Stenosis means narrowing, often discussed in terms of cholesterol build-up narrowing an artery. The spinal canal can also become stenotic. Some people have thick bone structure so their spinal canals are narrower than normal. In some others, with aging and arthritic changes in the spine, and/or if a vertebrae slips forward on another, stenosis develops.
In addition, the ligaments along the inside of the spinal column, called ligamenta flava, thicken with age and narrow the canal. The stenosis can usually be tolerated until standing causes such increased stenosis that walking irritates the spinal nerves, causing leg weakness and numbness (see SINC).
If the spine isn’t unstable, stenosis can be treated with microsurgery to remove some non-weight bearing bone (lamina) and ligamentum flavum with good success. If the vertebra move too much when standing, a minimally invasive fusion operation could be done at the same time.