The present study evaluated correlations between the presence or absence of typical LSS symptoms and four classifications of lumbar MRI: morphological grading of central stenosis and of LRS, presence of the sedimentation sign, and severity of FJE. It was found that only the most severe grade (D) of central stenosis was strongly associated with the presence of typical LSS symptoms.
Recent focus has been on the association between anatomical central stenosis on imaging and clinical symptoms. There are previous studies linking morphological stenosis with the LSS symptoms in hospital-based surveys7-10,24-26). According to these studies, it has remained controversial whether the morphological stenosis correlated with or without clinical LSS symptoms, even though various assessments of morphological stenosis, such as measurement of spinal canal area or diameter and each classification of stenosis grading, have been used for analyses27,28). In the general population study by Ishimoto et al., the prevalence of clinical symptoms significantly increased with increasing severity of central stenosis27). In the present study, the prevalence of typical LSS symptoms tended to increase significantly according to the severity of central stenosis and LRS, respectively. In addition, the agreement between the two studies suggests that the correlation between severe central stenosis and the presence of symptomatic LSS is more certain. Furthermore, to evaluate imaging findings for LSS, not only central canal stenosis but also lateral recess stenosis should be considered. It has been reported that the cross-sectional area of the lateral recesses was significantly smaller in the symptomatic LSS group than in the asymptomatic group28). Another study reported that there was a weak correlation between the Oswestry disability index and LRS grade in low back pain patients without central stenosis. However, the participants had low back pain, and it did not evaluate specific radicular symptoms11). In the present study, the prevalence of typical LSS symptoms increased significantly according to the severity of LRS compared with the group without typical LSS symptoms. It is known that degenerative spinal stenosis is primarily caused by age-related degeneration, such as protruding discs, osteophytes, hypertrophy of facet joints, and accompanying thickening of the ligamentum flavum1,12). Therefore, it is likely that advanced central stenosis is often associated with LRS. In the present study, the combination of higher severity grades of central stenosis (Grade C, D) and LRS (Grade 2, 3) was found in approximately 15%, and half of them were in the symptomatic LSS group. Since LRS showed a strong correlation (r> 0.7) with central stenosis in the present study, it was considered inappropriate to include both central stenosis and LRS in the logistic regression analysis due to their multicollinearity; therefore, the correlation between LRS and central stenosis was not evaluated. The present study showed that only the most severe central stenosis was strongly related to the presence of typical LSS symptoms. Conversely, this and another study27) found that not all of the higher severity grades of MRI imaging cases presented with typical LSS symptoms. In the present study, the LSS-SSHQ score of one case with Grade D central stenosis, determined not to have typical LSS symptoms, was 2 points in questions 1-4 and 1 point in questions 5-10. This case showed some symptoms suggestive of LSS, but did not meet the defining criteria of the LSS-SSHQ. Moreover, the severity of stenosis on MRI was not associated with preoperative disability and pain, or clinical outcome at 1 year26). Furthermore, in the natural history of symptomatic LSS, it was shown that more than half of symptomatic LSS subjects improved their symptoms, whereas 10% of asymptomatic LSS subjects developed clinically diagnosed symptomatic LSS at 1 year follow up6). According to the abovementioned studies, morphological spinal stenosis might not be equal to the presence of typical LSS symptoms.
The sedimentation sign was first reported as a finding with high sensitivity and specificity for symptomatic LSS13). The presence of a positive sedimentation sign was greater depending on the severity of the morphological grade29). However, validation of the sedimentation sign is insufficient in patients with mild to moderate anatomical LSS29,30). Although the prevalence of the positive sedimentation sign was significantly higher in the group with typical LSS symptoms (46.4%) than in the group without typical symptoms (29.3%), logistic regression analysis showed that the sedimentation sign was not a significant explanatory variable in the present study. These results suggest that the sedimentation sign itself was not associated with the presence or absence of typical LSS symptoms, just associated with the presence of anatomical central stenosis. This may be due to the fact that the present study involved a general population, and various degrees of anatomical LSS were included; therefore, these results might indicate a more generalized association between imaging findings and symptoms.
It has recently been reported that FJE may be associated with symptomatic LSS. In degenerative lumbar spinal disorders, high levels of inflammatory cytokines in facet joint tissue have been found to be released into the spinal canal, which is suspected to be the cause of pain11,16,17). In addition, increased facet fluid on MRI has been reported to be highly predictive of the dynamic reduction of DCSA detected on axial-loaded MRI in the clinical assessment of LSS14,15). In the present study, the severity of FJE was not associated with the presence or absence of typical LSS symptoms. However, in the present analysis, the highest severity was used as a representative value of the respective findings; the level and right/left sidedness of occurrence points were not taken into account. These factors might be useful to improve the accuracy of detecting symptomatic LSS.
The presence and severity of each MRI finding were often related to each other, suggesting a correlation between findings. Correlations strong enough to suggest multicollinearity were found only between central stenosis and LRS, but correlations between independent variables may have influenced the results of multivariate analysis. It was also necessary to evaluate whether combining each finding would result in a correlation with the presence or absence of symptoms; however, statistical analysis was difficult because the correlation between each finding resulted in a large bias in the distribution of the number of cases. A larger sample size may reduce the influence on multivariate analysis and allow us to analyze the association between the combination of findings and the presence of symptoms.
A strength of this study is that four different kinds of MRI evaluation items were performed in all participants. In addition, the distributions of each MRI item with and without typical LSS symptoms were evaluated and associations between them were analyzed using a logistic regression model. Therefore, various morphological findings were compared for the possibility of pathogenesis in symptomatic LSS. A second strength is that the data were obtained from a large community-dwelling population on which various analyses have been performed, including the present study. Therefore, in contrast to a hospital-based survey, these results reflect a real-world setting and relevance for pathogenesis of LSS.
This study has several limitations. First, all participants in this study were volunteers, so it is possible that those participants who had any symptoms or more severe LSS symptoms might self-select for receiving MRI. However, each item from the MRI findings was distributed across all grades, and participants without symptoms also agreed to undergo MRI. Therefore, compared to a hospital-based study, the benefit of this study was that all grades of morphological stenosis, including mild stenosis and no stenosis, could be evaluated. Second, the most severe grade was taken as representative of each finding, therefore, detailed analyses for relationships between the responsible anatomical stenosis level inferred from the site of the symptoms or multiple level lesions were not considered. Because there is no established method of evaluation that takes into account multiple level lesions, and because it requires detailed grouping combined with the severity of the disease, a larger number of cases is considered necessary for the analysis. Third, since the research location was in a rural and mountainous area, one may not be completely able to extrapolate the findings to a more typical Japanese (urban) population. Finally, this was a cross-sectional study, therefore no causal relationships between morphological and symptomatic LSS could be established.