The intervertebral disc is also gradually degenerating with age. Because MC is associated with a high probability of intervertebral disc degeneration, it seems reasonable that the prevalence of MC increases with age.18 However, it has been shown that the prevalence increases with age until 60 years, but the overall prevalence of MC appears to decline from 70 years of age, contrary to the previous view that MC is an exponential disease with age, which seems to be associated with disc infection and diminished resistance.5Modic changes occurred mostly in L4/5 and L5/S1, and age, gender, disc degeneration, abnormal physiological curvature of the lumbar spine, and changes in the concave angle of the endplate were all related factors, with gender and lumbar curvature being the most related factors of different types.19
There was a strong positive association between MC and LBP (OR ranged from 2.0 to 19.9 in statistically positive studies), and the presence of MC increased the occurrence of LBP during discography with a high probability. The positive association between MC and LBP is prevalent in most LBP patients in different countries as well as in different types of work.20Lv et al3 found that endplate defects appeared to increase the extent of invasion of MCI and MCII in severe LDD segments, but this may not be significantly associated with clinical symptoms. Unfortunately, progressive changes in endplate defects resulted in deterioration of VAS scores as well as ODI values at each follow-up time point from preoperative to six months after surgery. In addition, endplate defects may be one of the fundamental sources contributing to MC, disc degeneration, and facet joint degeneration. The endplate is the medium through which the vertebral body transmits stress to the intervertebral disc, and its center bears the greatest stress. More importantly, the morphological changes in the endplate can reflect the degree of degeneration of both the endplate as well as the intervertebral disc. Degeneration of the intervertebral disc causes greater stress on the periphery of the endplate and changes in endplate morphology, and the endplate flattens and increases the stress area of the vertebral body to reduce pressure.21
In a systematic review and meta-analysis by Herlin et al, there was no significant difference in the strength of association between MCI and MCII and LBP, and no difference in the intensity of low back pain or the degree of limitation of normal activity was found between patients with and without MC, which may be related to the coexistence of the two types of MC in the same disc or the transition from MCII to MCI. In addition, the correlation between the size of MC area and LBP does not seem to differ, and even small vertebral lesions reaching normal stimulation thresholds for pain may reach stable pain plateau segments.22 At the same time, in the study by Ohtor et al., percutaneous lumbar discectomy improved the lumbar clinical outcome in patients with lumbar disc herniation, and low back pain in patients with lumbar disc herniation was mainly caused by narrowing of the intervertebral space or compression of the nerve roots. Decompression surgery alone may be a good way to reduce lumbar pain in patients with MCI changes, but patients with spinal bone marrow MCI seem to have no significant difference in the level of clinical low back pain improvement compared with patients without bone marrow MC.23
Patients with LDD associated with lumbar MC did not appear to have a stronger association with lumbar pain and limitation levels than those without MC, and MC could not be considered a predictor of poor clinical outcome. We need more and more comprehensive research methods to validate the previous research content, and prospective studies may be a good research method.24Mok et al demonstrated that the presence of MC in the upper lumbar spine was tightly associated with the state of disc displacement or degeneration, whereas the presence of MC in the lower lumbar spine was associated with age, Schmorl 's nodules, BMI, and some adverse lifestyle factors. In addition, patients with MC of the lower lumbar spine appear to have an increased probability of developing LBP and symptomatic pain in the legs, and they appear to have more pain as well as relatively early onset of LBP.25
Xu et al also showed that VAS score for back pain and ODI score increased with longer follow-up time in the group with MC than in the group without MC, and were more common in patients with MCI.26 Patients with symptomatic MC with endplate chondritis showed significantly less satisfactory relief of back pain after endoscopic discectomy compared to MC patients without endplate chondritis.27 Although in a prospective study by Ohtori et al patients with lumbar disc degeneration with or without MC did not appear to show significant differences in improvement in lumbar VAS score and ODI score after endoscopic discectomy, there remains a lack of solid rationale for the necessity of fusion surgery in patients with MC type I signal.23 In previous studies, leg pain was significantly relieved after both fusion and PTED, but low back pain tended to rise within two years after surgery. Vertebral body fusion significantly improved biomechanical recovery, but patients treated with PTED had a good risk of postoperative recurrence and involvement in back pain.28 In Cao et al. 's study, posterior lumbar fusion appeared to be better at relieving low back pain than transforaminal endoscopic decompression alone in patients with LDD-MC.29 After our included study subjects had learned about both surgical modalities, they seemed to be more inclined to undergo minimally invasive simple discectomy. In Ohtori 's study, minimally invasive endoscopic discectomy significantly improved low back pain in patients with lumbar degenerative diseases, and patients with or without MCI type did not seem to have much impact on low back pain score improvement. Eventually they concluded that the degenerated disc compressed the nerve roots innervating the lumbar sensation causing low back pain in patients, and decompression surgery alone seemed to reduce low back pain in MCI patients.23 Fortunately, however, 82.81% of our patients achieved their expected results, proving that our procedure met expectations (as shown in Fig. 2 and Table 3).
In our study, there was a gradual rebound in VAS scores for low back pain in MCI patients compared to MCII patients from one to two years postoperatively, but ODI values appeared to have stabilized and did not rise over two years. This reflects that patients in our study would have a good improvement in spontaneous life function, with a faster recovery in the MCII group for low back pain and no significant difference at one year postoperatively (as shown in Fig. 1 and Table 2). Unfortunately, low back and leg pain appeared to rise in MCI one to two years after surgery, and although ODI did not rise temporarily, it is likely to rebound after being attacked by low back pain, which is something to be noted in our study. However, the resilience of low back pain after two years is not necessarily accompanied by the effects of the type of MCI, but may also be a progression of lumbar degeneration. In our study, all MCI patients had a tendency to have elevated low back and leg pain at the last follow-up, whereas there did not seem to be such a tendency in the MCII group (as shown in Fig. 1).
It has been reported that 78.97% of patients who did not present MC on preoperative MRI were ModicI, 20.56% were ModicII, and 0.47% were ModicIII in the late postoperative period.12 This may be related to the invasion of acnes bacilli in the human disc and the destruction of the endplate by surgical instruments during surgery, but the specific cause remains obscure.10, 12, 30 Bacteria play a role in lumbar disc degeneration and are associated with MCI type. Whether MCI associated low back pain is a result of contamination with these organisms or lumbar spine infection remains obscure and requires further investigation to determine.31 It was found that there was no difference in serum biomarkers between LBP patients with or without active lumbar disc degeneration, which is likely to be related to the inability of factors associated with lumbar disc degeneration to convert into detectable serum biomarkers.32Both severity and time span of diabetes are strongly associated with MC, but the association with severity of disc degeneration remains unclear.33Female patients, too obese and heavy physical work were all significantly associated with MC, and biomechanical factors appeared to play a critical role in the progressive changes in MC.34In our study, a significant number of patients engaged in excessive physical work, poor weight control or had various underlying diseases in rural areas(As shown in Table 1), which laid a hidden danger for clinical biomechanical changes, lumbar disc degeneration, and MC.
Limitations
Our study is not a randomized controlled study, and the number of patients and follow-up time remains insufficient. In addition, we only included patients with MCI/II, and we also needed patients with some other mixed types as well as transition status between them. Therefore, further studies are needed to validate our hypothesis.