Homeostatic Imbalances of the Spinal Cord: Spinal Stenosis

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.

Spinal stenosis usually develops slowly over a long period of time. This is because the main cause of spinal stenosis is spinal degeneration in later life. Symptoms rarely develop quickly when degeneration is the source of the problem. A severe injury or a herniated disc may cause symptoms to develop immediately. People with stenosis don't always feel back pain. Primarily, they have pain and weakness in their legs, usually in both legs at the some time. Some people say they feel that their legs are going to give out on them. Symptoms mainly affect sensation in the lower limbs. Nerve pressure from stenosis can cause a feeling of pins and needles in the skin where the spinal nerves travel. Reflexes become slowed. Some people report "charley horses" in their leg muscles. Others report strange sensation like water trickling down their legs. Symptoms change with the position of the low back. Flexion, or bending forward, widens the spinal canal and usually eases symptoms. That's why people with stenosis tend to get relief when they sit down or curl up to sleep. Activities such as reaching up, standing and walking require the spine to straighten or even extend (bend back slightly). This position of the low back makes the spinal canal smaller and often worsens symptoms. In cases of severe spinal stenosis, some people even lose bladder and bowel control.

Diagnosis begins with a complete history and physical examination. The doctor usually asks questions about symptoms and how the problem is affecting the daily the activities of the patient. This will also include question about pain and feelings of numbness or weakness in the legs. The doctor will want to know whether the symptoms are worse when standing up or walking and if they go away when sitting down. During the physical examination, the doctor will test to see which back movements cause pain or other symptoms. Skin sensation, muscle strength and reflexes are also tested. X-rays can show if the problems are from changes in the bones of the spine. The images can show if degeneration has caused the space between the vertebrae to collapse. X-rays may also show any bone spurs sticking into the spinal canal.

When more information is needed, the doctor may order a magnetic resonance imaging (MRI) scan. The MRI machine uses magnetic waves rather than x-rays to show the soft tissues of the body. This test gives a clear picture of the spinal canal and whether the nerves inside are being compressed. This machine creates pictures that look like slices of the area the doctor is interested in. The test does not require dye or a needle. Also, the computed tomography (CT) scan may be ordered. The CT scan is a detailed x-ray that lets the doctor see slices of bone tissue. The image can show any bone spurs that may be sticking into the