Relevant knowledge
C-reactive protein originally discovered by Tillett and Francis in 1930 as a substance in the serum of patients with acute inflammation that reacted with the C polysaccharide of pneumococcus. C-reactive protein is a member of the class of acute-phase reactants, synthesized by the liver, which can activate complement and promote phagocytosis of granulocyte and macrophage. C-reactive protein content is small, in healthy person, only lower than  10 mg/L, but it rises above normal limits within 4-6 hours, and peaks at 48-72 hours (100-1 000-fold), even 2 000-fold of normal level during inflammatory processes occurring in the body. C-reactive protein level is closely associated with tissue repair, and can not affluent by gender, age, anaemia, hyperglobulinemia, or pregnancy. In clinic, C-reactive protein levels are used as a index to evaluate disease conditions due to its fast reaction, sensitive and objective^[8-9] . Spinal tuberculosis is an infection of the
spine by the Mycobacterium tuberculosis bacterium. The resistance and immunity would decrease after infection, with Mycobacterium tuberculosis increasing and virulence enhancing, specific reaction and non specific reaction would present in human tissues. The increase of C-reactive protein levels are differed in tuberculosis patients at active stage with varying injury degree and repair duration^[10-11] . C-reactive protein levels are obviously increased at 24-72 hours surgical treatment, but decline into normal level with 5-7 days. However, its level will continuously increase with inflammation if the patients suffer concurrent infection or poor antituberculosis treatment.
The C-reactive protein levels will increase with inflammation when the spinal tuberculosis patients under condition of bacterial inflammation or decrease into normal level when the patient were controlled or cured. The later internal environment is benefit for bony fusion of bone graft.
Feng et al^[12] thought that monitoring indexes of ESR and C-reactive protein play an important role in middle or long-term follow-up of spinal tuberculosis patients following focal debridement, autologous iliac bone graft, as well as plate internal fixation. Tian^[13] study demonstrated that the variation of ESR and C-reactive protein related to multi-factors, such as course of disease, size of cold abscess, virulence of Mycobacterium tuberculosis, as well as multiple tuberculose focus, however, the diversity of ESR and C-reactive protein after treatment was inconsistent with tuberculosis symptoms. Accordingly, C-reactive protein diversity is possible associated to multi-factors, but the study required further investigation. In the experiment, the C-reactive protein levels were high before operation, but the bone fusion time was not too long, however, the C-reactive protein levels turned to be normal, and the bone fusion time was shortened correspondently, that is, there was a positive correlation between postoperative C-reactive protein levels and bone fusion time. Therefore, the C-reactive protein levels would decrease into normal level when the patient were controlled or cured, which is favor for the graft growth and bone fusion, while bone fusion is an important factor that determines the results of surgery treatment. Conversely, the C-reactive protein levels would continuously increase or transitional decreased followed by continuously increase if the antituberculosis treatment is poor or the treatment is not systematically. In this condition, the graft is hard to fuse or even be absorbed, leading to surgery failure.
The serum C-reactive protein levels differs when the injure degree and repair duration are different in tuberculosis patients at active stage. Kartaloglu et al[^14] demonstrated that the changes of C-reactive protein is similar to adenosine deaminase, which increased prior to treatment and gradually decreased at different time points after treatment. Thus, C-reactive protein level had served as one of the objective indexes for the evaluation of tuberculosis treatment response^[15-17] . The results of this experiment showed that, the bone graft fusion completed within 16 weeks after treatment in the mildly increase group (lower than 25 mg/L), which lasted for over 24 weeks in the extremely increase group (greater than 100 mg/L). Consequently, it is reasonable that the continuous increase of C-reactive protein predict the long bone graft fusion time. There were 6 patients had high C-reactive protein levels after treatment, which turned to normal level after receiving
second pipeline antituberculosis drugs. The CT confirmed that the bone fusion duration of these 6 patients were completed at 32 weeks after treatment. Generally speaking, patients with normal postoperative C-reactive protein levels or transitional increased followed by continuously decrease would obtain good prognoses or the bone fusion duration would be shortened. Mukhtar et al^[18] showed that, the ESR and C-reactive protein levels presented with diversity after treatment, but the diversity was inconsistent with tuberculosis symptoms. At the same time, the author point out dynamic observation of ESR and C-reactive protein levels are benefit for monitoring absorption of remnant tissues after focus clearance. Currently, more and more researchers realize that the ESR and C-reactive protein control or suitable postoperative immobilization not only play an key role in determining long-term effects of spinal tuberculosis treatment, but also important in preventing recurrence of spinal tuberculosis^[19] .
In the experiment, the mean level of C-reactive protein was 24.96 mg/L before operation, increased with surgery, peaked at 5 days after operation, then gradually decreased, and reached normal levels at 3-6 months. By observation, we had seen that there were a certain change laws of postoperative C-reactive protein. The monitoring of this law would predict the possibility of treatment outcomes and would be favor for pathogenetic condition recovery via in time intervention. This finding provided a theoretical basis for the duration of postoperative immobilization.

Bias or deficiency of this study
The cases number was small, the source was single, and whether graft material had effect on postoperative C-reactive protein remain poorly understood, the postoperative C-reactive protein time points were limited, all of these are shortcomings in this paper and required further improvement.

Clinical application significance
By observation change laws of postoperative C-reactive protein levels, we can predict the possibility of treatment outcomes and would be favor for pathogenetic condition recovery via in time intervention. This finding provided a theoretical basis for the duration of postoperative immobilization.