Pain due to a herniated, or slipped disk usually strikes suddenly and can be excruciating. In this Health Alert, Johns Hopkins explains what happens when disks herniate.
At some point in their lives, 10% of all Americans experience painful symptoms from a herniated disk – commonly known as a slipped disk. Over the years, the demand of supporting the body's weight causes the outer layer of the disk to weaken, become thinner, and develop microscopic tears. At the same time, the center of the disk slowly loses its water content and becomes progressively drier. These changes make the disk susceptible to herniation (protrusion), in which mild trauma, such as lifting an object or even sneezing, can cause the center of the disk to bulge through the weakened outer layer.
Painful symptoms usually result from pressure by the protruding disk on one or more of the spinal nerves emerging from the spinal column. In some cases, the disk presses on the spinal cord itself or on the cauda equina. This pressure causes pain not only in the back, but also pain in the part of the body served by the compressed and inflamed nerve. Although herniation can involve any disk, 90% to 95% of cases occur in the two lowest disks because they carry the greatest weight.
What happens? Each intervertebral disk is composed of two distinct regions: a tough, fibrous outer ring made up of many overlapping layers of collagen fibers (called the annulus fibrosus), and a soft, gel-like core (the nucleus pulposus).
In a normal, healthy disk, these tissues contribute to the remarkable flexibility of the spine: As the body moves, the annular fibers expand and contract, while the gel-like nucleus changes shape. Although each individual disk can only bend to a limited degree, their combined flexibility throughout the spine provides a great range of motion.
As we age, however, the disks gradually lose their resiliency. The annulus weakens, while the nucleus loses its water content, becoming progressively drier and more brittle. These changes make the disk more vulnerable to herniation -- commonly known as a slipped disk.
Herniation may produce only local back pain, or pain may radiate down the path of a spinal nerve if the nerve is compressed by the protruding disk.
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