Degenerative disc disease
Synonyms and keywords: Intervertebral disc herniation; intervertebral disc prolapse; slipped disc; degenerative disc disease

# Overview
Degeneration of the intervertebral disc, which is often called "degenerative disc disease" (DDD) of the spine, is a common disorder of the lower spine and for some people can cause low back pain and/or leg pain (sciatica). Disc degeneration can also lead to disorders such as spinal stenosis (narrowing of the spinal canal that houses the spinal cord and nerve roots; can be lumbar or cervical), spondylolisthesis (forward slippage of the disc and vertebra), and retrolisthesis (backward slippage of the disc and vertebra), and osteoarthritis (when bone spurs grow adjacent to the discs and pinch or put pressure on the nearby nerve roots or spinal canal).
DDD is in fact not a disease but, rather, a degenerative condition that can be painful and can greatly affect the quality of one's life. While disc degeneration is a normal part of aging and for most people is not a problem, for certain individuals a degenerated disc can cause pain.

# Pathophysiology

## Understanding disc pain
It is not clear why some degenerative discs are painful and some are not. After an injury, some discs become painful because of inflammation. Some people have nerve endings that penetrate more deeply into the annulus fibrosus, or outer layer of the disc, than others, making the disc more susceptible to becoming a source of pain. Pain that radiates down the leg, known as sciatica, can be the result of the nerve root encountering the inner disc material, the nucleus pulposus, an inflammatory substance that also puts pressure on the nerve. Some believe the healing process involved in the repair of trauma to the outer annulous results in the innervation of the resultant scar tissue, and subsequent pain in the disc, as these nerves become inflamed by nucleous pulposus material. Annular tearing can cause the leakage of inflammatory proteins produced in the degenerative nucleous onto adjacent nerve root tissue. These conditions can cause symptoms such as severe leg pain, difficulty standing and walking, and weakness or numbness in the legs. Degenerative disc disease can lead to a chronic debilitating condition and can have a serious negative impact on a person's quality of life. When pain from degenerative disc disease is severe, traditional nonoperative treatment is often ineffective.

# Causes
Aging is the most common cause of disc degeneration. As the body ages, the discs in the spine dehydrate, or dry out, and lose their ability to act as shock absorbers between the vertebrae. The bones and ligaments that make up the spine also become less flexible and thicken. Unlike muscles, there is minimal blood supply to the discs so they lack the ability to heal or repair themselves. Repetitive stress injury (RSI) and/or several injuries over time that involve the same disc can also increase the likelihood of disc degeneration as may a poor body mass index. However, an active lifestyle that combines regular light exercise and a good diet can help to repair or prolong the life of the disc.

# History and Symptoms
With symptomatic degenerative disc disease, chronic low back pain sometimes radiates to the hips, or there is an aching pain in the buttocks or thighs while walking; sporadic tingling or weakness through the knees may also be evident. Similar pain may be felt or may increase while sitting, bending, lifting, and twisting. While the degeneration of the disc will likely progress as a natural part of the aging process, symptoms such as low back pain often decrease over time.

# Treatment options
Often, degenerative disc disease can be successfully treated without surgery. One or a combination of treatments such as Physical therapy, osteopathy, anti-inflammatory medications such as nonsteroidal anti-inflammatory drugs, chiropractic treatments, or spinal injections often provide adequate relief of these troubling symptoms.
Surgery may be recommended if the conservative treatment options do not provide relief within 2 to 3 months. If leg or back pain limits normal activity, if there is weakness or numbness in the legs, if it is difficult to walk or stand, or if medication or physical therapy are ineffective, surgery may be necessary, most often spinal fusion. There are many surgical options for the treatment of degenerative disc disease.  The most common surgical treatmets include:
Anterior Cervical Discectomy and Fusion: A procedure that reaches the cervical spine (neck) through a small incision in the front of the neck. The intervertebral disc is removed and replaced with a small plug of bone or other graft substitute, and in time, that will fuse the vertebrae.
Cervical Corpectomy: A procedure that removes a portion of the vertebra and adjacent intervertebral discs to allow for decompression of the cervical spinal cord and spinal nerves. A bone graft, and in some cases a metal plate and screws, is used to stabilize the spine.
Facetectomy: A procedure that removes a part of the facet (a bony structure in the spinal canal) to increase the space.
Foraminotomy: A procedure that enlarges the foramen (the area where the nerve roots exit the spinal canal) to increase the size of the nerve pathway. This surgery can be done alone or with a laminotomy.
Laminoplasty: A procedure that reaches the cervical spine (neck) from the back of the neck. The spinal canal is then reconstructed to make more room for the spinal cord.
Laminotomy: A procedure that removes only a small portion of the lamina (a part of the vertebra) to relieve pressure on the nerve roots.
Micro-discectomy: A procedure that removes a disc through a very small incision using a microscope.
Spinal Laminectomy: A procedure for treating spinal stenosis by relieving pressure on the spinal cord. A part of the lamina (a part of the vertebra) is removed or trimmed to widen the spinal canal and create more space for the spinal nerves.
New treatments are emerging that are still in the beginning clinical trial phases. Glucosamine injections are thought to offer some pain relief for degenerative discs at best, and at worst, do nothing while also not affecting more aggressive treatment options. Artificial disc replacement is viewed cautiously as a possible alternative to fusion in carefully selected patients. Adult stem cell therapies for disc regeneration are in their infancy. Mesechymal stem cell therapy trials for knife-less fusion of vertebrae are now beginning in the US as well. Gene therapy, growth factor injections, and a variety of stabilization devices are also on the horizon.

# Related Chapters
- Spinal disc herniation
- Low back pain
- Sciatica
- Spinal stenosis