People are curious about the causes of scoliosis. They want to know if anything they did might have caused the scoliosis— or if they might have done something differently that would have prevented the curve.
In cases involving nonidiopathic scolioses, I can readily provide answers. Congenital scoliosis begins at birth. Children are born with an abnormal spinal column that grows asymmetrically. Neuromuscular scoliosis results from some abnormality in the neuromuscular system including abnormal control of muscles (in the case of cerebral palsy) or muscle paralysis due to an intrinsic muscle disorder (in the case of muscular dystrophy). Degenerative scoliosis stems from deterioration of the discs that cushion the vertebrae, arthritis in the facet joints, or loss of support in the spinal column (or all of these).
With idiopathic scolioses, however, the answers do not come as easily. Everything from poor posture to poor nutrition has been suggested as a possible cause. Most researchers exploring possible causes of scoliosis fall into one of two schools of thought.
The neurological, or neuromuscular, school considers scoliosis a secondary development resulting from an as-yet-undefined deficit or disease in the neuromuscular system. The underlying neurological defect or abnormality, according to these researchers, may involve motor-control mechanisms or postural-control mechanisms. This neurological dysfunction leads to abnormalities or anomalies in the muscles surrounding the spine. The abnormal action of these muscles then creates tension and exerts force that causes the spine to curve.
The second school of thought ascribes the origins of scoliosis to mechanical forces on the spine. Since the spine is a column, people in this school apply mechanical principles to explain how a column bends. The spinal column, like the columns in classical architecture, is exposed to a variety of forces that act upon it. According to researchers exploring possible mechanical causes of scoliosis, some spinal columns are unable to maintain shape in the face of forces such as gravity, the weight of the upper body, and movement.
Though I don’t know what causes scoliosis, I do know some of the right questions to ask. Any explanation of the causes of idiopathic scoliosis needs to account for the following:
- Why do more severe curves tend to afflict girls rather than boys? Researchers have not yet pinpointed which of the many differences between boys and girls might contribute to the higher incidence and faster rate of progression of scoliotic curves in girls. It could be that hormonal differences exacerbate scoliosis or accelerate curve progression in girls. Or these differences might be related to the fact that girls go through their growth spurt and achieve physical maturity at an earlier age than boys.
- Why do girls who get scoliosis tend to be taller and thinner than girls of the same age who dont have the condition? Girls who develop adolescent idiopathic scoliosis tend to grow faster than girls of the same age who maintain straight spines. The answer may lie in certain growth hormones that some researchers have associated with scoliosis, but what role these hormones might play in the development of scoliosis remains uncertain.
- Why are right thoracic curves so much more common than any of the other curves? No one knows why the thoracic spine is apparently more vulnerable to scoliotic developments than the lumbar or cervical spines, or why the vast majority of thoracic curves bend to the right. Complete answers to these questions would bring us much closer to understanding the origins of scoliosis.
- Why does the statistical risk of developing scoliosis increase so dramatically among family members of those who have scoliosis? The increased risk for family members of scoliosis patients would seem to suggest a genetic component to the etiology (development) of the disease. Since scoliosis does not follow a simple pattern of inheritance, a single gene that causes the disease seems an unlikely possibility. A more probable explanation involves the interaction of a number of different genes or a combination of genetic and environmental factors. If such genes or biochemical sequences do exist, however, neither they nor any possible environmental factors that might combine to cause the development of idiopathic scoliosis have been identified.
Researchers have indeed uncovered factors linked to scoliosis such as differences in disc contents (e.g., higher-than-normal collagen levels), hyperactive muscles adjacent to a scoliotic curve, and higher-than-normal calcium concentrations in muscles around the vertebrae. Yet all of these factors raise proverbial chicken-and-egg problems. Which came first? No evidence has yet proved that abnormalities of muscle, disc, bone, and collagen common among scoliosis patients are not a result of the scoliosis itself, rather than its cause. Unfortunately, despite the best efforts of countless scoliosis researchers, the cause or causes of idiopathic scoliosis remain unknown.