We have all seen the little old man who walks slowly, leaning forward on a cane or a walker. Frequently, that is a sign of stenosis. Stenosis means narrowing. People can have stenotic coronary arteries, for which they receive stents or by-passes in order to increase blood flow to the heart and prevent heart attacks. What we are talking about here is different. It is stenosis (narrowing) of the canals through which the nerves in your lower back pass.
There are two main type of stenosis, central and foraminal. Central stenosis is the narrowing of the central spinal canal. This is usually caused by a combination of arthritis, increased thickness of ligaments, and bulging discs. Most commonly it is found in older men, who are more likely to have those conditions. Women can also have stenosis, as can young people, especially if they are cursed by inheriting short spinal pedicles. With short pedicles, the spinal canal is narrow to begin with, and it is easy to narrow it further with arthritis, thickened ligaments, and/or bulging discs.
Foraminal stenosis is the narrowing of the canal in which the major nerve roots leave the spinal cord and go to the peripheral nervous system. It is usually caused by the same things that cause central stenosis.
Now, the reason the old man walks bent forward is this: that opens the space in his spine between the vertebrae, taking pressure off the spinal card and/or peripheral nerve roots, relieving his pain. If you remember the little guy Arty Johnson played on Laugh-in, with the white hair and mustache and leaning on the cane, you'll have an idea of what stenosis looks like. If you picture him, you can make the diagnosis, too.