated with the spinal column. They include the following:

• Muscle paralysis.
• Muscle deterioration from diseases such as muscular dystrophy, polio, or cerebral palsy.
• Injury to the spinal cord.
• Tumors, growths, or other small abnormalities on the spinal column. For example, syringomyelia, a disorder in which cysts form along the spine, can cause scoliosis. These spinal abnormalities may play a larger role in causing some cases of scoliosis than previously thought.
• Familial dysautonomia, a rare disorder in Jewish children of Ashkenazi descent. (Only about 500 cases have been reported.)
• Stress fractures and hormonal abnormalities that affect bone growth in young, competitive athletes.
• Birth defects, including spina bifida (an open spinal cord) and myelomeningocele (a hernia of the central nervous system).
• Turner's syndrome, a genetic disease in females that affects physical and reproductive development.
• Other diseases that can cause scoliosis are Marfan's syndrome, Aicardi syndrome, Friedreich ataxia, Albers-Schonberg disease, rheumatoid arthritis, Cushing's syndrome, and osteogenesis imperfecta.

Spina bifida is a congenital disorder (birth defect) in which the backbone and spinal canal do not close before birth. In severe cases, this can result in the spinal cord and its covering membranes protruding out of an affected infant's back. Spina bifida may also be nearly inconsequential, or may be repairable through surgery.

Causes of Nonstructural Scoliosis

Nonstructural scoliosis is usually not a serious problem, since the curve is side to side. It can develop from a number of physical problems, including the following:

• Unequal leg length. Injury, a shortened Achilles tendon, or other structural in-born problems can cause this very common condition. Unequal leg length rarely causes any problems and in most cases requires no treatment other than a lift in one of the shoes to equalize the length.
• Muscle spasms.