Cervical stenosis is caused by narrowing of the spinal canal in the neck, and the most common reason is age-related wear on the discs, bones, and ligaments of the cervical spine. About 5% of all adults have cervical stenosis, and that number climbs to nearly 9% in people over 70. While degeneration drives most cases, some people are born with a naturally narrow canal, and inflammatory diseases can contribute as well.
How Spinal Degeneration Narrows the Canal
The cervical spine carries the weight of your head and allows it to move in multiple directions. Over decades, this constant loading wears down the structures that keep the spinal canal open and spacious. The process typically begins with the intervertebral discs, the rubbery cushions between each vertebra. As these discs lose water content and height with age, the load distribution across the spine shifts. Vertebrae that once shared weight evenly now bear uneven stress, and the body responds by growing extra bone.
These bony growths, called bone spurs, form wherever stress concentrates. When the load balance of the cervical spine changes and isn’t restored, tissue remodels along the new stress planes: bone builds up in overloaded areas and gets reabsorbed where there’s less pressure. The spurs can grow along the front or back edge of the vertebrae or directly into the spinal canal and the small openings where nerves exit. As uneven loading accelerates, even more stress shifts to the small joints along the sides and back of the spine, which drives further spur formation in a self-reinforcing cycle.
Disc Herniation and Bulging
Each cervical disc has a tough outer ring surrounding a gel-like center. When the outer ring weakens, the inner material can push outward into the spinal canal or into the side openings where nerve roots pass through. This can happen suddenly from an injury or develop gradually as the outer fibers deteriorate over time.
Disc herniations come in several forms. In a protrusion, the inner material bulges but stays contained within the outer ring. In an extrusion, it breaks through the damaged outer fibers and enters the canal space. Sometimes a piece detaches entirely, forming a free fragment. Any of these can physically compress the spinal cord or a nerve root. Beyond the mechanical pressure, the displaced disc material also triggers a local inflammatory response that adds to nerve irritation.
Ligament Thickening
A flexible ligament runs along the back wall of the spinal canal, connecting the bony plates of each vertebra. In a healthy spine, this ligament is about 80% elastic fibers, which let it stretch during movement and then spring back without buckling into the canal. With age, the elastic fibers gradually break down and get replaced by stiffer collagen fibers. The ligament thickens, loses its elasticity, and can calcify or even partially turn to bone.
A healthy version of this ligament maintains a slight tension that prevents it from folding inward when you extend your neck. Once it thickens and stiffens, it loses that protective tension. During neck extension, the bulkier ligament protrudes into the spinal canal, compressing the spinal cord or nearby nerve segments from behind. This posterior compression often works in tandem with bone spurs or disc bulges pressing from the front, squeezing the cord from both directions.
Ossification of the Posterior Longitudinal Ligament
A separate ligament runs along the front wall of the spinal canal, directly behind the vertebral bodies. In some people, this ligament spontaneously converts into bone tissue over time, a condition known as OPLL. The cause isn’t fully understood, though genetic factors play a significant role. As the ligament ossifies, it forms a rigid bar of bone that progressively encroaches on the spinal canal from the front.
OPLL is most common in East Asian populations, with a prevalence of 2 to 4% in Japan compared to under 2% in non-Asian populations. A CT study of 1,500 patients in Japan found cervical OPLL in 8.3% of men and 3.4% of women. Because the ossification is progressive, people with early OPLL may have no symptoms for years before the canal narrows enough to cause problems.
Being Born With a Narrow Canal
Some people develop cervical stenosis not because their canal narrows over time, but because it was never wide enough to begin with. Congenital cervical stenosis is defined as a canal diameter under 10 millimeters at two or more vertebral levels, measured independently of any degenerative changes. For reference, a normal cervical canal measures roughly 14 to 23 millimeters across.
People with congenital narrowing often have no symptoms during their younger years. The problem is that they have almost no margin for error. Even mild age-related changes that wouldn’t bother someone with a normal-sized canal, like a small disc bulge or modest bone spur, can push the cord past its tolerance. This is why some people develop symptoms of spinal cord compression in their 30s or 40s while others with more dramatic degeneration on imaging remain symptom-free into their 70s. The prevalence of congenital cervical stenosis varies by race, which means some populations carry higher baseline risk.
Rheumatoid Arthritis and Inflammatory Disease
Rheumatoid arthritis primarily attacks the joints of the hands and feet, but the cervical spine is the third most common site of involvement. The upper neck is especially vulnerable. In RA, chronic inflammation of the joint lining creates an abnormal tissue called pannus, which erodes bone and weakens ligaments. At the junction between the first and second vertebrae, this erosion can loosen the ligaments that hold those bones in alignment, causing one vertebra to slip forward on the other.
This slippage, called subluxation, occurs in roughly 65% of RA patients with cervical involvement. In two-thirds of those cases, the pannus tissue around the peg-shaped bone of the second vertebra grows thicker than 3 millimeters, physically occupying space in the canal. In advanced cases, the combination of vertebral slippage, pannus growth, and bone erosion produces significant stenosis that can compress the spinal cord.
How Compression Affects Blood Flow
Cervical stenosis doesn’t just squeeze the spinal cord mechanically. As the cord gets compressed, its blood supply suffers too. The small blood vessels that feed the cord can become kinked or occluded, creating areas of reduced blood flow. Tiny clots may form and block supply to the most vulnerable regions of the cord, particularly the “watershed” zones where the territories of different blood vessels meet and overlap is minimal.
This ischemic component helps explain why some people with cervical stenosis deteriorate in a stepwise fashion rather than gradually, and why the degree of canal narrowing on imaging doesn’t always match the severity of symptoms. Two people with identical measurements on an MRI can have very different experiences depending on how well blood flow to the cord has been preserved.
Measuring the Narrowing
Cervical stenosis is generally defined as a canal diameter under 12 millimeters. Doctors also use a measurement called the Torg ratio, which compares the front-to-back width of the spinal canal to the width of the vertebral body on a lateral X-ray. A ratio of 0.80 or less supports a diagnosis of cervical stenosis. This ratio is particularly useful in athletes being evaluated after episodes of transient neurological symptoms, where a low value signals that the canal may be too narrow to safely absorb further impacts.
MRI provides the most detailed picture, showing not just bone but also disc bulges, ligament thickening, and any changes within the spinal cord itself. In many cases, imaging reveals multiple contributing factors at once: a disc bulge pressing from one direction, thickened ligaments pressing from another, and bone spurs encroaching from the sides. It’s this combination of causes, layered on top of whatever canal size you started with, that ultimately determines whether and when stenosis becomes symptomatic.