A controlled antibiotic release system to prevent orthopedic-implant associated infections: An in vitro study

A new device for local delivery of antibiotics is presented, with potential use as a drug-eluting fixation pin for orthopedic applications. The implant consists of a stainless steel hollow tubular reservoir packed with the desired antibiotic. Release takes place through several orifices previously drilled in the reservoir wall, a process that does not compromise the mechanical properties required for the implant. Depending on the antibiotic chosen and the number of orifices, the release profile can be tailored from a rapid release of the load (ca. 20 h) to a combination of rapid initial release and slower, sustained release for a longer period of time (ca. 200 h). An excellent bactericidal action is obtained, with 4-log reductions achieved in as little as 2 h, and total bacterial eradication in 8 h using 6-pinholed implants filled with cefazolin.

Staphylococcal persistence due to biofilm formation in synovial fluid containing prophylactic cefazolin

Antibiotic prophylaxis is standard for patients undergoing surgical procedures, yet despite the wide use of antibiotics, breakthrough infections still occur. In the setting of total joint arthroplasty, such infections can be devastating. Recent findings have shown that synovial fluid causes marked staphylococcal aggregation, which can confer antibiotic insensitivity. We therefore asked in this study whether clinical samples of synovial fluid that contain preoperative prophylactic antibiotics can successfully eradicate a bacterial challenge by pertinent bacterial species. This study demonstrates that preoperative prophylaxis with cefazolin results in high antibiotic levels. Furthermore, we show that even with antibiotic concentrations that far exceed the expected bactericidal levels, Staphylococcus aureus bacteria added to the synovial fluid samples are not eradicated and are able to colonize model implant surfaces, i.e., titanium pins. Based on these studies, we suggest that current prophylactic antibiotic choices, despite high penetration into the synovial fluid, may need to be reexamined.

The calcium phosphate matrix of FGF-2-apatite composite layers contributes to their biological effects

The purpose of the present study was to fabricate fibroblast growth factor (FGF)-2-apatite composite layers on titanium (Ti) pins in one step at 25 °C using a supersaturated calcium phosphate (CaP) solution, and to evaluate the physicochemical characteristics and biological effects of the coated Ti pins compared with coated Ti pins fabricated at 37 °C. Ti pins were immersed in a supersaturated CaP solution containing 0.5, 1.0, or 2.0 µg/mL FGF-2 at 25 °C for 24 h (25F0.5, 25F1.0, and 25F2.0) or containing 4.0 µg/mL FGF-2 at 37 °C for 48 h (37F4.0). Except for the 25F0.5, the chemical compositions and the mitogenic activity levels of FGF-2 of the composite layers formed by these two methods were similar, except for the Ca/P molar ratio, which was markedly smaller at 25 °C (1.55-1.56±0.01-0.02, p=0.0008-0.0045) than at 37 °C (1.67±0.11). Thus, either the apatite was less mature or the amount of amorphous calcium phosphate was higher in the composite layer formed at 25 °C. In vivo, the pin tract infection rate by visual inspection for 37F4.0 (45%) was lower than that for 25F1.0 (80%, p=0.0213), and the rate of osteomyelitis for 37F4.0 (35%) was lower than that for 25F0.5 (75%, p=0.0341). The extraction torque for 37F4.0 (0.276±0.117 Nm) was higher than that for 25F0.5 (0.192±0.117 Nm, p=0.0142) and that for 25F1.0 (0.176±0.133 Nm, p=0.0079). The invasion rate of S. aureus for 37F4.0 (35%) was lower than that for 25F0.5 (75%, p=0.0110). On the whole, the FGF-2-apatite composite layer formed at 25 °C tended to be less effective at improving fixation strength in the bone-pin interface and resisting pin tract infections. These results suggest that the chemistry of the calcium phosphate matrix that embeds FGF-2, in addition to FGF-2 content and activity, has a significant impact on composite infection resistance and fixation strength.

Comparison of 3 real-time, quantitative murine models of staphylococcal biofilm infection by using in vivo bioluminescent imaging

Biofilm formation represents a unique mechanism by which Staphylococcus aureus and other microorganisms avoid antimicrobial clearance and establish chronic infections. Treatment of these infections can be challenging, because the bacteria in the biofilm state are often resistant to therapies that are effective against planktonic bacteria of the same species. Effective animal models for the study of biofilm infections and novel therapeutics are needed. In addition, there is substantial interest in the use of noninvasive, in vivo data collection techniques to decrease the animal numbers required for the execution of infectious disease studies. To ad- dress these needs, we evaluated 3 murine models of implant-associated biofilm infection by using in vivo bioluminescent imaging techniques. The goal of these studies was to identify the model that was most amenable to development of sustained infections that could be imaged repeatedly in vivo by using bioluminescent technology. We found that the subcutaneous mesh and tibial intramedullary pin models both maintained consistent levels of bioluminescence for as long as 35 d after infection, with no implant loss experienced in either model. In contrast, a subcutaneous catheter model demonstrated significant incidence of incisional ab- scessation and implant loss by day 20 after infection. The correlation of bioluminescent measurements and bacterial enumeration was strongest with the subcutaneous mesh model. Among the 3 models we evaluated, the subcutaneous mesh model is the most appropriate animal model for prolonged study of biofilm infections by using bioluminescent imaging.

Characterization of Staphylococcus aureus strains in a rabbit model of osseointegrated pin infections

Staphylococcus aureus is a common infecting agent of many surgical sites. As a commensal organism to humans and rabbits, the infection process may occur due to native or exogenous S. aureus. We applied exogenous S. aureus ATCC 49230 once weekly to the surgical site of an osseointegrated pin in 20 New Zealand white rabbits. Clinical signs of infection resulted in euthanasia and at necropsy samples were collected from putatively infected sites. The predominant organism cultured was S. aureus. We observed various beta-hemolysis patterns of S. aureus on culture media and used pulsed field gel electrophoresis (PFGE) to determine whether there were distinct strains of S. aureus collected from various sites of the rabbits. On the basis of PFGE results, we found that the exogenous S. aureus ATCC 49230 was not the S. aureus cultured during necropsy, but that S. aureus native to the rabbits was in fact the infecting agent. We conclude that this rabbit model for S. aureus infection, which has not been described previously, may contribute to understanding the pathogenesis of S. aureus infections in future studies with simulated osseointegrated pin infections secondary to S. aureus.

Penetration of a selected antibiotic and antiseptic into a biofilm formed on orthopedic steel implants

BACKGROUND

The aim of the study was to determine the impact of octenidine hydrochloride and gentamicin on bacterial survival and reduction of biofilms formed on orthopaedic metal implants.

MATERIAL AND METHODS

We studied metal orthopaedic components (screws, nails, fragments of wires used in Ilizarov devices) and a bone sequester. The presence and intensity of biofilm formation on the medical biomaterials was determined using the method of Richards et al. by visual evaluation of 2,3,5-triphenyl tetrazolium chloride (TTC) reduction by viable bacteria. The presence and structure of the biofilm on the components of the Ilizarov device, screws and bone sequester was also studied by electron microscopy. Bacterial survival in the biofilm following exposure to the antibiotic and antiseptic was studied by CLSI microdilution method in microtitre plates using TTC. Results. Most of the 16 strains (S. aureus, S. epidermidis, E. coli, Enterobacter) isolated from orthopaedic implants were able to form a biofilm. Established biofilms were resistant to gentamicin and octenidine hydrochloride but demonstrated greater susceptibility to octenidine.

CONCLUSIONS

The results of the study indicate that octenidine hydrochloride is more effective than gentamicin in the treatment of infections associated with the formation of a biofilm on orthopaedic implants.

A simple practical protocol for care of metal-skin interface of external fixation

Patients treated with external fixation for limb reconsturciton or fracture stabilization equire regular and prolongedperiod of pin-tract care involving frequent visits to clinic and dressing traditionally carried out by trained nurses or medical assistants. A simple method of do-it-yourself dressing was introduced in our institution and this study was undertaken to evaluate the effectiveness of the protocol. Sixty patients (40 trauma-related problems and 20 congenital or developmental disorders) were enrolled into the study. Following application of external fixation, the patients and/or their caretakers were taught on how to do pin-site dressing using normal saline or drinking water as cleansing solution on daily basis. Patients were discharged on the second or third post-operative day and were followed-up every two weeks for an average 182 days (range 66 to 379 days) with special attention on identifying pin-tract infection. A simple grading system for pin-tract infections was proposed. Of 40 patients with trauma-related problems. 65% were post-traumatic infections. There were 788 metal-skin interfaces (239 half-pin fixations and 549 tensioned wire fixations. A total 143 metal-skin interface infections (18.1%) involving half-pin sites (41.3%) and tensioned wire sites (58.7%) was noted. Majority were grade I infections (79.7%), 18.8% grade II and only 1.4% grade III. Most infections (81%)were caused by Staphylococcus aureus. Grade I infections were successfully treated with frequent dressing, grade II by adjunctive oral antibiotic but grade III infections required removal of fixator. All eventually healed. Do yourself non-sterile dressing of metal-skin interfaces is a cost-effective method of pin-site care with a low infection rate. The infections were sucessfully treated using guidelines according to the proposed classification of pin-tract infections.

Can a pin-tract infection cause an acute generalized soft tissue infection and a compartment syndrome?

A patient who developed soft tissue infection and osteomyelitis secondary to pin tract infection after skeletal traction was evaluated. Tibial traction was performed on a patient who had exposed to a femoral pertrochanteric fracture after falling from a tree in a rural public hospital. On the first postoperative day shortly after development of soft tissue swelling, redness, and tenderness in the affected leg, compartment syndrome was noted with subsequent removal of the pin at the same health center. After arrival of the case in our center surgical decompression with an open faciatomy and proper antibiotherapy were instituted. Simultaneously hyperbaric oxygen was administered. After eradication of soft tissue infection we treated the fracture with a Richards compression screw-plate device. The patient was discharged with complete cure. This case presented how seriously a simple pin-tract infection can cause a grave clinical entity resulting in potential loss of an extremity.

Evaluation of effectiveness of 10% polyvinylpyrrolidone-iodine solution against infections in wire and pin holes for Ilizarov external fixators

CONTEXT AND OBJECTIVE

Superficial infection at wire and pin insertions in the skin is a frequent disorder among patients utilizing the Ilizarov method. The objective of this study was to evaluate the effectiveness of daily topical application of 10% polyvinylpyrrolidone-iodine solution against infections of the holes for Kirschner wires and Schanz pins among patients using Ilizarov external fixators, in comparison with cleaning these holes only with 0.9% sterile physiological saline solution.

DESIGN AND SETTING

Controlled randomized clinical trial, in the Orthopedics and Traumatology Outpatient Clinic, Hospital São Paulo, and Orthopedics and Traumatology Center of Jundiaí.

METHODS

30 patients were treated using the Ilizarov technique: 15 were instructed to apply 0.9% physiological saline dressing on the wire and pin insertions and 15 to apply 0.9% physiological saline plus 10% polyvinylpyrrolidone-iodine. Patients were evaluated at outpatient return visits for identification of signs and symptoms of superficial infection at wire and pin insertion sites. Samples were collected from cases of purulent exudate secretion, for culturing and clinical tests.

RESULTS

The chi-squared and Fischer exact tests were applied, but no statistically significant association between the intervention of topical polyvinylpyrrolidone-iodine solution and the prevention of infections at wire and pin insertions could be found.

CONCLUSIONS

Topical 10% polyvinylpyrrolidone-iodine solution applied daily to Kirschner wire and Schanz pin insertions did not reduce the incidence of superficial infection at these holes, in comparison with mechanical removal of dirt using 0.9% physiological saline solution.

Pin site care in external fixation sodium chloride or chlorhexidine solution as a cleansing agent

INTRODUCTION

Pin site infection is the most common complication using external fixators. This study investigated the differences in pin site infections, antibiotic use, pain, and complications using sodium chloride and chlorhexidine solution as cleansing agent in patients operated on by the hemicallotasis technique for knee deformities.

MATERIALS AND METHODS

The prospective study included 49 consecutive patients: 2 mg/ml chlorhexidine solution was used as cleansing agent in 30 patients (120 pins) and 9 mg/ml sodium chloride in 19 patients (76 pins). We evaluated the status of the pin sites, pain (VAS), uses of antibiotic and analgesic agents, and any complications (infections were graded according to the Checketts-Otterburns classification). Bacterial cultures were performed from each pin site at 1, 6, and 10 weeks and from the pins at removal.

RESULTS

Grade 1 infection was found in 14% of the sodium chloride group and in 8.5% of the chlorhexidine group, and grade 2 infection in and 3% and 0.5%, respectively. With sodium chloride there was a significantly higher relative risk for positive cultures (1.7) and for the presence of Staphylococcus aureus (3.3). The chlorhexidine group required significantly fewer antibotics reported significantly less pain at weeks 6 and 10.

CONCLUSIONS

Chlorhexidine solution (2 mg/ml) as cleansing agent in pin site care is preferable to sodium chloride in patients operated on by the hemicallotasis technique.

Bactericidal activity of antimicrobial coated polyurethane sleeves for external fixation pins

This study was conducted to assess the potential of gentamicin coated polyurethane sleeves to inhibit bacterial colonization on external fixation pins and wires. These antimicrobial sleeves have been designed to be fitted over the pins and wires, at the time of surgery, as a prophylactic approach to combat the major complication of external fixation treatment, pin tract infection. Elution testing was conducted to estimate the amount of gentamicin released into the pin tract. These gentamicin concentrations were compared to the gentamicin minimal inhibitory concentration (MIC) level for common pin tract pathogens. Elution testing revealed that the gentamicin coated polyurethane sleeves released significant quantities of the antibiotic for up to 26 weeks. The initial bolus release was characterized by predicted pin tract gentamicin concentrations of >80 microg/ml at the 2 h and 1 day elution time points. These amounts of gentamicin, delivered directly to the pin tract, are far beyond those that could be achieved via oral or intravenous administration. Furthermore, the expected concentration of gentamicin in the pin tract remained above the National Committee for Clinical Laboratory Standards (NCCLS) MIC breakpoint of 4 microg/ml, [Performance standards for antimicrobial susceptibility testing: twelfth informational supplement M100-S12, NCCLS, Wayne, PA, 2002], for at least 20 weeks. Data from the SENTRY antimicrobial surveillance program (1997-2002) established a high level of bactericidal activity for gentamicin, with 83.1% of the common pin tract pathogen isolates found to be susceptible to the antibiotic. The initial burst and subsequent long-term sustained local delivery of effective amounts of gentamicin from the antimicrobial sleeves would be expected to inhibit bacterial colonization on external fixation pins and wires. This inhibition of bacterial colonization should substantially reduce the incidence of pin tract infection, and improve the overall outcome and cost effectiveness of external fixation fracture management.

Pin site care during external fixation in children: results of a nihilistic approach

We prospectively followed 27 consecutive children with tibial circular external fixators applied between July 1, 1995, and June 30, 1997. A simple pin care system with no physical pin cleansing except that provided by daily showers was used. Children with inflamed or infected pin sites were placed on an oral antibiotic (cephalexin) for 10 days. Pin sites were graded according to the system of Dahl et al. on a 0 to 5 scale. A total of 4,473 observations was made. Patients developed 178 pin tract infections (4.0% per observation), with 151 (85%) grade 1 and 27 (15%) grade 2 infections. No pin was removed because of infection. Diaphyseal half pin sites were less commonly infected (1.6%) than periarticular wire or half pin sites (4.5%). We recommend only showering without other physical pin cleaning procedures in children undergoing external fixation procedures.