What anatomical change is primarily responsible for causing lumbar stenosis?

Lumbar stenosis primarily occurs due to the narrowing of the spinal canal in the lower back, which can lead to compression of the spinal nerves. This narrowing is most commonly caused by the enlargement or thickening of the ligamentum flavum, a ligament that runs along the back of the spinal canal. When this ligament becomes enlarged, it encroaches upon the space in the canal, effectively pressing on the nerves that travel through the area.

This anatomical change, specifically the enlarged ligament, can be a result of age-related degeneration, arthritis, or other factors that increase the size of the ligament. As a result, it often leads to symptoms such as pain, numbness, or weakness in the legs and lower back due to nerve compression.

While degeneration of discs and muscle spasms can contribute to back pain, they are not the primary anatomical changes that cause lumbar stenosis. Similarly, inflammation of the spinal cord itself relates more to other conditions such as myelitis rather than lumbar stenosis specifically.