Therapeutic outcome of spinal implant infections caused by Staphylococcus aureus: A retrospective observational study

Synthesis and evaluation of a novel vancomycin-infused, biomimetic bone graft using a rat model of spinal implant-associated infection

Background

Postoperative infection is a complication of spinal fusion surgery resulting in increased patient morbidity. Strategies including intraoperative application of powdered vancomycin have been proposed to reduce the incidence of infection; however, such antimicrobial effects are short-lived.

Methods

Instrumentation of the L4-L5 vertebrae was performed mimicking pedicle screw and rod fixation in 30 rats. Titanium instrumentation inoculated with either PBS or 1×105 CFU bioluminescent MRSA, along with biomimetic bone grafts infused with varying concentrations of vancomycin and 125 µg of rhBMP-2 (BioMim-rhBMP-2-VCM) were implanted prior to closure. Infection was quantified during the six-week postoperative period using bioluminescent imaging. Arthrodesis was evaluated using micro-CT.

Results

Infected animals receiving a bone graft infused with low-dose (0.18 mg/g) or high-dose vancomycin (0.89 mg/g) both exhibited significantly lower bioluminescent signal over the six-week postoperative period than control animals inoculated with MRSA and implanted with bone grafts lacking vancomycin (p=.019 and p=.007, respectively). Both low and high-dose vancomycin-infused grafts also resulted in a statistically significant reduction in average bioluminescence when compared to control animals (p=.027 and p=.047, respectively), independent of time. MicroCT analysis of animals from each group revealed pseudoarthrosis only in the control group, suggesting a correlation between infection and pseudoarthrosis. MRSA-inoculated control animals also had significantly less bone volume formation on micro-CT than the PBS-inoculated control cohort (p<.001), the MRSA+low-dose vancomycin-infused bone graft cohort (p<.001), and the MRSA+high-dose vancomycin-infused bone graft cohort (p<.001).

Conclusion

BioMim-rhBMP-2-VCM presents a novel tissue engineering approach to simultaneously promoting arthrodesis and antimicrobial prophylaxis in spinal fusion. Despite mixed evidence of potential osteotoxicity of vancomycin reported in literature, BioMim-rhBMP-2-VCM preserved arthrodesis and osteogenesis with increasing vancomycin loading doses due to the graft's osteoinductive composition.

Strategies to improve the performance of polyetheretherketone (PEEK) as orthopedic implants: from surface modification to addition of bioactive materials

Polyetheretherketone (PEEK), as a high-performance polymer, is widely used for bone defect repair due to its homogeneous modulus of elasticity of human bone, good biocompatibility, excellent chemical stability and projectability. However, the highly hydrophobic surface of PEEK is biologically inert, which makes it difficult for cells and proteins to attach, and is accompanied by the development of infections that ultimately lead to failure of PEEK implants. In order to further enhance the potential of PEEK as an orthopedic implant, researchers have explored modification methods such as surface modification by physical and chemical means and the addition of bioactive substances to PEEK-based materials to enhance the mechanical properties, osteogenic activity and antimicrobial properties of PEEK. However, these current modification methods still have obvious shortcomings in terms of cost, maneuverability, stability and cytotoxicity, which still need to be explored by researchers. This paper reviews some of the modification methods that have been used to improve the performance of PEEK over the last three years in anticipation of the need for researchers to design PEEK orthopedic implants that better meet clinical needs.

[Translated article] Descriptive study of spinal instrumentation-related infections in a tertiary hospital

INTRODUCTION

Spinal instrumentation-related infections (SIRI) are one of the main causes of post-surgical complication and comorbidity. Our objective was to describe the clinical and microbiological characteristics, treatment and prognosis of these infections.

MATERIAL AND METHODS

We conducted a retrospective study in our institution (2011-2018) including adult patients undergoing spinal instrumentation who met the diagnostic criteria for confirmed infection. Superficial surgical wound and deep intraoperative samples were processed for microbiological culture. The medical and orthopaedic team was always the same.

RESULTS

Forty-one cases were diagnosed of which 39 patients (95.1%) presented early infection (<3 months after initial surgery) with symptoms in the first two weeks, mean CRP at diagnosis was 133mg/dl and 23% associated bacteremia. The remaining two patients (4.8%) were chronic infections (symptoms >3 months after surgery). The treatment of choice in early infections was the Debridement, Antibiotics and Implant Retention (DAIR) strategy without removal of the bone graft, which successfully resolved 84.2% of the infections. The main aetiology was gram-positive (Staphylococcus aureus: 31.7%), followed by gram-negative and polymicrobial flora. Antibiotics were optimised according to cultures with a mean duration of 12 weeks.

CONCLUSIONS

In early infections, early diagnosis and DAIR strategy (with bone graft retention) demonstrated a healing rate higher than 80%.

Descriptive study of spinal instrumentation-related infections in a tertiary hospital

INTRODUCTION

Spinal instrumentation-related infections (SIRI) are one of the main causes of post-surgical complication and comorbidity. Our objective was to describe the clinical and microbiological characteristics, treatment and prognosis of these infections.

MATERIAL AND METHODS

We conducted a retrospective study in our institution (2011-2018) including adult patients undergoing spinal instrumentation who met the diagnostic criteria for confirmed infection. Superficial surgical wound and deep intraoperative samples were processed for microbiological culture. The medical and orthopaedic team was always the same.

RESULTS

Forty-one cases were diagnosed of which 39 patients (95.1%) presented early infection (<3 months after initial surgery) with symptoms in the first two weeks, mean CRP at diagnosis was 133mg/dl and 23% associated bacteremia. The remaining two patients (4.8%) were chronic infections (symptoms >3 months after surgery). The treatment of choice in early infections was the Debridement, Antibiotics and Implant Retention (DAIR) strategy without removal of the bone graft, which successfully resolved 84.2% of the infections. The main etiology was gram-positive (Staphylococcus aureus: 31.7%), followed by gram-negative and polymicrobial flora. Antibiotics were optimized according to cultures with a mean duration of 12 weeks.

CONCLUSIONS

In early infections, early diagnosis and DAIR strategy (with bone graft retention) demonstrated a healing rate higher than 80%.

Rifampin Based Therapy for Patients With Staphylococcus aureus Native Vertebral Osteomyelitis: A Systematic Review and Meta-analysis

BACKGROUND

Native vertebral osteomyelitis (NVO) caused by Staphylococcus aureus is associated with high risk of treatment failure and increased morbidity. The role of rifampin-based therapy for the treatment of this condition is controversial. The goal of this systematic review and meta-analysis is to explore the efficacy and safety of rifampin-based therapy for the treatment of S. aureus NVO.

METHODS

We searched Cochrane, Embase, Medline, Scopus, and Web of Science databases for studies published up to May 2023, focusing on adults with NVO treated with or without rifampin-containing regimens. A random-effects model meta-analysis estimated relative risks and risk difference with 95% confidence intervals (CI).

RESULTS

Thirteen studies (2 randomized controlled trials and 11 comparative cohort studies), comprising 244 patients with S. aureus NVO who received rifampin and 435 who did not, were analyzed. Meta-analysis showed that rifampin-based regimens were associated with lower risk of clinical failure (risk difference, -14%; 95% CI, -19% to -8%; P < .001; I2 = 0%; relative risk, 0.58; 95% CI, .37-.92, P = .02, I2 = 21%). Only 1 study reported on adverse events. All studies had a high or uncertain risk of bias, and the certainty of evidence was rated as very low.

CONCLUSIONS

Adjunctive rifampin therapy might be associated with lower risk of S. aureus NVO treatment failure; however, the low certainty of evidence precludes drawing definitive conclusions that would alter clinical practice. A randomized trial is necessary to corroborate these findings.

Efficacy of single antibiotic therapy versus antibiotic combination in implant-free staphylococcal post-surgical spinal infections: a retrospective observational study

BACKGROUND

Post-surgical spinal infections (pSSIs) are a serious complication of spinal surgeries, with Staphylococcus spp. being one of the most prominent bacteria identified. Optimal antimicrobial therapy for staphylococcal spinal infections without spinal implants is not well documented.

METHODS

This single center retrospective 7-year observational study described and compared the outcome (treatment failure or mortality rate one year after diagnosis) of 20 patients with staphylococcal-implant-free pSSI treated with single or combination antibiotics.

RESULTS

Median duration of treatment was 40 days (IQR 38-42), with 6 days (IQR 5-7) on intravenous antibiotics and 34 days (IQR 30-36) on oral therapy. Four patients (20%) underwent new surgical debridement, all due to surgical failure, and 1 patient died within the first year without significant differences between both treatment group.

CONCLUSION

This study raises the possibility of single antibiotic therapy for patients with implant-free post-surgical spinal infections due to Staphylococcus spp.

Clinical outcomes of rifampicin combination therapy in implant-associated infections due to staphylococci and streptococci: A systematic review and meta-analysis

OBJECTIVES

Adjunctive rifampicin for implant-associated infections is controversial. This study investigated the clinical outcomes of rifampicin combination therapy compared with monotherapy in treating prosthetic joint infection (PJI) or prosthetic valve endocarditis (PVE) due to staphylococci and streptococci.

METHODS

A systematic search was performed from inception to 13 June 2022 in Embase, MEDLINE, Cochrane and Web of Science to investigate the clinical outcomes of rifampicin combination therapy compared with monotherapy in treating staphylococcal and streptococcal PJI or PVE. Randomised controlled trials (RCTs) and observational studies were included in the systematic review and meta-analysis.

RESULTS

Fourteen studies were included. A moderate quality of evidence was found in favour of rifampicin in patients with staphylococcal PJI who underwent a debridement, antibiotics and implant retention (DAIR) procedure [odds ratio = 2.49, 95% confidence interval (CI) 1.93-3.23]. Including the two RCTs only, adding rifampicin to the antibiotic regimen after DAIR was also in favour of rifampicin, but this was not statistically significant (risk ratio = 1.27, 95% CI 0.79-2.04; n = 126). Pooling data for patients with staphylococcal PJI who underwent a two-stage procedure showed that adding rifampicin was not associated with therapeutic success. Limited evidence was found for the use of rifampicin for PVE caused by staphylococci.

CONCLUSIONS

Adding rifampicin in the treatment of staphylococcal PJI treated by DAIR clearly increased the likelihood for therapeutic success. The clinical benefit of adjunctive rifampicin in the treatment of other staphylococci and streptococci implant-associated infections is still unclear.

Micro-arc oxidation (MAO) and its potential for improving the performance of titanium implants in biomedical applications

Titanium (Ti) and its alloys have good biocompatibility, mechanical properties and corrosion resistance, making them attractive for biomedical applications. However, their biological inertness and lack of antimicrobial properties may compromise the success of implants. In this review, the potential of micro-arc oxidation (MAO) technology to create bioactive coatings on Ti implants is discussed. The review covers the following aspects: 1) different factors, such as electrolyte, voltage and current, affect the properties of MAO coatings; 2) MAO coatings affect biocompatibility, including cytocompatibility, hemocompatibility, angiogenic activity, corrosion resistance, osteogenic activity and osseointegration; 3) antibacterial properties can be achieved by adding copper (Cu), silver (Ag), zinc (Zn) and other elements to achieve antimicrobial properties; and 4) MAO can be combined with other physical and chemical techniques to enhance the performance of MAO coatings. It is concluded that MAO coatings offer new opportunities for improving the use of Ti and its alloys in biomedical applications, and some suggestions for future research are provided.

A novel rodent model of chronic spinal implant-associated infection

BACKGROUND CONTEXT

Bacterial infection of spinal instrumentation is a significant challenge in spinal fusion surgery. Although the intraoperative local application of powdered vancomycin is common practice for mitigating infection, the antimicrobial effects of this route of administration are short-lived. Therefore, novel antibiotic-loaded bone grafts as well as a reliable animal model to permit the testing of such therapies are needed to improve the efficacy of infection reduction practices in spinal fusion surgery.

PURPOSE

This study aims to establish a clinically relevant rat model of spinal implant-associated infection to permit the evaluation of antimicrobial bone graft materials used in spinal fusion.

STUDY DESIGN

Rodent study of chronic spinal implant-associated infection.

METHODS

Instrumentation anchored in and spanning the vertebral bodies of L4 and L5 was inoculated with bioluminescent methicillin-resistant Staphylococcus aureus bacteria (MRSA). Infection was monitored using an in vivo imaging system (IVIS) for 8 weeks. Spines were harvested and evaluated histologically, and colony-forming units (CFUs) were quantified in harvested implants and spinal tissue.

RESULTS

Postsurgical analysis of bacterial infection in vivo demonstrated stratification between MRSA and phosphate-buffered saline (PBS) control groups during the first 4 weeks of the 8-week infection period, indicating the successful establishment of acute infection. Over the 8-week chronic infection period, groups inoculated with 1 × 105 MRSA CFU and 1 × 106 MRSA CFU demonstrated significantly higher bioluminescence than groups inoculated with PBS control (p = 0.009 and p = 0.041 respectively). Histological examination at 8 weeks postimplantation revealed the presence of abscesses localized to implant placement in all MRSA inoculation groups, with the most pervasive abscess formation in samples inoculated with 1 × 105 MRSA CFU and 1 × 106 MRSA CFU. Quantification of CFU plated from harvested spinal tissue at 8 weeks post-implantation revealed the 1 × 105 MRSA CFU inoculation group as the only group with a significantly greater average CFU count compared to PBS control (p = 0.017). Further, CFU quantification from harvested spinal tissue was greater than CFU quantification from harvested implants across all inoculation groups.

CONCLUSION

Our model demonstrated that the inoculation dosage of 1 × 105 MRSA CFU exhibited the most robust chronic infection within instrumented vertebral bodies. This dosage had the greatest difference in bioluminescence signal from control (p < 0.01), the lowest mortality (0% compared to 50% for samples inoculated with 1 × 106 MRSA CFU), and a significantly higher amount of CFUs from harvested spine samples than CFUs from control harvested spine samples. Further, histological analysis confirmed the reliability of this novel rodent model of implanted-associated infection to establish infection and biofilm formation of MRSA for all inoculation groups.

CLINICAL SIGNIFICANCE

This model is intended to simulate the infection of instrumentation used in spinal fusion surgeries concerning implant locality and material. This model may evaluate potential antimicrobial and osteogenic biomaterials and investigate the relationship between implant-associated infection and failed fusion.

Surgical Site Infection After Polymethyl Methacrylate Pedicle Screw Augmentation in Osteoporotic Spinal Vertebrae: A Series of 537 Cases

BACKGROUND

Retrospective observational study of prospectively collected outcomes.

OBJECTIVE

The use of transpedicular screws augmented with polymethyl methacrylate (PMMA) is an alternative for patients with osteoporotic vertebrae. To investigate whether using PMMA-augmented screws in patients undergoing elective instrumented spinal fusion (ISF) is correlated with an increased risk of infection and the long-term survival of these spinal implants after surgical site infection (SSI).

METHODS

We studied 537 consecutive patients who underwent ISF at some point within a 9-year period, involving a total of 2930 PMMA-augmented screws. Patients were classified into groups: (1) those whose infection was cured with irrigation, surgical debridement, and antibiotic treatment; (2) those whose infection was cured by hardware removal or replacement; and (3) those in whom treatment failed.

RESULTS

Twenty eight of the 537 patients (5.2%) developed SSI after ISF. An SSI developed after primary surgery in 19 patients (4.6%) and after revision surgery in 9 (7.25%). Eleven patients (39.3%) were infected with gram-positive bacteria, 7 (25%) with gram-negative bacteria, and 10 (35.7%) with multiple pathogens. By 2 years after surgery, infection had been cured in 23 patients (82.15%). Although there were no statistically significant differences in infection incidence between preoperative diagnoses (P = 0.178), the need to remove hardware for infection control was almost 80% lower in patients with degenerative disease. All screws were safely explanted while vertebral integrity was maintained. PMMA was not removed, and no recementing was done for new screws.

CONCLUSIONS

The success rate for treatment of deep infection after cemented spinal arthrodesis is high. Infection rate findings and the most commonly found pathogens do not differ between cemented and noncemented fusion. It does not appear that the use of PMMA in cementing vertebrae plays a pivotal role in the development of SSIs.

LEVEL OF EVIDENCE: 4

Intra-wound versus systemic vancomycin for preventing surgical site infection induced by methicillin-resistant S. aureus after spinal implant surgery in a rat model

BACKGROUND

Systemic vancomycin administration pre-operatively for the infection prophylaxis of spinal implant surgery remains unsatisfactory. This study aimed to explore the efficacy and dosage of local use of vancomycin powder (VP) in preventing surgical site infections after spinal implant surgery in a rat model.

METHODS

Systemic vancomycin (SV; intraperitoneal injection, 88 mg/kg) or intraoperative intra-wound VP (VP0.5: 44 mg/kg, VP1.0: 88 mg/kg, VP2.0: 176 mg/kg) was applied after spinal implant surgery and methicillin-resistant S. aureus (MRSA; ATCC BAA-1026) inoculation in rats. General status, blood inflammatory biomarkers, microbiological and histopathological evaluation were performed during 2 weeks post-surgery.

RESULTS

No post-surgical deaths, wound complications and obvious signs of vancomycin adverse effects were observed. Bacterial counts, blood and tissue inflammation were reduced in the VP groups compared with the SV group. VP2.0 group showed better outcomes in weight gain and tissue inflammation than the VP0.5 and VP1.0 group. Microbial counts indicated that no bacteria survived in the VP2.0 group, whereas MRSA was detected in VP0.5 and VP1.0 groups.

CONCLUSIONS

Intra-wound VP may be more effective than systemic administration in preventing infection caused by MRSA (ATCC BAA-1026) after spinal implant surgery in a rat model.

Phage and Antibiotic Combinations Reduce Staphylococcus aureus in Static and Dynamic Biofilms Grown on an Implant Material

Staphylococcus aureus causes the majority of implant-related infections. These infections present as biofilms, in which bacteria adhere to the surface of foreign materials and form robust communities that are resilient to the human immune system and antibiotic drugs. The heavy use of broad-spectrum antibiotics against these pathogens disturbs the host's microbiome and contributes to the growing problem of antibiotic-resistant infections. The use of bacteriophages as antibacterial agents is a potential alternative therapy. In this study, bioluminescent strains of S. aureus were grown to form 48-h biofilms on polyether ether ketone (PEEK), a material used to manufacture orthopaedic implants, in either static or dynamic growth conditions. Biofilms were treated with vancomycin, staphylococcal phage, or a combination of the two. We showed that vancomycin and staph phages were able to independently reduce the total bacterial load. Most phage-antibiotic combinations produced greater log reductions in surviving bacteria compared to single-agent treatments, suggesting antimicrobial synergism. In addition to demonstrating the efficacy of combining vancomycin and staph phage, our results demonstrate the importance of growth conditions in phage-antibiotic combination studies. Dynamic biofilms were found to have a substantial impact on apparent treatment efficacy, as they were more resilient to combination treatments than static biofilms.

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

Background

Deep surgical site infections after spinal instrumentation represent a significant source of patient morbidity and poorer outcomes. Given lack of evidence or guidelines on the variety of procedural options in the management of deep spine surgical site infections, the purpose of this survey was to document and investigate the use of these techniques across Canada.

Methods

A 34-question survey evaluating surgical techniques for irrigation and debridement in postoperative thoracolumbar infection was distributed to Canadian adult spine surgeons. Results were analyzed qualitatively, and comparisons by specialty, years of training, and number of cases were completed using Fischer's exact tests. We defined consensus as >70% agreement.

Results

We received 53 responses (62% response rate) from a comprehensive sample of Canadian adult spine surgeons. 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. Surgeons varied significantly 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. Additionally, specialty or surgeon experience had no impact on management strategy.

Conclusions

This survey demonstrates significant heterogeneity amongst Canadian adult spine surgeons regarding key steps in the surgical management of deep instrumented spine infection, concordant with scarce literature addressing these steps.

Biodegradable Bone Implants as a New Hope to Reduce Device-Associated Infections-A Systematic Review

Bone fractures often require fixation devices that frequently need to be surgically removed. These temporary implants and procedures leave the patient more prone to developing medical device-associated infections, and osteomyelitis associated with trauma is a challenging complication for orthopedists. In recent years, biodegradable materials have gained great importance as temporary medical implant devices, avoiding removal surgery. The purpose of this systematic review was to revise the literature regarding the use of biodegradable bone implants in fracture healing and its impact on the reduction of implant-associated infections. The systematic review followed the PRISMA guidelines and was conducted by searching published studies regarding the in vivo use of biodegradable bone fixation implants and its antibacterial activity. From a total of 667 references, 23 studies were included based on inclusion and exclusion criteria. Biodegradable orthopedic implants of Mg-Cu, Mg-Zn, and Zn-Ag have shown antibacterial activity, especially in reducing infection burden by MRSA strains in vivo osteomyelitis models. Their ability to prevent and tackle implant-associated infections and to gradually degrade inside the body reduces the need for a second surgery for implant removal, with expectable gains regarding patients' comfort. Further in vivo studies are mandatory to evaluate the efficiency of these antibacterial biodegradable materials.

Postoperative Spinal Implant Infections (PSII)-A Systematic Review: What Do We Know So Far and What is Critical About It?

STUDY DESIGN

Systematic review.

OBJECTIVES

Postoperative spinal implant infections (PSII) are an increasing challenge in the daily clinical routine. This review summarizes existing knowledge in the field of PSII, including definitions, epidemiology, classifications, risk factors, pathogenesis, symptoms, diagnosis, and treatment.

METHODS

A systematic review was performed using a structured PubMed analysis, based on the PRISMA criteria. The search terminology was set as: "spinal implant associated infection OR spinal implant infection OR spinal instrumentation infection OR peri spinal implant infection." PubMed search was limited to the categories randomized controlled trials (RCT), clinical trials, meta-analysis and (systematic) reviews, whereas case reports were excluded. Studies from January 2000 to December 2020 were considered eligible. A total of 572 studies were identified, 82 references included for qualitative synthesis, and 19 for detailed sub analysis (12 meta-analysis, 7 prospective RCT).

RESULTS

Structural problems in the field of PSII were revealed, including (1) limited level of evidence in clinical studies (missing prospective RCT, metanalyzes), (2) small patient numbers, (3) missing standardized definitions, (4) heterogeneity in patient groups, and (5) redundancy in cited literature.

CONCLUSION

Evidence-based knowledge about spinal implant-associated infections is lacking. All involved medical fields should come together to define the term PSII and to combine their approaches toward research, training, and patient care.

Surgical Site Infection Management following Spinal Instrumentation Surgery: Implant Removal vs. Implant Retention: an Updated Systematical Review

Background

The number of lumbar spine surgery increased in recent years. Spinal instrumentation surgery was an integral component in the treatment of spinal pathologies, which can cause surgical site infection (SSI). Surgical site infections (SSIs) are the leading cause of mortality and morbidity after spinal instrumentation surgery. The management of SSI was implant retention and removal is still unclear.

Objective

The objective of this literature is to systematically review the implant removal and retention method for SSI management after spinal instrumentation surgery.

Methods

We searched in PubMed and ScienceDirect for cohort and randomized control trial studies in English, published between 2002 and 2022, which had data on patients with spinal instrumentation surgery. The underlying disease, comorbidities, common bacteria, type of infection, the onset of infection, implant removal, and retention percentage and recommendation were analyzed. Bias analysis using Newcastle-Ottawa Quality Assessment.

Results

We included 15 studies with a total sample were 2.584 with an average of age 15 to 66 years old. The most common organism detected were S. Aureus, MRSA, and S. Epidermis. The most common surgical procedure indications were degenerative followed by scoliosis. Implant removal and retention rate were 0-100% and 0-90,32% respectively. Implant removal is more frequently used in patients after spinal instrumentation surgery than the implant retention method.

Conclusion

Implant retention can be performed in case of SSI is < 3 months after surgery. Implant removal is recommended if the incidence of SSI is > 3 months. Empirical antibiotics therapy is necessary to reduce the possibility of implant removal after debridement. Further studies on the effect of implant removal and retention in patients on infection recurrence, pain, and quality of life of patients are needed.

Animal Models for Postoperative Implant‐Related Spinal Infection

Postoperative infections following implant‐related spinal surgery are severe and disastrous complications for both orthopaedic surgeons and patients worldwide. They can cause neurological damage, disability, and death. To better understand the mechanism of these destructive complications and intervene in the process, further research is needed. Therefore, there is an urgent need for efficient, accurate, and easily available animal models to study the pathogenesis of spinal infections and develop new and effective anti‐bacterial methods. In this paper, we provide a general review of the commonly used animal models of postoperative implant‐related spinal infections, describe their advantages and disadvantages, and highlight the significance of correctly choosing the model according to the infection aspect under investigation. These models are valuable tools contributing to the better understanding of postoperative spinal infections and will continue to facilitate the invention of novel preventative and treatment strategies for patients with postoperative spinal infections. However, although they are valid and reproducible in some respects, the current animal models present certain limitations. Future ideal spinal infection animal models may assess the bacterial load of the same animal in real‐time in vivo, and better mimic the human anatomy as well as surgical techniques. Strains other than Staphylococcus aureus account for a large proportion of postoperative spinal infections, and thus, the establishment of models to evaluate other types of microbial infections is expected in the future. Furthermore, novel transgenic models established on advancements in genome editing are also likely to be developed in the future.

Predictive Factors for Successful Treatment of Deep Incisional Surgical Site Infections following Instrumented Spinal Surgeries: Retrospective Review of 1832 Cases

Background: Surgical site infection (SSI) is a major complication in spinal instrumentation that is often difficult to treat. The purpose of this study was to identify and determine prognostic indicators for successful treatment of spine instrumentation SSI. Methods: Retrospectively, spine surgery cases were examined on SSI diagnosis. Post-instrumentation SSI patients were categorized as “Successful” if SSI subsided after single debridement. Patients in whom SSI did not subsided and/or required removal of instrumentation were classified as “Challenging”. We investigated the relation of treatment outcomes to patients and treatment factors. Results: A total of 1832 spinal instrumentation cases were recognized with 44 (2.40%) SSI cases. White blood cell count, C-reactive protein (CRP) levels, causative bacteria (i.e., S. Aureus or MRSA), trauma injury, and early-stage antimicrobial agent sensitivity correlated with treatment prognosis. Multivariate analysis highlighted CRP levels and applying early-stage sensitive antibiotics as potential impactful predictive factors for successful treatment. Conclusions: Our results demonstrated that early selection of sensitive antimicrobial agents is critical and emphasizes the potential for early-stage classification methods such as Gram staining. Additionally, S. Aureus and MRSA SSI formed significantly more challenging infections to treat, thus requiring consideration when deciding on instrumentation retention. These factors offer promising aspects for further large-scale studies.

Development of zinc oxide/hydroxyapatite/poly(D,L-lactic acid) fibrous scaffold for tissue engineering applications

Scaffolds based on polymeric fibers represent an engaging biomedical device due to their particular morphology and similarity with extracellular matrices. The biggest challenge to use fibrous materials in the biomedical field is related to their favorable platform for the adhesion of pathogenic microorganisms. Therefore, their optimum performance not only depends on their bioactive potential but also on their antimicrobial properties. The aim of this work was the design of antimicrobial (zinc oxide, ZnO) and bioactive (hydroxyapatite, Hap) fibrous materials using poly(D, L-lactic acid) (PDLLA) as the polymer fiber substrate. Fiber based composite scaffolds were developed using the Forcespinning® technique. For analysis purposes, the morphological, thermal, antimicrobial and biological properties of the fibrous hybrid system obtained at a concentration of 5 wt% of ZnO and 5 wt% of Hap were studied. The incorporation of the aforementioned nanoparticles (NPs) mixture in PDLLA led to an increase in viscosity and a pseudo-plastic tendency of the precursor solution, which caused an increase in fiber diameters and their dispersion of values. Small cavities and certain roughness were the main surface morphology observed on the fibers before and after NPs incorporation. The fiber thermal stability decreased due to the presence of the NPs. The antimicrobial properties of the hybrid fibrous scaffold presented a growth inhibition (GI) of 70 and 85% for E. coli and S. aureus strains, respectively. Concerning the osteoblast-cell compatibility, PDLLA and hybrid PDLLA scaffold showed low toxicity (cell viabilities above 80%), allowing cell growth inside its three-dimension structure and favorable cell morphology extended along the fibers. This behavior suggests a promising potential of this hybrid PDLLA scaffold for bone application.

Removal of instrumentation for postoperative spine infection: systematic review

OBJECTIVE

Currently, no consensus exists as to whether patients who develop infection of the surgical site after undergoing instrumented fusion should have their implants removed at the time of wound debridement. Instrumentation removal may eliminate a potential infection nidus, but removal may also destabilize the patient's spine. The authors sought to summarize the existing evidence by systematically reviewing published studies that compare outcomes between patients undergoing wound washout and instrumentation removal with outcomes of patients undergoing wound washout alone. The primary objectives were to determine 1) whether instrumentation removal from an infected wound facilitates infection clearance and lowers morbidity, and 2) whether the chronicity of the underlying infection affects the decision to remove instrumentation.

METHODS

PRISMA guidelines were used to review the PubMed/MEDLINE, Embase, Cochrane Library, Scopus, Web of Science, and ClinicalTrials.gov databases to identify studies that compared patients with implants removed and patients with implants retained. Outcomes of interest included mortality, rate of repeat wound washout, and loss of correction.

RESULTS

Fifteen articles were included. Of 878 patients examined in these studies, 292 (33%) had instrumentation removed. Patient populations were highly heterogeneous, and outcome data were limited. Available data suggested that rates of reoperation, pseudarthrosis, and death were higher in patients who underwent instrumentation removal at the time of initial washout. Three studies recommended that instrumentation be uniformly removed at the time of wound washout. Five studies favored retaining the original instrumentation. Six studies favored retention in early infections but removal in late infections.

CONCLUSIONS

The data on this topic remain heterogeneous and low in quality. Retention may be preferred in the setting of early infection, when the risk of underlying spine instability is still high and the risk of mature biofilm formation on the implants is low. However, late infections likely favor instrumentation removal. Higher-quality evidence from large, multicenter, prospective studies is needed to reach generalizable conclusions capable of guiding clinical practice.

Antibacterial Titanium Implants Biofunctionalized by Plasma Electrolytic Oxidation with Silver, Zinc, and Copper: A Systematic Review

Patients receiving orthopedic implants are at risk of implant-associated infections (IAI). A growing number of antibiotic-resistant bacteria threaten to hamper the treatment of IAI. The focus has, therefore, shifted towards the development of implants with intrinsic antibacterial activity to prevent the occurrence of infection. The use of Ag, Cu, and Zn has gained momentum as these elements display strong antibacterial behavior and target a wide spectrum of bacteria. In order to incorporate these elements into the surface of titanium-based bone implants, plasma electrolytic oxidation (PEO) has been widely investigated as a single-step process that can biofunctionalize these (highly porous) implant surfaces. Here, we present a systematic review of the studies published between 2009 until 2020 on the biomaterial properties, antibacterial behavior, and biocompatibility of titanium implants biofunctionalized by PEO using Ag, Cu, and Zn. We observed that 100% of surfaces bearing Ag (Ag-surfaces), 93% of surfaces bearing Cu (Cu-surfaces), 73% of surfaces bearing Zn (Zn-surfaces), and 100% of surfaces combining Ag, Cu, and Zn resulted in a significant (i.e., >50%) reduction of bacterial load, while 13% of Ag-surfaces, 10% of Cu-surfaces, and none of Zn or combined Ag, Cu, and Zn surfaces reported cytotoxicity against osteoblasts, stem cells, and immune cells. A majority of the studies investigated the antibacterial activity against S. aureus. Important areas for future research include the biofunctionalization of additively manufactured porous implants and surfaces combining Ag, Cu, and Zn. Furthermore, the antibacterial activity of such implants should be determined in assays focused on prevention, rather than the treatment of IAIs. These implants should be tested using appropriate in vivo bone infection models capable of assessing whether titanium implants biofunctionalized by PEO with Ag, Cu, and Zn can contribute to protect patients against IAI.

Implications for diagnosis and treatment of peri-spinal implant infections from experiences in periprosthetic joint infections-a literature comparison and review

Both, periprosthetic joint infection (PJI) and peri-spinal implant infection (PSII) are serious complications occurring in arthroplasty and spine instrumentation with absolute numbers expected to rise in the next years. The currently existing literature data describing the characteristics of PSII are limited when compared to PJI studies. However, both PJI and PSII exhibit similarities concerning pathogenesis, symptoms, diagnosis, treatment and prognosis. This literature review aims at comparing PJI and PSII and to develop implications for diagnosis and treatment of PSII from existing studies about PJI. The review was performed on the basis of a structured PubMed, Cochrane Library, and Medline analysis and existing guidelines, with 99 references being included. The results indicate that specific terms like re-infection should be defined in the context of PSII based on existing definitions of PJI, that in vitro biofilm studies and studies analyzing different prosthesis surfaces in arthroplasty could be used for PSII, and that histopathology as an additional standard tool in PSII diagnosis might be helpful. In addition, the development of a standardized algorithm-based treatment system with antibiotic protocols, including long term suppression, for PSII similar to the ones existing for PJI is necessary.

Susceptibility to biofilm formation on 3D-printed titanium fixation plates used in the mandible: a preliminary study

Background: In the oral and maxillofacial surgery, fixation plates are commonly used for the stabilization of bone fragments. Additive manufacturing has enabled us to design and create personalized fixation devices that would ideally fit any given fracture. Aim: The aim of the present preliminary study was to assess the susceptibility of 3D-printed titanium fixation plates to biofilm formation. Methods: Plates were manufactured using selective laser melting (SLM) from Ti-6Al-4 V. Reference strains of Streptococcus mutans, Staphyloccocus epidermidis, Staphylococcus aureus, Lactobacillus rhamnosus, and Candida albicans, were tested to evaluate the material's susceptibility to biofilm formation over 48 hours. Biofilm formations were quantified by a colorimetric method and colony-forming units (CFU) quantification. Scanning electron microscopy (SEM) visualized the structure of the biofilm. Results: Surface analysis revealed the average roughness of 102.75 nm and irregular topography of the tested plates. They were susceptible to biofilm formation by all tested strains. The average CFUs were as follows: S. mutans (11.91 x 107) > S.epidermidis (4.45 x 107) > S. aureus (2.3 x 107) > C.albicans (1.22 x 107) > L. rhamnosus (0.78 x 107). Conclusions: The present preliminary study showed that rough surfaces of additively manufactured titanium plates are susceptible to microbial adhesion. The research should be continued in order to compare additively manufactured plates with other commercially available osteotomy plates. Therefore, we suggest caution when using this type of material.

Transcriptomic analysis of stress response to novel antimicrobial coatings in a clinical MRSA strain

Multi-drug resistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) cause nosocomial infections that can have deleterious effects on human health. Thus, it is imperative to find solutions to treat these detrimental infections as well as to control their spread. We tested the effect of two different antimicrobial materials, functionalised graphene oxide (GOX), and AGXX® coated on cellulose fibres, on the growth and transcriptome of the clinical MRSA strain S. aureus 04-02981. In addition, we investigated the effect of a third material as a combination of GOX and AGXX® fibres on S. aureus 04-02981. Standard plate count assay revealed that the combination of fibres, GOX-AGXX® inhibited the growth of S. aureus 04-02981 by 99.98%. To assess the effect of these antimicrobials on the transcriptome of our strain, cultures of S. aureus 04-02981 were incubated with GOX, AGXX®, or GOX-AGXX® fibres for different time periods and then subjected to RNA-sequencing. Uncoated cellulose fibres were used as a negative control. The antimicrobial fibres had a huge impact on the transcriptome of S. aureus 04-02981 affecting the expression of 2650 genes. Primarily genes related to biofilm formation and virulence (such as agr, sarA, and those of the two-component system SaeRS), and genes crucial for survival in biofilms (like arginine metabolism arc genes) were repressed. In contrast, the expression of siderophore biosynthesis genes (sbn) was induced, a probable response to stress imposed by the antimicrobials and the conditions of iron-deficiency. Genes associated with potassium transport, intracellular survival and pathogenesis (kdp) were also differentially expressed. Our data suggest that the combination of GOX and AGXX® acts as an efficient antimicrobial against S. aureus 04-02981. Thus, these materials are potential candidates for applications in antimicrobial surface coatings.

Rabbit model of Staphylococcus aureus implant-associated spinal infection

Post-surgical implant-associated spinal infection is a devastating complication commonly caused by Staphylococcus aureus. Biofilm formation is thought to reduce penetration of antibiotics and immune cells, contributing to chronic and difficult-to-treat infections. A rabbit model of a posterior-approach spinal surgery was created, in which bilateral titanium pedicle screws were interconnected by a plate at the level of lumbar vertebra L6 and inoculated with a methicillin-resistant S.aureus (MRSA) bioluminescent strain. In vivo whole-animal bioluminescence imaging (BLI) and ex vivo bacterial cultures demonstrated a peak in bacterial burden by day 14, when wound dehiscence occurred. Structures suggestive of biofilm, visualized by scanning electron microscopy, were evident up to 56 days following infection. Infection-induced inflammation and bone remodeling were also monitored using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) and computed tomography (CT). PET imaging signals were noted in the soft tissue and bone surrounding the implanted materials. CT imaging demonstrated marked bone remodeling and a decrease in dense bone at the infection sites. This rabbit model of implant-associated spinal infection provides a valuable preclinical in vivo approach to investigate the pathogenesis of implant-associated spinal infections and to evaluate novel therapeutics.

Summary: A model of post-surgical methicillin-resistant Staphylococcus aureus implant-associated spinal infection was created in rabbits, recapitulating acute infection as well as chronic low-burden infection, with structures suggestive of biofilm formation and bone remodeling.

Real-world experience of the role of 18F FDG PET-computed tomography in chronic spinal implant infection

OBJECTIVES

The presence of postinstrumentation back pain in patients after undergoing spinal surgery is a well established phenomenon. So too is the presence of infection, both overt and subclinical which can be a source of pain. The accurate assessment of infection in patients with spinal implants in situ and no overt radiological or biochemical abnormalities frequently presents a diagnostic challenge. We present our experience spanning 5 years of using 2-deoxy-2-[18F]fluoro-D-glucose positron emission tomography (18F FDG PET)-computed tomography (CT) scans to aid the diagnostic process in treating presumed low-grade chronic implant infection.

METHODS

We undertook a retrospective analysis of all patients with spinal implants in place who were referred for 18F FDG PET-CT imaging over a 5-year period. All available images, case notes and laboratory results were reviewed.

RESULTS

Data pertaining to 49 patients were analysed, with infection diagnosed on 18F FDG PET-CT in 24 (45%) of those sent for scanning. Fifteen patients in the cohort underwent revision surgery, and 11 of whom had been diagnosed as infected on PET-CT. Confirmation of infection with positive microbiological sampling occurred in 8/11 giving a positive predictive value of 0.72 in our series.

CONCLUSION

We present a real-world experience of using 18F FDG PET-CT as a diagnostic tool in the evaluation of patients with chronic pain after undergoing spinal implantation. We have found PET-CT to be a promising modality and would recommend multicentre collaboration to ensure reproducibility across more centres.

Outcomes of additional instrumentation in elderly patients with pyogenic vertebral osteomyelitis and previous spinal instrumentation

BACKGROUND CONTEXT

In patients with pyogenic vertebral osteomyelitis (PVO) and previous instrumentation requiring surgical treatment, a decision must be made between a less-invasive noninstrumented surgery, including retaining the previous instrumentation, or a more invasive additional instrumented surgery involving the complete removal of the infected tissue and firm restabilization.

PURPOSE

To evaluate the clinical outcomes of using additional instrumentation in patients with PVO and previous instrumentation and determine the significant risk factors related to recurrent infection.

STUDY DESIGN/SETTING

Retrospective cohort study (case control study).

PATIENT SAMPLE

PVO patients with previous instrumentation.

OUTCOME MEASURES

Recurrence of PVO and mortality.

METHODS

Patients were divided into two groups (instrumented or noninstrumented) according to the presence or absence of additional instrumentation. The baseline characteristics, infection profile, and treatment outcomes were compared between the two groups, and a multivariate logistic regression analysis was performed to identify the risk factors for infection recurrence.

RESULTS

A total of 187 postoperative patients with PVO and previous spinal instrumentation were included. There were no significant differences in the baseline characteristics except the presence of a titanium cage. Surgery for additional instrumentation in patients with PVO and previous instrumentation showed similar rates of infection recurrence and mortality compared with noninstrumented surgery despite a larger number of involved vertebral levels and greater incidence of epidural abscesses. However, instrumented patients with PVO and previous instrumentation who experienced infection recurrence had worse clinical outcomes than those of the noninstrumented patients with PVO. Severe medical comorbidities, the presence of a psoas abscess, and methicillin-resistant Staphylococcus aureus infection were associated with a higher risk of infection recurrence.

CONCLUSIONS

Surgery for additional instrumentation in patients with PVO and previous instrumentation showed similar rates of infection recurrence and mortality to those who underwent noninstrumented surgery despite a larger number of involved vertebral levels and an increased frequency of epidural abscesses.

Comparison of pyogenic postoperative and native vertebral osteomyelitis

BACKGROUND CONTEXT

Postoperative vertebral osteomyelitis (PVO) after spinal surgery is a clinical challenge. However, there is a paucity of evidence regarding the most likely etiologic organisms to guide the choice of empirical antibiotic therapy, and previous reports of treatment outcomes for PVO are scarce.

PURPOSE

To compare the microbiology, clinical characteristics, and outcomes of pyogenic PVO with native vertebral osteomyelitis (NVO).

STUDY DESIGN

Retrospective comparative study.

PATIENT SAMPLE

Patients with microbiologically proven vertebral osteomyelitis from three university-affiliated hospitals in South Korea between January 2005 and December 2015 with follow-up of at least 12 months after completion of antibiotics or until the patient was transferred. Patients who had a spine operation in the same location within 1 year of diagnosis, and all patients with remnant implants at the time of the vertebral osteomyelitis diagnosis, were defined as having PVO. The remainder of the patients was considered to have NVO. Spinal operations included discectomy, laminectomy, arthrodesis, and instrumentation for stabilization of the spine.

OUTCOME MEASURES

Overall mortality, neurologic outcomes, treatment failure, and relapse of infection.

METHODS

Demographic data, comorbidities, presenting symptoms, microbiological data, radiographic characteristics, laboratory data (including white blood cell counts, erythrocyte sedimentation rate, and C-reactive protein), surgical treatment, and neurologic outcomes for each patient were reviewed from electronic medical records and analyzed. Mortality rate, treatment failure, and relapse of infection were calculated for the two groups. Factors associated with treatment outcome were evaluated using univariate and multivariate logistic regression analyses.

RESULTS

The study evaluated 104 patients with PVO and 441 patients with NVO. In PVO, the most common isolate was Staphylococcus aureus (34%, n=35), followed by coagulase-negative staphylococci (31%, n=32). In NVO, the most common isolates were S. aureus (47%, n=206) and streptococci (21%, n=94). Of the staphylococci, the proportion of methicillin-resistant strains was significantly higher in PVO than that in NVO (75% vs. 39%, p<.001). The proportion of patients with gram-negative bacilli was 14% in PVO and 20% in NVO. Pre-existing or synchronous nonspinal infection was observed more frequently in NVO than in PVO (33% vs. 13%, p<.001). Although the duration of antibiotic use was similar in both groups, surgery for infection control was performed more frequently in PVO. The mortality rate was similar in both groups. However, the treatment failure and relapse rates at 12 months were higher in the PVO group (23% vs. 13%, p=.009; 14% vs. 7%, p=.028, respectively). Methicillin-resistant S.aureus was significantly associated with treatment failure or relapse via logistic regression (odds ratio 3.01, 95% confidence interval [1.71-5.32], p<.001; odds ratio 2.78, 95% confidence interval [1.40-5.49], p=.003).

CONCLUSIONS

Coverage of methicillin-resistant staphylococci should be considered when prescribing empirical antibiotics for PVO. Although surgery was performed more often in PVO than NVO, the treatment failure and relapse rates at 12 months were higher in PVO.