At first, the vertebrae curve to one side forming the C-shaped curve you mentioned.At first, a C-shaped curve causes the shoulders and hips to tilt down on one side. In an effort to keep the head in the middle, the spine may com-pensate by curving the lower part of the spine in the other direction, forming an S-curve. If the scoliosis progresses, the vertebrae may rotate, which makes the waist, hips, or shoulders appear uneven.

A specific cause of scoliosis is unknown. We call this idiopathic. Idiopathic scoliosis is the most common type. It tends to run in families and is more common in girls than in boys. Most often it develops in middle or late childhood during a rapid growth spurt.

So whether it is caused by hormonal changes, genetic mutations, or sudden and rapid growth spurts remains a mystery. And why it starts in one part of the spine instead of another is also an unknown.

Scientists are studying the position of the pelvis and sacrum at the bottom of the spine to see if there's any connection. Pelvic angles and pelvic tilt are important to spinal alignment. Perhaps too much tilt one way or the other causes the bones to shift or grow more in the front than in the back.

Taking X-rays of thousands of normal children and comparing them later to X-rays of those children who develop scoliosis may help piece the puzzle together. Smaller studies of this type are already underway.