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Lumbar Spinal Stenosis

by David Borenstein, MD

In a previous article on low back pain, I reviewed the anatomy of the spine and discussed three causes of low back pain: muscle strain, herniated intervertebral disk with sciatica, and osteoarthritis (OA) of the joints connecting the vertebrae. In that article, I discussed how people begin to be affected by muscle strain in their 20’s, by disk herniation in their 30’s and 40’s, and by OA of the lower (lumbar) spine in their 50’s. Here I will examine a disorder that mainly affects people in their 60’s and older: lumbar spinal stenosis.

The spine

First, let’s review what you learned about the spine in my previous article. The spine has five parts: the cervical spine, the thoracic spine, the lumbar spine, the sacrum, and the coccyx. The cervical spine attaches to the base of the skull and is in the neck and upper back, the thoracic spine is in the middle back, and the lumbar spine is in the lower back. The sacrum and coccyx sit below the lumbar spine.

The three main sections of the spine (cervical, thoracic, and lumbar) are made up of bones called vertebrae that sit one on top of another. Each vertebra is separated from its neighboring vertebrae by gel-filled disks called intervertebral disks, which act as shock absorbers for the spine. The back portion of each vertebra is shaped like an arch, and these arches form a vertical column known as the spinal canal. The spinal cord — the bundle of nerves that transport messages and bring sensation to all parts of the body — runs down this canal from the brain to the highest vertebra of the lumbar spine. Through the whole length of the spinal cord, smaller nerves branch off and exit the spinal canal from openings in the vertebrae known as neural foramina. At the highest lumbar vertebra, the spinal cord itself branches out into smaller nerves, which exit the spine through the neural foramina of the lumbar spine.

What is spinal stenosis?

Spinal stenosis refers to narrowing in the spinal canal or neural foramina that puts pressure on the nerves within. As people age, the intervertebral disks get thinner, the vertebral arches grow bone spurs (known as osteophytes), and the neural foramina lose height. All of these changes can put pressure on the spinal nerves, either in the center of the spinal canal, on the sides of the spinal canal (known as the lateral canal), or in the neural foramina. (See an illustration of vertebrae with and without stenosis.) Although stenosis can occur in any part of the spine, it is common in the lumbar spine.

When a spinal nerve is compressed, blood flow to the nerve — and therefore the nerve’s supply of oxygen — is cut off. Without oxygen, the nerve loses its ability to function. A loss of nerve function can result in pain, numbness, or weakness in the areas of the body that the affected nerve supplies. For example, if a nerve in the lower back that supplies sensation to the left foot is constricted, the result may be pain and numbness in the left foot. Reestablishing blood flow to the compressed nerve can quickly restore function and is the goal of therapy for lumbar spinal stenosis.

Who gets it?

According to the most recent data from the United States Census Bureau, the baby boom generation (those born from 1946 to 1964) includes 78.2 million people, or about a quarter of the total US population. Studies of x-rays have shown that up to one-fourth of people older than 40 have significant narrowing in the lumbar spine. From this data, we can calculate that in 20 years, almost 20 million Americans will have or be at risk for lumbar spinal stenosis.

Symptoms of spinal stenosis

Lumbar spinal stenosis can cause pain in any combination of locations from the low back to the feet, including the buttocks, thighs, and lower legs. Pain in the legs may be accompanied by numbness, tingling, and weakness. Even though lumbar spinal stenosis occurs in the lower back, the condition does not always cause back pain.

In people with spinal stenosis, certain physical activities cause more symptoms because of the effect these activities have on the amount of space in the spinal canal. Bending backwards, for example, tends to decrease the space in the spinal canal and neural foramina. Bending forward tends to increase the space in the canal. People with spinal stenosis may enjoy going to the grocery store, where they can walk while bending over the shopping cart.

The symptoms of spinal stenosis may depend on the location of the narrowing. Stenosis that affects the center of the spinal canal may compress more than one spinal nerve, and symptoms may occur in one or both legs. Narrowing in the side (lateral) portion of the canal tends to affect a single nerve and therefore only one leg. Stenosis in the neural foramina causes the most persistent leg pain, which may not be relieved by a change in position.

Last Reviewed on July 27, 2011

David Borenstein is a rheumatologist and Clinical Professor of Medicine at The George Washington University Medical Center in Washington, DC. Over the course of his 32-year career, his major medical interest has been the evaluation and treatment of spinal disorders.

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