Intervertebral discs are circular ring-like flat structures that function as cushions between two spinal vertebrae, allowing spinal flexibility and acting as shock absorbers. Each intervertebral disc contains a nucleus (center) surrounded by a sack of fibrocartilage (fibrous, connective tissue), rich in collagens (fibrous protein). A herniated disc occurs when the outer sack partially ruptures and the interior of the sack expands, pushing part of the disc into the spinal canal near to where the spinal cord and other nerve roots are located. This causes either chronic or acute pain in the back or in the neck, and movement restriction of the affected area due to pressure exerted on the spinal nerve roots. This condition is also known as a slipped disc, an intervertebral disc hernia, a herniated intervertebral disc, and a herniated nucleus pulposus.
Intervertebral disc disease is among the most common causes of neck and back pain. Cervical disc herniations (in the neck region) are less common than lumbar (lower back) herniations. Lumbar disc herniations affect an estimated four out of five patients complaining of back pain. Several factors may contribute to a herniated disc, such as poor posture, work-related strain, traumatic injuries due to falls or blows in the back, improper weight lifting, obesity, and sport-related muscular strain. Disc herniation may also occur because of age-related degenerative processes that cause progressive loss of disc elasticity.
Herniated disc is a common problem, with approximately one in 32, or 8.4 million people in the United States affected each year.
Causes and symptoms
Degenerative disc disease, usually related to aging, is more common in the lumbar area, where much of the wear-and-tear of a lifetime of activity is exerted, resulting in chronic back pain. However, in the cervical area the disc degenerative process usually starts with a traumatic twisting of the disc space that leads to chronic inflammatory pain in the neck, and may result in arm pain and numbness. The degenerative process may also be associated with occupational repetitive movements such as those required in construction, farming, mining, and other professional activities where workers are required to handle heavy loads.
Herniated discs sometimes cause pain that is incapacitating, and the condition accounts for a major cause of work disability and health care expense in the United States. Lumbar disc hernias are commonly associated with sciatica (inflammation of the sciatic nerve in the lower back) due to disc protrusion or herniation that compresses the spinal nerve root radiating to the femoral or sciatic nerve. A sensation of sharp, painful electric-like shock is felt during acute sciatica both in the back and along the involved limb. Other symptoms are a burning pain in the back, numbness or tingling sensation in the related leg, and weakness in one or both legs.
Growing scientific evidence also points to genetic factors in disc herniation, especially in families with a history of predisposition to early-onset sciatica and disk herniation. The causation factor seems to be a mutation in one of the three genes (COL9A1, COL9A2, and COL9A3), which are related to the formation of collagen.
A clinical record of chronic back pain and progressive leg pain points to the possibility of a degenerative disc disease in progression; and physical palpation (examination by touch) by the physician may reveal whether a nerve root is affected. The straight leg-raising test (raising the leg straight, with no bend at the knee, until pain is experienced in the thigh, buttocks, and calf) can also point to nerve root irritation in the lumbosacral area due to herniated disc. X ray of the affected spinal area is the standard test for confirmation of a herniated disc. When surgery is being considered, other imaging tests are performed, such as a magnetic resonance imaging (MRI) scan or computed tomagraphy (CT) scan, for confirmation of the diagnosis.
The orthopedist is the medical specialist often first consulted, and many orthopedic clinics offer the services of physical therapists whose interventions will be prescribed by the physician. In more severe cases, the intervention of a neurologist, neurosurgeon, or an orthopedic surgeon, along with a pain specialist may be required.
In most cases, conservative treatments such as over-the-counter painkillers, anti-inflammatory drugs, and muscle relaxants associated with a period of bed rest are enough to curb the acute phase. To prevent further acute pain, physical therapy and specific exercises may be recommended by the physician, along with the identification of poor postural habits and posture-correction exercises. However, in more severe cases where conservative treatment fails, further treatment may be necessary, such as injections with cortisone. Surgery is only a real necessity when a progressive loss of neurological function is experienced, leading, for instance, to bladder or bowel incontinence or limb paralysis. In cases of frequently recurrent acute pain, the person with a herniated disc chooses surgical intervention to decrease pain and improve quality of life.
The vast majority of people (more than 90%) treated for herniated disc experience improvement with pain and mobility. About 5% of people who have experienced a herniated disc will eventually have recurring pain, and another 5% will experience a herniated disc at another vertebral site.
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National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). 1 AMS Circle, Bethesda, MD 20892-3675. (301) 495-4484 or (877) 22-NIAMS; Fax: (301) 718-6366. firstname.lastname@example.org. <http://www.niams.nih.gov/>.