Scoliosis affects about 2 - 3% of the population (about 6 million people in the United States). It can occur in adults but is more commonly diagnosed for the first time in children aged 10 - 15 years. About 10% of adolescents have some degree of scoliosis, but less than 1% of them develop scoliosis that requires treatment. The condition also tends to run in families. Among persons with relatives who have scoliosis, about 20% develop the condition.
Scoliosis that is not linked to any physical impairment, as well as scoliosis linked to a number of spine problems, may be seen in the adult population as well.
Vertebrae. The spine is a column of small bones, or vertebrae, that support the entire upper body. The column is grouped into three sections of vertebrae:
Each vertebra can be designated by using a letter and number; the letter reflects the region (C=cervical, T=thoracic, and L=lumbar), and the number signifies its location within that region. For example, C4 is the fourth bone down in the cervical region, and T8 is the eighth thoracic vertebra.
Below the lumbar region is the sacrum, a shield-shaped bony structure that connects with the pelvis at the sacroiliac joints. At the end of the sacrum are 2 - 4 tiny, partially fused vertebrae known as the coccyx or "tail bone."
The Spinal Column and its Curves. Altogether, the vertebrae form the spinal column. In the upper trunk the column normally has a gentle outward curve (kyphosis) while the lower back has a reverse inward curve (lordosis).
The Disks. Vertebrae in the spinal column are separated from each other by small cushions of cartilage known as intervertebral disks. Inside each disk is a jelly-like substance called the nucleus pulposus, which is surrounded by a tough, fibrous ring called the annulus fibrosis. The disk is 80% water. This structure makes the disk both elastic and strong. The disks have no blood supply of their own, relying instead on nearby blood vessels to keep them nourished.
Processes. Each vertebra in the spine has a number of bony projections, known as processes. The spinous and transverse processes attach to the muscles in the back and act like little levers, allowing the spine to twist or bend. The particular processes form the joints between the vertebrae themselves, meeting together and interlocking at the zygapophysial joints (more commonly known as facet or z joints).
Spinal Canal. Each vertebra and its processes surround and protect an arch-shaped central opening. These arches, aligned to run down the spine, form the spinal canal, which encloses the spinal cord, the central trunk of nerves that connects the brain with the rest of the body.
Scoliosis is an abnormal curving of the spine. The normal spine has gentle natural curves that round the shoulders and make the lower back curve inward. Scoliosis typically causes deformities of the spinal column and rib cage. In scoliosis, the spine curves from side-to-side to varying degrees, and some of the spinal bones may rotate slightly, making the hips or shoulders appear uneven. It may develop in the following way:
Scoliosis most commonly develops in the area between the upper back (the thoracic area) and lower back (lumbar area). It may also occur only in the upper or lower back. The doctor attempts to define scoliosis by the following characteristics:
The severity of scoliosis is determined by the extent of the spinal curve and the angle of the trunk rotation (ATR). It is usually measured in degrees. Curves of less than 20 degrees are considered mild and account for 80% of scoliosis cases. Curves that progress beyond 20 degrees need medical attention. Such attention, however, usually involves periodic monitoring to make sure the condition is not becoming worse.
Scoliosis is often categorized by the shape of the curve, usually as either structural or nonstructural.
Other abnormalities of the spine that may occur alone or in combination with scoliosis include hyperkyphosis (an abnormal exaggeration in the backward rounding of the upper spine) and hyperlordosis (an exaggerated forward curving of the lower spine, also called swayback).
The location of a structural curve is defined by the location of the apical vertebra. This is the bone at the highest point (the apex) in the spinal hump. This particular vertebra also undergoes the most severe rotation during the disease process.
The direction of the curve in structural scoliosis is determined by whether the convex (rounded) side of the curve bends to the right or left. For example, a doctor will diagnose a patient as having right thoracic scoliosis if the apical vertebra is in the thoracic (upper back) region of the spine, and the curve bends to the right.
The magnitude of the curve is determined by taking measurements of the length and angle of the curve on an x-ray view.
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