See why changes to the disc cause painful symptoms.

Lumbar spinal stenosis (LSS) is a narrowing of the spinal canal that occurs in the lower part of the spine (lumbar region).

The problem with a narrowed spinal canal is that it reduces the space allowed for nerves to exit from the spinal canal. When a nerve in the lower back becomes pinched, it can cause pain, tingling, weakness, or numbness that radiates from the lower back into the buttocks and legs.

There are two types of LSS, degenerative (age related) and congenital (present at birth). Degenerative LSS develops slowly and usually affects people in their 50s or 60s. Symptoms generally occur over several years and gradually get worse. However, individual symptoms and symptom severity vary from person to person.

What causes LSS?

In a healthy spine, there is sufficient space for nerves to exit from the spinal canal and travel to the rest of the body. Aging and everyday wear and tear on the lower spine can cause a number of changes that narrow the spinal canal area—resulting in a pinched nerve.

Changes to the discs

Discs are elastic pads of cartilage located between the vertebrae. Healthy discs cushion the bones and act as shock absorbers. Aging can cause the disc to dry out, wear down, or thin. An injury can cause the disc to become swollen and protrude between the vertebrae and into the spinal canal. These changes to the shape and structure of the disc can narrow the spinal canal.

A worn-out disc can also cause one vertebra to slide over the one below it. This condition, called spondylolisthesis, can also narrow the spinal canal.

Changes to the bone structure

Loss of cartilage between joints in the spine and other changes can cause bony projections to form along the joints. These bony formations, called osteophytes or bone spurs, can grow into—and narrow—the spinal canal area.

Changes to the ligamentum flavum

A large, long elastic band of soft tissue, called the ligamentum flavum, runs along the inside of the spinal canal. It connects the vertebrae to one another and helps provide spinal stability. Aging can cause the ligament to lose elasticity and become coarse and thicken. These changes can cause the ligament to take up more space in the spinal canal—reducing the room available for the spinal cord or spinal nerves.

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