In this study, we showed two novel findings. First, patients with improper lumbar sagittal alignment had a higher occurrence of Modic and endplate defect.
Previous studies regarding sagittal balance have demonstrated that lumbar malalignmentafter spine surgery may cause poor clinical outcomes.[15, 16] patients should be provided propercorrection of the spinal alignment in order to prevent complications to occur. However, there is no studies focus attention on the effectof lumbar sagittal alignmenton the progression of Modic changes and endplate defects before surgery until now. Thus, we conducted a study that mainly focused on the effect of lumbar sagittal alignment on the occurrence of Modic changes and endplate defects.
We think that the mechanism regarding the association between lumbar sagittal alignment and Modic changes or endplate defects is multifaceted. The lumbar segment with MCs or endplate defects tends to lumbar disk degeneration, the latter of which destabilizes the lumbar spine in turns and ultimately form a vicious cycle. Moreover, the vertebral endplate fulfills the critical function of disc nutrient transport. MCs decrease nutrition transmit ability of endplate, infection factors serving as initial pathogenesis. In addition, morphological changes such as fatty infiltration or change in cross-sectional area of lumbar muscles were observed in patients with low back pain. Patients with low back pain demonstrate a significantly higher prevalence of MCs and endplate defect with an unclear mechanism. We hypothesize that the change of lumbar sagittal alignment leads to lumbar muscles of these MCs patients fail to support spinal stability and finally led to fatty infiltration or change in cross-sectional area of lumbar muscles.
The unstable lumbar spine is able to enlarge the range of movement, which accelerates the degeneration of endplate and lumbar disc. Finally, the interaction between the two makes the disease to develop into a serious direction. In this study lumbar sagittal parameter was measured in patients with low back pain and we found that lumbar sagittal parameter in volunteers with MCs or endplate defect was larger than those in subjects without MCs or endplate defect. A significant correlation between lumbar sagittal parameter, MCs, and endplate defect was found in logistic regression analysis. We speculated that increased lumbar sagittal alignment could increase lateral shear force, leading to the destroyed structure of endplate and formation of MCs.
In terms of the Modic and endplate defect, the prevalence of Modic and endplate defect was 79.16% (76/96) inwith Modic and endplate defect group and 21.5% (20/96) in without Modic and endplate defect group. Meanwhile, differences in the presurgical lumbar sagittal alignment were observed in two groups. Thus, we hypothesize that presurgical lumbar sagittal alignment, measured by PI, PT, SS, LL, and PI-LL, was related to the incidence of Modic and endplate defect in symptomatic subjects.
In terms of the lumbar parameters, the results indicated that PT, SS, and PI-LL in the without Modic and endplate defect group were significantly higher than those in the Modic and endplate defect group, whereas xx and xx in both groups demonstrated no significant difference. To the author's knowledge, no previous literature focuses attention on the relationship between lumbar sagittal alignment and without Modic and endplate defect. It is generally accepted that physiological cervical sagittal balance is important for normal spine function, and the maintenance of and improvements to cervical spine function are bound to have an effect on clinical efficacy and outcomes.25,26 As a result, Modic changes and endplate defect may be caused by malalignment of the lumbar spine. However, previous studies emphasized that there exist a relationship between sagittal alignment and degenerative changes only in the cervical spine. In terms of the lumbar spine, Baron et al. Showed that spinopelvic sagittal alignment plays a predisposingrole in the pathogenesis of lumbar degeneration.
Even though we couldn't confirm whether these characteristics were the effect or the predictor of lumbar degeneration in the current retrospective study, they have potential clinical implications. Lumbar sagittal alignment plays a crucial role in predicting the development of Modic changes and endplate defects in symptomatic patients. Meanwhile, in the corrective surgery for patients with lumbar deformity, emphasis should be placed on the reconstruction of the lumbar sagittal alignment. Furthermore, lower lumbar muscles dystrophy because of a surgical exposure can contribute to postoperative deformities. Li et al. reported that there is a correlation between spinopelvic alignment and degeneration of lower lumbar paraspinal muscles in elderly patients in a recent study. Hence, the paraspinal muscle-strengthening exercises of lower lumbar levels could slow the progression of Modic changes and endplate defects. Longitudinal studies with subject outcomes need to be performed to validate our hypotheses.
Several limitations existed in this study. First, bias could not be avoided due to the nature of retrospective studies. Second, the study mainly focused on preoperative lumbar sagittal alignment and prevalence of Modic changes and endplate defects and not postoperative lumbar alignment or changes in lumbar alignment. Third, a high standard deviation of lumbar sagittal parameters reflects the flexibility of the lumbar spine. Thus, we should determine the reproducibility of lumbar sagittal parameters in further research. In addition, the lack of patient medical records made it difficult to verify the differences in clinical scores between patients with the imbalance and normal balance.