Degenerative disc disease (DDD) is part of the natural process of growing older. Unfortunately, as we age, our intervertebral discs lose their flexibility, elasticity, and shock absorbing characteristics. The fibrous outer portion of the disc, called the annulus fibrosis, becomes brittle and is more prone to tearing. At the same time, the soft gel-like center of the disc, called the nucleus pulposus, starts to dry out and shrink. The combination of damage to the intervertebral discs, the development of bone spurs, and a gradual thickening of the ligaments that support the spine can all contribute to degenerative arthritis of the spine.
Degenerative disc disease is as certain as death and taxes, and to a certain degree this process happens to everyone. However, not everyone who has degenerative changes in their spine has pain. Many people who have "normal" backs have MRI examinations that show disc herniations, degenerative changes, and narrowed spinal canals. Every individual is different, and it is important to realize that not everyone with degenerative changes as seen on an MRI and x-ray films develops symptoms, and not everyone who develops symptoms does so as a result of degenerative disc disease.
When degenerative disc disease becomes painful or symptomatic, it can cause several different symptoms, including pain and weakness that results from compression of the nerve roots. These symptoms result because worn out discs are a source of pain since they do not function as well as they once did, and as they shrink, the space available for the nerve roots also shrinks. As the discs between the vertebrae start to wear out, the entire spine becomes less flexible. As a result, people complain of pain and stiffness, especially towards the end of the day.
Furthermore, the less flexible degenerative spine is more susceptible to injuries. When a degenerative spine is subject to loads that it can no longer handle, the disc can tear; bulge or extrude (herniated) through a tear (resulting in nerve root compression and pain, numbness, tingling and/or weakness); and/or irritate nerve roots, which become swollen and inflamed (also resulting in leg symptoms).
Herniated Disc
Herniation describes an abnormality of the intervertebral disc that is also known as a "slipped," "ruptured," or "torn" disc. This process occurs when the inner core of the intervertebral disc (nucleus pulposus) bulges out through the outer layer of ligaments that surround the disc (annulus fibrosis). This tear in the annulus fibrosis causes pain at the point of herniation. If the protruding disc presses on a spinal nerve, the pain may spread to the area of the body that is served by that nerve. Between each vertebra in the spine are a pair of spinal nerve roots, which branch off from the spinal cord to a specific area in the body. Any part of the skin that can experience hot and cold, pain or touch refers that sensation to the brain through one of these nerves. In turn, pressure on a spinal nerve from a herniated disc will cause pain in the part of the body that is served by that nerve.
Most disc ruptures will occur when a person is in his or her 30s or 40s when the nucleus pulposus is still a gelatin-like substance. Oddly enough, most disc herniations will occur in the morning. The causes of this phenomenon are not entirely known, but are probably due to the physiology of the spine and the changes in the water content of the disc that occur throughout the day.
Herniated Disc
Spondylolisthesis
Spondylolisthesis occurs when one vertebra slips forward on the adjacent vertebrae. This will produce both a gradual deformity of the lower spine and also a narrowing of the vertebral canal. Pain is the primary symptom associated with spondylolisthesis.
Spondylolisthesis
Stenosis
Spinal stenosis involves a gradual narrowing of the spinal canal. This narrowing happens as a result of the degeneration of both the facet joints and the intervertebral discs. In this condition, bone spurs, called osteophytes, which develop because of the excessive load on the intervertebral disc, grow into the spinal canal. The facet joints also enlarge, as they become arthritic, which contributes to a decrease in the space available for the nerve roots. The ligaments of the spinal column, especially the ligamentum flavum, become stiff, less flexible, and thicker with age, which also contributes to spinal stenosis. These processes narrow the spinal canal and may begin to impinge and put pressure on the nerve root and spinal cord, creating the symptoms of spinal stenosis.
Stenosis may occur in the central spinal canal (central stenosis) where the spinal cord or cauda equina are located, in the tract just before the nerve root exits the central canal (lateral recess stenosis) or in the lateral foramen (foraminal stenosis) where the individual nerve roots exit the spine.
Some distortion of the spinal canal will occur in virtually every person as they age, but the severity of the symptoms will depend on the size of a person's spinal canal and encroachment on the neural elements. The rate of deterioration varies greatly from person to person, and not everyone will feel symptoms.
Spinal stenosis may be caused by a number of processes that decrease the amount of space in the spinal canal available for the neural elements. Degenerative causes are the most common, but there are a few unusual causes of stenosis. These include calcium pyrophosphate crystal deposition, amyloid deposition, and intradural spinal tumors. Why stenosis causes weakness and pain is the subject of a significant amount of debate and medical research. Pain, which is a common symptom of spinal stenosis, may be associated with the compression of the micro-vascular structures carrying blood flow to the nerve roots. At the same time, the symptoms of spinal stenosis may be the direct result of physical compression of the nerve roots. Each of these processes may interfere with the normal function of the nerve roots and decrease the effectiveness and endurance of the spinal nerves.
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