About 10% of people experience symptoms from a herniated disk at some point in their lives. Autopsy studies reveal, however, that most people actually had a herniated disk during their lifetime but never experienced any symptoms.
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, so that it becomes progressively drier. These changes make the disk susceptible to herniation (protrusion), in which mild trauma such as lifting an object or even sneezing causes the center of the disk to bulge through the weakened outer layer.
Symptoms of a Herniated Disk
Symptoms usually occur when the protruding disk presses on one or more of the spinal nerves emerging from the spinal column. In some people, the disk 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, disk fragments may break free, a condition referred to as sequestration. Although any disk can herniate, about 90 to 95% of cases occur in the two lowest disks, which bear the greatest weight.
When a disk herniates, both the site and extent of the rupture determine the location and severity of the symptoms. For example, a herniated lumbar disk may cause pain, numbness, or weakness in one leg (sciatica). However, a herniated cervical disk may produce similar symptoms in one arm or hand (less commonly, both sides can be affected).
In general, a spasm of the back muscles plus difficulty walking or standing straight indicate a herniated disk; the spasm creates a recognizable leaning to one side in about half of those affected.
Pain due to a herniated disk usually strikes suddenly. The person may “feel something snap” before the pain begins—and the pain may start as a mild tingling or a “pins and needles” sensation before increasing in severity.
If the herniated disk compresses the sciatic nerve, 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 disk is the most common cause of sciatica.
If a ruptured disk compresses nerves in the neck, pain may radiate down the arms and be accompanied by weakness and numbness in the arms and hands.