Effect of various concentrations of antibiotics on osteogenic cell viability and activity

Covalent immobilization of KR-12 peptide onto a titanium surface for decreasing infection and promoting osteogenic differentiation

Covalent immobilization of KR-12 peptide onto titanium surface for anti-bacteria and promoting osteogenic differentiation.

Biomaterials approaches to treating implant-associated osteomyelitis

Orthopaedic devices are the most common surgical devices associated with implant-related infections and Staphylococcus aureus (S. aureus) is the most common causative pathogen in chronic bone infections (osteomyelitis). Treatment of these chronic bone infections often involves combinations of antibiotics given systemically and locally to the affected site via a biomaterial spacer. The gold standard biomaterial for local antibiotic delivery against osteomyelitis, poly(methyl methacrylate) (PMMA) bone cement, bears many limitations. Such shortcomings include limited antibiotic release, incompatibility with many antimicrobial agents, and the need for follow-up surgeries to remove the non-biodegradable cement before surgical reconstruction of the lost bone. Therefore, extensive research pursuits are targeting alternative, biodegradable materials to replace PMMA in osteomyelitis applications. Herein, we provide an overview of the primary clinical treatment strategies and emerging biodegradable materials that may be employed for management of implant-related osteomyelitis. We performed a systematic review of experimental biomaterials systems that have been evaluated for treating established S. aureus osteomyelitis in an animal model. Many experimental biomaterials were not decisively more efficacious for infection management than PMMA when delivering the same antibiotic. However, alternative biomaterials have reduced the number of follow-up surgeries, enhanced the antimicrobial efficacy by delivering agents that are incompatible with PMMA, and regenerated bone in an infected defect. Understanding the advantages, limitations, and potential for clinical translation of each biomaterial, along with the conditions under which it was evaluated (e.g. animal model), is critical for surgeons and researchers to navigate the plethora of options for local antibiotic delivery.

D-amino acid inhibits biofilm but not new bone formation in an ovine model

BACKGROUND

Infectious complications of musculoskeletal trauma are an important factor contributing to patient morbidity. Biofilm-dispersive bone grafts augmented with D-amino acids (D-AAs) prevent biofilm formation in vitro and in vivo, but the effects of D-AAs on osteocompatibility and new bone formation have not been investigated.

QUESTIONS/PURPOSES

We asked: (1) Do D-AAs hinder osteoblast and osteoclast differentiation in vitro? (2) Does local delivery of D-AAs from low-viscosity bone grafts inhibit new bone formation in a large-animal model?

METHODS

Methicillin-sensitive Staphylococcus aureus and methicillin-resistant S aureus clinical isolates, mouse bone marrow stromal cells, and osteoclast precursor cells were treated with an equal mass (1:1:1) mixture of D-Pro:D-Met:D-Phe. The effects of the D-AA dose on biofilm inhibition (n = 4), biofilm dispersion (n = 4), and bone marrow stromal cell proliferation (n = 3) were quantitatively measured by crystal violet staining. Osteoblast differentiation was quantitatively assessed by alkaline phosphatase staining, von Kossa staining, and quantitative reverse transcription for the osteogenic factors a1Col1 and Ocn (n = 3). Osteoclast differentiation was quantitatively measured by tartrate-resistant acid phosphatase staining (n = 3). Bone grafts augmented with 0 or 200 mmol/L D-AAs were injected in ovine femoral condyle defects in four sheep. New bone formation was evaluated by μCT and histology 4 months later. An a priori power analysis indicated that a sample size of four would detect a 7.5% difference of bone volume/total volume between groups assuming a mean and SD of 30% and 5%, respectively, with a power of 80% and an alpha level of 0.05 using a two-tailed t-test between the means of two independent samples.

RESULTS

Bone marrow stromal cell proliferation, osteoblast differentiation, and osteoclast differentiation were inhibited at D-AAs concentrations of 27 mmol/L or greater in a dose-responsive manner in vitro (p < 0.05). In methicillin-sensitive and methicillin-resistant S aureus clinical isolates, D-AAs inhibited biofilm formation at concentrations of 13.5 mmol/L or greater in vitro (p < 0.05). Local delivery of D-AAs from low-viscosity grafts did not inhibit new bone formation in a large-animal model pilot study (0 mmol/L D-AAs: bone volume/total volume = 26.9% ± 4.1%; 200 mmol/L D-AAs: bone volume/total volume = 28.3% ± 15.4%; mean difference with 95% CI = -1.4; p = 0.13).

CONCLUSIONS

D-AAs inhibit biofilm formation, bone marrow stromal cell proliferation, osteoblast differentiation, and osteoclast differentiation in vitro in a dose-responsive manner. Local delivery of D-AAs from bone grafts did not inhibit new bone formation in vivo at clinically relevant doses.

CLINICAL RELEVANCE

Local delivery of D-AAs is an effective antibiofilm strategy that does not appear to inhibit bone repair. Longitudinal studies investigating bacterial burden, bone formation, and bone remodeling in contaminated defects as a function of D-AA dose are required to further support the use of D-AAs in the clinical management of infected open fractures.

Local Injection of Aminoglycosides for Prophylaxis Against Infection in Open Fractures

BACKGROUND

The purpose of this study was to determine the efficacy of local wound cavity injections of aqueous aminoglycosides (gentamicin and tobramycin), in conjunction with systemic antibiotics, to lower the prevalence of infection in patients with open fractures.

METHODS

Three hundred and fifty-one open fractures were identified by Current Procedural Terminology codes 11011 and 11012. Data on patient demographic characteristics, injury characteristics, infection, and fracture union were obtained from the electronic medical records. Patients in the control group (183 fractures) received systemic antibiotics only. Patients in the intervention group (168 fractures) received, in addition to systemic antibiotics, a locally administered aminoglycoside (2 mg/mL) at the time of the index surgical procedure. At the discretion of the attending surgeon, some wounds also received postoperative irrigations of aqueous aminoglycoside (n = 34). For wounds that could not be closed and wounds that received postoperative irrigations, negative pressure dressings were used.

RESULTS

The deep and superficial infection rate in the control group was 19.7% (thirty-six of 183 fractures), but it was significantly lower (p = 0.010) in the intervention group at 9.5% (sixteen of 168 fractures). When comparing only the deep infections, the infection rate in the control group was 14.2% (twenty-six of 183 fractures) compared with 6.0% (ten of 168 fractures) in the intervention group (p = 0.011). After multivariate analysis to adjust for possible confounding factors, the administration of local antibiotics was found to be an independent predictor of lower infection rates in both deep and superficial infections (odds ratio, 2.6 [95% confidence interval, 1.2 to 5.6]; p = 0.015) and deep infections only (odds ratio, 3.0 [95% confidence interval, 1.1 to 8.5]; p = 0.034). The use of local antibiotics did not have an impact on nonunion rate (p = 0.881), with a type-I error rate of α = 0.05 and 0.8 power.

CONCLUSIONS

This study suggests that local aqueous aminoglycoside administration as an adjunct to systemic antibiotics may be effective in lowering infection rates in open fractures; further research with higher-level research designs are needed.

3D printed bioceramics for dual antibiotic delivery to treat implant-associated bone infection

Surgical implant-associated bone infections (osteomyelitis) have severe clinical and socioeconomic consequences. Treatment of chronic bone infections often involves antibiotics given systemically and locally to the affected site in poly (methyl methacrylate) (PMMA) bone cement. Given the high antibiotic concentrations required to affect bacteria in biofilm, local delivery is important to achieve high doses at the infection site. PMMA is not suitable to locally-deliver some biofilm-specific antibiotics, including rifampin, due to interference with PMMA polymerisation. To examine the efficacy of localised, combinational antibiotic delivery compared to PMMA standards, we fabricated rifampin- and vancomycin-laden calcium phosphate scaffolds (CPS) by three-dimensional (3D) printing to treat an implant-associated Staphylococcus aureus bone infection in a murine model. All vancomycin- and rifampin-laden CPS treatments significantly reduced the bacterial burden compared with vancomycin-laden PMMA. The bones were bacteria culture negative in 50 % of the mice that received sustained release vancomycin- and rifampin-laden CPS. In contrast, 100 % of the bones treated with vancomycin monotherapy using PMMA or CPS were culture positive. Yet, the monotherapy CPS significantly reduced the bacterial metabolic load following revision compared to PMMA. Biofilm persisted on the fixation hardware, but the infection-induced bone destruction was significantly reduced by local rifampin delivery. These data demonstrate that, despite the challenging implant-retaining infection model, co-delivery of rifampin and vancomycin from 3D printed CPS, which is not possible with PMMA, significantly improved the outcomes of implant-associated osteomyelitis. However, biofilm persistence on the fixation hardware reaffirms the importance of implant exchange or other biofilm eradication strategies to complement local antibiotics.

Applications of Local Antibiotics in Orthopedic Trauma

Local antibiotics have a role in orthopedic trauma for both infection prophylaxis and treatment. They provide the advantage of high local antibiotic concentration without excessive systemic levels. Nonabsorbable polymethylmethacrylate (PMMA) is a popular antibiotic carrier, but absorbable options including bone graft, bone graft substitutes, and polymers have gained acceptance. Simple aqueous antibiotic solutions continue to be investigated and appear to be clinically effective. For established infections, such as osteomyelitis, a combination of surgical debridement with local and systemic antibiotics seems to represent the most effective treatment at this time. Further investigation of more effective local antibiotic utilization is ongoing.

Combined local and systemic antibiotic treatment is effective against experimental Staphylococcus aureus peri-implant biofilm infection

We hypothesized that systemic ceftriaxone and high concentration local antibiotics might eradicate peri-implant sepsis. Experiment 1: Eighty-four implants inoculated with biofilm-forming Staphylococcus aureus were treated in vitro with gentamicin, vancomycin, gentamicin + rifampin, or vancomycin + rifampin for 2, 4, or 8 days. Experiment 2: Forty-five implants were wired in vivo to rat femurs and inoculated with 1 × 10(6) CFU S. aureus. After 48 h, rats were treated once daily for 5 days with systemic ceftriaxone, local tobramycin or ceftriaxone, and tobramycin. Experiment 3: Forty implants with established S. aureus biofilms were wired in vivo to rat femurs. After 48 h, rats were treated with systemic ceftriaxone alone or in combination with local gentamicin, gentamicin and rifampin, or vancomycin. Experiment 1: 100% of implants treated in vitro with gentamicin were sterile after 48 h. The other treatments did not become sterile until 4 days. Experiment 2: No implant was culture negative. The combination of systemic ceftriaxone and local tobramycin was significantly better than others (p < 0.008). Experiment 3: Systemic ceftriaxone alone was ineffective. All implants treated with systemic ceftriaxone and local gentamicin were sterile (p < 0.001), the other groups were less effective.

A resorbable antibiotic eluting bone void filler for periprosthetic joint infection prevention

Periprosthetic joint infection (PJI) following total knee arthroplasty is a globally increasing procedural complication. These infections are difficult to treat and typically require revision surgery. Antibiotic-loaded bone cement is frequently utilized to deliver antibiotics to the site of infection; however, bone cement is a nondegrading foreign body and known to leach its antibiotic load, after an initial burst release, at subtherapeutic concentrations for months. This work characterized a resorbable, antibiotic-eluting bone void filler designed to restore bone volume and prevent PJI. Three device formulations were fabricated, consisting of different combinations of synthetic inorganic bone graft material, degradable polymer matrices, salt porogens, and antibiotic tobramycin. These formulations were examined to determine the antibiotic's elution kinetics and bactericidal potential, the device's degradation in vitro, as well as osteoconductivity and device resorption in vivo using a pilot rabbit bone implant model. Kirby-Bauer antibiotic susceptibility tests assessed bactericidal activity. Liquid chromatography with tandem mass spectrometry measured antibiotic elution kinetics, and scanning electron microscopy was used to qualitatively assess degradation. Results indicated sustained antibiotic release from all three formulations above the Staphylococcus aureus minimum inhibitory concentration for a period of 5 to 8 weeks. Extensive degradation was observed with the Group 3 formulation after 90 days in phosphate-buffered saline, with a lesser degree of degradation observed in the other two formulations. Results from the pilot rabbit study showed the Group 3 device to be biocompatible, with minimal inflammatory response and no fibrous encapsulation in bone. The device was also highly osteoconductive-exhibiting an accelerated mineral apposition rate. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1632-1642, 2016.

Local antibiotic therapy strategies in orthopaedic trauma: Practical tips and tricks and review of the literature

The use of local antibiotics for the prevention of infection in the setting of open fractures and as part of the treatment of osteomyelitis is well established. Antibiotics are most commonly incorporated into polymethylmethacrylate (PMMA) cement, which can then be formed into beads, moulded to fit a bone defect or used to coat a guide wire or IM nail. Newer delivery vehicles and techniques are being evaluated to improve upon these methods. Many factors influence how local antibiotics are applied. Treatment strategies are challenging to standardise due to the variability of clinical presentations. The presence of hardware, upper versus lower extremity, healed versus non-healed fracture and quality of soft tissues overlying the affected bone, as well as patients' comorbidities all need to be considered. Despite the accepted use of local antibiotic therapy in orthopaedic trauma, high-quality evidence regarding the use of local antibiotics is lacking. Indications, techniques, dosages, types of antibiotics, elution properties and pharmacokinetics are poorly defined in the clinical setting. The purpose of our manuscript is to review current strategies and provide practical tips for local application of antibiotics in orthopaedic trauma. We focus on delivery vehicles, types of antibiotics, dosage recommendations when mixed with PMMA and indications.

Efficacy of Antibiotics Sprayed into Surgical Site for Prevention of the Contamination in the Spinal Surgery

Study Design

Retrospective study.

Purpose

To evaluate the effect of intraoperative wound application of vancomycin on preventing surgical wound contamination during instrumented lumbar spinal surgery.

Overview of Literature

Postoperative infection is the one of the most devastating complications of lumbar surgery. There are a few reports showing the benefits of intraoperative wound application of vancomycin during spinal surgery. However, there is no report about the effectiveness of local vancomycin instillation in prevention of surgical wound contamination.

Methods

Eighty-six patients underwent instrumented lumbar spinal surgery. Mean patient age was 65.19 years (range, 23-83 years). There were 67 females and 19 males. During surgery, vancomycin powder was applied into the surgical site before closure in 43 patients (antibiotic group) and vancomycin powder was not applied into the surgical site before closure in 43 patients (control group). The tip of the surgical drain was cultured to evaluate surgical wound contamination. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were measured on the first, third, seventh, and fourteenth day after the operation.

Results

We found two patients with a positive culture from the tip of surgical drains in the antibiotic group, and one patient with a positive culture from the tip of the surgical drain in the control group. Postoperative ESR and CRP levels did not show significant differences between the two groups. On the third postoperative day, ESR in patients of the antibiotic group was more significantly decreased than that in patients of the control group, while CRP level did not show a significant difference between the two groups.

Conclusions

There was no evidence to suggest that intraoperative vancomycin application is effective in decreasing the risk of postoperative wound infection after instrumented posterior lumbar fusion surgery.

Novel Antibiotic-loaded Point-of-care Implant Coating Inhibits Biofilm

BACKGROUND

Orthopaedic biomaterials are susceptible to biofilm formation. A novel lipid-based material has been developed that may be loaded with antibiotics and applied as an implant coating at point of care. However, this material has not been evaluated for antibiotic elution, biofilm inhibition, or in vivo efficacy.

QUESTIONS/PURPOSES

(1) Do antibiotic-loaded coatings inhibit biofilm formation? (2) Is the coating effective in preventing biofilm in vivo?

METHODS

Purified phosphatidylcholine was mixed with 25% amikacin or vancomycin or a combination of 12.5% of both. A 7-day elution study for coated titanium and stainless steel coupons was followed by turbidity and zone of inhibition assays against Staphylococcus aureus and Pseudomonas aeruginosa. Coupons were inoculated with bacteria and incubated 24 hours (N = 4 for each test group). Microscopic images of biofilm were obtained. After washing and vortexing, attached bacteria were counted. A mouse biofilm model was modified to include coated and uncoated stainless steel wires inserted into the lumens of catheters inoculated with a mixture of S aureus or P aeruginosa. Colony-forming unit counts (N = 10) and scanning electron microscopy imaging of implants were used to determine antimicrobial activity.

RESULTS

Active antibiotics with colony inhibition effects were eluted for up to 6 days. Antibiotic-loaded coatings inhibited biofilm formation on in vitro coupons (log-fold reductions of 4.3 ± 0.4 in S aureus and 3.1 ± 0 for P aeruginosa in phosphatidylcholine-only coatings, 5.6 ± 0 for S aureus and 3.1 ± 0 for P aeruginosa for combination-loaded coatings, 5.5 ± 0.3 for S aureus in vancomycin-loaded coatings, and 3.1 ± 0 for P aeruginosa for amikacin-loaded coatings (p < 0.001 for all comparisons of antibiotic-loaded coatings against uncoated controls for both bacterial strains, p < 0.001 for comparison of antibiotic-loaded coatings against phosphatidylcholine only for S aureus, p = 0.54 for comparison of vancomycin versus combination coating in S aureus, P = 0.99 for comparison of antibiotic- and unloaded phosphatidylcholine coatings in P aeruginosa). Similarly, antibiotic-loaded coatings reduced attachment of bacteria to wires in vivo (log-fold reduction of 2.54 ± 0; p < 0.001 for S aureus and 0.83 ± 0.3; p = 0.112 for P aeruginosa).

CONCLUSIONS

Coatings deliver active antibiotics locally to inhibit biofilm formation and bacterial growth in vivo. Future evaluations will include orthopaedic preclinical models to confirm therapeutic efficacy.

CLINICAL RELEVANCE

Clinical applications of local drug delivery coating could reduce the rate of implant-associated infections.

Intrasite vancomycin powder for the prevention of surgical site infection in spine surgery: a systematic literature review

BACKGROUND CONTEXT

Deep surgical site infections (SSIs) following spinal surgery are a significant burden to the patient, patient's family, and the health-care system. Because of increasing pressures to reduce SSIs and control costs, some spine surgeons have begun placing lyophilized vancomycin powder directly into the surgical wound at the conclusion of the procedure. However, the literature supporting this practice remains limited.

PURPOSE

To review the current literature examining the use of prophylactic intrasite vancomycin powder to control SSIs in spinal surgery and determine if any standard recommendations can be made.

STUDY DESIGN

A systematic review.

METHODS

Ovid Medline and PubMed were searched to identify English language articles.

RESULTS

No current guidelines are available for the use of intrasite vancomycin powder in preventing SSIs, and no standard dosage for the drug exists. Based on the limited literature and evidence currently available, there appears to be a protective effect of intrasite vancomycin powder on the incidence of SSI, without evidence of side effects. However, case reports do exist describing the systemic side effects after intrasite vancomycin powder during spine surgery.

CONCLUSIONS

The interpretation of the available evidence supporting the use of intrasite vancomycin powder in surgical wounds is limited, and its extrapolation should be performed with caution. Despite the lack of significant high-quality evidence available in the literature, many surgeons have adopted this practice; anecdotally, it continues to provide protection from infection without apparent significant risk of side effects.

Chimeric peptides as implant functionalization agents for titanium alloy implants with antimicrobial properties

Implant-associated infections can have severe effects on the longevity of implant devices and they also represent a major cause of implant failures. Treating these infections associated with implants by antibiotics is not always an effective strategy due to poor penetration rates of antibiotics into biofilms. Additionally, emerging antibiotic resistance poses serious concerns. There is an urge to develop effective antibacterial surfaces that prevent bacterial adhesion and proliferation. A novel class of bacterial therapeutic agents, known as antimicrobial peptides (AMP's), are receiving increasing attention as an unconventional option to treat septic infection, partly due to their capacity to stimulate innate immune responses and for the difficulty of microorganisms to develop resistance towards them. While host- and bacterial- cells compete in determining the ultimate fate of the implant, functionalization of implant surfaces with antimicrobial peptides can shift the balance and prevent implant infections. In the present study, we developed a novel chimeric peptide to functionalize the implant material surface. The chimeric peptide simultaneously presents two functionalities, with one domain binding to a titanium alloy implant surface through a titanium-binding domain while the other domain displays an antimicrobial property. This approach gains strength through control over the bio-material interfaces, a property built upon molecular recognition and self-assembly through a titanium alloy binding domain in the chimeric peptide. The efficiency of chimeric peptide both in-solution and absorbed onto titanium alloy surface was evaluated in vitro against three common human host infectious bacteria, S. mutans, S. epidermidis, and E. coli. In biological interactions such as occurs on implants, it is the surface and the interface that dictate the ultimate outcome. Controlling the implant surface by creating an interface composed chimeric peptides may therefore open up new possibilities to cover the implant site and tailor it to a desirable bioactivity.

Heparinized nanohydroxyapatite/collagen granules for controlled release of vancomycin

The purpose of this study was to develop a bone substitute material capable of preventing or treating osteomyelitis through a sustainable release of vancomycin and simultaneously inducing bone regeneration. Porous heparinized nanohydroxyapatite (nanoHA)/collagen granules were characterized using scanning electron microscopy, micro-computed tomography and attenuated total reflectance Fourier transform infrared spectroscopy. After vancomycin adsorption onto the granules, its releasing profile was studied by UV molecular absorption spectroscopy. The heparinized granules presented a more sustainable release over time, in comparison with nonheparinized nanoHA and nanoHA/collagen granules. Vancomycin was released for 360 h and proved to be bioactive until 216 h. Staphylococcus aureus adhesion was higher on granules containing collagen, guiding the bacteria to the material with antibiotic, improving their eradication. Moreover, cytotoxicity of the released vancomycin was assessed using osteoblast cultures, and after 14 days of culture in the presence of vancomycin, cells were able to remain viable, increasing their metabolic activity and colonizing the granules, as observed by scanning electron microscopy and confocal laser scanning microscopy. These findings suggest that heparinized nanoHA/collagen granules are a promising material to improve the treatment of osteomyelitis, as they are capable of releasing vancomycin, eliminating the bacteria, and presented morphological and chemical characteristics to induce bone regeneration.

Antimicrobial delivery systems for local infection prophylaxis in orthopedic- and trauma surgery

Infectious complications occur in a minor but significant portion of the patients undergoing joint replacement surgery or fracture fixation, particularly those with severe open fractures, those undergoing revision arthroplasty or those at elevated risk because of poor health status. Once established, infections are difficult to eradicate, especially in the case of bacterial biofilm formation on implanted hardware. Local antibiotic carriers offer the prospect of controlled delivery of antibiotics directly in target tissues and implant, without inducing toxicity in non-target organs. Polymeric carriers have been developed to optimize the release and targeting of antibiotics. Passive polymeric carriers release antibiotics by diffusion and/or upon degradation, while active polymeric carriers release their antibiotics upon stimuli provided by bacterial pathogens. Additionally, some polymeric carriers gelate in-situ in response to physiological stimuli to form a depot for antibiotic release. As antibiotic resistance has become a major issue, also other anti-infectives such as silver and antimicrobial peptides have been incorporated in research. Currently, several antibiotic loaded biomaterials for local infection prophylaxis are available for use in the clinic. Here we review their advantages and limitations and provide an overview of new materials emerging that may overcome these limitations.

STUDY OF THE DIFFERENT RELEASE CHARACTERISTICS OF ANTIBIOTICS FROM PATIENTS: A DYNAMIC ELUTING SYSTEM TO INVESTIGATE DRUG RELEASE FROM ANTIBIOTIC-IMPREGNATED CALCIUM SULFATE DELIVERY

Background: Antibiotic-impregnated calcium sulfate delivery systems (ACDS) are commonly used to treat chronic osteomyelitis. Our research is to investigate drug release in vitro over a longer period, as a cautious predictor of in vivo release. Methods: The local release behavior of antibiotic in vitro was simulated. The consecutive dynamic eluting experiment was performed based on the pro-operative characteristic of osteomyelitis patients and the determined results of drug concentration in the human drainage tissue fluid (DTF). The concentration of each drug in the receiving solution was detected by ultra-performance liquid chromatography-tandem quadrupole detector mass spectrometry. The ACDS was reviewed by scanning electronic microscopy (SEM) after 48 h, and prepared to be eluted for another examination after 33 days. The mechanism of antibiotic release was analyzed by using the Ritger–Peppas and Weibull equations. Results: The cumulative release rate of vancomycin in a vancomycin-calcium sulfate delivery system (VCDS) was 77.50 % (3.0 mm diameter) and 72.43 % (4.8 mm diameter), while that of the tobramycin in a tobramycin-calcium sulfate delivery system (TCDS) was 88.0 % (3.0 mm diameter) and 84.55 % (4.8 mm diameter). At the 15th day, approximately 27.92% of vancomycin was and 29.35% of tobramycin was released from the local implant in vivo. Using SEM, numerous vancomycin and tobramycin particles were found to be attached to the columnar calcium sulfate crystals at the start of the experiment. The release behavior of the two antibiotics followed a combination of Fickian diffusion and Case II transport mechanisms within the first 48 h, and a Fickian diffusion mechanism during the subsequent time period. The correlation coefficient of tobramycin and vancomycin in vivo and in vitro was 0.9704–0.9949 and 0.9549–0.9782, respectively. Conclusion: A good correlation of the in vivo and in vitro cumulative release rates was observed by comparing the cumulative release rate of drugs in vitro by means of the dynamic eluting model, and in the DTF. Therefore, our study has proved that it is possible to use the dynamic eluting model as a cautious predictor of in vivo release.

In vitro assessment of nanosilver-functionalized PMMA bone cement on primary human mesenchymal stem cells and osteoblasts

Peri-prosthetic infections caused by multidrug resistant bacteria have become a serious problem in surgery and orthopedics. The aim is to introduce biomaterials that avoid implant-related infections caused by multiresistant bacteria. The efficacy of silver nanoparticles (AgNP) against a broad spectrum of bacteria and against multiresistant pathogens has been repeatedly described. In the present study polymethylmethacrylate (PMMA) bone cement functionalized with AgNP and/or gentamicin were tested regarding their biocompatibility with bone forming cells. Therefore, influences on viability, cell number and differentiation of primary human mesenchymal stem cells (MSCs) and MSCs cultured in osteogenic differentiation media (MSC-OM) caused by the implant materials were studied. Furthermore, the growth behavior and the morphology of the cells on the testing material were observed. Finally, we examined the induction of cell stress, regarding antioxidative defense and endoplasmatic reticulum stress. We demonstrated similar cytocompatibility of PMMA loaded with AgNP compared to plain PMMA or PMMA loaded with gentamicin. There was no decrease in cell number, viability and osteogenic differentiation and no induction of cell stress for all three PMMA variants after 21 days. Addition of gentamicin to AgNP-loaded PMMA led to a slight decrease in osteogenic differentiation. Also an increase in cell stress was detectable for PMMA loaded with gentamicin and AgNP. In conclusion, supplementation of PMMA bone cement with gentamicin, AgNP, and both results in bone implants with an antibacterial potency and suitable cytocompatibility in MSCs and MSC-OM.

Vancomycin-bearing synthetic bone graft delivers rhBMP-2 and promotes healing of critical rat femoral segmental defects

BACKGROUND

Bone grafts simultaneously delivering therapeutic proteins and antibiotics may be valuable in orthopaedic trauma care. Previously, we developed a poly(2-hydroxyethyl methacrylate)-nanocrystalline hydroxyapatite (pHEMA-nHA) synthetic bone graft that, when preabsorbed with 400-ng rhBMP-2/7, facilitated the functional repair of critical-size rat femoral defects. Recently, we showed that pHEMA-nHA effectively retains/releases vancomycin and rhBMP-2 in vitro. The success of such a strategy requires that the incorporation of vancomycin does not compromise the structural integrity of the graft nor its ability to promote bone healing.

QUESTIONS/PURPOSES

(1) To evaluate the ability of pHEMA-nHA-vancomycin composites in combination with 3-µg rhBMP-2 to repair 5 mm rat femoral segmental defects, and (2) To determine if the encapsulated vancomycin impairs the graft/rhBMP-2-assisted bone repair.

METHODS

pHEMA-nHA-vancomycin, pHEMA-nHA, or collagen sponge control with/without 3-µg rhBMP-2 were press-fit in 5 mm femoral defects in SASCO-SD male rats (289-300 g). Histology, microcomputed tomography, and torsion testing were performed on 8- and 12-week explants to evaluate the extent and quality of repair. The effect of vancomycin on the temporal absorption of endogenous BMP-2 and stromal cell-derived factor-1 was evaluated by immunohistochemistry. These factors are important for bone healing initiation and stem cell recruitment, respectively.

RESULTS

Partial bridging of the defect with bony callus by 12 weeks was observed with pHEMA-nHA-vancomycin without rhBMP-2 while full bridging with substantially mineralized callus and partial restoration of torsional strength was achieved with 3-µg rhBMP-2. The presence of vancomycin changed the absorption patterns of endogenous proteins on the grafts, but did not appear to substantially compromise graft healing.

CONCLUSIONS

The composite pHEMA-nHA-vancomycin preabsorbed with 3-µg rhBMP-2 promoted repair of 5 mm rat femoral segmental defects. With the sample sizes applied, vancomycin encapsulation did not appear to have a negative effect on bone healing.

CLINICAL RELEVANCE

pHEMA-nHA-vancomycin preabsorbed with rhBMP-2 may be useful in the repair of critical-size long bone defects prone to infections.

Osteocompatibility of biofilm inhibitors

The demand for infection prevention therapies has led to the discovery of several biofilm inhibitors. These inhibiting signals are released by bacteria, fungi, or marine organisms to signal biofilm dispersal or disruption in Gram-positive, Gram-negative, and fungal microorganisms. The purpose of this study was to test the biocompatibility of five different naturally-produced biofilm chemical dispersal and inhibition signals with osteoblast-like cells: D-amino acids (D-AA), lysostaphin (LS), farnesol, cis-2-decenoic acid (C2DA), and desformyl flustrabromine (dFBr). In this preliminary study, compatibility of these anti-biofilm agents with differentiating osteoblasts was examined over a 21 days period at levels above and below concentrations active against bacterial biofilm. Anti-biofilm compounds listed above were serially diluted in osteogenic media and added to cultures of MC3T3 cells. Cell viability and cytotoxicity, after exposure to each anti-biofilm agent, were measured using a DNA assay. Differentiation characteristics of osteoblasts were determined qualitatively by observing staining of mineral deposits and quantitatively with an alkaline phosphatase assay. D-AA, LS, and C2DA were all biocompatible within the reported biofilm inhibitory concentration ranges and supported osteoblast differentiation. Farnesol and dFBr induced cytotoxic responses within the reported biofilm inhibitory concentration range and low doses of dFBr were found to inhibit osteoblast differentiation. At high concentrations, such as those that may be present after local delivery, many of these biofilm inhibitors can have effects on cellular viability and osteoblast function. Concentrations at which negative effects on osteoblasts occur should serve as upper limits for delivery to orthopaedic trauma sites and guide development of these potential therapeutics for orthopaedics.

Local intrawound vancomycin powder decreases the risk of surgical site infections in complex adult deformity reconstruction: a cost analysis

STUDY DESIGN

Retrospective cohort analysis.

OBJECTIVE

To evaluate the rate of surgical site infections (SSIs) and cost-effectiveness of the use of intraoperative vancomycin powder in thoracolumbar adult deformity procedures.

SUMMARY OF BACKGROUND DATA

The rates of SSI remain unacceptably high in adult spinal deformity surgery despite routine intravenous antibiotics. Vancomycin powder applied directly to the wound intraoperatively has shown promise for decreasing SSI in spine surgery.

METHODS

Adults who underwent adult deformity reconstruction by 2 surgeons between 2008 and 2012 with a minimum of 3 months of clinical follow-up were retrospectively reviewed. The patients were subdivided into those who had received only routine perioperative intravenous antibiotics (control) and those who received intravenous antibiotics and 2 g of vancomycin powder applied into the surgical wound. The primary outcome was SSI within 90 days. Secondary outcomes included surgical/clinical parameters and SSI-related medical costs based on hospital billing records.

RESULTS

Two hundred fifteen patients were evaluated-controls (n=64) and vancomycin powder group (n=151). The average number of levels fused was 10 (5-17, control) and 12 (5-19, vancomycin). The mean follow-up was 34 months (3-68 mo, control) and 18 months (3-35 mo, vancomycin) (P<0.05). There were significantly fewer hospital readmissions within 90 days for SSI in patients who received vancomycin powder (2.6%; 4/151) compared with controls (10.9%; 7/64) (P=0.01). There were no reported adverse events related to the intrawound vancomycin use. The average cost per patient of treating a postoperative SSI was higher in the control group ($34,388) than in the study group ($28,169). With the use of vancomycin powder, there was a cost saving of $244,402 per 100 complex spinal procedures.

CONCLUSION

Local application of vancomycin powder significantly decreased SSI for adults undergoing spinal reconstructive surgery. This resulted in cost savings of $244,402 per 100 thoracolumbar adult deformity procedures.

LEVEL OF EVIDENCE

3.

Safety of topical vancomycin for pediatric spinal deformity: nontoxic serum levels with supratherapeutic drain levels

STUDY DESIGN

Retrospective cohort analysis.

OBJECTIVE

To establish if drain levels exceed the minimum inhibitory concentrations for common pathogens (methicillin-resistant Staphylococcus aureus, methicillin-sensitive Staphylococcus aureus, and Propionibacterium acnes-2 μg/mL; Staphylococcus epidermidis, Enterococcus faecalis-4 μg/mL). Evaluate the safety of topical vancomycin in pediatric patients undergoing spinal deformity surgery and determine if postoperative serum levels approach toxicity (25 μg/mL).

SUMMARY OF BACKGROUND DATA

The application of topical vancomycin powder has decreased postoperative wound infections in retrospective analyses in the adult population with minimal local and systemic risks. The safety and efficacy of vancomycin powder has not been completely evaluated in the pediatric population after deformity surgery.

METHODS

Topical vancomycin powder (1 g) was applied during wound closure after instrumented posterior spinal fusion. All patients received intravenous perioperative antibiotics and a subfascial drain was used. Serum and drain vancomycin levels were collected immediately postoperatively and during the first 2 postoperative days (PODs). Complications were recorded.

RESULTS

The study population consisted of 25 patients with a mean age of 13.5 years (9.5-17.1 yr) and mean ± standard deviation body weight of 44.5 ± 18 kg. Underlying diagnoses included: adolescent idiopathic scoliosis (12), neuromuscular scoliosis (10), and kyphosis (3). Mean serum vancomycin levels trended downward from 2.5 μg/mL (POD 0) to 1.9 μg/mL (POD 1) to 1.1 μg/mL (POD 2). Mean drain levels also trended downward from 403 μg/mL (POD 0) to 251 μg/mL (POD 1) to 115 μg/mL (POD 2). No vancomycin toxicity or deep wound infections were observed. One patient with neuromuscular scoliosis developed a superficial wound dehiscence that was managed with dressing changes.

CONCLUSION

Topical application of vancomycin powder in pediatric spinal deformity surgery produced local levels well above the minimum inhibitory concentration for common pathogens and serum levels below the toxicity threshold (25 μg/mL). There were no deep wound or antibiotic related complications.

LEVEL OF EVIDENCE

3.

Electrospun vancomycin-loaded coating on titanium implants for the prevention of implant-associated infections

The objectives of this work were to develop an antibiotic coating on the surface of a titanium plate to determine its antibacterial properties in vitro and in vivo. To prepare vancomycin-coated titanium implants, we adopted the electrospinning nanotechnique. The surface structure of the coating implants was observed using a scanning electron microscope. An elution method and a high-pressure liquid chromatography assay were used to characterize the release behavior of vancomycin from the coating. The antibacterial efficacy and the cytotoxicity of the coated titanium implants on osteoblasts were investigated in vitro. In addition, X-ray, white blood cell count, C-reactive protein, erythrocyte sedimentation rate, and pathological examination were performed to validate its antimicrobial efficacy in vivo. The antibiotic coating released 82.7% (approximately 528.2 μg) of total vancomycin loading in the coating in vitro. The release behavior of vancomycin from nanofiber coatings exhibited a biphasic release pattern with an initial burst on day 1, followed by a slow and controlled release over 28 days. There was no cytotoxicity observed in vitro for the vancomycin-loaded coating. The vancomycin-coated titanium implants were active in treating implant-associated infection in vivo. Thus, vancomycin-coated titanium implants may be a promising approach to prevent and treat implant-associated infections.

Composite chitosan and calcium sulfate scaffold for dual delivery of vancomycin and recombinant human bone morphogenetic protein-2

A biodegradable, composite bone graft, composed of chitosan microspheres embedded in calcium sulfate, was evaluated in vitro for point-of-care loading and delivery of antibiotics and growth factors to prevent infection and stimulate healing in large bone injuries. Microspheres were loaded with rhBMP-2 or vancomycin prior to mixing into calcium sulfate loaded with vancomycin. Composites were evaluated for set time, drug release kinetics, and bacteriostatic/bactericidal activity of released vancomycin, induction of ALP expression by released rhBMP-2, and interaction of drugs on cells. Results showed the composite set in under 36 min and released vancomycin levels that were bactericidal to S. aureus (>MIC 8-16 μg/mL) for 18 days. Composites exhibited a 1 day-delayed release, followed by a continuous release of rhBMP-2 over 6 weeks; ranging from 0.06 to 1.49 ng/mL, and showed a dose dependent release based on initial loading. Released rhBMP-2 levels were, however, too low to induce detectable levels of ALP in W20-17 cells, due to the affinity of rhBMP-2 for calcium-based materials. With stimulating amounts of rhBMP-2 (>50 ng/mL), the ALP response from W-20-17 cells was inhibited when exposed to high vancomycin levels (1,800-3,600 μg/mL). This dual-delivery system is an attractive alternative to single delivery or preloaded systems for bone regeneration since it can simultaneously fight infection and deliver a potent growth factor. Additionally, this composite can accommodate a wide range of therapeutics and thus be customizable for specific patient needs, however, the potential interactive effects of multiple agents must be investigated to ensure that functional activity is not altered.

D-amino acids enhance the activity of antimicrobials against biofilms of clinical wound isolates of Staphylococcus aureus and Pseudomonas aeruginosa

Within wounds, microorganisms predominantly exist as biofilms. Biofilms are associated with chronic infections and represent a tremendous clinical challenge. As antibiotics are often ineffective against biofilms, use of dispersal agents as adjunctive, topical therapies for the treatment of wound infections involving biofilms has gained interest. We evaluated in vitro the dispersive activity of D-amino acids (D-AAs) on biofilms from clinical wound isolates of Staphylococcus aureus and Pseudomonas aeruginosa; moreover, we determined whether combinations of D-AAs and antibiotics (clindamycin, cefazolin, oxacillin, rifampin, and vancomycin for S. aureus and amikacin, colistin, ciprofloxacin, imipenem, and ceftazidime for P. aeruginosa) enhance activity against biofilms. D-Met, D-Phe, and D-Trp at concentrations of ≥ 5 mM effectively dispersed preformed biofilms of S. aureus and P. aeruginosa clinical isolates, an effect that was enhanced when they were combined as an equimolar mixture (D-Met/D-Phe/D-Trp). When combined with D-AAs, the activity of rifampin was significantly enhanced against biofilms of clinical isolates of S. aureus, as indicated by a reduction in the minimum biofilm inhibitory concentration (MBIC) (from 32 to 8 μg/ml) and a >2-log reduction of viable biofilm bacteria compared to treatment with antibiotic alone. The addition of D-AAs was also observed to enhance the activity of colistin and ciprofloxacin against biofilms of P. aeruginosa, reducing the observed MBIC and the number of viable bacteria by >2 logs and 1 log at 64 and 32 μg/ml in contrast to antibiotics alone. These findings indicate that the biofilm dispersal activity of D-AAs may represent an effective strategy, in combination with antimicrobials, to release bacteria from biofilms, subsequently enhancing antimicrobial activity.

Characterization and cytocompatibility of an antibiotic/chitosan/cyclodextrins nanocoating on titanium implants

A novel ciprofloxacin loaded chitosan nanoparticle-based coating onto titanium substrates has been developed and characterized to obtain an orthopaedic implant surface able to in situ release the antibiotic for the prevention of post-operative infections. Ciprofloxacin loaded chitosan nanoparticles were obtained using the combination of sulfobutyl ether-beta-cyclodextrin and gamma-cyclodextrin. The resulting nanoparticulate system was characterized by TEM, HPLC and XPS. Particle size was in the range 426-552 nm and zeta potential values were around +30 mV. This antibacterial coating was able to in vitro inhibit two nosocomial Staphylococcus aureus strains growth, with a reduction of about 20 times compared to controls. No impairment in MG63 osteoblast-like cells viability, adhesion and gene expression were detected at 48 h, 7 and 14 days of culture. Overall, the investigated coating represents a promising candidate for the development of a new antibiotic carrier for titanium implants.

[Application of vancomycin powder into the wound during spine surgery: systematic review and meta-analysis]

OBJECTIVE

To determine the effects of applying vancomycin powder within the surgical wound on the risk of surgical infections, pseudo-arthrosis and adverse events, in patients undergoing spinal surgery.

MATERIAL AND METHODS

A meta-analysis was carried out, including controlled studies that evaluated the risk of postoperative infections and/or pseudo-arthrosis in patients undergoing spinal surgery in which vancomycin powder was applied within the surgical wound.

RESULTS

were presented as pooled relative risks, with its 95% confidence intervals. Additionally, the frequency of complications attributable to vancomycin was also assessed.

RESULTS

A total of six controlled studies (3,379 subjects) were included. Pooled relative risks were: surgical site infection, 0.11 (95%CI: 0.05-0.25; P<.00001), and pseudo-arthrosis, 0.87 (95%CI; 0.34-2.21; P=.77). No statistically significant heterogeneity was found in both analyses. In 1,437 patients treated with vancomycin, there were no recorded vancomycin-related adverse events.

CONCLUSIONS

Application of vancomycin powder into the wound was associated with a significantly reduced risk of surgical site infections, without increasing pseudo-arthrosis or adverse events. However, randomized controlled trials are needed, in order to confirm the present results and make recommendations with more certainty.

The use of vancomycin powder reduces surgical reoperation in posterior instrumented and noninstrumented spinal surgery

BACKGROUND

Surgical site infections can complicate posterior spine surgery. Multiple hospital admissions may be required to adequately treat a surgical site infection, which is associated with increased costs and lower patient satisfaction. The objective of this study was to evaluate the efficacy of prophylactic intra-wound vancomycin powder in reducing the incidence of repeat surgery for infections after posterior instrumented and noninstrumented spine surgery.

METHODS

A series of consecutive patients who underwent instrumented or noninstrumented posterior spine surgery for any indication by two surgeons from July 2010 to July 2012 were reviewed. The preoperative antibiotic regimens of both surgeons were identical, except that one surgeon applied 1 g vancomycin powder directly to the surgical bed before wound closure, while the other did not. Patient demographics, operative details, and rates of reoperation for wound infection in the control and the treatment groups were compared.

RESULTS

Both the control group and treatment group consisted of 150 patients; mean ages were 58.33 and 54.14 years, respectively. Both groups had low rates of deep infection requiring surgical intervention. The treatment group had a significantly lower rate of infection requiring reoperation or surgical debridement (0 %; 95 % CI: 0 %-2.4 %) compared with the control group (4 %; 95 % CI: 1.5 %-8.5 %) (P = 0.0297). The six infections identified in the control group resulted in 12 repeat operative debridement procedures. Gram-positive organisms were identified in 66.7 % of infections. No complications were related to the application of vancomycin powder.

CONCLUSIONS

The results of this study demonstrate that adjunctive vancomycin powder applied directly to the surgical bed before closure seems effective in preventing deep infections that require operative debridement following posterior spine surgery.

PREPARATION AND CHARACTERIZATIONS OF ANTIBIOTIC IMPREGNATED MICROPOROUS NANO-HYDROXYAPATITE FOR OSTEOMYELITIS TREATMENT

In this study, preparation and characterization of antibiotic-impregnated microporous nano-hydroxyapatite (HA) aiming to function as both antibiotic carrier and bone graft for osteomyelitis treatment were carried out. Microporous nano-hydroxyapatite was prepared by low temperature phosphorization of three-dimensional printed calcium sulfate sample and was impregnated by three types of antibiotics including vancomycin, fosfomycin and gentamicin. Materials properties and antibacterial performance including phase composition, microstructure, degradability, total drug loading, antibacterial activity and shelf life were investigated and reported. Microporous nano-hydroxyapatite having porosity and mean pore size of 63.92% and 0.15 microns was prepared and showed greater resorbability than typical high-temperature sintering samples. Sustained release of antibiotic from the impregnated samples for longer than 29 days was observed, but the difference in the efficiency was related to the difference in the molecular weight, mechanism of action, spectrum of activity of each antibiotic. No deterioration in the antibacterial activity of the prepared antibiotic-impregnated hydroxyapatite was observed after storing for up to 12 months. No cytotoxic potential by MTT assay at all extraction periods was observed for vancomycin-impregnated hydroxyapatite. Gentamicin and fosfomycin impregnated hydroxyapatites showed cytotoxic potential only on day 1 extraction, but no cytotoxic potential was observed on day 2 extraction onward. This could be related to the concentration and characteristics of each released antibiotics.

Analysis of parameters influencing the release of antibiotics mixed with bone grafting material using a reliable mixing procedure

Local infections arising from fracture fixation, defect reconstruction or joint replacement can cause extreme pain and impaired healing, lead to revision operations, prolong hospital stay and increase costs. Treatment options including prophylaxis are afforded by the use of grafts and biomaterials loaded with antibiotics. These can produce local therapeutic concentrations with a reduced systemic concentration and reduced systemic side-effects. Patient-specific loading of osteogenic graft materials with antibiotic could be an important option for orthopaedic surgeons. A local therapeutic concentration must be available for the desired duration and cytotoxic effects must be kept within an acceptable range. The present study investigates a simple and reliable mixing procedure that could be used for the perioperative combination of antibiotic powders and solutions with bone grafting materials. The potential influence of concentration and sampling regime on the release kinetics of gentamicin, tobramycin and vancomycin was studied over a period of 56days and potency and cytotoxicity were evaluated. In all treatment groups, gentamicin and tobramycin were completely released within 3days whilst vancomycin was released over a period of 14days. The results clearly show that the main parameter influencing release is the molecular weight of the drug. Growth of Staphylococcus aureus was inhibited in all 3 treatment groups for at least 3days. Cell viability and alkaline phosphatase activity of primary osteoblast-like cells were not significantly affected by the antibiotic concentrations obtained from the elution experiments. Bone grafting is an established component of surgery for bone defect filling and for biological stimulation of healing. Patient-specific enhancement of such procedures by incorporation of antibiotics for infection prevention or by addition of cytokines for promotion of impaired healing or for treatment of critical size defects will be a relevant issue in the future.

Improved antibacterial activity and biocompatibility on vancomycin-loaded TiO2 nanotubes: in vivo and in vitro studies

The goal for current orthopedic implant research is to design implants that have not only good biocompatibility but also antibacterial properties. TiO₂ nanotubes (NTs) were fabricated on the titanium surface through electrochemical anodization, which added new properties, such as enhanced biocompatibility and potential utility as drug nanoreservoirs. The aim of the present study was to investigate the antibacterial properties and biocompatibility of NTs loaded with vancomycin (NT-V), both in vitro and in vivo. Staphylococcus aureus was used to study the antibacterial properties of the NT-V. There were three study groups: the commercially pure titanium (Cp-Ti) group, the NT group (nonloaded vancomycin), and the NT-V group. We compared NT-V biocompatibility and antibacterial efficacy with those of the NT and Cp-Ti groups. Compared with Cp-Ti, NT-V showed good antibacterial effect both in vitro and in vivo. Although the NTs reduced the surface bacterial adhesion in vitro, implant infection still developed in in vivo studies. Furthermore, the results also revealed that both NTs and NT-V showed good biocompatibility. Therefore, the NTs loaded with antibiotic might be potentially used for future orthopedic implants.

Evaluation of antibiotic releasing porous polymethylmethacrylate space maintainers in an infected composite tissue defect model

This study evaluated the in vitro and in vivo performance of antibiotic-releasing porous polymethylmethacrylate (PMMA)-based space maintainers comprising a gelatin hydrogel porogen and a poly(dl-lactic-co-glycolic acid) (PLGA) particulate carrier for antibiotic delivery. Colistin was released in vitro from either gelatin or PLGA microparticle loaded PMMA constructs, with gelatin-loaded constructs releasing colistin over approximately 7 days and PLGA microparticle-loaded constructs releasing colistin for up to 8 weeks. Three formulations with either burst release or extended release at different doses were tested in a rabbit mandibular defect inoculated with Acinetobacter baumannii (2×10(7) colony forming units ml(-1)). In addition, one material control that released antibiotic but was not inoculated with A. baumannii was tested. A. baumannii was not detectable in any animal after 12 weeks on culture of the defect, saliva, or blood. Defects with high dose extended release implants had greater soft tissue healing compared with defects with burst release implants, with 8 of 10 animals showing healed mucosae compared with 2 of 10 respectively. Extended release of locally delivered colistin via a PLGA microparticle carrier improved soft tissue healing compared with implants with burst release of colistin from a gelatin carrier.

The use of antimicrobial-impregnated PMMA to manage periprosthetic infections: controversial issues and the latest developments

Despite improvements in intraoperative antimicrobial procedures, in surgical techniques and in implant design for joint replacement, periprosthetic infection after arthroplasty is still one of the most challenging problems encountered by orthopedic surgeons. Systemic antibiotics are not sufficiently effective to eradicate such deep infections because of the impaired blood circulation and low antibiotic concentration at the implantation site. As a local drug delivery system, antibiotic-impregnated PMMA (polymethylmethacrylate) bone cements have been widely used for prophylaxis or treatment of deep infections after total joint replacement. However, the effectiveness of antibiotic-loaded PMMA in preventing infections after arthroplasty is still controversial. Furthermore, the outcomes of established deep infections treated with this technique are not consistent. The local use of antibiotics has led to the emergence of antibiotic-resistant bacterial strains and has adverse effects on the function of osteogenic cells. Recently, many efforts have been made to identify new antibacterial agents that can be loaded into PMMA. These antimicrobial agents should exhibit good antibacterial activity against antibiotic-resistant strains and should simultaneously enhance osteointegration between the PMMA and the bone tissue. PMMA loaded with chitosan or chitosan derivatives has been demonstrated to induce improved osteogenic activity and to exhibit antibacterial activity in a preclinical study.

Local gentamicin application does not interfere with bone healing in a rat model

For the prophylaxis and treatment of bony infections antibiotics are locally used. Since several decades antibiotics mixed with bone cement (methylmethacrylate) are successfully used in prosthetic surgery and a gentamicin coated tibial nail is approved in Europe for fracture stabilization. The goal of the present study was to investigate if gentamicin, locally applied from a polymeric coating of intramedullary nails, might interfere with the bone healing process. Female Sprague Dawley rats (n = 72) were used and the tibiae were intramedullary stabilized with Kirschner-wires (k-wires) after osteotomy. This model was established earlier and shows a delayed healing with a prolonged inflammatory reaction. The open approach is clinically more relevant compared to a closed one because it mimics the clinically critical case of an open fracture, which has a higher risk of infection. The k-wire was either coated with the polymer poly(d,l-lactide) (control group) or with 10% gentamicin incorporated into the polymer (gentamicin group). In vivo μCT analyses were performed at days 10, 28, 42, and 84 after osteotomy. Mechanical torsional testing and histological evaluation were done at the days of sacrifice: 28, 42, and 84. The μCT analyses revealed an increase in tissue mineral density (TMD) over the healing period in both groups. In the control group, the torsional stiffness and maximum load did not reach the values of the intact contralateral side at any time point. At day 84 the gentamicin treated tibiae, however, showed significantly better maximum load compared to the control group. The histology showed no bony bridging in the control, whereas in 2 of 5 calluses of the gentamicin group mineralized bridging occurred. Significantly more mineralized tissue was measured in the gentamicin group. This study shows that the local gentamicin application does not negatively interfere with the long term healing process. Local infection prophylaxis is effective without negative effects on bone healing.

Intrawound vancomycin powder reduces surgical site infections in posterior cervical fusion

STUDY DESIGN

Retrospective comparative study using prospectively collected data.

OBJECTIVE

To compare the rate of infection with and without the use of vancomycin powder application during posterior cervical instrumentation.

SUMMARY OF BACKGROUND DATA

Surgical site infections (SSI) are a significant source of morbidity in multilevel posterior-instrumented fusions for cervical spondylotic myelopathy (CSM). Local delivery of antibiotics has been associated with decreased rates of SSI in posterior-instrumented fusions, but no study has addressed the effects of these measures on a population composed of exclusively multilevel posterior cervical instrumentation performed with decompression for CSM.

METHODS

All patients undergoing multilevel posterior decompression and instrumentation for CSM by a single surgeon from 2003-2011 were included. Post hoc analysis of prospectively collected data was analyzed comparing consecutive patients treated without the use of vancomycin powder with those treated after the initiation of vancomycin powder prophylaxis. Intervention cohort and controls were examined for differences in SSI rate, body mass index, neurological status, comorbidities, and complications.

RESULTS

A total of 112 patients were included in the study. Intervention (n = 40) and control (n = 72) groups were statistically similar with regard to age, body mass index, comorbidities, estimated blood loss, and operative time. Univariate analysis showed a significant decrease in infection rate in the intervention group (0%) compared with the control group (15%) in this high-risk population (P = 0.007; power = 81%). No adverse events were noted in the intervention group associated with the use of vancomycin powder.

CONCLUSION

The local application of vancomycin was associated with a significant reduction in the risk of SSI in multilevel posterior cervical-instrumented fusions for CSM. This study supports the growing body of evidence that vancomycin powder placed in the wound can reduce the incidence of postoperative wound infections, and is the first that addresses this specific population.

LEVEL OF EVIDENCE

2.

Decreased risk of wound infection after posterior cervical fusion with routine local application of vancomycin powder

STUDY DESIGN

A retrospective cohort study.

OBJECTIVE

To assess the ability of local vancomycin powder to prevent wound infection after posterior cervical fusion.

SUMMARY OF BACKGROUND DATA

Wound infections are a significant source of morbidity and cost associated with spine surgery. Intraoperative application of vancomycin powder to the wound edges has been shown to lower the infection risk after posterior instrumented thoracolumbar fusion. There is little data on the efficacy and safety of local vancomycin powder in cervical spine surgery.

METHODS

All cases of posterior cervical fusion by a single surgeon were reviewed from 2007 to 2011. Routine application of 1 gram of vancomycin powder was started in August 2009. Baseline characteristics, operative details, and rates of wound infection and pseudarthrosis were compared between untreated patients and those who received vancomycin powder.

RESULTS

A total 171 patients underwent posterior cervical fusion between 2007 and 2011. Baseline and operative variables were similar between untreated patients (n = 92) and those who received vancomycin powder (n = 79). Patients were followed for a minimum of 1 year (range, 1.1-5.7 yr). The infection rate fell from 10.9% to 2.5% (P = 0.0384) following the introduction of vancomycin powder. The untreated and treated groups had similar rates of pseudarthrosis (5.4% vs. 5.1%). No complications attributable to vancomycin powder were identified.

CONCLUSION

Routine local application of vancomycin powder is a low-cost effective strategy for preventing wound infection after posterior cervical fusion. Further studies are needed to optimize dosing, assess long-term safety, and evaluate use in other spinal operations.

LEVEL OF EVIDENCE

2.

Cell viability, collagen synthesis and cytokine expression in human osteoblasts following incubation with generated wear particles using different bone cements

In total hip arthroplasty, wear particles generated at articulating surfaces and interfaces between bone, cement and implants have a negative impact on osteoblasts, leading to osteolysis and implant loosening. The aim of this experimental study was to determine the effects of particulate wear debris generated at the interface between straight stainless steel hip stems (Exeter(®)) and three different bone cements (Palacos(®) R, Simplex™ P and Cemex(®) Genta) on cell viability, collagen synthesis and cytokine expression in human osteoblasts. Primary osteoblasts were treated with various concentrations of wear particles. The synthesis of procollagen type I and different cytokines was analysed, and markers for apoptosis and necrosis were also detected. The cytokine synthesis rates in the osteoblasts were initially increased and varied, depending on incubation time and particle concentration. Specific differences in the synthesis rates of interleukin (IL)‑6, IL-8, vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) were observed with the different bone cements examined. The negative effect of the particles on the synthesis of procollagen type I and increased rates of cell apoptosis and necrosis were observed with all three cements analysed. Our present data suggest that wear particles from the interface between the total hip stem and bone cement have a significant effect on viability, cytokine expression and collagen synthesis in human osteoblasts, depending on the bone cement used.

Quaternized chitosan as an antimicrobial agent: antimicrobial activity, mechanism of action and biomedical applications in orthopedics

Chitosan (CS) is a linear polysaccharide with good biodegradability, biocompatibility and antimicrobial activity, which makes it potentially useful for biomedical applications, including an antimicrobial agent either alone or blended with other polymers. However, the poor solubility of CS in most solvents at neutral or high pH substantially limits its use. Quaternary ammonium CS, which was prepared by introducing a quaternary ammonium group on a dissociative hydroxyl group or amino group of the CS, exhibited improved water solubility and stronger antibacterial activity relative to CS over an entire range of pH values; thus, this quaternary modification increases the potential biomedical applications of CS in the field of anti-infection. This review discusses the current findings on the antimicrobial properties of quaternized CS synthesized using different methods and the mechanisms of its antimicrobial actions. The potential antimicrobial applications in the orthopedic field and perspectives regarding future studies in this field are also considered.

Perspectives on the interface of drug delivery and tissue engineering

Controlled drug delivery of bioactive molecules continues to be an essential component of engineering strategies for tissue defect repair. This article surveys the current challenges associated with trying to regenerate complex tissues utilizing drug delivery and gives perspectives on the development of translational tissue engineering therapies which promote spatiotemporal cell-signaling cascades to maximize the rate and quality of repair.

Preliminary investigation of crosslinked chitosan sponges for tailorable drug delivery and infection control

Local versus systemic antibiotic delivery may be an effective strategy for treating musculoskeletal infections, especially when antibiotic-resistant bacteria are present. Lyophilized uncrosslinked, genipin crosslinked, and genipin crosslinked with poly(N-isopropylacrylamide) (PNIPAM) chitosan sponges were analyzed for their in vitro degradation rate, chemical crosslinking, antibiotic uptake, elution, biologic activity, and cytotoxicity. These evaluations were pursued to determine if crosslinking with genipin could be used to create a tailorable point of care loaded sponge for local infection control. Crosslinking the chitosan sponges decreased degradation in phosphate-buffered saline from 4.48 ± 2.28 wt % remaining of the uncrosslinked sponges to 78.82 ± 1.15 and 73.87 ± 1.27 wt % remaining at week 1 for the genipin and PNIPAM/genipin crosslinked sponges, respectively. The PNIPAM/genipin crosslinked sponges exhibited the most sustained release of biologically active antibiotics, with an average antibiotic release 63% higher than uncrosslinked and 37% higher than genipin crosslinked sponges, after 96 h. No significant cytotoxic effects from sponges or eluates were exhibited with NIH 3T3 fibroblasts. These preliminary results indicate that genipin crosslinked chitosan sponges, with or without PNIPAM, have potential as local delivery systems for adjunctive therapy for infection control, especially when longer degradation periods and higher antibiotic elutions are desired.

Local delivery of small and large biomolecules in craniomaxillofacial bone

Current state of the art reconstruction of bony defects in the craniomaxillofacial (CMF) area involves transplantation of autogenous or allogenous bone grafts. However, the inherent drawbacks of this approach strongly urge clinicians and researchers to explore alternative treatment options. Currently, a wide interest exists in local delivery of biomolecules from synthetic biomaterials for CMF bone regeneration, in which small biomolecules are rapidly emerging in recent years as an interesting adjunct for upgrading the clinical treatment of CMF bone regeneration under compromised healing conditions. This review highlights recent advances in the local delivery small and large biomolecules for the clinical treatment of CMF bone defects. Further, it provides a perspective on the efficacy of biomolecule delivery in CMF bone regeneration by reviewing presently available reports of pre-clinical studies using various animal models.

Induced osteoclastogenesis by fluoroquinolones in unstimulated and stimulated human osteoclast precursor cells

Fluoroquinolones (FQs) are a class of antibiotics with a broad spectrum of activity, known to disturb bone metabolism. The aim of this work was to characterize the cellular and molecular effects of five FQs (ofloxacin, norfloxacin, ciprofloxacin, levofloxacin and moxifloxacin) in unstimulated and stimulated human osteoclast precursors. Peripheral blood mononuclear cells (PBMC) were cultured in the absence (unstimulated) or in the presence of osteoclastogenic factors (M-CSF and RANKL, stimulated), and were treated with FQs (0.3×10(-9)-10(-3) M), for 21 days. In unstimulated PBMC cultures, FQs (excepting moxifloxacin) exhibited a high osteoclastogenic potential, as shown by a significant increase in the expression of osteoclastic genes, TRAP activity and, specially, number of TRAP-positive multinucleated cells and calcium phosphate resorbing ability, suggesting the presence of mature and functional osteoclasts. Norfloxacin and levofloxacin induced the higher effect, followed by ciprofloxacin and ofloxacin. A decrease on apoptosis and an increase on M-CSF expression might have a possible contribution in the observed cellular behavior. In stimulated PBMC cultures, FQs further increase the osteoclastogenic response induced by M-CSF and RANKL (except ofloxacin). However, the osteoclastogenic response was much lower than that observed in unstimulated PBMC cultures. Both in unstimulated and stimulated PBMC cultures, for most of the FQs, the osteoclastogenic effects were observed in a wide range of concentrations, representative of plasmatic and tissue levels attained in several clinical settings. The various FQs differed on the stimulatory concentration range, the extent of the induced osteoclastogenic response and, also, on the dose- and time-dependent profile. Nevertheless, at high concentrations all the FQs seemed to elicit an increase on apoptosis. Additionally, some differences were noted in the intracellular signaling pathways tested, namely NFkB, MEK and PGE2 production. Results suggest that, considering the inter-individual variability of the FQs pharmacokinetics, the detailed biological profile of each FQ on bone cells is of utmost importance to clarify the effects of these compounds on bone metabolism.

Physical characterization and osteogenic activity of the quaternized chitosan-loaded PMMA bone cement

Gentamicin-loaded polymethylmethacrylate (PMMA), widely used for primary cemented arthroplasty and revision surgery for preventing or treating infections, may lead to the evolution of antibiotic-resistant bacteria and dysfunction of osteogenic cells, which further influence the osteointegration of bone cement. In a previous study, we reported that a new quaternized chitosan derivative (hydroxypropyltrimethyl ammonium chloride chitosan, HACC) that was loaded into PMMA significantly inhibited the formation of biofilms caused by methicillin-resistant Staphylococcus strains. In the present study, we further investigated the surface morphology, hydrophilicity, apatite formation ability and osteogenic activity of HACC-loaded PMMA. Chitosan-loaded PMMA, gentamicin-loaded PMMA and PMMA without antibiotic were also investigated and compared. The results showed that, compared to other PMMA-based cements, HACC-loaded PMMA had improved properties such as a lower polymerization temperature, prolonged setting time, porous structures after immersion in phosphate-buffered saline, higher hydrophilicity, more apatite formation on the surface after immersion in simulated body fluid, and better attachment and spreading of the human-marrow-derived mesenchymal stem cells. We also found better stem cell proliferation, osteogenic differentiation, and osteogenesis-associated genes expression on the surface of the HACC-loaded PMMA compared to the gentamicin-loaded PMMA. Therefore, this new anti-infective bone cement had improved physical properties and osteogenic activity, which may lead to better osteointegration of the bone cement in cemented arthroplasty.

Effect of coadministration of vancomycin and BMP-2 on cocultured Staphylococcus aureus and W-20-17 mouse bone marrow stromal cells in vitro

In this study, we aimed to establish an in vitro bacterium/bone cell coculture model system and to use this model for dose dependence studies of dual administration of antibiotics and growth factors in vitro. We examined the effect of single or dual administration of the antibiotic vancomycin (VAN) at 0 to 16 μg/ml and bone morphogenetic protein-2 (BMP-2) at 0 or 100 ng/ml on both methicillin-sensitive Staphylococcus aureus and mouse bone marrow stromal cells (W-20-17) under both mono- and coculture conditions. Cell metabolic activity, Live/Dead staining, double-stranded DNA (dsDNA) amounts, and alkaline phosphatase activity were measured to assess cell viability, proliferation, and differentiation. An interleukin-6 (IL-6) enzyme-linked immunosorbent assay (ELISA) kit was used to test the bone cell inflammation response in the presence of bacteria. Our results suggest that, when delivered together in coculture, VAN and BMP-2 maintain their primary functions as an antibiotic and a growth factor, respectively. Most interestingly, this dual-delivery type of approach has shown itself to be effective at lower concentrations of VAN than those required for an approach relying strictly on the antibiotic. It may be that BMP-2 enhances cell proliferation and differentiation before the cells become infected. In coculture, a dosage of VAN higher than that used for treatment in monoculture may be necessary to effectively inhibit growth of Staphylococcus aureus. This could mean that the coculture environment may be limiting the efficacy of VAN, possibly by way of bacterial invasion of the bone cells. This report of a coculture study demonstrates a potential beneficial effect of the coadministration of antibiotics and growth factors compared to treatment with antibiotic alone.

Drug release and bone growth studies of antimicrobial peptide-loaded calcium phosphate coating on titanium

Preventing infection is one of the major challenges in total hip and joint arthroplasty. The main concerns of local drug delivery as a solution have been the evolution of antibiotic-resistant bacteria and the potential inhibition of osseointegration caused by the delivery systems. This work investigated the in vitro drug release, antimicrobial performance, and cytotoxicity, as well as the in vivo bone growth of an antimicrobial peptide loaded into calcium phosphate coated Ti implants in a rabbit model. Two potent AMP candidates (HHC36: KRWWKWWRR, Tet213: KRWWKWWRRC) were first investigated through an in vitro cytotoxicity assay. MTT absorbance values revealed that HHC36 showed much lower cytotoxicity (minimal cytotoxic concentration 200 μg/mL) than Tet 213 (50 μg/mL). The AMP HHC36 loaded onto CaP (34.7 ± 4.2 μg/cm(2)) had a burst release during the first few hours followed by a slow and steady release for 7 days as measured spectrophotometrically. The CaP-AMP coatings were antimicrobial against Staphylococcus aureus and Pseudomonas aeruginosa strains in colony-forming units (CFU) in vitro assays. No cytotoxicity was observed on CaP-AMP samples against MG-63 osteoblast-like cells after 5 days in vitro. In a trabecular bone growth in vivo study using cylindrical implants, loading of AMP HHC36 did not impair bone growth onto the implants. Significant bone on-growth was observed on CaP-coated Ti with or without HHC36 loading, as compared with Ti alone. The current AMP-CaP coating thus offers in vivo osteoconductivity to orthopedic implants. It also offers in vitro antimicrobial property, with its in vivo performance to be confirmed in future animal infection models.