When learning about spinal stenosis, it is helpful to have a clear visual of spinal anatomy and how spinal stenosis develops.
The vertebral column in the spine and sacrum (at the bottom of the spine) are like a stack of bony blocks that serve to support the body.
Each of these bones has additional bony attachments that serve to help stabilize the spine and to protect the spinal cord or nerves passing downward from the brain to organs, muscles, and sensory structures of the body. Each vertebral body and its attachments and the disc between the adjacent vertebrae are known as a spinal segment.
The entire length of the spinal column has a large central canal or passage (the bone channel described above) through which the spinal cord descends, and holes to each side of the canal to allow emergence of spinal nerves at each level. These holes are call the neuro-foramen.
How Spinal Stenosis Affects the Spine
Normally, there is ample space for spinal canal and for the nerve roots as they exit the spine through the neuro-foramen. With spinal stenosis, however, development of bony growths from osteoarthritis and/or other degenerative changes constrict the space for the spinal cord and/or spinal nerves.
The spinal cord stops at the upper part of the low back, usually at about the T12-L1 level. Individual nerves then extend off the end of the spinal cord and travel down the central canal, and exit the spinal canal through those neuro-foramen. The spinal cord and the individual nerves in the spinal canal move within a fluid-filled sac. It is like the spinal cord and the nerves are encased in a garden hose. In this manner, the spinal cord and the nerves can bend along with the spine, and still be protected within that garden hose. The strong outer membrane that encases the cord and the nerve is called the dura (tough) mater (mother).
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The area where the nerves extend off the spinal cord is called the cauda equina, as it looks like a horses tail. While rare, it is possible for lumbar spinal stenosis affect the cauda equina and cause a condition known as cauda equina syndrome. This is a serious medical condition requiring immediate medical attention.