Seok Woo Kim, MD, PhD, et al. Is Cervical Lordosis Relevant in Laminoplasty? In The Spine Journal. August 2013. Vol. 13. No. 8. Pp. 914-921
Problems in the neck that can cause severe pain, numbness down the arms, and sometimes even paralysis are referred to as cervical myelopathy. Cervical myelopathy can be caused by several changes that occur over time. The first is ossification (hardening) of the ligament that goes down the back of the spine (posterior longitudinal ligament or PLL). Another is the herniation of several discs in the cervical spine (neck) with resultant spinal canal stenosis (narrowing caused by disc material pushing into the canal).
A successful treatment for this problem is laminoplasty surgery to take pressure off the spinal cord and stabilise the spine. In this study, surgeons from Korea examine the effect of doing a double-door laminoplasty in 58 patients diagnosed with cervical myelopathy. This type of surgery splits the spinous process down the middle and then opens them up like french doors, or two windows that open toward you. The spinous process is the bone along the back of the vertebra that you feel as a ‘bump’ down the spine.
The effect of this procedure is to allow the spinal cord to shift backwards or ‘move away’ from the front of the spine. Many people who have cervical myelopathy have a cervical spine that is too straight, referred to as kyphotic. The natural (normal) alignment of the bones in the neck is a slight backward (lordotic) curve.
With these other degenerative changes (disc herniation, ossification of the ligaments), the straighter-than-normal (kyphotic) cervical spine can put enough pressure on the spinal to cause cervical myelopathy. But not everyone has cervical kyphosis associated with symptomatic cervical myelopathy. Some patients have the more normal neck curve.
The question this group of researchers asked was whether or not this kyphotic alignment would compromise surgical results. There is less room for the spinal cord in the canal when the spine is so straight. The posterior shift made possible by the laminoplasty may place the already (posteriorly) shifted spinal cord too far back to achieve (and maintain) the positive benefit of the procedure.
They studied 58 patients with cervical myelopathy who were all treated with this double-door laminoplasty. Patients ranged in ages from 32 to 74 years old. X-rays were used to measure the amount of cervical spine curvature. The patients were divided into two groups: those with cervical lordosis (normal curvature) and those considered “nonlordotic” (abnormal curve).
Two methods of classification (Cobb angle and Toyama classification) made by radiographs were used to determine who was considered lordotic and who was nonlordotic. Comparing how cervical lordosis is measured was a second feature of this study. The patients with 10 to 15 degrees of lordosis were in the lordotic group. Angles less than 10 degrees were nonlordotic.
Anyone with more than 15 degrees of kyphosis was not included. Other tools used to measure outcomes included the Japanese Orthopaedic Association (JOA) score (for function), neck disability index (NDI), and visual analog scale (VAS) (for pain).
They found that the degree of lordosis or the method of measuring didn’t make any difference in results. In other words, preoperative cervical alignment was not a factor in how well patients maintained the benefits of the double-door laminoplasty procedure.
The authors noted that there are many different ways to perform a laminoplasty to decompress the spinal cord in the presence of cervical myelopathy. This posterior approach has more advantages than disadvantages when there are protruding discs at several levels. Likewise, this posterior laminectomy works well when there are bone spurs along the front of the vertebral bones or a stiff, tight ligament along the back of the vertebrae. With the posterior decompression, discs, spurs, and ligaments remain untouched.
In summary, cervical nonlordosis (the presence of kyphosis or reverse cervical curve) was once considered a reason to avoid the double-door laminoplasty. The results of this study suggest preoperative alignment may not be as important as some other factors. For now, it looks like laminoplasty can be done on patients with milder forms of cervical kyphosis.
Future studies are needed to confirm the findings of this study as well as look at other reasons why long-term results may not be maintained (such as age, number of levels involved, presence of ligamentous ossification).