Spinal tuberculosis is the most common form of extrapulmonary tuberculosis (1). It has become a major health concern in developing countries due to the emergence of drug-resistant strains (2, 3). Surgical treatment is known to be the best solution in case the anti-tuberculosis treatment fails (4). However, surgeries are sometimes associated with certain unexpected complications. The results of Zhou et al.'s study revealed that 102 patients with L1–2 vertebral tuberculosis had 14 patients with pulmonary complications after the surgery (5). Zhuang et al. applied oblique lateral interbody fusion to lumbar spinal tuberculosis with 10 (16.95%) complications, including peritoneal injury, neurological injury, infection of incisions, segmental artery, iliac vein lacerations, and instrument failure. However, the anterior-only approach was associated with 37.5% complications (4). Similarly, Susanta et al. reported one case (2.3%) of sinus formation and two cases (4.7%) of superficial wound infection after thoracic tuberculosis surgery (6). Surgeons should completely understand the surgical approach and post-operative complications of spinal tuberculosis, which is of great significance in treating the disease (7).

The global tuberculosis situation is particularly tense in developing countries. The incidence of pulmonary or spinal tuberculosis is low in developed countries, however, the incidence is high in developing countries. The incidence of tuberculosis is high in the African region, which accounted for 71% of global tuberculosis and AIDS cases in 2018 (8). The backward economies of developing countries cannot provide good sanitation and treatment facilities, which is also the reason for the high incidence of tuberculosis (9). Insufficient course of antituberculosis therapy after spinal tuberculosis surgery due to financial burden, which may increase the recurrence of spinal surgery.

In the past, our team's research had found that there were various complications of spine surgery. There was a potential risk of cerebrospinal fluid leakage and reduced albumin after surgery for spinal tuberculosis (10, 11). In addition, we also found a risk of internal fixation failure following spinal surgery (12). In a recent study of spinal tuberculosis, our team found that spinal tuberculosis was prone to recurrence after surgery and the risk of pulmonary embolism after multiple surgical treatments (13). Therefore, we collected a large number of clinical data on spinal tuberculosis surgery with the aim of predicting the risk of complications of spinal tuberculosis.

Although PSM analysis has been favored in spinal surgery, including cervical spine surgery (14), thoracic surgery (15), and lumbar spine surgery (16), only a few reports are available on spinal tuberculosis with PSM analysis. However, a combination of PSM analysis and logistic regression analysis for spinal tuberculosis analysis has not been reported. This study was the first to apply a combination of PSM analysis and logistic regression analysis to study the complications after spinal tuberculosis. We compared the clinical data of complication and without complication groups and explored the factors related to complications after tuberculosis surgery.

The clinical data of patients with spinal tuberculosis were collected in our hospital from June 2012 to June 2021, including general information, laboratory results, surgical information, post-operative complications, and hospitalization costs. A total of 495 patients were enrolled in the study, including 298 males and 197 females. All data were divided into two groups: complication group with 146 patients (Figures 1–3) and without complication group with 349 patients. In this study, 292 patients were included in the PSM analysis: 146 patients in the complication group and 146 patients in the without complication group. The criteria for inclusion were as follows: (1) without other diseases that affected post-operative recovery except hypertension and diabetes, (2) diagnosed with spine tuberculosis by pathological examination, (3) without a history of surgery affecting the spine, (4) complete clinical data, and (5) Lesions involving any part of the spine, including cervical, thoracic, lumbar, and sacral. The criteria for exclusion were as follows: (1) other diseases that affected post-operative recovery except for hypertension and diabetes, (2) without diagnosis of spinal tuberculosis by pathological examination, (3) with a history of surgery affecting the spine, and (4) incomplete clinical data. Post-operative complications of spinal tuberculosis were defined as post-operative wound infection or systemic infection, failure of internal fixation, recurrence of tuberculosis, and surgery-related diseases such as pulmonary embolism, cerebral infarction, and myocardial infarction. According to the fixed vertebral body at the upper end and the fixed vertebral body at the lower end, we choose the appropriate length of incision. “Bottle” was defined as the unit of measurement for albumin quantity. Each bottle of albumin injection was 50 ml, of which albumin accounted for 20%. This study was approved by the Ethics Committee of the First Affiliated Hospital of Guangxi Medical University.

There were differences in baseline data before propensity matching, but none were statistically significant after propensity matching (Table 1). The histogram showed a difference between categorical variables, including gender (Figure 4A), hypertension (Figure 4B), diabetes (Figure 4C), abscess (Figure 4D), titanium cage (Figure 4E), and internal fixation (Figure 4F), before and after matching. The frequency distribution graph showed a difference in quantitative variables, including BMI (Figure 5A), age (Figure 5B), percentage of lymphocytes (Figure 5C), albumin (Figure 5D), and lesion segment (Figure 5E) before and after matching. The balance of the standardized differences of covariates was evaluated using the standard difference method; the results showed that the standardized difference of the matched data was significantly smaller than that of the unmatched data (Figure 5F).

The general data between the two groups using the PSM analysis revealed that the P-value of appetite and occupation was <0.1, and that of other parameters was more than 0.1 (Table 2). The laboratory results showed that only the comparison of AST/ALT between the two groups was <0.1 (P = 0.067), and there were no significant differences in other parameters (Table 3). The albumin quantity (Figure 6A), operation time (Figure 6B), incision length (Figure 6C), and hospital stay (Figure 7F) in the complication group were 1.71 ± 2.82 bottles, 162 ± 74.1 min, 11.2 ± 4.76 cm, and 14.7 ± 9.34 days, respectively, and these values in the without complication group were 0.740 ± 2.44 bottles, 138 ± 60.5 min, 10.2 ± 3.56 cm, and 11.7 ± 7.44 days, respectively (Table 4). There were statistical differences between the two groups (P < 0.05). In addition, there were statistical differences in the surgical approach between the two groups (P < 0.1). The laboratory costs (Figure 7A), examination costs (Figure 7B), guardianship costs (Figure 7C), oxygen costs (Figure 7D), and total costs (Figure 7E) in the complication group were 2,900 ± 2,080 RMB, 425 ± 826 RMB, 791 ± 1,940 RMB, 154 ± 210 RMB, and 51,700 ± 31,800 RMB, respectively, and those in the without complication group were 2,280 ± 1,360 RMB, 272 ± 422 RMB, 441 ± 186 RMB, 103 ± 106 RMB, and 42,800 ± 24,200 RMB, respectively (Table 5). These costs were higher in the complication group than in the without complication group (P < 0.05). There were no significant differences in other costs, including antibacterial costs, western medicine costs, surgical costs, anesthesia costs, transfusion costs, high consumable costs, care costs, and consultation costs, between the two groups (P > 0.05).

We constructed a logistic regression model to further explore the risk factors that affected the complications. The parameters with P-values <0.1 were included in the logistic regression analysis, including appetite, occupation, AST/ALT, albumin quantity, surgical approach, operation time, and incision length. There was a significant difference in the albumin quantity using the logistic regression model analysis (Table 6). Furthermore, there was a significant difference in the intercept of the regression model (P < 0.05). However, there were no statistical differences in other parameters, including appetite, occupation, AST/ALT, surgical approach, operation time, and incision length (P > 0.05).

The goodness of fit of the logistic regression model was assessed by HL-test and the chi-square value. P-values were 4.534 and 0.806, respectively. The confidence interval of the odds ratio (Table 6) was further used to evaluate the logistic regression model. The ROC curve was applied to evaluate the validity of the logistic regression model. The area under the curve (AUC) was 0.75 (Figure 8).

In this study, various complications occurred after spinal tuberculosis surgery during post-operative follow-up (Table 7). Eight patients were transferred to ICU for treatment due to post-operative respiratory failure, hypoxia, and inability to remove the ventilator. Wound infection occurred in 77 patients. After intensive wound management or two-stage debridement, they can recover well. Pedicle screw fracture occurred in 1 patient, requiring a second surgery to re-implant the internal fixation device.

Spinal tuberculosis surgery has become the most common treatment for spinal tuberculosis, including anterior (28), posterior (29), and combined anterior and posterior approaches (30). Moreover, the literature reports that spinal tuberculosis surgery includes minimally invasive procedures and combined open and minimally invasive procedures (7). However, post-operative complications are often unexpected and also a challenge for surgeons (31, 32). The complications of spinal tuberculosis vary depending on the location. The complications in cervical tuberculosis have been reported to be more than in non-cervical tuberculosis (33). In addition, post-operative complications of spinal tuberculosis vary depending on the surgical approach. The complications of the anterior approach were higher than in the posterior approach (7).

The parameters with a P-value <0.05 in the univariate analysis included albumin quantity, operation time, and incision length. Patients with classic spinal tuberculosis were often accompanied by weight loss (34); these patients who underwent surgical treatment were prone to poor wound healing due to post-operative nutritional insufficiency (35–37). Under such conditions, clinicians often use albumin supplementation to promote the recovery of patients (38). In addition, a longer surgical incision results in more secretion of fluid from the incision and increased susceptibility to wound infection (39). This could be the reason that the length of the incision in the complication group in this study was longer than that in the without complication group, and the albumin quantity in the former was more than that in the latter. If the operation time exceeded 3 h, the second group of antibiotics often needed to be increased, which potentially increased the risk of post-operative infection and other complications in case of prolonged operation time (40). Therefore, the operation time in the complication group was higher than in the without complication group.

Various costs, including hospital stay, laboratory costs, examination costs, guardianship costs, oxygen costs, and total costs, were higher in the complication group than in the without complication group. Research by Marah et al. showed that post-operative respiratory failure increased the cost of surgery by more than 50% (41). Mark et al. studied the relationship between surgical complications and hospitalization costs and found that hospitalization costs were on an average of $19,626 higher in patients with complications than in those without complications (42). The findings of Hunt et al. showed that post-operative complications not only increased the length of hospital stay but also increased the cost of hospitalization (43). This was consistent with the results of our study.

In the present study, only the albumin quantity was significantly different by multivariate logistic regression analysis. In addition, the albumin quantity in the complication group was higher than that in the without complication group. Li et al.'s study of spinal tuberculosis found that the albumin in the anterior approach group decreased from 37 g/L pre-operatively to 24.2 g/L post-operatively and that in the posterior approach group decreased from 38.6 to 28.2 g/L, with pneumonia and other complications in both groups of surgical approaches (44). A close relationship existed between albumin and post-operative complications (45), and albumin supplementation may accelerate the recovery of the post-operative condition (46).

The logistic regression model was tested through the HL test method, and the P-value was 0.806 (P > 0.05), which implied no difference between the logistic regression model and the actual application. The value of the area under the ROC curve was 0.75, implying that this regression model can be used in clinical applications.

PSM analysis strategies, such as tumor chemotherapy (47), cervical spine surgery (48), robot-assisted surgery (49), and other areas, are widely used in medical research. The PSM analysis can reduce the difference between the two groups of comparable data and decrease the effect of interfering factors on the results by adjusting the balance of baseline data (22). Such a model allows the researchers to measure the probability of an outcome event occurring between treatment and control groups (50). The pre-matched imbalance and post-matched balance were assessed using the balance standardized differences (23). We found a significant difference in the laboratory results of albumin value between the complication and without complication groups, which inevitably became a disturbing factor for another result that the albumin quantity was an independent risk by the logistic regression analysis. The albumin values of the two groups before the operation were adjusted to be the same by the PSM analysis, and the results of the study were more comparable.

However, this study had certain limitations. (1) Some data were lost after the PSM analysis. (2) More sample data should be collected to obtain more pairs. (3) This subject was a single-center study, and the results need to be verified by a multi-center study.

In this study, the costs in the complication group were generally higher than in the without complication group. Multivariate logistic regression analysis found that albumin quantity could be an independent factor for predicting post-operative complications of spinal tuberculosis. Therefore, surgeons should pay more attention to the patient's economy and the occurrence of post-operative complications in clinical work.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.

The studies involving human participants were reviewed and approved by Ethics Committee of the First Affiliated Hospital of Guangxi Medical University. The patients/participants provided their written informed consent to participate in this study.

LC wrote the article and prepared Figures 1–8 and Tables 1–6. All authors reviewed the article, including SH, TC, HL, TL, ZY, WC, XS, JJ, JC, HG, YY, SL, CY, BF, SW, and XZ. All authors contributed to the article and approved the submitted version.

This work was sponsored by the National Natural Science Foundation of China (81560359) and National Natural Science Foundation of China (81860393). Funding bodies had no role in the study design, collection, analysis, and interpretation of the data or in writing the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.