Cervical spinal stenosis(CSS) is a common degenerative disorder, with the aging of the population getting worse its incidence is also increasing year by year. Cervical spondylotic myelopathy (CSM) is also a common disease in older people, which is characterized by numbness, limb weakness, walking difficulties, and serious paralysis. CSS may predispose patients to CSM or myelopathy, which bring a serious burden to the family and community[22-24].
Although several research groups have studied the relationship between the radiologic parameters and clinical manifestations or outcomes, radiological findings still can not be used as a predictive factor in clinical severity or decide on treatment options[4, 5, 10, 12, 25]. At the beginning, most of the research on CCS focused on the X-ray and CT without considering the epidural fat between the dural sac and the bony spinal canal[4-6] [26, 27]. After entering the 21th century with the rise of MRI technology, the assessment of CSS resumed in various studies. Laurencin et al contrasted the interobserver agreement among the qualitative evaluation of cervical spinal stenosis on CT myelograms and MR images. It showed MRI fared slightly better than CT myelograms with regard to level of stenosis. But it didn’t come up with a specific grading system only with a degree (none, mild, moderate, or severe), and the observed kappa values were 0.31 and 0.22 respectively. The fair agreement also indicated the importance of a unified and specific standard that can be accepted and used in practical application. The Mentioned previously grading system of Claus Muhle et al was based on the occlusion of the subarachnoid space around the spinal cord and Spinal compression or displacement at maximum flexion and extension. This classification indicated that cervical spinal motion may contribute to the development of cervical spondylotic myelopathy but had no use to the diagnosis of CCS. Yusuhn Kang et al classified CCS into 4 grades according to the T2-weighted sagittal images considering subarachnoid space, spinal compression and the change of the spinal cord signal. However, although there are many scholars had assessed the cervical stenosis based on sagittal MRI, but they did not further verify if there were the differences between their grading systems, and the guiding function to clinical diagnosis and treatment. In addition to there is no consensus and universally adopted scheme of classification between radiologists and clinicians. This will hinder the communication between doctors, as well as further research on CCS. Therefore, it is still necessary to continue to explore a more practical and reliable grading system.
We applied our CCS grading system for T2-weighted axial images, decided by Cerebrospinal fluid(CSF) space, spine cord form and the character of the protrusion. We assumed that the remaining CSF space of the dural sac and the character of the protrusion were an important factor in predicting the development of the CCS, and the spine cord form was the key to determine the patient's current treatment strategy.
We have repeatedly explored how to ensure our new grading system is consistent with the degree of stenosis and makes it easier to understand. According to our results, the Interobserver variability among readers with different levels was in a range of 75%-86%, which was a fairly high level of agreement. This finding implied that the grading system was sufficient as a reliable method to assess the degree of CCS and could be learned and understood easily.
About the clinical severity of CCS and the effective sagittal spinal canal(ESSC), many studies have mentioned the relationship between the symptoms of spinal stenosis and ESSC[4, 25]. Our purpose is not to prove the diagnostic value of ESSC for CCS, but rather to compare the differences of CCS among all levels according to our new grading system. Statistically significant differences were recorded for ESSC between CCS grades at C2-C7 disc levels (Table 3). The difference between grade 1 and grade 2 is not obvious. We consider this may be because the cerebrospinal fluid space(CSF) on one side is small, and the differences between individuals further narrow this difference. However, there was a difference between grade 1 and grade 2 in clinical data analysis. There is only 18.75% of patients with grade 1 finally had surgery by December, 2017, compared with nearly 70% of patients with grade 2. According to the Muhle, with the anterior or posterior of cerebrospinal fluid space, when patients with grade 1 stenosis do flexion and extension activities the cervical canal cord still has a full activity space. But patients with grade 2 with no cerebrospinal fluid space of all cases, when patients do activities in flexion and extension, anterior and posterior cord impingement can be observed, thus inducing CSM or other symptoms of spinal cord. Therefore, we insist grade 1 and grade 2. In addition, due to the small number of cases in grade 4B, this result may be biased.
For a new classification system, the information to be conveyed should not only be concise, but also play a guiding role in clinical treatment. Some scholars thought that the severity of spinal cord compression is proportional to the severity of clinical symptoms and the high signal intensity on the T2-weighted MRI indicates a poor prognosis[29, 30]. Once the oppression occurs, the condition of most patients will gradually deteriorate within a few years[17, 31]. Grade 3 and 4 in our grading system are mainly based on the degree of compression of the spinal cord. According to our results (Table 4), once the stenosis reaches grade 4, the patient's JOA score will drop rapidly, and always accompanied by a stenosis of the adjacent stage (the data is not shown). At this time a single-stage decompression cannot meet the surgical needs. And there is evidence that about 5% of asymptomatic spinal cord compression patients begin to have symptoms each year. In other words, patients with grade 2 stenosis are more likely to progress to higher grades of cervical spinal stenosis and myelopathy. Our results also show doctors will suggest that most patients with grade 2 stenosis to choose a surgical treatment. This is another reason why we still have to distinguish between grade 1 and 2. Therefore, we recommend active drug intervention for patients with grade 2 stenosis and surgical treatment if necessary.
In terms of 1-year improvement rate, patients with grade 3B had a low improvement rate. We considered that patients with 3B were more likely to have severe never damage. Because a sharp injury was more severe than blunt stresses. For grade 4B patient who undergo anterior surgery, bony compression was often difficult to remove and always accompanied by adjacent stenosis, simple anterior surgery was difficult to achieve a satisfactory improvement rate. That’s why we indicated a patients with 4B would receiver a posterior surgery.
There are also many limiting factors in our research. First, patients with grade 3B and 4B have a small sample size. This will reduce the credibility of our results. Second, this study was conducted at a single medical research center. And a multi-center research is needed, in order to ensure the universality of the classification. Third, Lack of forward-looking research. In order to verify the effect of our grading system on clinical practice, we will continue to track the outpatient, grade them by stenosis and collect them outcomes.
In conclusion, we suggest our new grading system can provided as a reliable assessment that can guide clinical treatment for Cervical Canal Stenosis.