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Analysis of adolescent idiopathic scoliosis population for Surgical Site Infection Risk Factors
⁎Corresponding author: John G. Thometz. jthometz@childrenswi.org
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
The incidence of surgical site infection (SSI) in adolescent idiopathic scoliosis (AIS) patients undergoing surgical correction varies but is commonly reported between 0.5 and 6.7 %. The identification of modifiable risk factors is crucial to preventing these infections in the AIS population. Some potential modifiable risk factors include the use of stainless-steel implants, a larger volume of instrumentation and an increased volume of blood products transfused. However, evidence in support of these factors and others representing true risk for the development of SSI is limited and often varies. We aimed to determine the incidence of SSI in AIS undergoing primary scoliosis fusion at our hospital, and explore demographic and clinical variables in the development of SSI in AIS.
This was a case control retrospective study. Patients aged 10-19 year-old that underwent posterior spinal fusion for initial correction of AIS at our hospital between the years 2012–2020 were eligible. Patients with any previous spine surgery or spine fracture were excluded. A descriptive analysis was then performed on the data.
Of the 334 patients on which data was collected, one SSI was identified resulting in an incidence of infection of 0.3 %. The largest ethnicity represented was Caucasian with 254 patients. The average age was 14.3 years with averaged follow-up of 6.6 years. The majority of patients (252) received implants composed of titanium and cobalt chrome. The average operation duration was 5 h and 7.7 min, and the average hospital stay was 4.2 days. The average amount of blood loss was 553 ml. Chlorhexidine wipes or some other antimicrobial preparation was used on 197 patients and betadine solution was used on 321.185 patients were recorded to have received either antibiotic-loaded allograft or antibiotic powder and 326 patients were recorded to have received intraoperative antibiotics.
The long term clinical follow up of our study and low incidence of infection provide additional evidence for the benefit of antimicrobial techniques and risk factor mitigation previously suggested in the literature for the prevention of SSI in AIS.
Level III.
Keywords
Adolescent idiopathic scoliosis
Surgical site infection
Spinal fusion
1 Introduction
The incidence of surgical site infection (SSI) in adolescent idiopathic scoliosis (AIS) patients undergoing surgical correction varies but is commonly reported between 0.5 and 6.7 %.1 This is notably lower than the incidence of infection in patients with a primary diagnosis of neuromuscular scoliosis, which ranges from 4.3 to 14.3 %.1 Current literature suggests that this discrepancy in infection incidence is related to the presence of unmodifiable risk factors in the neuromuscular population such as severe cognitive impairment as well as urinary and bowel incontinence1,2. As such, recent literature has focused on the identification of modifiable risk factors for infection and current best practice guidelines (BPG) derived from expert consensus identify Body Mass Index (BMI) >30, thirteen levels of fusion or greater, and fusion to the pelvis, among other factors, as “high-risk” for infection.3 However, evidence in support of these factors and others representing true risk for infection is limited and often varies2,3. Current BPG also advocate for the employment of infection prevention strategies including preoperative antibiotics, chlorhexidine skin prep, intraoperative wound irrigation, and topical/intrawound antibiotics, yet again with limited supportive evidence3,4. The development of SSI is a cause of significant morbidity and cost to patients and their families, often resulting in increased length of hospital stay, increased rates of readmission, and the need for additional surgical procedures.5 Given the substantial physical, psychological, and financial burden associated with SSI, further exploration of risk factors for SSI and strategies to prevent them is warranted. We hypothesized that multiple key factors including BMI, antimicrobial prophylaxis, instrumentation variables, and others are associated with an increased risk of SSI in the AIS population. We aimed to determine the incidence of SSI in patients with AIS undergoing primary scoliosis fusion at our hospital, explore demographic and clinical variables in the development of SSI in AIS patients, and compare SSI prevention strategies noted in the literature and used at our hospital.
2 Materials and methods
This was a case control retrospective study utilizing the electronic medical record. Patients aged 10–19 that underwent posterior spinal fusion for initial correction of AIS at our hospital between the years of 2012–2020 were eligible. Patients with any previous spine surgery or spine fracture were excluded. Patient charts were reviewed from the date of operation up to the present day with minimal two-year follow-up. In total, 818 patient charts were reviewed and 333 met inclusion criteria. Data was collected on the following variables: age, sex, race, BMI, number of vertebral levels fused, instrumentation material, graft usage, blood loss, blood transfused, operation duration, antimicrobial prophylaxis, and length of hospitalization. SSI was defined as positive wound culture in the presence of additional signs of infection including, but not limited to fever, increased wound drainage, increased wound erythema, and poor wound healing. For patients diagnosed with SSI, data was collected on postoperative elapsed time to infection diagnosis, pathogen identity, infection treatment, and if instrumentation was able to be salvaged. All personnel in the operation room wore a surgical hood to cover any exposed hair which potentially could be a source of infection. A descriptive analysis was performed on the data. This project was approved by our hospital's Institutional Review Board.
3 Results
Of the 333 patients on which data was collected, one SSI was identified resulting in an incidence of infection of 0.3 %. The largest ethnicity represented was Caucasian (253), followed by Black (49) (Table 1). The average age at the time of operation was 14.3 years and the average BMI was 21.8. The average length of fusion was 10.3 vertebral levels and only one patient required instrumentation extending into the pelvis. All patients received a mixture of auto- and allograft, 251 patients received implants composed of titanium and cobalt chrome, and 22 patients received implants composed of stainless steel. The average amount of blood loss was 404 ml, and 27 patients were recorded to have received an intraoperative blood transfusion with an average amount transfused of 388 ml. The average operation duration was 5 h and 8 min, and the average hospital stay was 4.2 days. The average length of follow up was 6.6 years.
| Variables | Mean ± Standard deviation |
| Age (years) | 14.3 ± 1.99 |
| Sex (F, M) | 259 F, 74 M |
| Race/Ethnicity | 253 Caucasian, 49 Black, 9 Asian, 6 Latino, 2 Other |
| BMI | 21.8 ± 4.76 |
| Length of fusion (vertebral levels) | 10.3 ± 2.07 |
| Patients with instrumentation extending into pelvis | 1 |
| Instrumentation material | 251 Titanium/Cobalt Chrome, 24 Cobalt Chrome, 4 Titanium, 22 Stainless Steel, 32 NA |
| Operation duration (hours, minutes) | 5 h, 8 min ± 1.06 h |
| Blood loss (ml) | 404 ± 290.12 |
| Patients with blood transfusions | 27 |
| Amount transfused (ml) | 388 ± 123.57 |
| Chlorhexidine wipes | 196 |
| Betadine solution | 320 |
| Antibiotic loaded allograft or antibiotic powder | 224 |
| Intraoperative antibiotics | 325 |
| Length of hospitalization (days) | 4.2 ± 1.37 |
| Length of follow up (years) | 6.6 ± 1.81 |
Regarding infection prevention techniques, 325 patients were recorded to have received preoperative antibiotics with the most common being Cefazolin (270/333) followed by Clindamycin (36/333). Chlorhexidine prep or some other form of antimicrobial preparation was recorded to have been used on 196 patients and intraoperative irrigation with betadine solution was used on 320. The use of either antibiotic-loaded bone graft or the application of antibiotic powder to the bone graft site was used in 224 patients.
The sole SSI identified occurred in a fourteen-year-old Black male with a BMI of 22.4 who underwent posterior fusion of nine vertebral levels. The operation duration was approximately 6.6 h, and he did not require a blood transfusion. The surgical site was prepped with chlorhexidine prep, he received preoperative antibiotics, intraoperative irrigation with betadine was used, and antibiotic powder was applied to the fusion site. Infection was diagnosed nine days postoperatively upon presentation to the Emergency Department for continued wound dehiscence. Wound cultures taken at that time returned positive for Mycoplasma hominis and the patient returned to the operating room for an incision and drainage procedure with removal of bone graft and placement of a wound vacuum. He required one additional operative procedure for wound closure and was treated successfully with approximately eight weeks of antibiotics (Vancomycin, Meropenem, Doxycycline). Instrumentation was able to be retained and he was doing well at two-year follow-up.
4 Discussions
The Centers for Disease Control and Prevention's National Healthcare Safety Network (CDC/NHSN) defines superficial SSIs as those involving only the skin and subcutaneous tissue of the incision, and developing within 30 days of surgery.6 They define deep SSIs as those involving deep soft tissues of the incision and occurring within one year of surgery if implantation is left in place. Much of the current literature cites these definitions of superficial and deep SSIs and uses them to construct study methodology with a focus on identifying either early or late developing infections. As such, many studies only include infections that develop less than one year after surgery.5,7–12 However, other studies focus on late developing infections and have identified infections occurring up to seven years postoperatively.13,14 This study is unique in that patient charts were reviewed from the date of surgery up until present day, allowing for both early and late developing infections to be included.
4.1 Infection prevention techniques
The incidence of infection of 0.3 % is on par with the lowest reported incidence of SSI in AIS patients undergoing primary scoliosis fusion in the literature. We suspect that this low incidence of infection is related to the employment of several infection prevention techniques at our institution that are supported by the literature and current BPG. Protocols for the avoidance of SSI in pediatric scoliosis patients in line with BPG are increasingly being implemented in hospitals across the US and a common element of these protocols is the administration of preoperative antibiotics.15 The choice of antibiotic has been reported to vary widely between hospitals, but prophylaxis against gram positive bacteria with first generations cephalosporins is common.16 In patients deemed to be of higher risk for developing SSI, such as those with a primary diagnosis other than AIS, broad-spectrum antibiotic prophylaxis is more common.17 Failure to administer preoperative antibiotics as well as inappropriate dosing and timing of preoperative antibiotics has been associated with increased risk of SSI2,7,.18 As 325 of 333 subjects in this study were recorded to have received preoperative antibiotics, we suspect that this decreased infection risk in this population.
In addition to preoperative antibiotics, the use of chlorhexidine prep to clean the surgical site prior to incision is a common element in SSI prevention protocols in the pediatric scoliosis population and has been associated with decreased risk of infection15,18. Tipper et al. described the implementation of an SSI prevention protocol at a children's hospital in the UK that included the use of chlorhexidine prep in preoperative skin cleaning.8 Four years after the implementation of this protocol, the hospital's incidence of infection dropped from 8.6 % to 2.2 %. As 196 patients in this study were recorded to have received skin preparation prior to incision with chlorhexidine or another antimicrobial preparation, this could also have contributed to the low incidence of infection.
Intraoperative betadine irrigation is commonly used to disinfect surgical wounds and is another common element of SSI prevention protocols in the pediatric scoliosis population despite the limited availability of evidence supporting its use in this population2,15. There is, however, significant evidence in support of its benefit in the adult population. Chang et al. conducted a prospective, randomized study to evaluate the safety and effectiveness of betadine solution in spinal surgeries in which the trial group received betadine irrigation just prior to bone grafting and instrumentation.19 No infections were identified in the study group (120 patients) compared to six infections in the control group (124 patients) with minimal differences in wound healing, success of fusion, and clinical outcome, leading the authors to conclude that betadine is safe and effective in reducing SSI risk. Tomov et al. also explored the safety and efficacy of betadine irrigation in combination with intra-wound vancomycin powder in reducing SSI in spinal surgery and reported a decrease in SSI rates by 50 %.20 Intraoperative betadine irrigation was recorded to have been used in 320 patients in this study and could have contributed to the low incidence of infection.
In addition to these measures, 224 of 333 patients in this study were recorded to have received antibiotic-loaded bone graft or had antibiotic powder applied directly to the bone graft site. This strategy is thought to decrease the risk of SSI by increasing the concentration of antibiotic at the wound site while limiting systemic toxicity.1 It is included in current BPG and there is evidence to support this as an effective strategy.15 Borkhuu et al. conducted a retrospective analysis of 220 children with cerebral palsy that underwent spinal fusion and found that the incidence of deep wound infection significantly decreased from 15.2 % to 3.9 % with the use of antibiotic-loaded bone graft.21 Furthermore, Kang et al. conducted a systemic literature review focused on the use of intra-site vancomycin powder to prevent SSI in spine surgery and concluded that while limited evidence regarding its benefit is available, it is commonly done and is thought to decrease the risk of infection with limited side effects.22 As such, it's possible that the use of antibiotic-loaded allograft and the application of antibiotic power to the wound site in many of the patients in this study contributed to the low incidence of infection.
4.2 BMI
Along with the infection prevention strategies noted above, we believe that the average BMI of patients in this study could have also contributed to the low incidence of infection. Current BPG identify BMI >30 as a factor associated with “high risk” for SSI and there is evidence in the literature to support this2,3,.18 In a review of 2122 patients that underwent posterior spinal fusion for correction of AIS, Newton et al. identified obesity as the only statistically significant risk factor for infection.9 A similar review by De la Garza Ramos et al., of 2712 patients that underwent spinal fusion for correction of AIS reported that obese patients were significantly more likely to develop a deep wound infection compared to normal weight patients.10 The Centers for Disease Control defines obesity as a BMI equal to or greater than the 95th percentile per age.23 The average BMI for patients in this study of 21.8 is far below the 95th percentile for the average patient age of 14.3 years and thus could have contributed to the low incidence of infection.
4.3 Operative variables
There are multiple operative variables that could have contributed to the low incidence of infection in this study as well. Current BPG identify thirteen levels of fusion or greater and fusion to the pelvis as factors associated with “high risk” for SSI and there is additional support for this in the literature3,11,.24 Even lower levels of fusion have been associated with increased risk of infection with one study identifying a length of fusion of greater than ten levels as a risk for SSI in pediatric spinal fusion.7 However, a study by Ho et al. reported that the number of spinals levels instrumented was not associated with increased risk of SSI.13 The average length of fusion in our study was 10.3 vertebral levels and only one patient required instrumentation extending into the pelvis.
The minimal use of stainless-steel implants (22/333) and patients requiring blood transfusion intraoperatively (27/333) are additional operative variables that could also have contributed to the low incidence of infection in this study. Di Silvestre et al. reported a higher incidence of infection in AIS patients undergoing posterior fusion with stainless steel implants as opposed to those made of titanium-alloy.12 Soultanis et al. reported similar findings with six AIS patients out of 50 developing SSI following fusion with stainless-steel implants compared to one out of 45 patients with titanium implants.14 Regarding blood loss, Milstone et al. reported that median estimated blood loss was significantly higher for pediatric scoliosis patients who developed SSI after fusion than for those for those who didn't, and that loss of an entire blood volume approximately doubles the risk of SSI.7 Ho et al. reported that AIS patients undergoing spinal fusion that received a blood transfusion were three times more likely to develop a delayed infection than those who didn't.13 However, several literature reviews concluded that there is limited evidence that blood loss and blood transfusions are risk factors for SSI in the pediatric scoliosis population2,24. Given the conflicting evidence currently available for which operative variables pose an increased risk for SSI, further research on this topic is warranted.
4.4 Limitations
Due to the identification of a single SSI in this study, we are unable to provide statistically significant evidence to comment on which factors represent a true risk for SSI in the AIS population. In a similar study conducted by Rhin et al., it was estimated that thousands of patients would be required in both the infection and non-infection groups in order to detect statistically significant differences in patient reported outcomes.25 It can be assumed that similar numbers would be required in order to detect significant differences between the groups in the many variables that have been suggested as possible risk factors for SSI. Given the rarity with which these infections occur in the AIS population, an extremely large multi-center study conducted over many years would be required to achieve this data and thus, is not feasible at the current time. As is the case with much of the current literature, a retrospective case-control study was deemed the only viable option to explore infection risk factors and prevention techniques in this population, and this study is limited by its retrospective nature.
This study was also limited by the use of the electronic medical record (EMR) to collect data. In an effort to include as many subjects as possible, data was collected from patients that underwent primary scoliosis fusion as early as 2012, the year in which the EMR was adopted at our institution. Due to the infancy of the EMR at that time, patient charts often lacked much of the information we sought to collect and limited our ability to accurately reflect the events from this period.
5 Conclusion
The extensive period of chart review in this study allowed for the inclusion of both early and late developing SSIs in the evaluation of risk factors for SSI and infection prevention strategies in the AIS population. Taken in consideration with the low incidence of infection, this study provides additional evidence for the benefit of infection prevention strategies described in current BPG such as the use of antimicrobial surgical site preparation, preoperative antibiotics, antibiotic-loaded allograft, antibiotic powder applied to the bone graft site, and intraoperative wound irrigation. Additionally, the data from this study can be used to support several population and operative variables previously suggested as risk factors for SSI.
CRediT authorship contribution statement
Jesse Fletcher: involved in, Data curation, data collection. Xue-Cheng Liu: assisted in, design of the study, verifying the statistical results. John G. Thometz: involved in, development of conception of the study and development of methodology of the study, as well as the validation of the results and revised / finalized the manuscript.
Consents
Analysis of Pediatric Scoliosis Population for Surgical Site Infection Risk Factors.
Consents were not required.
Ethical statement
Analysis of Pediatric Scoliosis Population for Surgical Site Infection Risk Factors.
PRO00045968 - Analysis of Pediatric Scoliosis Population for Surgical Site Infection Risk Factors (IRBNet 1761896) has been approved by Medical College of WI IRB committee.
Funding statement
Analysis of Pediatric Scoliosis Population for Surgical Site Infection Risk Factors.
No funding sources to report.
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