Management of deep surgical site infections of the spine: a Canadian nationwide survey

Introduction

Deep surgical site infections occur after posterior thoracolumbar instrumentation of the spine at a rate of 2–20% (1-5). These are associated with significant patient morbidity, prolonged hospitalization (6), poorer long-term outcomes (7) and high costs to the healthcare system (8,9). Generally, the approach to treatment involves surgical irrigation and debridement with subsequent antimicrobial therapy (10). Failure to achieve eradication of infection after surgical debridement and antibiotic therapy has been reported in up to 24% of patients (11).

The irrigation and debridement procedure generally involve a meticulous, layer by layer removal of any devitalized tissue, with fluid irrigation of the surgical site (10). There are currently no best practice guidelines with more specific recommendations regarding the surgical details of this procedure in the literature. Furthermore, no consensus guidelines from any major spine surgical organization exist on the advised best practice management of this surgical complication.

The volume, type of solvent, irrigation pressure and management of bone graft have not been studied. Bone graft, especially allograft, may be considered a nidus for infection and risk factor for infection recurrence (12); however, if removed in full this increases the risk for pseudarthrosis and hardware related complications. While there are theoretical benefits to hardware exchange, some authors suggest higher rates of reoperation and death with removal of hardware at initial washout (13). Other investigations have advocated for complete removal and exchange of hardware at the time of initial washout (14-16). Closure techniques vary (17) and the use of drains (17) or vacuum assisted closure (14,15) has mixed recommendations.

Given the lack of research and consensus on the variety of procedural options involved in the management of deep surgical site infections, the purpose of this survey was to investigate the surgical techniques amongst complex adult spine surgeons across Canada. We present the following article in accordance with the SURGE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-22-47/rc).

Methods

Survey development

A multi-stage development strategy was utilized to create our survey. Following a detailed review of the available literature on management options, a template was developed in keeping with previously published guidelines for academic survey development (18-20). Following this, a five-person focus group reviewed the template including two academic orthopaedic spine surgeons, one academic neurosurgeon and two spine surgery fellows. The focus group provided increased clarity, readability, and generalizability to the survey, while minimizing bias.

Ultimately, a 34-item questionnaire was developed by the authors with a 6-question demographic section (see Table 1) and 28-question practice preference section; divided into management of acute, and recurrent infection (see Table 2). The survey was administered via SurveyMonkey (https://www.surveymonkey.com/, Palo Alto, California). The survey link was delivered via three rounds of emails, delivered weekly over a three-week period to current practicing Canadian complex adult spine surgeons. Surgeons were identified at every Canadian centre providing spine surgery through departmental pages, and individual contacts at each site were queried to ensure that other respondents, potentially situated at satellite campuses, were not missed. A cover letter introducing the study to potential survey respondents was created by the study team and sent by the project Principal Investigator (C Oitment), to outline the study objective, explain passive consent via survey completion, emphasising the confidential and anonymized nature of the questionnaire, and providing an approximate time for survey completion. No incentives were provided for completion of the survey. Given that this was a questionnaire of expert clinicians with no appeal to patient specific information, Ethics Board approval was not required based on institutional guidelines.

The questionnaire was divided into two parts; acute and recurrent infection (see Table 2). Part I, “Acute Infection”, provided the following prompt: “For the purposes of this questionnaire, assume an acute infection to refer to a clinically obvious infection of an instrumented thoracolumbar fusion, which occurs during the immediate post-operative period”. We allowed respondents to determine the time period that defined an infection as acute. Part II, “Recurrent Infection”, began with the following prompt: “For the purposes of this survey, consider recurrent infection to represent ongoing, clinically obvious infection after initial irrigation and debridement. The sample case would be a 2–3 level instrumented lumbar decompression and fusion which recurs after initial washout”.

The survey began with an initial screening question asking whether the respondent would routinely manage an infection of the instrumented thoracolumbar spine. If the respondent indicated that they did not routinely manage this condition, the respondent was immediately disqualified, and no further responses were collected.

Respondents

Participants were selected from each academic institution as being surgeons mainly practicing in complex adult spine surgery. Responses were requested from surgeons practicing at every major academic institution in Canada, across all provinces. Surgeons practicing primarily in pediatric spine surgery were excluded. Neurosurgeons with primarily non-spine practices were also excluded.

Statistical analysis

Data were anonymized, and statistical analyses were conducted in the program R; version 4.1.0. Categorical data are summarized as counts and reported in Table 1 and Table 2. Fischer’s exact test accounted for the differences between categorical data. P values were two-tailed, with an a priori alpha value defined at 0.05 for statistical significance. Data was 94% complete with missing data imputed with multiple imputations using chained equations technique (R package mice). Imputed values used predictive mean matching using the first iteration with five imputations. The response rate was calculated by dividing the number of responses [53] by the number of invitations distributed [86]. Questions were optional (respondents were not required to answer all to proceed) and completion was only considered achieved when respondents answered all questions in the survey.

Consensus

The aim of this survey is to identify areas of consensus or discordance between surgeons in management strategies. Though ‘consensus’ is difficult to define, we a priori defined consensus liberally as >70% agreement between respondents.

Results

Eighty-six complex adult spine surgeons were contacted with first administration of the survey on January 15, 2022. Shortly following a second reminder email on January 27, a 61.6% response rate (53 responses) was achieved. Three of 53 respondents indicated that they were not comfortable managing infected posterior thoracolumbar instrumentation at which point the survey was terminated. These were counted as incomplete surveys. Survey completion rate was 77% with a 7-minute average time to completion. Demographic information regarding participants is included in Table 1. Most respondents (52.5%, 21/40) considered acute infections to be within a timeframe of 12 weeks, and 32.5% (13/40) defined their cut-off at 6 weeks. Results are divided into details of the irrigation and debridement (type of fluids, volume of fluids, method of fluid administration), management of bone graft, management of hardware, topical antibiotics and closure and post-operative antibiotics. Complete individual questions and responses are available in Table 2.

Irrigation and debridement

The primary method of irrigation for acute infection was gravity/manual pouring of fluids for 61.0% (26/42) of participants, with 26.8% (11/42) utilizing power/pulse lavage and 12.2% (5/42) utilizing manual bulb syringe. For acute posterior thoracolumbar infections, the primary solution was normal saline in 49% (21/42) of participants with 39% (16/42) utilizing bacitracin solution. Most respondents utilized adjuncts such as proviodine (56%) or peroxide (53%), few used chlorhexidine (6%; 2/34), and 29.4% (10/32) of respondents indicated using no adjuncts other than their main irrigant. No respondents indicated using bleach or Dakin’s solution. For recurrent/ongoing thoracolumbar infections, 51% (21/41) utilized normal saline primarily, 37% used bacitracin (13/41), and 13% preferred “alternative solutions” such as a vancomycin wash.

In terms of volume used, for acute thoracolumbar infections, 27% (11/42) utilized <3.1 L for washout, 44% (19/42) utilized 3.1–6.0 L, 24% (10/42) used 6.1–9.0 L and 4.9% (2/42) utilized >9.0 L. In the setting of recurrent/ongoing infection 28% (11/41) used <3.1 L, 32% (13/41) used 3.1–6.0 L, 32% (13/41) used 6.1–9.0 L, and 10% (4/41) of participants utilized >9.0 L.

Management of bone graft

For acute thoracolumbar infections, 5% (2/42) of participants removed allograft only, 32% (14/42) removed all bone graft, 9.8% (4/42) retained all bone graft and 54% (22/42) removed only loose graft (whether allograft or autograft). If bone graft was removed, 10% (4/39) placed new autograft at the time of washout, 8% (3/39) replaced the graft with allograft, 10% (4/39) staged a fusion procedure when the infection was cleared, 51% (20/39) return for grafting only if the patient becomes symptomatic with pseudarthrosis or loose hardware, and 20% (8/39) do not place new graft under any circumstances.

In recurrent/ongoing infections no (0%) participants removed allograft only, 54% (22/41) removed all graft, 5% (2/41) retained all graft and 41% (17/42) removed only loose graft. In this case, 8% (3/39) place new autograft at the time of washout, 5% (2/39) use allograft, 15% (6/39) stage bone grafting, 49% (19/39) only return for bone graft if the patient becomes symptomatic, and 23% (9/39) do not place graft under any circumstances.

Management of hardware

Participants were instructed to assume that hardware was stable (not loose) and in satisfactory position and then questioned as to their management of the hardware in the settings of both acute and recurrent infection. For acute infections, 83% (34/41) indicated that they routinely retain all hardware, 15% (6/41) performed a partial hardware exchange (set screws/rods) and no respondents (0%) exchanged all hardware. A single respondent reported removing hardware acutely and returning to re-instrument once the infection is cleared. Forty-three percent (18/42) of respondents indicated that they had considered a partial hardware exchange for acute infections in the last year.

In recurrent infections, 34% (14/39) retain all hardware, 20% (8/39) perform partial hardware exchange, and 46% (19/39) exchange all hardware.

For interbody implants, respondents were asked to distinguish between stable and loose implants. Interbody implants were routinely retained by 95% (40/42) of respondents for acute infections, with 5% (2/42) only removing cages if loose. In recurrent/ongoing infection, 71% (29/41) retain cages, 10.0% (4/41) exchange cages, 5.0% (2/41) remove cages all together and 15% (6/41) remove loose cages.

Topical antibiotics and closure

For acute thoracolumbar infections, prior to closure, topical glycopeptides (e.g., vancomycin powder) were used by 59% (25/42) of respondents, one respondent (2%) used aminoglycosides (e.g., tobramycin powder/pellets), 33% (14/42) used no topical antibiotic and 5% (2/42) utilized other topical agents.

For ongoing/recurrent infection topical glycopeptides are used by 66% (27/41) of respondents, 17% (7/41) utilize aminoglycosides, 15% (6/41) utilize no topical antibiotics and one used topical Cefazolin.

In acute infection, fascia was closed with braided absorbable sutures (such as Vicryl) by 62% (26/42) of participants, 2% (1/42) used braided nonabsorbable (such as Ticron), 21% utilized an absorbable monofilament (9/42) and 14% (6/42) utilized a nonabsorbable monofilament suture. Skin was closed using nonabsorbable monofilament by the majority of respondents; 52% (22/42). Thirty-three percent (14/42) used staples, 12% (5/42) preferred absorbable monofilament, and 2% (1/42) used braided absorbable sutures.

Similarly, in recurrent/ongoing infections 61% (25/41) used braided absorbable suture, 2% (1/41) used nonabsorbable braided, 27% (11/41) used absorbable monofilament, and 10% (4/41) used nonabsorbable monofilament. For skin closure in recurrent infection, 61% (25/41) utilize nonabsorbable monofilament, 24% (10/41) use staples, 12% (5/41) utilize absorbable monofilament, and 2.5% (1/41) use absorbable braided suture.

Negative pressure vacuum assisted closure was utilized by 38% (16/42) of respondents for acute infection.

Analysis by specialty, years of training, and number of cases

Fischer’s exact tests failed to identify any statistical differences between type of training (Orthopedic vs. Neurosurgery) and answer responses to any questions. These tests also failed to provide any statistical difference in years of training or number of cases performed yearly, in response to any of the questions on the survey.

Discussion

Deep spinal surgical site infections are a challenging complication of instrumented thoracolumbar spine surgery. Herein we present a relatively large survey of Canadian complex spine surgeons with a high response rate. There was a consensus to retain hardware (80%) and interbody implants (93%) in acute infection, to retain interbody implants in chronic/recurrent infection (71%), and application of topical antibiotics in recurrent infection (85%). There was consensus on the use of absorbable suture to close fascia in acute (83%) and chronic (87%) infection. Eighty-five percent of surgeons used nonabsorbable materials such as Nylon or staples for skin closure in chronic infection, however, there was no consensus in acute infection. Aside from these points, there was significant heterogeneity in type, volume and pressure of fluids, adjuvant solvents, graft management, use of topical antibiotics acutely, and the use of negative pressure wound therapy. Partial hardware exchange was controversial.

Currently no level one evidence exists, and there are no published guidelines from major spine society organizations regarding surgical management of spinal infections. A recent systematic review by Lall et al. (21) on the management of surgical site infection after spinal instrumentation found that all published literature advocated for early surgical debridement and antibiotic therapy. They also found that hardware retention was generally successful in acute infection, whereas removal was necessary in delayed hardware infections with high rates of treatment failure with hardware retention. This is consistent with the answers from our respondents.

Hersh et al. (13) [2021] performed a systematic review of removal of instrumentation of post-operative spine infections. Five of 15 studies were found to document rates of instrumentation removal in early and late infection. Seventeen of 160 (11%) patients underwent instrumentation removal in early infections compared to 99/172 (58%) of patients with instrumentation removal in chronic infections (13). The author concluded that retention of hardware in early infections is preferred to maintain spinal stability. However, in late infection, removal of hardware is often necessary to eradicate colonized bacteria in the mature biofilm adherent to the hardware.

The decision to remove hardware can also be influenced by location of the infection and length of construct. Pull ter Gunne et al. (22) suggest that infections superficial to the fascia do not require hardware removal and in their series, 73% (35/48) of superficial surgical site infections were treated without surgical debridement. It should be noted that in practice differentiation of superficial and deep infections can be difficult and treating most infections as deep has been suggested (23). In addition, increasing length of the instrumented construct may be associated with lower rates of hardware exchange in the setting of infection (24), however, this survey was not designed to detect such differences.

Failure to eradicate infection in the setting of chronic infection with hardware retention range from 50% (25) to 100% (26). Our survey indicates that Canadian surgeons have higher rates of hardware exchange with recurrent/ongoing infection; however still 34% of respondents retain all hardware and 20% perform a partial hardware exchange (set screw/rod removal with retention of screws) for recurrent infection. To our knowledge, there is no evidence in the literature currently to support partial hardware exchange.

Interestingly, despite risks for non-union/pseudarthrosis and delayed hardware complications, few surgeons provide any graft substitute when removing graft at the time of surgical debridement. Most surgeons remove all graft at the initial debridement. In recurrent infection, most surgeons indicate they would either stage a procedure for fusion or return if the patient becomes symptomatic from nonunion.

With respect to preferred irrigation technique in the setting of a deep spinal infection, most surgeons utilize gravity/manual pouring of fluids over more aggressive pressure washing/pulse lavage, with normal saline being the preferred primary solution for both acute and chronic infections. Counter-intuitively, the strategy for clearing infection does not appear to rely on volume of fluid, nor antimicrobial fluid irrigation, as similar volume and type of fluid was utilized for both acute and recurrent infection. The responses that changed significantly between acute and recurrent infection management were removal of bone graft, and tendency toward hardware exchange, both of which were more frequent in chronic/recurrent infection.

We report on a comprehensive population of surgeons across the country with a diversity of experience and background. The Canadian healthcare system is unique in being a single-payer public system, so this may bias some respondents towards resource conservation. Despite this unique commonality, we still found little agreement in our data and believe our results to be generalizable to other populations and countries offering complex spine surgery. Our data analysis did not yield any significant differences in management strategy based on surgical background (orthopedic versus neurosurgery), years of training, or number of cases performed yearly. This reflects the fact that neither specialty nor experience can inform practice management in the absence of clinically relevant data. There is a need for future studies to clarify the rates of failed irrigation/debridement, quantify the morbidity and costs associated with deep surgical site infections as well as subsequent failed treatment. This study is limited by the complexity of clinical decision-making around infection management, the case-specific factors of which are difficult to capture in a multiple-choice survey. Given survey anonymity, we are unable to comment on demographic differences of non-responders, which may be a potential source of bias. Even so, this survey demonstrates that this is a complex problem with variable management strategies predicted neither by surgeon background nor by patient factors. Given the heterogeneity of practice across Canadian surgeons, a consensus statement is needed to guide the treatment of surgical site infections. The areas of controversy in this questionnaire should be targeted for areas of future study, including type, volume and pressure of fluids, adjuvant solvents, management of graft, and use of topical antibiotics.

Conclusions

This survey is the first to investigate opinions regarding surgical management of instrumented spine surgical site infection across the entire body of Canadian adult spine surgeons. The results demonstrate scant agreement between surgeons in the management of deep surgical site infection following instrumented thoracolumbar fusion. We highlight the need for higher quality evidence and subsequently, guidelines for surgical management. We have identified eight main areas for future study including type, volume and pressure of fluids, adjuvant solvents, management of graft and hardware, utility of intrawound antibiotics, and closure techniques.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the SURGE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-22-47/rc

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-22-47/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-22-47/coif). MB has received grants/contracts from the following entities in the past 36 months: Canadian Institutes of Health Research (CIHR), National Institutes of Health (NIAMS & NICHD), Physicians’ Services Incorporated (PSI) and the U.S. Department of Defense. MB is also a committee member of the International Society of Orthopaedic Surgery & Traumatology (SICOT). The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Smith JS, Shaffrey CI, Sansur CA, et al. Rates of infection after spine surgery based on 108,419 procedures: a report from the Scoliosis Research Society Morbidity and Mortality Committee. Spine (Phila Pa 1976) 2011;36:556-63. [Crossref] [PubMed]
2. Zhou J, Wang R, Huo X, et al. Incidence of Surgical Site Infection After Spine Surgery: A Systematic Review and Meta-analysis. Spine (Phila Pa 1976) 2020;45:208-16. [Crossref] [PubMed]
3. Collins I, Wilson-MacDonald J, Chami G, et al. The diagnosis and management of infection following instrumented spinal fusion. Eur Spine J 2008;17:445-50. [Crossref] [PubMed]
4. Gerometta A, Rodriguez Olaverri JC, Bitan F. Infections in spinal instrumentation. Int Orthop 2012;36:457-64. [Crossref] [PubMed]
5. Kasliwal MK, Tan LA, Traynelis VC. Infection with spinal instrumentation: Review of pathogenesis, diagnosis, prevention, and management. Surg Neurol Int 2013;4:S392-403. [Crossref] [PubMed]
6. Aleem IS, Tan LA, Nassr A, et al. Surgical Site Infection Prevention Following Spine Surgery. Global Spine J 2020;10:92S-8S. [Crossref] [PubMed]
7. Haddad S, Núñez-Pereira S, Pigrau C, et al. The impact of deep surgical site infection on surgical outcomes after posterior adult spinal deformity surgery: a matched control study. Eur Spine J 2018;27:2518-28. [Crossref] [PubMed]
8. Blumberg TJ, Woelber E, Bellabarba C, et al. Predictors of increased cost and length of stay in the treatment of postoperative spine surgical site infection. Spine J 2018;18:300-6. [Crossref] [PubMed]
9. Excess cost and inpatient stay of treating deep spinal surgical site infections. Accessed February 19, 2022. Available online: https://journal.nzma.org.nz/journal-articles/excess-cost-and-inpatient-stay-of-treating-deep-spinal-surgical-site-infections
10. Daldal I, Senkoylu A. Strategies of management of deep spinal infection: from irrigation and debridement to vacuum-assisted closure treatment. Ann Transl Med 2020;8:33. [Crossref] [PubMed]
11. Manet R, Ferry T, Castelain JE, et al. Relevance of Modified Debridement-Irrigation, Antibiotic Therapy and Implant Retention Protocol for the Management of Surgical Site Infections: A Series of 1694 Instrumented Spinal Surgery. J Bone Jt Infect 2018;3:266-72. [Crossref] [PubMed]
12. Hegde V, Meredith DS, Kepler CK, et al. Management of postoperative spinal infections. World J Orthop 2012;3:182-9. [Crossref] [PubMed]
13. Hersh A, Young R, Pennington Z, et al. Removal of instrumentation for postoperative spine infection: systematic review. J Neurosurg Spine 2021; Epub ahead of print. [Crossref] [PubMed]
14. Chang CW, Fu TS, Chen WJ, et al. Management of Infected Transforaminal Lumbar Interbody Fusion Cage in Posterior Degenerative Lumbar Spine Surgery. World Neurosurg 2019;126:e330-41. [Crossref] [PubMed]
15. Cho OH, Bae IG, Moon SM, et al. Therapeutic outcome of spinal implant infections caused by Staphylococcus aureus: A retrospective observational study. Medicine (Baltimore) 2018;97:e12629. [Crossref] [PubMed]
16. Bémer P, Corvec S, Tariel S, et al. Significance of Propionibacterium acnes-positive samples in spinal instrumentation. Spine (Phila Pa 1976) 2008;33:E971-6. [Crossref] [PubMed]
17. Sasso RC, Garrido BJ. Postoperative spinal wound infections. J Am Acad Orthop Surg 2008;16:330-7. [Crossref] [PubMed]
18. Thornley P, de Sa D, Evaniew N, et al. An international survey to identify the intrinsic and extrinsic factors of research studies most likely to change orthopaedic practice. Bone Joint Res 2016;5:130-6. [Crossref] [PubMed]
19. Burns KE, Duffett M, Kho ME, et al. A guide for the design and conduct of self-administered surveys of clinicians. CMAJ 2008;179:245-52. [Crossref] [PubMed]
20. Eysenbach G. Improving the quality of Web surveys: the Checklist for Reporting Results of Internet E-Surveys (CHERRIES). J Med Internet Res 2004;6:e34. [Crossref] [PubMed]
21. Lall RR, Wong AP, Lall RR, et al. Evidence-based management of deep wound infection after spinal instrumentation. J Clin Neurosci 2015;22:238-42. [Crossref] [PubMed]
22. Pull ter Gunne AF, Mohamed AS, Skolasky RL, et al. The presentation, incidence, etiology, and treatment of surgical site infections after spinal surgery. Spine (Phila Pa 1976) 2010;35:1323-8. [Crossref] [PubMed]
23. Abbey DM, Turner DM, Warson JS, et al. Treatment of postoperative wound infections following spinal fusion with instrumentation. J Spinal Disord 1995;8:278-83. [Crossref] [PubMed]
24. Oikonomidis S, Altenrath L, Westermann L, et al. Implant-Associated Infection of Long-Segment Spinal Instrumentation: A Retrospective Analysis of 46 Consecutive Patients. Asian Spine J 2021;15:234-43. [Crossref] [PubMed]
25. Ho C, Skaggs DL, Weiss JM, et al. Management of infection after instrumented posterior spine fusion in pediatric scoliosis. Spine (Phila Pa 1976) 2007;32:2739-44. [Crossref] [PubMed]
26. Hedequist D, Haugen A, Hresko T, et al. Failure of attempted implant retention in spinal deformity delayed surgical site infections. Spine (Phila Pa 1976) 2009;34:60-4. [Crossref] [PubMed]