About Lumbar Spinal Stenosis > Understanding the Anatomy of Lumbar Spinal Stenosis

Understanding the Anatomy of Lumbar Spinal Stenosis

Lumbar spinal stenosis is the narrowing of the spinal canal, which leads to pain that radiates from the lower back into the buttocks and down the leg(s).

Often, back pain is the product of a muscle spasm or some other temporary problem. But, when the pain is caused by the age-related changes to the spine associated with degenerative lumbar spinal stenosis, it’s unlikely that significant improvement will occur as long as the underlying back anatomy is unchanged.¹

This section is intended to help you understand the following:

How lumbar spinal stenosis develops
Why lumbar spinal stenosis causes leg and back pain
Why lumbar spinal stenosis symptoms may not significantly improve without changes to the underlying anatomy¹

The Different Areas of the Spine

There are 5 different areas of the spine, which are named after the different classifications of vertebrae:

The cervical spine is in the neck (7 vertebrae).
The thoracic spine is in the upper back (12 vertebrae).
The lumbar spine is in the lower back (5 vertebrae). About 75% of spinal stenosis occurs in the lumbar region of the back.
The sacral spine is near the base of the spine (5 vertebrae), just below the lumbar spine. These vertebrae are normally fused together to form the saccrum.
The coccyx—or tailbone—is comprised of 4 vertebrae that are fused together.

Figure 1: L5 Lateral

Figure 2: L5 Posterior

The Elements of the Spine

Even the slightest movement of the back involves the interplay of the following:

Vertebra and lamina, which both provide structural support and protection
Vertebral discs, which provide cushioning between the bones
Ligaments, which provide flexibility
Spinal cord, which is made up of nerves

How the Elements of the Spine Work Together

The spinal cord relays messages between the body and the brain. Together, the spinal cord and the brain make up the body's central nervous system.

Spinal Cord, Vertebrae, and Laminas

The spinal cord lies within the spinal canal, which is surrounded and protected by vertebrae—the bones that make up the spine. The spinal cord is also protected by the lamina. For each vertebra, two laminas connect to form the roof of your spinal canal.

How lumbar spinal stenosis develops: When the spinal canal becomes narrowed, the result can be pinched nerves and pain.

Vertebral Discs

Vertebrae are separated from each other by vertebral discs. These discs act like cushions between the vertebrae and allow the spine to move more freely.

Discs have a more solid outer surface, but their inner portion is gel-like. As we age, the wear and tear on the discs causes them to dehydrate and become stiffer. This can cause the discs to herniate, meaning the disc swells, bulges, or ruptures.

How lumbar spinal stenosis develops: If discs herniate, disc material can intrude into the spinal canal, causing pinched nerves and pain.

Spinous Processes

From the back of the vertebrae, small projections of bone called spinous processes enable the muscles and ligaments to attach to the spine.

The spinous processes are often removed with the lamina during a laminectomy. New advances in treating the symptoms of lumbar spinal stenosis, such as interspinous spacers, preserve and work with your anatomy to create space for the nerves.

Ligaments

Vertebrae are connected to each other by muscle and ligaments, which are bands of tissue.

Changes can occur with aging, especially to the ligamentum flavum.

How lumbar spinal stenosis develops: This ligamentum flavum can become thickened and take up more space in the spinal canal. Or, as deteriorating discs lose some of their height, this ligament can buckle to some extent and lead to pinched nerves.

Nerve Roots and Foramina

On each side of the vertebrae, there are nerve roots that branch out from the spinal cord. The nerve roots exit the spine through small openings in the vertebrae called foramina. The nerves extend out to all parts of the body, carrying messages from the brain.

How lumbar spinal stenosis develops: As the disc degenerates, loss of height can narrow the foramen, causing pinched nerves. Small growths of bone (osteophtye), disc, or ligament can also narrow the foramina and pinch the nerves, which results in pain.

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References:

Sheehan JM, Shaffrey CI, Jane JA Sr. Degenerative lumbar stenosis: the neurosurgical perspective. Clin Orthop Relat Res 2001 (384) p. 61-74.