SSI has been found to be the most common complication in spinal surgeries serious consequences like debridement negative impact on patient-reported clinical outcomes, potential need for instrumentation removal, and increasing patient mortality. Therefore, SSI causes huge healthcare and economic burden. Previous studies have shown that the SSI rate following posterior cervical spine surgery range from 1.4%-13% higher than anterior cervical spine5,6,19. In our study, patients who had surgery for osteomyelitis, discitis, epidural abscess, primary or metastatic tumors were excluded due to their inherent risk of SSI. the overall rate of clinically significant SSI after posterior cervical spine surgery was 4.93%. the incidence of SSI reported in our study was consistent with that reported previously in the literature.
In previous reports on SSI, many estimated risk factors were reported. However, there are many debates regarding the risk factors of SSI. In this study, we performed univariate and multivariate analyses to investigate the impact of related risk factors for development of SSI. In the univariate analysis, subcutaneous FT (P < 0.001), ratio of subcutaneous FT/MT (P < 0.001), preoperative JOA Scores (P < 0.01), preoperative serum albumin (P < 0.01), postoperative drainage (P < 0.01), time of draining (P < 0.001) were identified as significant risk factors. in the multivariate logistic regression model, we entered all variables, except for those identified in the univariate analysis as no significant (P > 0.05) effects. With subsequent multivariate analysis, we were able to identify 4 independent factors ratio of subcutaneous FT/MT (P < 0.01), preoperative JOA scores (P < 0.01), preoperative serum albumin (P < 0.001), time of draining (P < 0.001) influenced patients’ risks of SSI following posterior cervical spine surgeries.
High BMI was a recognized, independent risk factor in SSI following spine surgery11,20. Currently, more and more studies have found that the distribution of subcutaneous fat at the site of surgery not high BMI has been previously shown to affect the risk of SSI following lumbar spine fusion, with the subcutaneous FT being an independent risk factor for infection21–23. This association has also been previously shown to increase the risk of SSI after spine surgery procedures. Obese patients are at a greater risk of SSI because of the increased the subcutaneous FT at the surgical site. The increased FT may require a longer incision, wider dissection, and increased retraction. Operative time is also increased because of the increased difficulty of the surgery in these patients. As retraction is prolonged, the duration of decreased blood flow becomes longer, increasing tissue necrosis at the surgical site. Besides, redundant soft tissues and a poor wound healing environment making closure of the wound challenging, which were possible reasons for an increased risk of SSI resulting from tissue necrosis in obese patients. In the present study, the MT was not a risk factor for SSI, demonstrating that FT is at the highest risk for necrosis while MT not. Thick subcutaneous FT may allow for the development of a dead space after wound closure. This can play a role in the development of SSI following posterior cervical spine surgery. In this study, we demonstrated that the most useful predictor of incisional SSI is the ratio of FT/MT, which reflects the distribution of subcutaneous fat more accurately excluding individually influence.
At present, the relationship between SSI following posterior cervical spine surgeries and surgical site drains is still controversial. The surgical site drain was mainly started in cervical spine surgeries to prevent the formation of epidural hematoma or seroma which may cause neurological deficit and increasing the tension on the incisions resulting in wound-related complications namely SSI and wound dehiscence24. Wound drain apart from supposedly aiding in SSI prevention, could cause retrograde infection, increase post-operative blood loss which increases the need for blood transfusion. In our study, drainage time was an independent risk factor for postoperative SSI. In addition, Payhs et al.25 suggested that surgical site drains in the posterior cervical spine in combination with alcohol foam or vancomycin powder are associated with reduced odds of SSI among patients undergoing any posterior cervical spine surgery.
Current evidence demonstrates a strong and independent association between malnutrition and infectious and wound complications following posterior cervical spine surgeries15,16. Our results support the use of laboratory nutritional screening as a component of preoperative patient assessment and optimization to solve the difficulty of assessment of nutritional status of different people. In this study, decreased preoperative serum albumin (< 3.5 g/dL) significantly increased the risk of postoperative SSI. Additionally, low albumin level would suppress the patients’ immune function and impaired the wound healing, which increased the risk of SSI. Cooper et al.26 reported nutritional supplementation may provide a small reduction in infections in the spine trauma population. At present, the relationship between SSI following posterior cervical spine surgeries and preoperative malnutrition is still controversial, which needs to be confirmed by multicenter and large sample randomized controlled study.
At present, there are no study on the role of preoperative JOA score in SSI. In this study, we demonstrated an interesting result that preoperative JOA score was an independent risk factor of SSI following posterior cervical spine surgery. No clinical research pointed out this view before. A poor preoperative JOA score usually suggested to denervation, pressure sores and urinary retention. In one basic research, chronically denervated tissue is more susceptible to bacterial growth and difficulty in wound healing27,28. Poor nerve function may associate with difficulty getting out of bed resulting in pressure sores, and urinary retention may result in urinary tract infection. Those several reasons may attribute to SSI following posterior cervical spine surgery.
This study didn’t support for vancomycin predicting SSI possibly due to small infection rates while previous studies supported4,29−31. A possible theory for our results that are in contrast to those of other vancomycin studies is that local vancomycin may not have enough capacity to overcome the increased infection risk factors seen in patients undergoing fusion. Thus, the addition of other treatment modalities may be needed to prevent SSIs in the high-risk fusion population, such as improved nutrition or more stringent patient selection criteria. An additional consideration is that the current dosing of intrawound vancomycin may not be adequate, or the delivery of the medication does not last long enough in the local environment to completely control bacterial growth for these large, deep incisions.
In prior studies, DM was identified as a significant risk factor for SSI after spinal surgery32. However, in our study, DM was not significantly associated with SSI. Blood glucose were well controlled before operation, the smaller number of patients with DM, and the inclusion of several potential risk factors in the final multivariate logistic model may have been responsible for these results. Due to the same types of surgery, the intraoperative segments are mostly 3 or 4, so the operation time is relatively close. Similarly, gender, steroid use, current smoking, history of previous SSI, estimated blood loss, and surgical procedure were not identified as risk factors in our study, although they have been found to be significant risk factors for SSI in previous studies33.
First, this was a retrospective nonrandomized case-control study, and the number of patients with SSI in this study was relatively small.
Our study has several limitations. First, this was a retrospective nonrandomized case-control study, and the number of patients with SSI in this study was relatively small. The low rate of SSI could have prevented us from detecting correlations and statistical differences on some variables. Multicentric data pooling could help increase the included number of patients and overcome this limitation. Second, some variables that have potential to influence the development of SSI were not included because they were not considered before the start of the study, such as type of cervical pathology, anticoagulation used, neurological outcomes, cause of death and adverse reaction to transfusion. In addition, in some cases, such as those vancomycin-related reactions, and liver disease, the sample size was too small to allow investigation of their effects on SSI occurrence. Owing to these limitations, high-quality observational studies and basic experimental studies are still needed to investigate new risk factors for SSI further in the future.