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The Influence of Spinal Stenosis on Cervical Spondylotic Myelopathy

Posted on: 10/23/2008
This study from Japan highlights a problem faced by many Japanese adults. It's called cervical spondylotic myelopathy (CSM). Cervical refers to the cervical spine or neck. Spondylotic means there is bone involvement. In this case, the vertebral bones with the opening for the spinal cord are the center of attention. Myelopathy tells us the spinal cord is affected.

Myelopathy can be caused by many different things. The most common is a narrowing of the spinal canal (opening for the spinal cord). Anything that causes this narrowing can put pressure on the spinal cord, resulting in neurologic deficits. This narrowing called spinal stenosis can occur as a result of bone spurs or thickening or hardening of the spinal ligament (posterior longitudinal ligament).

Tumors, infection, trauma, and age-related degenerative changes in the spine can also contribute to stenosis. With aging, the vertebral bodies compress and develop a lip around the edge. Even a small amount of collapse alters the position of the facet (spinal) joints.

At the same time, the intraforaminal space where the spinal nerve roots leave the spinal cord get compressed. Likewise, the discs between the vertebral bodies are under increased pressure. All of these factors together create the CSM condition.

But in the Japanese population, it appears that the major cause of CSM is a congenital decrease in the size of the spinal canal. This occurs without an equal decrease in the size of the spinal cord going through the canal. The condition is referred to as developmental stenosis since it is present at birth.

How does this problem affect patients? And what are the results after surgery to relieve pressure on the spinal cord? Those are the two questions posed by Japanese surgeons at the Nara Medical University in Kashihara, Japan. They performed a bilateral open-door laminoplasty on 194 adults with CSM.

An open-door laminoplasty refers to a single incision along the lamina bone of the vertebra with a partial incision on the other side. The lamina is the bridge of bone that connects the spinous process (bony projection out from the vertebra felt as a bump along the back of your spine) to the main body of the vertebra. The lamina is present on both sides of the spinous process.

The surgeon then swings one side of the bone open like a door and away from the spinal cord. Bilateral means the procedure was done on both sides of the vertebra. In this study, the surgeons used a modification of the open-door laminoplasty called the double-door laminoplasty. The surgeon removed the spinous process. The center of the lamina was split and opened like double doors. This technique enlarges the spinal canal more than a single open-door procedure.

After surgery, bedrest was advised for up to one week. A cervical collar was worn for up to two months. Everyone was followed for at least two years (some as long as 15 years). Results were measured using neck range-of-motion, Japanese Orthopedic Association (JOA) scores, and X-ray measurements of the spine. JOA scores provided a measure of function by examining ability to eat, walk, and maintain bladder control.

They compared results between two groups of CSM patients: with and without developmental stenosis. It turned out that half of the patients with CSM included in the study had developmental stenosis, so the groups were about equal in size. Stenosis was defined as a spinal canal diameter less than 14 mm in men and less than 13 mm in women.

Age, duration of symptoms, and recovery rates were the same for both groups. JOA scores measuring function before and after surgery were equal between the two groups. Neck motion was less in the group with developmental stenosis, but this didn't appear to affect the final outcome.

The authors conclude that the presence of developmental stenosis in adults with cervical spondylotic myelopathy (CSM) does not make a difference in results after surgery. In other words, the stenosis was not an important or influencing factor when doing a laminoplasty to treat this problem.

Hideki Shigematsu, MD, et al. Does Developmental Canal Stenosis Influence Surgical Results of Bilateral Open-Door Laminoplasty For Cervical Spondylotic Myelopathy? In Journal of Neurosurgery. October 2008. Vol. 9. No. 4. Pp. 358-362.

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