What Causes a Herniated Disc?

About 10 percent of people experience symptoms from a herniated disc at some point in their lives. Autopsy studies reveal, however, that most people actually have a herniated disc but never experienced any symptoms.

Over the years, the demand of supporting the body’s weight causes the outer layer of the disc to weaken, become thinner and develop microscopic tears. At the same time, the center of the disc slowly loses its water content and it becomes progressively drier.

These changes make the disc susceptible to herniation (protrusion), in which mild trauma from lifting an object or even sneezing causes the center of the disc to bulge through the weakened outer layer.

Symptoms usually occur when the protruding disc presses on one or more of the spinal nerves emerging from the spinal column. In some people, the disc presses on the spinal cord itself or on the cauda equina. This causes pain not only in the back, but also in the part of the body served by the compressed and inflamed nerve.

In some cases, disc fragments may break free, a condition referred to as sequestration. Although any disc can herniate, about 90 to 95 percent of cases occur in the two lowest discs, which bear the greatest weight.

When a disc herniates, both the site and extent of the rupture determine the location and severity of the symptoms. For example, a herniated lumbar disc may cause pain, numbness, or weakness in one leg (sciatica). A herniated cervical disc may produce similar symptoms in one arm or hand (less commonly on both sides).

Pain due to a herniated disc usually strikes suddenly. The person may “feel something snap” before the pain begins. The pain may start as a mild tingling or a “pins and needles” sensation before increasing in severity.

If the herniated disc compresses a lumbar nerve root, pain later radiates into a specific area of one leg. A decrease in back pain may be accompanied by increasingly severe pain, numbness and weakness in one leg, along with changes in reflexes.

In fact, a herniated lumbar disc is the most common cause of sciatica. If a ruptured disc compresses nerves in the neck, pain may radiate down the arms and be accompanied by weakness and numbness in the arms and hands.