A herniated disc – also known as a slipped, bulging, protruding or ruptured disc – occurs when the cartilage (tough, elastic, fibrous connective tissue) of an intervertebral disc bulges out and in many cases compresses a spinal nerve root. This can result in pain that ranges from mild to severe in intensity.

The severity of pain does not necessarily correspond to the extent of damage to the disc. A large amount of damage sometimes will cause little pain, whereas a small amount of damage may cause excruciating pain.

The back is made up of a network of bones, ligaments, muscles and nerves that work together to balance and bear the weight of the body. The spine (vertebral column) is made up of 33 bones (vertebrae), some of them fused, held together by zygapophysial (facet) joints and by fibrous bands (ligaments). There are seven cervical vertebrae in the neck and 12 thoracic vertebrae in the middle of the back. The five large lumbar vertebrae of the lower back carry most of the body’s weight. Below the lumbar vertebrae in the pelvis are the wedge-like sacrum, made from five fused vertebrae, and the coccyx (tailbone).

The spine supports the weight of the head and houses and protects the spinal cord. The spinal cord is part of the central nervous system and extends from the base of the skull to the lower back. Two nerves extend out at each vertebral level. There are 31 pairs of these spinal nerves in the back and neck. In the part of the back where the spinal cord ends, a group of nerves (the cauda equina) continue down the spinal canal.

Most vertebrae are separated by an intervertebral disc, which acts like a “shock absorber” that prevents the vertebrae from hitting each other during activities such as walking, running or jumping. Each disc is made up of an outer ring of tough, fibrous tissue (annulus fibrosus) that has a jelly–like substance in the center (nucleus pulposus). The interior of each intervertebral disc is mostly composed of water (80 percent) and has no blood supply of its own. The nucleus pulposus hardens with age, beginning in a person’s 30s.

Muscles extend up and down the back to support the spine, contracting or relaxing to help a person stand, twist, bend or stretch. Tendons connect muscles to bones. The muscles of the abdomen and trunk also support, protect and move the spine.

Intervertebral discs are under constant pressure. Herniated discs may result from injury or disc degeneration due to aging or disease, such as degenerative disc disease or spondylosis (spinal osteoarthritis).

Herniated discs occur most often in the lower (lumbar) vertebrae. This a common cause of sciatica, in which the sciatic nerve serving the leg is compressed, often causing tingling, numbness, pain or weakness (paresthesia) down the leg and into the foot. The second most common site of herniated discs, the cervical (neck) area, can cause paresthesia in the shoulder and arm. Both of these complications are examples of a pinched nerve.

In some cases, cartilage that is pushed into the spinal canal may compress the bundle of lumbar and sacral nerve roots at the end of the cauda equina. This condition, cauda equina syndrome, demands immediate medical attention. Left untreated, cauda equina syndrome can cause permanent neurological damage.

Herniated discs are most likely to affect people in their 30s to 50s, as the discs become flatter and begin to dry out with age. In some cases, the pain caused by a herniated disc can make it difficult to perform routine tasks, such as sitting, standing, working or playing.

There are several options for treating this pain, ranging from medications to surgery. In most cases, the portion of a herniated disc that protrudes and pressures the nerve tends to shrink within six months to a year after injury, relieving symptoms.