In our study, multivariate logistic regression analysis revealed that BMI, diabetes mellitus, preoperative hemoglobin level, operation time, and posterior approach were independent risk factors for PMA in STB patients.
4.1 Clinical findings: diabetes mellitus and BMI
Diabetes was found as an independent risk factor for PMA in STB patients. We observed that STB patients complicated by diabetes had higher risk to develop PMA. Diabetes has been associated with an increased risk of surgical site infections, higher hospitalization costs, postoperative blood transfusions, and prolonged hospital stays in patients underwent spinal surgery (16), which is consistent with our findings. Ugolini et al. found that diabetes can lead to increased postoperative blood loss in patients undergoing thoracic surgery because diabetes causes hypercoagulation and changes in microvessels that could negatively affect the retraction and vasoconstriction of the damaged microvessels before the hemostasis coagulation phase (17). Moreover, diabetes leads to an adverse effect in angiogenesis in healing wounds, which leads to a decrease in the density of blood vessels and capillaries (factors vital to wound healing) in the surgical incision, leading to prolonged wound healing time, increased postoperative incision drainage, and invisible blood loss, further aggravating the decrease in postoperative hemoglobin level (18–20). In summary, diabetes leads to increased postoperative blood loss and is the leading cause of PMA in patients with STB.
BMI was also found as an independent risk factor for PMA in STB patients. We found that a BMI of > 19.5 kg/m2 can reduce the risk of PMA. We referred to the BMI classification of the World Health Organization (WHO), as follows: normal (18.5 kg/m2 ≤ BMI < 25 kg/m2), overweight (25 kg/m2 ≤ BMI < 30 kg/m2), and obese (BMI ≥ 30 kg/m2) (21). BMI < 19.5 kg/m2 is considered nearly malnutrition, and BMI levels were negatively associated with the prevalence of anemia; thus, patients with STB with BMI < 19.5 kg/m2 have a higher risk of developing anemia (22). High BMI may be a favorable prognostic factor in patients with chronic diseases such as STB, as patients with a higher BMI may have higher reserves in nutrition, which can benefit the postoperative treatment of patients with STB (23, 24). However, overly high BMI is associated with adverse effects, as overweight patients have a higher incidence of low-back pain and spinal disease requiring multiple surgeries (25, 26). Obesity, defined as a BMI of ≥ 30 kg/m2, is closely related to longer hospitalization and greater intraoperative blood loss in patients undergoing spinal fusion surgery, indicating that an overly high BMI may cause greater perioperative blood loss in patients with STB (27). In our study, a BMI within 19.5–30 kg/m2 was determined to be beneficial in preventing PMA in patients with STB.
4.2 Laboratory test finding: preoperative hemoglobin level
In our study, we found that the preoperative hemoglobin level is an independent risk factor for PMA in STB patients and whose value less than 120 g/L can raise the risk of PMA. Considering the WHO definition of anemia and our previous findings, we can conclude that preoperative anemia is an independent risk factor for PMA in STB patients (28). Anemia is closely associated with tuberculosis. The odds of developing tuberculosis in patients with anemia are 3.56 times higher than in patients without anemia, and 35% of patients undergoing orthopedic surgery have preoperative anemia (29, 30). Preoperative anemia is independently related to mortality, postoperative complications, and prolonged hospitalization in orthopedic surgeries (31). Seicean et al. reported that preoperative anemia should be considered as an independent risk factor for postoperative complications that warrants attention before an elective spine surgery, further emphasizing the importance of the preoperative hemoglobin level in predicting PMA in patients with STB (8). Interestingly, when anemia was complicated simultaneously with a known risk factor before operation, it led to a significant aggravation in the impact of this risk factor on the outcomes of noncardiac surgeries (32). Thus, preoperative anemia determined by the preoperative hemoglobin level had the greatest weight in the scoring scale.
4.3 Operation-related findings: operation time and surgical approach
Many studies have shown that surgical blood loss, operative trauma, and duration of anesthesia are risk factors for postoperative complications, including anemia (33, 34). In the current study, operation time, which can reflect surgical blood loss, operative trauma, and anesthesia duration, was identified as an independent risk factor for PMA. The average operation time in patients who presented with PMA was 220.13 ± 58.32 min, whereas that in patients who did not develop PMA was 196.08 ± 52.67 min (P = 0.002). The ROC curve analysis revealed that an operation time of 205 min was the optimal cutoff value for PMA. Controlling the operation time less than 205 min can decrease the possibility of PMA in patients with STB.
In STB focus debridement, anterior and posterior surgical approaches are usually performed. Our study found that the use of the posterior approach is an independent risk factor for PMA, whereas the use of the anterior approach is not. The anterior approach is superior to the posterior approach in terms of operation time, intraoperative blood loss, and correction of the Cobb angle (35, 36). Moreover, the advantages of anterior approach are also including adequate debridement, less muscle injury, better decompression, and better interbody fusion cage placement. However, due to the establishment of the surgical channel the anterior approach may lead to some unsatisfactory orthopedic outcome like more serious pain and even more complications in chest and abdomen (37). In contrast, the posterior surgical approach can not only achieve more steady implant fixation but also better kyphosis correction. However, it’s disadvantages including insufficient lesion removal and nerve decompression, increased surgical blood loss, and longer operation time (38). In summary, the anterior approach has better decompression effects and a lower PMA risk, whereas the posterior approach has better orthopedic effects but a higher PMA risk.
4.4 Scoring scale
Patients with STB have poorer immunity, experience bigger operative trauma, and have a higher risk of developing postoperative adverse events (15, 39). The establishment of a scoring scale for predicting PMA after STB debridement surgery is crucial for the perioperative management of patients and can effectively help physicians in making decisions about postoperative treatment strategies. To our knowledge, this is the first study to quantify the risk of PMA in patients with STB. However, there were some limitations to the develop the scoring scale. Owing to the small sample size of the validation set, the diagnostic accuracy of the scale cannot be fully validated. As the sensitivity of the scale was not high, a significant rate of missed diagnosis may exist. In addition, there may have been other independent clinical risk factors that were not analyzed in the present study. Further studies are warranted to confirm the validity of the scoring scale and improve it for the risk assessment of PMA in patients with STB.
4.5 Recommended level of preoperative hemoglobin
Studies on PMA in patients with STB are lacking. Accordingly, no study has provided recommendations on the adequate preoperative hemoglobin level in patients with STB. Therefore, our study may be the first of its kind. We found that one of the independent risk factors vital to the occurrence of PMA in patients with STB was the preoperative hemoglobin level. On the basis of the treatment principles of personalized and precision medicine, we believe that it is necessary to further explore the adequate preoperative hemoglobin level in patients with STB (40, 41). Therefore, we established a scoring scale for PMA in patients with STB, on the basis of which we divided the patients into the low-, moderate-, and high-risk groups. Thereafter, we obtained the values of the perioperative hemoglobin level changes in the three groups. By combining the WHO diagnostic criteria for moderate anemia (hemoglobin level < 90 g/L) and the values of the perioperative hemoglobin level changes in the three groups, the recommended preoperative hemoglobin levels for the three groups of patients with STB were determined as follows: low-risk group, 110 g/L; moderate-risk group, 115 g/L; and high-risk group, 120 g/L. Interestingly, the recommended preoperative hemoglobin level for the high-risk group was compatible with the diagnostic criteria for mild anemia, and the recommended preoperative hemoglobin levels for the low- and moderate-risk groups were both < 120 g/L, which indicates that preoperative mild anemia in some patients with STB is acceptable from the perspective of preventing PMA.
We found that the probability of PMA in low-risk patients is very low. For such patients, if the preoperative hemoglobin level is > 110 g/L, active intervention measures are not needed but close attention must be paid to postoperative hemoglobin changes. However, for the moderate- and high-risk groups, especially the high-risk group, if the preoperative hemoglobin level is lower than the recommended value, we believe that preoperative interventions are necessary, such as iron and erythropoietin supplementation for iron deficiency anemia, vitamin B12 supplementation for megaloblastic anemia, application of tranexamic acid before surgery, optimization of the surgical process, and preoperative blood transfusion if necessary (42, 43). We hope that the recommendations on the preoperative hemoglobin level in this study would help improve the trend in postoperative hemoglobin level changes and reduce the occurrence of PMA in patients with STB.
This study had some limitations. First, there may be some risk factors that we did not consider. Second, the sample size of the validation set was small. Third, we did not perform validation of the recommended preoperative hemoglobin levels. Future studies addressing these issues are required to confirm our results.