Stenosis means "closing in" or "choking". Spinal stenosis describes a condition in which the nerves in the spinal canal are closed in, or compressed. The spinal canal is the hollow vertical hole formed by the bones of the spinal column. Anything that causes this bony hole to shrink can squeeze the nerves inside. This narrowing can irritate the nerve roots that branch out from the spinal cord, or it can squeeze and irritate the spinal cord itself. This may cause pain, numbness, or weakness, most often in the legs, feet and buttocks. As a result of many years of wear and tear on the parts of the spine, the tissues nearest the spinal cord sometimes press against the nerves. The actual narrowing of the spinal canal does not cause symptoms. Symptoms develop when the spinal cord or nerve roots are compressed. Spinal stenosis may affect the cervical, thoracic or lumbar spine. The most common area affected is the lumbar spine followed by the cervical spine. Although many people older than age 50 have some narrowing of the spinal canal, not all experience symptoms. This helps explain why lumbar spinal stenosis is a common cause of back problems in adults over 50 years old.
In the lumbar spine, the spinal canal usually has more than enough room for the spinal nerves. The canal is normally 17 to 18 millimeters around, slightly smaller than a penny. Spinal stenosis develops when the canal shrink to 12 millimeters or less. When the size drops below 10 millimeters, severe symptoms of lumbar spinal stenosis occur. There are many reasons why symptoms of spinal stenosis develop. Some of the more common reasons include congenital stenosis (being born with a small spinal canal), spinal degeneration, spinal instability and disc herniation.
Congenital stenosis happens when someone is born with a spinal canal that is narrower than normal. They may not feel problems early in life. However, having a narrow spinal canal puts them at risk for stenosis. Even a minor back injury can cause pressure against the spinal cord. People born with a narrow spinal canal often have problems later in life, because the canal tends to become narrower due to the effect of aging.
Degeneration is the most common cause of spinal stenosis. Wear and tear on the spine from again and from repeated stresses and strains can cause many problems in the lumbar spine. The intervertebral disc can begin to collapse and the space between each vertebrae shrinks. Because discs are 80% water, as you age, they dry out and the space shrinks. Bone spurs may form that stick into the spinal canal and reduce the space available to the spinal nerves. The ligaments that hold the vertebrae together may thicken and also push into the spinal canal. All of these conditions cause the spinal canal to narrow.
Spinal instability can cause spinal stenosis. Spinal instability means that the bones of the spine move more than they should. Instability in the lumbar spine can develop is the supporting ligaments have been stretched or torn from a severe back injury. People with diseases that loosen their connective tissues may also have spinal instability. What ever the cause, extra movement in the bones of the spine can lead to spinal stenosis.
When an interverebral disc in the low back herniates or ruptures, spinal stenosis can occur. Normally, the shock-absorbing disc is able to handle the downward pressure of gravity and the strain from daily activities. However, if the pressure on the disc is too strong, such as landing from a fall in a sitting position, the nucleus inside the disc may rupture through the outer annulus and squeeze out of the disc. This is called a disc herniation. If an intervertebral disc herniates straight backward, it can press against the nerves in the spinal canal, causing symptoms of spinal stenosis.
Other causes of lumbar spinal stenosis include facet joint hypertrophy, spondylolisthesis, Paget's disease and fluorosis. These ailments are not as common....
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