In our study we found that the postoperative fusion rate of patients with cervical Modic changes is lower than that of normal cervical patients.
Stress theory and integration
Anterior cervical discectomy and fusion (ACDF) is considered the gold standard for the treatment of degenerative cervical disease. Intervertebral fusion is one of the most important indicators to evaluate the success of ACDF [10–11]. For example see figue 3.Firm bone fusion is the key to the best long-term prognosis. MCs are considered to be part of the changes in inflammation, edema and congestion. Modic et al. believe that [1–2] Type 1 changes indicate the inflammatory phase of the degenerative process; Type 2 changes represent fatty degeneration of subchondral bone and bone marrow; Type 3 changes indicate the healing stage of intervertebral disc degeneration.According to the biomechanical hypothesis, with age, the intervertebral disc degeneration will become heavier and heavier, the cartilage endplate is gradually replaced by the bony endplate, the loss of the interdiscal space and the degeneration of the facet joints change the biomechanics, Leading to microfracture of the endplate.Bendix et al.  proved that patients with a lot of labor are more likely to have microfractures of the endplate, resulting in Modic changes.The histological characteristics of type 1 MCs are the thickened trabecular bone of the endplate and granulation tissue and fibrous tissue that infiltrate and destroy blood vessels, while the destruction of type 2 MCs endplate is caused by chronic repetitive hematopoietic tissue damage and replacement of bone marrow and fat. organization. The histological feature of type 2 MCs is the formation of bone sclerosis, confirming the above hypothesis. According to Woff's theory, tensile stress can promote bone fusion, while tensile stress inhibits bone fusion. Modic changes in patients with increased pressure load, which inhibits the formation of new bone.These articles just confirmed this point of view.In this study, the percentage of cervical spine 3 and 4 fusions in the patients without cervical Modic change was greater than that of the Modic change group, as shown in Fig. 4. That is, the fusion effect of the cervical spine without Modic change group was better than that of the cervical spine modic group. Change has changed.
Changes in the microenvironment and fusion
Studies have shown that for patients with MCs, the local microenvironment at the surgical level may affect fusion [15–17]. Toyone et al.  found that Modic type 1 patients had poorer stability than those without Modic changes. Another study found that the endplate damage caused by Modic3 inhibits the nutrition and blood supply of the bone graft area, which may also affect fusion . Changes in the microenvironment will affect the nutrient supply of the endplate, leading to the delay of endplate repair. A large number of active osteoclasts and osteoblasts will cause increased woven bone, thickening of trabecular bone and microstructure changes, which will affect fusion. Other studies have shown that the endplate is milky white in the fresh state, and its tissue contains a variety of biological factors including tumor necrosis factor (TNF) and protein gene products (PGP), as well as biological factors such as interleukins produced by immunogenic activation 6, 8 and prostaglandin E2 have been confirmed to be related to Modic changes. In this study, Modic changed the percentage of grade 3 and 4 fusion in type I cases than Modic II and III, as shown in Fig. 5.The author believes that the hematoma formation period is equivalent to the Modic altered inflammation period, in which a large number of osteoblasts are formed, and the growth of new capillaries is a key factor in the occurrence of new bone.While the original callus formation period and the plastic period of callus transformation are equivalent to the steatosis period and the bone sclerosis period, a large amount of fat deposits and red bone marrow turn into yellow bone marrow, resulting in slower healing after fusion.The conclusion of this study that the fusion rate of patients with cervical Modic changes in the early and middle postoperative period is lower than that of normal cervical patients. However, the influence of cervical Modic changes on the effect of intervertebral fusion is still controversial, and the specific relationship needs further research.
Of course, there are many factors that affect fusion, in addition to the above reasons, such as age, cartilage endplate treatment, follow-up time, etc. Choi et al.  found the extensor CSAs were related to fusion rate and timing. In particular, as the extensor CSAs increased, fusion timing decreased.Ren Ba et al. Through univariate and multivariate analysis, the most important finding of this study is that the slopes of C2-C7, C2-C7 ROM, C2-C7 SVA and T1 are positively correlated with cage nonunion after ACDF.Kim  reported that the high slope of T1 is a predictive risk factor for kyphosis caused by poor fusion.These will affect the fusion of the cervical spine.
In this study, cervical Modic changes did not affect the final fusion, but delayed healing occurred during follow-up. For delayed healing cases, delayed fusion patients may have more implant complications, such as broken screws and screws Fractures and false joints, in order to avoid loosening and non-fusion of internal fixation, patients are required to reduce neck activities and extend the wearing time of neck brace. Cause patients to complain about the inconvenience of life. Delayed healing may be related to Modic changes, the specific mechanism is not clear.
This article has certain limitations. Some unknown factors may affect the relationship between Modic changes and fusion of the cervical spine, such as the amount of bone graft, the parameters of the cervical spine sagittal plane, the degree of cartilage endplate and residual soft tissue processing. There are few studies on cervical Modic changes and fusion in the literature, and there are not many references. In addition, the sample size of this study is relatively small, and it is necessary to collect more cytological and molecular data on cervical Modic changes and fusion in a large-sample multi-center study to further prove.