Aim. Galleria mellonella larvae is a well-known insect infection model that has been used to test the virulence of bacterial and fungal strains as well as for the high throughput screening of antimicrobial compounds against infections. Recently, we have developed insect infection model G. mellonella larvae to study implant associated biofilm infections using small K-wire as implant material. Here, we aimed to further expand the use of G. mellonella to test other materials such as bone cement with combination of gentamicin to treat implant-associated infections. Method. The poly methyl methacrylate (PMMA) with and without gentamicin and liquid methyl methacrylate (MMA) were kindly provided by Heraeus Medical GmbH, Wehrheim. To make the bone cement implants as cubes, Teflon plate (Karl Lettenbauer, Erlangen) with specified well size was used. The Radiopaque polymer and monomer were mixed well in a bowl, applied over on to the Teflon plate and pressed with spatula to form fine and uniform cubes. After polymerization, the bone cement implants were taken out of the Teflon well plate with the help of pin. For the infection process, bone cement cubes were pre-incubated with S. aureus EDCC 5055 culture at 5×10. 6. CFU/ml for 30 min at 150 rpm shaking conditions. Later, these implants were washed with 10ml PBS and implanted in the larvae as mentioned. Survival of the larvae were observed at 37°C in an incubator. To analyze the susceptibility of the bacterial infections towards gentamicin, survival of the larvae compared with control group implanted only with bone cement. The effect of gentamicin was also measured in terms of S. aureus load in larvae on 2. nd. day. SEM analysis was performed to see the effect of gentamicin on biofilm formation on bone cement. Results. Our experiments established the G. mellonella as an excellent model to screen bone cement with antimicrobial compounds against bacterial infections. The gentamicin bone cement samples showed excellent S. aureus bacterial load reduction after the implantation in G. mellonella model. The bone cement with gentamicin showed better survival of larvae infected with S. aureus compared to control. Finally, the gentamicin also affected the biofilm formation on the bone cement surface with S. aureus. Conclusions. Thus, our work showed G. mellonella is a rapid, cheap economical pre-clinical model to study the bone cement associate bacterial infections as well as screening of the various antimicrobial compounds

Two-stage revision surgery is the current gold standard for treating prosthetic joint infections (PJI). Between the first and the second stage gentamicin-loaded (G) spacers are widely used but the rate of gentamicin resistant staphylococci is increasing. The potential benefit of vancomycin + gentamicin-loaded (V/G) spacers has not yet been evaluated. The aim of our study was to compare the microbiological eradication and infection control rates in PJI treated with G- or V/G-spacers. 147 PJIs treated in our institution were retrospectively reviewed. From 2003 to 2009 G-spacers (Tecres®) were used (group G) and from 2010 to 2013 V/G-spacers (Group V/G). Gender, age, body mass index (BMI), co-morbidities, ASA score, type of infection, microorganisms isolated in the first and second stages, time between stages, infection outcome at last visit were collected. The 2 main outcome variables were microbiological eradication in the second stage (≤1 positive culture out of 6) and infection control after the second stage. Univariate and multivariate analysis were performed using SPSS®. There were 83 patients in group G and 63 in group V/G. The mean (SD) age was 71.5 (10.3) years and 54% were female. Groups were similar in gender, age, BMI, ASA score, time with spacer, microorganism isolated in the first stage, or type of infection (acute or chronic) (p>0.05). The presence of ≥2 positive cultures in the second stage was significantly higher in group G (23.2%) than in group V/G (6.7%, P<0.05). Logistic regression model identified polymicrobial infections (OR: 4.26, CI95%: 1.44–12.64) and the use of G-spacers (OR: 5.88, CI95%: 1.60–21.74) as independent predictors of failure in microbiological eradication. The global rate of infection control was 75% after a mean (SD) follow-up of 56 (32) months. Infection control was higher in chronic than acute PJI (83.6% vs 59.6%, P<0.05), when cultures during second stage were negative (81.5%) vs positive (61%, P<0.05), and there was a trend towards a higher control rate when V/G-spacers (82%) vs G-spacers (69.5%) were used (P=0.09). Multivariate analysis identified chronic PJI (OR: 5.43, CI95%: 2.20–13.51) and, at the limit of significance, the use of V/G spacers (OR: 2.36, CI95%: 0.97–5.71) as predictors of infection control. Vancomycin loaded spacers were significantly associated with a higher microbiological eradication and there was a trend towards a higher infection control than gentamicin loaded spacers

Aim. Chronic bone infections and infected fractures are often treated with excision of the dead bone and implantation of biomaterials which elute antibiotics. Gentamicin has been a preferred drug for local delivery, but this could induce renal dysfunction due to systemic toxicity. This is a particular concern in patients with pre-existing chronic renal disease treated with new antibiotic carriers which achieve very high peak levels of gentamicin in the first few days after surgery. Method. 163 patients (109 males; average age 51.6 years) with Cierny-Mader Type 3 or 4 chronic osteomyelitis had a single-stage operation with excision of the dead bone, filling of the osseous defect with a calcium sulphate-hydroxyapatite carrier, containing gentamicin and immediate soft tissue closure. 2. No patient was given systemic gentamicin or other renal toxic antibiotics. Mean carrier volume was 10.9mls (range 1–30mls) and mean gentamicin dosing was 190.75mg (maximum 525mg). Seven patients had pre-existing renal disease (4 diabetic nephropathy, 1 nephrotic syndrome, 1 renal transplant and 1 previous acute kidney injury). Serum creatinine levels were collected pre-operatively and during the first seven days post-operatively. Glomerular filtration rate (GFR) was calculated using the CKD-epi creatinine equation. Renal function was defined using the Chronic Kidney Disease (CKD) Staging system. Results. 155 cases had adequate data to allow calculation of pre- and post-operative GFR. Pre-operative CKD staging demonstrated 118 Class I (normal renal function), 30 Class II, 3 Class IIIa, 3 Class IIIb, and 1 Class V disease. Mean pre-operative GFR (99.7ml/min/1.73m. 2. , SD 21.0) was no different to post-operative GFR (103.2ml/min/1.73m. 2. , SD 21.3), p= 0.0861. Four cases had a >10% decline in GFR below normal, with only one case dropping a CKD stage, from I (normal) to II (mildly decreased). Only 1/7 cases with pre-existing renal disease had a GFR drop of >10% (from 11ml/min/1.73m. 2. to 8ml/min/1.73m. 2. ). 70/155 (45.2%) had a temporary GFR drop post-operatively, with the biggest drop occurring a mean 3.06 days following surgery (SD 2.1). No patient had clinical signs of new acute renal impairment post-operatively. Conclusions. Renal function is not significantly affected by local implantation of gentamicin up to 525mg. The presence of pre-existing renal disease is not a contraindication to local gentamicin therapy

Introduction. The treatment of chronic bone infection often involves excision of dead bone and implantation of biomaterials which elute antibiotics. Gentamicin is a preferred drug for local delivery, but its systemic use carries a well-established risk of nephrotoxicity. We aim to establish the risk of renal injury with local delivery in a ceramic carrier. Materials and Methods. 163 consecutive patients with Cierny-Mader Type 3 or 4 chronic osteomyelitis were treated with a single-stage operation which included filling of the osseous defect with a calcium sulphate-hydroxyapatite carrier containing gentamicin. The mean carrier volume used was 10.9mls, leading to a mean implanted gentamicin dose of 191.3mg (maximum 525mg). Serum creatinine levels were collected pre-operatively and during the first seven days post-operatively. Renal impairment was graded using the Chronic Kidney Disease (CKD) Staging system, and AKI was assessed using the RIFLE criteria. Results. 155 cases had adequate data to allow calculation of pre- and post-operative GFR. 7 patients had pre-existing renal disease. 70 patients (45.2%) had a temporary eGFR drop post-operatively, with the greatest decrease occurring a mean 3.06 days following surgery. Twenty cases had a >10% decline in eGFR, but 12 resolved within 7 days. 7 patients transiently fell into the “Risk” category according to RIFLE criteria, but no patient had a change consistent with “Injury”, “Failure” or “Loss” of renal function and none had clinical signs of new acute renal impairment post-operatively. Conclusions. The implantation of up to 525mg of gentamicin contained within Cerament G, as part of the surgical treatment of osteomyelitis, is safe and carries minimal risk of significant acute kidney injury. A small, transient increase in serum creatinine may be observed in the early post-operative period, and attention should be paid to limit patients exposure to other nephrotoxic agents. The majority of patients will return to their baseline renal function within 7 days following the operation. The presence of pre-existing renal disease is not a contraindication to local gentamicin therapy

Aim. Ciprofloxacin is recommended as anti-biofilm therapy for gram-negative periprosthetic joint infection. With ciprofloxacin monotherapy, resistance in gram-negative bacteria was observed. Therefore, we evaluated in vitro synergistic activity of fosfomycin, ciprofloxacin and gentamicin combinations against biofilms formed by E. coli and P. aeruginosa strains. Method. E. coli ATCC 25922, P. aeruginosa ATCC 27853 and 15 clinical isolates were used for this study. MIC values were determined by Etest. Biofilms were formed on porous sintered glass beads for 24h and exposed to antibiotics for further 24h. Viability of bacteria on the glass beads after antibiotic treatment was detected by cfu counting of the sonicated beads. The minimum biofilm eradication concentration (MBEC) was defined as the lowest concentration of antibiotic required to kill biofilm cells. Synergistic activity against biofilm was evaluated by calculation of the fractional inhibitory concentration index (FICI). Results. Table 1 summarizes the antimicrobial susceptibility of planktonic (MIC), biofilm bacteria (MBEC) and synergism. Among 9 E. coli isolates, the synergism was observed in 78% of isolates treated with fosfomycin/gentamicin, 44% treated with gentamicin/ciprofloxacin and 22% treated with fosfomycin/ciprofloxacin. Among 8 P. aeruginosa isolates, the synergism was observed 75% of isolates treated with gentamicin/ciprofloxacin, 63% treated with fosfomycin/gentamicin and 50% treated with fosfomycin/ciprofloxacin. Conclusions. Based on our results, fosfomycin in combination with gentamicin seems to be a promising therapeutic approach against E. coli biofilm related infections. Combination of gentamicin with ciprofloxacin represent the most optimal treatment option for P. aeruginosa biofilm. For any figures or tables, please contact the authors directly

Aim. Local treatment with gentamicin may be an important tool in the prevention and treatment of surgical site infections in high-risk procedures and patients. The aim of this study was to evaluate the pharmacokinetic profile of gentamicin in bone and surrounding tissue, released from a controlled application of a GentaColl sponge in a porcine model. Method. In 8 female pigs, a GentaColl sponge of 10×10 cm (1.3 mg gentamicin/cm. 2. ) was placed in a cancellous bone cavity in the proximal tibia. Microdialysis was used for sampling of gentamicin concentrations over 48 hours from the cavity with the implanted GentaColl sponge, cancellous bone parallel to the cavity over and under the epiphyseal plate, cortical bone, the intramedullary canal, subcutaneous tissue, and the joint cavity of the knee. Venous blood samples were obtained as reference. Results. The main finding was a mean peak drug concentration (95-CI) of gentamicin in the cancellous bone cavity containing the implanted GentaColl sponge of 11,315 (9,049–13,581) μg/ml, persisting above 1000 μg/ml until approximately 40 hours after application. Moreover, the concentrations were low (< 1 μg/ml) in the surrounding tissues as well as in plasma. Conclusions. The mean peak gentamicin concentration from the cancellous bone cavity after a controlled application of a GentaColl sponge was high and may be adequate for the prevention of biofilm formation. However, high MIC strains and uncontrolled application of the GentaColl sponge may jeopardize this conclusion

It has been reported that some of the local anaesthetic agents possess antimicrobial activity against clinically-significant bacteria. Although bupivacaine exhibits a bacteriostatic effect at concentrations above 0.25% there are concerns that it might interact with some of the other antibiotics administered to patients. Whilst these interactions may be potentially benign, the risk is that they are antagonistic and that local bupivacaine might predispose the patient to a higher risk of infection. Bupivacaine is commonly administered as a local anaesthetic following knee arthroplasy; the purpose of this study was to assess its potential interactions with gentamicin eluting from the cement used to fix the device. A strain of Saphylococcus aureus (29213) with established susceptible Minimal Inhibition Concentration (MIC) and Minimal Bactericidal Concentration (MBC) for gentamicin was used. This organism was inoculated into four types of broth; Mueller-Hinton broth (MH), MH with different concentrations of gentamicin, MH with 0.25% and 0.125% bupivacaine and MH with various combinations of gentamicin and bupivacaine. The broths were incubated at 37C and at 0.5, 1, 2, 3, 6 and 24 hours post inoculation the number of bacteria remaining were counted. From these data kill-curves were generated describing the absolute and individual rates of killing seen with bupivacaine and gentamicin alone and when in combination. Bupivacaine showed a bacteriostatic effect only at concentrations of 0.25% and higher. All concentrations of gentamicin above or equal to the expected MBC showed bactericidal effect. However, in combination with both strengths of Bupivacaine (0.25 and 0.125%) the bacteriocidal effect of gentamicin was seen at a lower concentration and the rate of killing of bacteria was enhanced. Bupivacaine has bacteriostatic effect at concentrations above 0.25% in line with published data. In these experiments we have shown that the use of bupivacaine together with gentamicin does not reduce the bactericidal property of the antibiotic and that the bactericidal effect of gentamicin appears to be enhanced by bupivacaine. This would suggest that the local use of bupivacaine is unlikely to increase the risk of infection in patients undergoing knee arthroplasty and may actually be beneficial

Aim. Fracture-related infection (FRI) is a serious complication after trauma. More often resistant micro-organisms are cultured. Gentamicin covers a wide variety of causative agents for FRI. A bio-absorbable antibiotic carrier, Cerament-G®, combines dead space management with local release of gentamicin in a one-stage approach. The achieved tissue concentrations of locally applied antibiotics are 4–8 thousand times higher than after systemic administration. Does Cerament-G® have antimicrobial activity towards bacteria that are not susceptible to systemic gentamicin administration. Method. The four most often cultured bacterial species found in FRI were used; Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Enterobacter cloacae. For each species, four different isolates were obtained, each with a different susceptibility for gentamicin. This susceptibility, expressed in the minimal inhibitory concentration (MIC), varied from completely susceptible (MIC 0,064 mg/L – 4mg/L), minimal resistance (4mg/L – 16mg/L), moderate resistance (8 mg/L – 96 mg/L) to high resistance (24 mg/L - >1024 mg/L), depending on each different organism. Antimicrobial activity of Cerament-G. ®. was determent by a Kirby-Bauer test, according to the EUCAST disc protocol. Each test was done in five-fold for each of the 16 cultured isolates, four of each species. The zone of inhibition (ZOI), obtained by the test, was compared between each bacterial isolate and within each of the four separate species. Results. Cerament-G. ®. shows antimicrobial activity against S. aureus, S. epidermidis, P. aeruginosa and E. cloacae. ZOI-values varied from 11 to 44 mm. It was negatively correlated with the MIC; the higher the MIC, the less the antimicrobial effect of Cerament-G. ®. Between bacterial isolates with the same MIC, within the same species, there was no significant difference in ZOI between the five-fold repetitions of the test, indicating an accurate test. The ZOI of the different bacterial isolates (with different MIC's), belonging to the same bacterial species, differed significantly. Of all 16 isolates, only the S. aureus with a MIC of >1024 mg/L did not show antimicrobial activity of Cerament-G. ®. ; ZOI =0mm. Conclusions. This study shows that Cerament-G. ®. has antimicrobial activity against bacterial isolates, resistant to gentamicin when systemically treated. This confirms that the cut-off point for systemic application is not very useful for the local use of Cerament-G. ®. and emphasizes the need for optimization and change of current antibiotic protocols to increase the durability and sustainability of antibiotic FRI treatment

Prosthetic joint infection(PJI) still remains a concern in orthopaedic practice. Antibiotic-loaded acrylic-cement(ALAC) is a proven means of lowering the incidence of PJI. However, increasing antimicrobial resistance has complicated both prophylaxis and treatment, prompting the use of combination antimicrobial therapy, with the addition of vancomycin to gentamicin-containing ALAC commonly used. The new antimicrobial, daptomycin, has better activity than vancomycin and we studied its elution from ALAC in comparison with vancomycin, along with its impact on the co-elution of gentamicin. Cement beads were prepared from PalacosRG containing, 1g/2g daptomycin, 1g/2g vancomycin and without additional antibiotics. Six replicates of each combination were eluted in PBS at 37oC, at timed intervals, for up to 90days, the antibiotic loss was assessed using validated assays. The mean recovery of gentamicin after 90days was 1.1mg with half eluted within the first 6 hours. Recovery was significantly increased by 60% and 40% with addition of 1g&2g of daptomycin(two-tail t-test: p=0.004 and p=0.02), respectively. Although there was a slight increase in gentamicin recovery in vancomycin loaded samples, this was not statistically significant(p>0.05). The significant increases in gentamicin elution from Palacos RG when supplemented with daptomycin, along with a superior activity, may provide a better synergistic effect than PalacosRG supplemented with vancomycin in the management of PJI

Aim. To investigate the local intra-operative concentration of gentamicin needed to prevent biofilm formation in a porcine model of implant-associated osteomyelitis. Method. In total 24 pigs were allocated to six groups. Group A (n=6) was inoculated with saline. Groups B (n=6), C (n=3), D (n=3), E (n=3) and F (n=4) were inoculated with 10 μL saline containing 10. 4. CFU of Staphylococcus aureus, however, different minimal inhibitory concentrations (MIC) of gentamicin were added to the inoculum of Groups C(160xMIC), D(1600xMIC), E(16000xMIC) and F(160000xMIC). The inoculums were injected into a pre-drilled implant cavity proximally in the right tibial bone. Following inoculation, a steel implant (2 × 15 mm) was placed in the cavity. The pigs were euthanized after five days. The implants were sonicated and swabs were taken from the implant cavity for microbiological evaluation. The peri-implant tissue was analyzed by histopathology including estimation of neutrophil infiltration. Results. The microbiological samples from Group A pigs were sterile. All implants and implant cavities of pigs inoculated with bacteria and bacteria + 160 or 1.600xMIC were positive for S. aureus. In each of the Groups E (16000xMIC) and F (160000xMIC) only one animal was found positive and 1/3 and 3/4 of the implants were sterile after sonication, respectively. All positive swabs were confirmed to be same spa-type as used for inoculation. By adding Groups C + D (<10000xMIC) and Groups E + F (>10000xMIC) a strong significant decrease (one-way ANOVA, P value = 0.001) of implant attached bacteria was only seen between the high MIC values and Group B (bacteria only). The histological examination demonstrated that 1600, 16000 and 160000 × MIC resulted in a peri-implant tissue reaction, including neutrophil estimation, comparable to saline inoculated animals. Patho-morphologically, it was not possible to distinguish between pigs inoculated with bacteria and bacteria + 160xMIC as both groups had a strong inflammatory response and an equal estimation of neutrophils. Discussion. The antibiotic susceptibility for prevention of an in vivo biofilm infection is influenced by body fluids, host immune response, extracellular host proteins like fibrin, tissue necrosis and development of an anaerobic environment. With the present in-vivo setup, we have demonstrated that local intra-operative gentamicin might be given in concentrations of more than 10000 times the MIC value in order to prevent biofilm formation by planktonic bacteria. Our study supports that biofilm susceptibility testing performed in-vitro is yet still unreliable for prediction of prophylactic and therapeutic success

To document early in-vivo concentrations of gentamicin in plasma and drain fluid after bone defect reconstruction using a gentamicin-eluting bone graft substitute. Introduction. Reconstruction of bone defects after surgical bone tumor resection is associated with an increased risk of infection and some surgeons therefore prefer extended antibiotic prophylaxis in these patients. A gentamicin-eluting bone graft substitute consisting of sulphate and apatite has been shown to be effective for treatment of osteomyelitis(1) and may be a valuable addition to the therapeutic and/or prophylactic antibiotic regime for this and many other indications. We performed a prospective pilot study from December 2014 to February 2015 in 7 patients (M/F: 4/3, mean age 51 (37–79) years) who underwent bone defect reconstruction with a gentamicin-eluting bone graft substitute (CERAMENT™|G – BONESUPPORT AB) containing 175 mg gentamicin per 10 mL. Indications for surgery were metastatic bone disease (n=3, proximal humerus), giant cell tumor (n=2, distal femur), aseptic prosthetic loosening (n=1, knee) and chondroid tumor (n=1, distal femur). Additional endoprosthetic reconstruction with a tumor prosthesis was performed in 3 patients (2 proximal humerus and 1 distal femur). Drain fluid and plasma was collected immediately postoperatively and each postoperative day until the drain was removed. In 2 cases we were unable to collect drain fluid directly postoperatively due to minimal fluid production. Gentamicin concentrations were analyzed using an antibody technique (Indiko™ – Thermo Scientific). A mean of 14 (10–20) mL gentamicin-eluting bone graft substitute was used, either alone or in combination with cancellous allograft and/or a bone graft substitute not containing gentamicin (CERAMENT™|BVF – BONESUPPORT AB). Mean drain fluid concentrations of gentamicin were 1200 (723–2100) mg/L immediately postoperative (0–2 hours), 1054 (300–1999) mg/L on day 1 (17–23 hours) and 509 (38–1000) mg/L on day 2 (39–45 hours). Mean plasma concentrations of gentamicin were 1.26 (1.08–1.42) mg/L immediately postoperative, 0.95 (0.25–2.06) mg/L on day 1 and 0.56 (0.20–0.88) mg/L on day 2. Discussion. As gentamicin induces a concentration-dependent bacterial killing effect, the obviously high local peak concentrations of gentamicin found in this study would be expected to deliver a substantial prophylactic effect after long operations with an increased risk of intraoperative bacterial contamination. Local implantation of a gentamicin-eluting bone graft substitute for bone defect reconstruction results in high concentrations of gentamicin in the drain fluid in the first postoperative days and low plasma concentrations

In September 2011 our departmental protocol for peri-operative prophylactic antibiotic administration was altered from cefuroxime to gentamicin/flucloxacillin, in response to reported links between cephalosporin use and Clostridium difficile (C. diff) infection. As both gentamicin and flucloxacillin are known to be nephrotoxic in some patients, we investigated whether the new regimen increases the risk of Acute Kidney Injury (AKI) in patients undergoing elective and trauma hip and knee surgery, classified by severity (AKI Network criteria). The incidence of C. diff was noted. 10 out of 202 (5%) patients receiving cefuroxime (group A) developed AKI, compared with 23 of 210 (11%) patients receiving gentamicin and flucloxacillin (group B) (p=0.012). The severity of the renal injury was higher in the group B patients with 16 sustaining stage II/III AKI, whereas in Group A only one patient sustained a stage II injury and none stage III. The increased AKI rate in group B was observed equally in hip fracture patients and elective hip/knee replacement patients. However, 3 of 80 (4%) patients with hip fractures who received doses of cefuroxime developed C. diff, with none in the other groups (p=0.04). The choice of prophylactic antibiotics depends on a careful assessment of benefits and risks. Our data suggests that whereas hip fracture patients may have benefitted from the protocol change with reduced C. diff incidence, elective hip and knee replacement patients sustained additional harm. Different antibiotic regimens may be appropriate for these two groups

Objective . A clinical investigation into a new bone void filler is giving first data on systemic and local exposure to the anti-infective substance after implantation. Method . A total of 20 patients with post-traumatic/post-operative bone infections were enrolled in this open-label, prospective study. After radical surgical debridement, the bone cavity was filled with this material. The 21-day hospitalisation phase included determination of gentamicin concentrations in plasma, urine and wound exudate, assessment of wound healing, infection parameters, implant resorption, laboratory parameters, and adverse event monitoring. The follow-up period was six months. . Results . Systemic exposure to gentamicin after implantation was very low as local gentamicin concentrations were measured in wound exudate after six to ten hours. There were no signs of infectious complication throughout the clinical phase. Four patients had recurrent infections several weeks to months after implantation. The outcome was deemed successful by remission of infection in 16 (80%) of these problematic long-term treated patients. Safety laboratory measurements did not indicate nephrotoxic or hepatotoxic effects. . Conclusions . Local application of calcium sulphate/carbonate bone void filler comprising gentamicin revealed sufficient active local levels of the antibiotic by simultaneous significant low systemic exposure in patients with mostly chronic osteomyelitis/osteitis. The material was safe and well tolerated. Cite this article: Bone Joint Res 2014;3:223–9

Introduction. Acute renal dysfunction (ARD) following orthopaedic surgery is known to increase morbidity, mortality, and length of hospital stay. The aim of this study was to compare the incidence of new acute post-operative renal dysfunction between two cohorts of elective orthopaedic surgical patients receiving either cefuroxime or a combination of gentamicin and flucloxacillin as prophylactic antibiotic regimes. The study was initiated following a change in antibiotic prophylaxis within our unit from cefuroxime to gentamicin and flucloxacillin. Method. Using a standardised data collection tool we retrospectively reviewed medical records of 238 patients who had received 1.5g of cefuroxime (TKR: n = 128; THR: n=110). This data was compared to prospectively collected data from 254 patients (TKR=117 THR=137) who had received Flucloxacillin 2g and Gentamicin (with the dose based on height). Primary outcome measure for the study was the RIFLE criteria which grades renal impairment: 0-Nil, 1-Risk, 2-Injury, 3-Renal failure. Results. In a cohort of 238 patients who underwent arthroplasty and were administered cefuroxime, there were 4 patients (1.68%) who developed renal impairment. All 4 patients were grade 1 RIFLE (Risk) and all resolved by day 3 post-op. Of the 254 patients who received the new antibiotic regime of Flucloxacillin and Gentamicin, 24 (9.45%) had new onset renal impairment. 12 were RIFLE grade 1 (Risk), 7 RIFLE Grade 2 (Injury) and 5 were Grade 3 (Renal Failure) (p=0.0001, Fishers exact test). 7 of these patients remained in acute renal impairment between day 5 and day 7 post-op. Discussion. Patients who received the combination of Flucloxacillin and Gentamicin had a significant increased risk of renal impairment which was also likely to be more severe and last longer. Following analysis of this study we have now reverted back to Cefuroxime for antibiotic prophylaxis

Aim. To evaluate the ability of different combinations of antibiotic loaded cement to inhibit bacteria growth and biofilm formation. Method. Cement beads were aseptically prepared using Palacos R (plain 40g PMMA cement) or Palacos R+G (40g PMMA cement containing industrially added 0.5g of gentamicin), with or without supplementary antibiotics as follows: Palacos R; Palacos R+G; Palacos R plus 1g / 2g daptomycin; Palacos R+G plus 1g / 2g of daptomycin; Palacos R plus 1g / 2g vancomcyin; and Palacos R+G plus 1g / 2g vancomycin. After production, each antibiotic loaded acrylic cement (ALAC) combination was allocated into two groups (group 1 and 2). The group 2 cement beads were initially eluted in broth at 37. o. C for 72hours then transferred to fresh broth containing a known concentration of bacteria. The group 1 samples were not eluted but directly immerse in culture broth containing bacteria. All samples were thereafter incubated at 37. o. C for 24 hours. After incubation, group 1 samples were visually assessed for bacterial growth, while for the group 2 samples, biofilm formation were quantified using ultrasonication and viable bacteria counting technique. Three proficient biofilm forming Staphylococcus epidermidis bacterial strains (1457, 1585-RA and 5179-R1) were used for all experiments and the bacteria counts were expressed as colony forming units / ml (CFU/ml). Results. In the group 1 samples, all the ALAC combinations were able to inhibit growth of all the three biofilm bacteria strains assessed except the gentamicin only samples in which biofilm growth were observed within 24hours. Meanwhile, in group 2, bacterial growth and biofilm formation by all three bacterial strains were observed on all the ALAC combinations, with the least biofilm formation being on the Palacos R+G plus 2g daptomycin combinations (mean CFU/ml: 1.04E +06) and the greatest on the gentamicin only cement (mean CFU/ml: 2.3E +07). Conclusions. Our study demonstrates that the highest antimicrobial activity of ALAC is seen in the first 24 hours. However, after 72 hours of antibiotic release, fresh bacterial exposure in fresh broth resulted in varying degrees of biofilm colonisation of all ALAC surfaces. Nonetheless, the overall biofilm formation was least on the gentamicin / daptomycin combinations and the results were statistically significant when compared to plain cement (p < 0.05, two tail t-test)

Aim. The treatment of chronic orthopedic device-related infection (ODRI) often requires multiple surgeries and prolonged antibiotic therapy. In a two-stage exchange procedure, the treatment protocol includes device removal and placement of an antibiotic-loaded bone cement spacer to achieve high local antibiotic concentrations. At the second stage, further surgery is required to remove the spacer and replace it with the definitive device. We have recently developed a thermo-responsive hyaluronan hydrogel (THH) that may be loaded with antibiotics and used as delivery system. Since the material is bio-resorbable, it does not require surgical removal and may therefore be suitable for use as treatment strategy in a single-stage exchange. This aim of this study was to evaluate gentamicin sulphate (Genta)-loaded THH (THH-Genta) for treating a chronic Staphylococcus aureus ODRI in sheep using a single-stage procedure. Methods. Twelve Swiss-alpine sheep received an IM tibia nail and an inoculation of a gentamicin-sensitive clinical strain of Staphylococcus aureus. After letting a chronic infection develop for 8 weeks, a revision procedure was performed: the implant was removed, the IM canal debrided and biopsies were taken for culture. The IM canal was then filled with 25ml THH-Genta (1% Genta) or left empty (control group) prior to the implantation of a sterile nail. An ultrafiltration probe was placed within the IM cavity to collect extracellular fluid and determine local antibiotic levels for 10 days. Both groups received systemic amoxicillin and clavulanic acid for 2 weeks, followed by 2 weeks without treatment for antibiotic washout. At euthanasia, IM nail, bone marrow, bone and tissue samples were harvested for quantitative bacteriology. Results. All sheep were infected at revision surgery as confirmed by cultures of biopsies and sonication of the IM nail. Local Genta concentrations ranged on average from 830µg/ml postoperatively to below 5µg/ml after 8 days. At euthanasia, S. aureus was detected in 5/5 IM nails, 5/5 bone marrow samples, and 8/25 superficial soft tissue samples in the control group (one control sheep was excluded for having a superinfection). In the THH-Genta group, S. aureus was cultured from 0/6 IM nails, 1/6 bone marrow samples, and 1/30 superficial soft tissue samples. Conclusions. The THH showed a Genta release pattern that started with high local concentrations and decreased to low concentrations within 10 days. Local Genta delivery by THH combined with systemic antibiotics significantly reduced infection rates whereas systemic therapy alone was unable to eradicate infection in any animal

Aim. Since July 2013 our group has been using an antibiotic bone substitute, composed of calcium sulphate, hydroxyapatite and gentamicin sulphate (CSH + HA + GS), in the treatment of osteomyelitis (OM) in diabetic foot. The aim of this work was to evaluate the mid-term efficacy of this treatment regime on outcomes. A favourable outcome in diabetic foot includes no recurrence of OM, healed soft tissues and the ability to weight-bear. Method. To date we have used the CSH + HA + GS bone substitute in 24 diabetic patients with OM. In this study we reviewed patients treated from July 2013 to December 2014, in which we used CSH + HA + GS to treat OM of the forefoot, midfoot and hind foot, and evaluated how many patients are able to walk and fully weight-bear at present. We identified 11 pts treated during this time period; 1 with bilateral 1. St. metatarsal-head OM due to plantar ulcers, 5 with midfoot OM secondary to Charcot deformities and ulcers, 5 with hind foot OM due to pressure ulcers or Charcot deformity. We continuously monitored the patients for recurrence of OM, ulcers and soft tissue inflammation in our outpatient department. Results. Of the 11 patients, two died during follow up (both patients had calcaneal ulcers; one died in the 1. st. month and one in the 2. nd. month after treatment, both due to cardiovascular disease). For the remaining nine patients, we had an average of 25 (17–33) months follow-up. One patient did not heal, presenting with a persistent mid-foot lesion in a Charcot foot. Another patient with bilateral forefoot ulcers had a plantar ulcer recurrence under the left 1. st. metatarsal foot, 19 months after bone substitute application and primary healing. This patient is still weight-bearing on the right foot, as are the remaining 6 patients. In 7 patients (1 with bilateral forefoot, 4 with mid-foot and 3 with hind foot OM) no recurrence of OM or ulcers was observed. Conclusions. This study suggests that a CSH + HA + GS bone substitute can be used to treat diabetic foot OM. Our mid-term results show good clinical outcomes in terms of ulcer healing, no recurrence of OM and weight-bearing

Background

The aim of the study was to analyze effectiveness and safety of packing the medullary canal of the tibia and femur with Herafill (Heraeus Medical GmbH, Wehrheim, Germany), a void filler and antibiotic carrier, during second stage revision total knee arthroplasty(TKA) for periprosthetic joint infection (PJI). We used hybrid cementation technique for the fixation of TKA components with antibiotic-loaded bone cement for femoral and tibial component and cementless stem extensions.

Aim

This study describes and correlates the radiographic and histologic changes which develop in a Gentamicin-eluting synthetic bone graft substitute* in the management of bone defects after resection of chronic osteomyelitis (COM).

To test the hypothesis that: CERAMENT[™]|G (C-G) would improve new bone growth and decrease infection rate after debridement as compared with 1) CERAMENT|BONE VOID FILLER (CBVF) and 2) no void filler in a rat osteomyelitis model.

72 Sprague Dawley rats were injected with 1.5 × 10∧6 CFU of S. aureus into a drill hole in the right tibia. After 3 weeks, the osteomyelitic defect was debrided, and filled with either: 1) C-G (n=32), 2) CBVF (n=20), or 3) nothing (n=20). 6 weeks after the second surgery, 20 rats from each group were sacrificed and the right tibias were harvested. A long-term group (n=12) of C-G treated rats were also sacrificed at 6 months after the second surgery. The tissues were sonicated and the colony forming units in the sonicate were quantified by serial dilutions and culture. MicroCT was used to quantify the new bone growth (BV/TV) in the debrided osteomyelitic void. Histological samples were analyzed for the presence of a neutrophil response by a blinded pathologist.

(*: p<0.05)

Positive cultures in:

○ 30% of animals treated with CBVF

Neutrophil reaction in:

○ 35% of animals treated with CBVF

The BV/TV in:

○ C-G treated rats was 24% greater than CBVF treated rats (*)

Animals sacrificed at 6 months which were treated with C-G did not have any evidence of infection by culture or histology. The bone mass of the implanted limb was higher than the contralateral (non-operated) side.

CERAMENT|G decreased the rate of infection and increased new bone growth as compared with both CBVF and no void filler in a debrided osteomyelitic environment. Animals treated with C-G at 6 months showed no evidence of infection and retained a higher bone mass relative to the contralateral (non-operated) side.

This study supports the use of CERAMENT|G as a readily available void filler which could be used in osteomyelitic environments after debridement.