What is a herniated disc?
A herniated disc is a common cause of lower back pain. Disks are round, flat, plate-like structures between the vertebrae (back bones) in the spinal column. They have a tough covering over a soft, gelatinous inside (nucleus pulposus), and their purpose is to cushion the back bones and allow the back to flex. A hernia is a tear in the covering of the disc that allows the soft interior to bulge out. The bones of the spine are cushioned by small discs, which are round and flat with a tough, outer shell (capsule) that surrounds a jelly-like material (nucleus). When discs are healthy, they act as shock absorbers for the spine, keeping the spine flexible. When discs are damaged by injury, disease or normal wear and tear, they may bulge or rupture, becoming a herniated disc (sometimes called a slipped or ruptured disc).
The discs of the spine are located in between the vertebrae (bony building blocks of the spine). The disc is designed somewhat like a jelly donut being composed of an inner gelatin-like core (the nucleus pulposus) surrounded by a firm outer ring (the annulus fibrosus). Each disk is composed of a gelatinous material in the center, called the nucleus pulposus, surrounded by rings of a fiberous tissue (annulus fibrosus). In disk herniation, an intervertebral disc's central portion herniates or slips through the surrounding annulus fibrosus into the spinal canal, putting pressure on a nerve root. Disk herniation most commonly affects the lumbar region between the fifth lumbar vertebra and the first sacral vertebra. However, disc herniation can also occur in the cervical spine. The incidence of cervical disc herniation is most common between the fifth and sixth cervical vertebrae. The second most common area for cervical disk herniation occurs between the sixth and seventh cervical vertebrae. Disk herniation is less common in the thoracic region.
When a disc begins to deform or a portion of the nucleus pulposus squeezes through a disc tear, then a bulge into the area of the spinal canal can develop. When a disc is noted to bulge into the area of nerves, this can lead to irritation of the nerves and is commonly called a "slipped disc". Nerve irritation may result from chemical irritation of the disc material in addition to compression from the disc itself. If an actual piece of disc separates off from the remainder of the disc and sits freely in the spinal canal, this is called a disc extrusion or sequestered disc fragment. When the disc structure wears, because of processes such as aging or trauma, it becomes weakened and susceptible to injury. In this condition, stresses on the spine can cause the inner core to protrude outward through the boundary of the disc's outer ring. The is referred to as herniation of the disc. Although injury to the outer covering of a disc can cause pain, often a herniated disc by itself does not cause any discomfort. Pain occurs when pressure from the herniated disc is put on the nerve roots or spinal cord. Pain or numbness may occur in the area of the body affected by the nerve. For example, a herniated disc that presses on one of the nerve roots of the large nerve that extends from the lower back down the back of the leg may cause pain and numbness in the leg (a condition called sciatica).
In some people, mostly middle-aged adults, a disk's tough outer shell develops an area of weakness or a small tear. When this happens, part of the disk's soft inner core can bulge out of its normal position (herniate), producing a condition called a herniated disc. If the herniated disc presses on nerves in the nearby spinal canal, this can cause variety of nerve related symptoms, including pain, numbness and muscle weakness. In the most severe cases, a herniated disc can compress nerves that control the bowel and bladder, causing urinary incontinence and loss of bowel control.
More than 80% of herniated discs occur in the lower back. They are most common among people aged 30 to 50 years. Between these ages, the covering weakens. The interior, which is under high pressure, may squeeze through a tear or a weakened spot in the covering and bulge out. After age 50, the interior of the disk begins to harden, making a herniation less likely. A disk may herniate because of a sudden, traumatic injury or repeated minor injuries. Being overweight or lifting heavy objects, particularly lifting improperly, increases the risk.
A ruptured or herniated disc can cause low back pain. A disc has a tough covering and a soft, jelly-like interior. If a disc is suddenly squeezed by the vertebrae above and below it (as when lifting a heavy object), the covering may tear (rupture), causing pain. The interior of the disc can squeeze through the tear in the covering, so that part of the interior bulges out (herniates). This bulge can compress, irritate, and even damage the spinal nerve root next to it, causing more pain. A ruptured or herniated disk also commonly causes sciatica.