SSI secondary to spinal surgery is considered to be related to many factors [6, 7], some of which are related to the patients themselves, while some are related to the treatment methods. In this study, advanced age, surgical duration >3 h, serum albumin concentration <30 g/L, hemoglobin concentration <80 g/L, combined diabetes and blood loss >1,000 mL were the independent risk factors of SSI after spinal surgery in our hospital. Some studies have shown that age is an important factor that affects the incidence of SSI after spinal surgery [8, 9]. In particular, for elderly subjects aged >60 y, the incidence of SSI after spinal surgery increases significantly. It has been reported that the risk of SSI after spinal surgery in the elderly aged ≥60 y is 3 times higher than that in the younger age group [10]. Schoenfeld et al. [11] analyzed 126 patients with SSI secondary to spinal internal fixation via the posterior approach and found that the risk of postoperative infection in patients aged 60–70 y, 71–80 y, and ≥81 y was significantly higher than that in those aged ≤59 y. Fang et al. [10] reviewed 1,095 patients undergoing spinal internal fixation via the posterior approach; the average age of SSI patients was 47.8 y. Among the 48 patients with SSI, 17 were >60 y old, accounting for 35.4% of the patients with infection. Thus, it was concluded that patients aged >60 y had a higher risk of SSI. In the present study, advanced age was also a factor of SSI following spinal surgery. According to logistic regression analysis, the OR value of SSI after spinal surgery in elderly patients in this study was about 3. The immune systems of elderly patients degenerate, and they typically have multiple underlying diseases. In our study, of the 4,350 patients undergoing spinal internal fixation via the posterior approach, 1,680 were aged >60 y old. Elderly patients always present with degeneration of the immune system, mostly accompanied by multiple underlying diseases. Heart disease leads to a decline in the cardiac ejection capability and a decrease in blood supply to the tissues. Moreover, the decrease in local blood supply causes weakness of local resistance and self-healing ability in the body that increases the infection risk. In addition, hypertension can cause vascular lesions and reduce the local blood supply to the surgical site.
Long surgical duration will increase the risk of SSI secondary to spinal internal fixation via the posterior approach. Long surgical duration increases the risk of wound infection in patients that may be caused by the extension of surgical duration, increased duration of tissue traction; further, soft-tissue traction leads to local tissue ischemia and necrosis. The extension of surgical duration also increases the chance of wound contamination in patients. Our study showed that the rate of postoperative SSI increased significantly in patients with surgical duration >3 h. Apisarnthanarak et al. [12] reported that the incidence of postoperative infection increased significantly when the duration of spinal surgery was >3 h. In addition, combined diabetes is an important risk factor for incision infection in patients undergoing spinal surgery. A relevant study showed that the risk of postoperative infection in diabetic patients was much higher than that in non-diabetic patients [13]. Abdul-Jabbar et al. [14] retrospectively analyzed 6,628 hospitalized surgical patients and found that diabetes significantly increased the SSI risk. Olsen et al. [13] considered diabetes as an independent risk factor for SSI. Our results showed that diabetes was correlated with SSI after spinal surgery. The OR value of patients with diabetes was 4.47, indicating that the risk of postoperative infection in patients with diabetes was nearly 4 times higher than that in patients without diabetes. SSI after spinal surgery in patients with diabetes is mainly associated with diabetes-related autoimmune disorders, decreased wound healing ability, and capillary lesions. Diabetic microangiopathy can cause local tissue ischemia and hypoxia and reduce the antibiotic concentration in tissues [15]. The immune cell function of patients with diabetes is damaged, leading to relative inhibition of the immune function of the body. If there is pathogen invasion, it is very prone to infection [16]. The function of platelet-derived growth factor in patients with diabetes is also affected, resulting in a decline in the wound healing ability. Moreover, serum albumin concentration <30 g/L was an independent risk factor for postoperative SSI, consistent with the report by Klein et al. [17]. Further, intraoperative blood loss >1,000 mL combined with postoperative hidden blood loss [18] is another independent risk factor for postoperative SSI. Severe anemia can reduce the ability of tissue repair and anti-infection, increasing the risk of postoperative infection. Research [19] has shown that when the hemoglobin level is <80 g/dL, the oxygen-carrying capacity of blood is seriously reduced, and local tissue hypoxia reduces the local resistance to infection. In addition, patients with anemia present with a severe shortage of transporters needed to repair tissues, thereby leading to the decrease in the local repair ability and susceptibility to infection, consistent with the results of our study. This investigation showed that all patients underwent routine blood biochemical examination after the surgery; the postoperative changes in albumin, hemoglobin, and other nutritional status indicators were detected timely, and treatment was given. Moreover, the patients were asked to strengthen their nutritional status and eat a high-protein diet. Parenteral nutrition support was needed when the nutritional status indicators were very poor. Some patients also required albumin infusion and blood transfusion.
How to reduce the incidence of SSI secondary to spinal internal fixation via the posterior approach has always been a challenging issue. First, the surgical indications should be strictly grasped, and surgical treatment can be considered after ineffective conservative treatment. Second, underlying diseases should be controlled and treated. For elderly patients with anemia and low serum albumin concentration, the underlying diseases and general conditions should be strictly evaluated, blood glucose should be actively controlled, and anemia and hypoalbuminemia should be corrected. In this study, although smoking was not a risk factor for SSI following spinal surgery, smoking cessation could effectively improve respiratory function, increase functional residual capacity, and reduce the incidence of postoperative pulmonary complications. Therefore, patients with long-term smoking should give up smoking for 2 wk before the surgery [20]. If necessary, lung CT and lung function tests should be performed to evaluate the lung condition of patients. Our study showed that the beginning time of surgery was not a risk factor for SSI following spinal infection. However, on the morning of one day, surgeons are energetic and can perform the operation more precisely. Reasonable design of the surgical plan, the concept of small incision, minimal invasion, and reduction in intraoperative blood loss and surgical duration are needed. The aseptic management of the operating room should be strengthened, and the aseptic concept of surgeons and nurses should be improved. Furthermore, postoperative care should be strengthened, patients should be guided toward early activities, postoperative wound management should be improved, the wound status should be frequently monitored, and antibiotics should be administered reasonably as per the wound and the general conditions. The risk factors are relatively independent; however, more often, they are interrelated and influenced by each other. To reduce infection rate, rather than controlling a certain factor in isolation, we need to understand the basic condition of patients with respect to all the aspects and design a reasonable treatment plan as per the condition. Only in this way can we effectively reduce the rate of SSI secondary to spinal internal fixation via the posterior approach.
This study also has certain limitations, such as the fact that only one spinal cord research center in Western China was the study setting. Considering the cross-sectional nature of this study, causality between the results and the investigation variables could not be evaluated. In order to better understand the risk factors related to infection secondary to spinal internal fixation via the posterior approach in China, a longitudinal cohort study is required for a deeper understanding of the factors involved in the infection after spinal surgery and the effects of these factors on the infection rate. Moreover, the inclusion of non-randomly selected participants may lead to unpredictable biases. Despite the above limitations, this study identified factors closely related to infection secondary to spinal internal fixation via the posterior approach and proposed improvement strategies and intervention measures that will ultimately reduce the infection rate after spinal surgery.