Objectives. The objective of this study was to determine if combining variations in mixing technique of antibiotic-impregnated polymethylmethacrylate (PMMA) cement with low frequency ultrasound (LFUS) improves antibiotic elution during the initial high phase (Phase I) and subsequent low phase (Phase II) while not diminishing mechanical strength. Methods. Three batches of vancomycin-loaded PMMA were prepared with different mixing techniques: a standard technique; a delayed technique; and a control without antibiotic. Daily elution samples were analysed using flow injection analysis (FIA). Beginning in Phase II, samples from each mix group were selected randomly to undergo either five, 15, 45, or 0 minutes of LFUS treatment. Elution amounts between LFUS treatments were analysed. Following Phase II, compression testing was done to quantify strength. A-priorit-tests and univariate ANOVAs were used to compare elution and mechanical test results between the two mix groups and the control group. Results. The delayed technique showed a significant increase in elution on day one compared with the standard mix technique (p < 0.001). The transition point from Phase I to Phase II occurred on day ten. LFUS treatments significantly increased elution amounts for all groups above control. Delayed technique resulted in significantly higher elution amounts for the five-minute- (p = 0.004) and 45-minute- (p < 0.001) duration groups compared with standard technique. Additionally, the correlations between LFUS duration and total elution amount for both mix techniques were significant (p = 0.03). Both antibiotic-impregnated groups exhibited a significant decrease in offset yield stress compared with the control group (p < 0.001), however, their lower 95% confidence intervals were all above the 70 MPa limit defined by International Standards Organization (ISO) 5833-2 reference standard for acrylic bone cement. Conclusion. The combination of a delayed mix technique with LFUS treatments provides a reasonable means for increasing both short- and long-term antibiotic elution without affecting mechanical strength. Cite this article: Dr. T. McIff. Combination of modified mixing technique and low frequency ultrasound to control the elution profile of vancomycin-loaded acrylic bone cement. Bone Joint Res 2016;5:26–32. doi: 10.1302/2046-3758.52.2000412

Aims. Poly(methyl methacrylate) (PMMA)-based bone cements are the industry standard in orthopaedics. PMMA cement has inherent disadvantages, which has led to the development and evaluation of a novel silorane-based biomaterial (SBB) for use as an orthopaedic cement. In this study we test both elution and mechanical properties of both PMMA and SBB, with and without antibiotic loading. Methods. For each cement (PMMA or SBB), three formulations were prepared (rifampin-added, vancomycin-added, and control) and made into pellets (6 mm × 12 mm) for testing. Antibiotic elution into phosphate-buffered saline was measured over 14 days. Compressive strength and modulus of all cement pellets were tested over 14 days. Results. The SBB cement was able to deliver rifampin over 14 days, while PMMA was unable to do so. SBB released more vancomycin overall than did PMMA. The mechanical properties of PMMA were significantly reduced upon rifampin incorporation, while there was no effect to the SBB cement. Vancomycin incorporation had no effect on the strength of either cement. Conclusion. SBB was found to be superior in terms of rifampin and vancomycin elution. Additionally, the incorporation of these antibiotics into SBB did not reduce the strength of the resultant SBB cement composite whereas rifampin substantially attenuates the strength of PMMA. Thus, SBB emerges as a potential weight-bearing alternative to PMMA for the local delivery of antibiotics. Cite this article: Bone Joint Res 2021;10(4):277–284

Aim. The aim of this study is to evaluate if the gentamycin elution from bone cement is influenced by the timing of application of the antibiotic powder. Method. This was an experimental in vitro study that compared the elution properties of different formulation of gentamycin from a commercially available hip, knee and shoulder cement spacers. Four different experimental models were prepared. Five different spacers were prepared for each experimental mode and for each joint. We compared four different formulation of cement spacers: spacer #1, in which the spacer was prepared with a premixed bone-cement antibiotic mixture; spacer #2, in which the spacer was prepared by adding antibiotic powder to the bone cement at the time of spacer preparation; spacer #3, in which the spacer was prepared as spacer #2 but was stored for two months before starting the experiment; spacer #4, in addition to the gentamycin, other two antibiotics (tobramycin and vancomycin) were added to the bone cement. Gentamycin concentration was documented at seven intervals of time: T0 = 0h, T1 = 1h, T2 = 24h, T3 = 1W, T4 = 2W, T5 = 1M, T6 = 3M and T7 = 6M. The gentamycin elution at each interval of time was evaluated by using a T-student test. Results. Spacer #2, in which the gentamycin powder was added to the bone cement at the time of spacer preparation showed the higher gentamycin elution at each interval of time observed. In addition, Spacer #1, in which gentamycin powder was premixed with the bone cement showed a higher gentamycin elution when compared with spacer #3, in which the spacers were stored for two months to simulate the preformed spacers. Lastly, the addition of different antibiotic to the bone cement increases the gentamycin elution from the spacers (as demonstrated by spacer #4 model). Conclusions. a higher gentamycin elution was observed if spacer was prepared at the time of surgery when compared with preformed spacer. Lastly, our study confirmed the synergistic effect of adding one or more antibiotics with the aims to increase gentamycin elution

Objectives. The aim of this study was to analyze drain fluid, blood, and urine simultaneously to follow the long-term release of vancomycin from a biphasic ceramic carrier in major hip surgery. Our hypothesis was that there would be high local vancomycin concentrations during the first week with safe low systemic trough levels and a complete antibiotic release during the first month. Methods. Nine patients (six female, three male; mean age 75.3 years (sd 12.3; 44 to 84)) with trochanteric hip fractures had internal fixations. An injectable ceramic bone substitute, with hydroxyapatite in a calcium sulphate matrix, containing 66 mg of vancomycin per millilitre, was inserted to augment the fixation. The vancomycin elution was followed by simultaneously collecting drain fluid, blood, and urine. Results. The antibiotic concentration in the drain reached a peak during the first six hours post-surgery (mean 966.1 mg/l), which decreased linearly to a mean value of 88.3 mg/l at 2.5 days. In the urine, the vancomycin concentration reached 99.8 mg/l during the first two days, followed by a logarithmic decrease over the next two weeks to reach 0 mg/l at 20 days. The systemic concentration of vancomycin measured in blood serum was low and decreased linearly from 2.17 mg/l at one hour post-surgery to 0 mg/l at four days postoperatively. Conclusion. This is the first long-term pharmacokinetic study that reports vancomycin release from a biphasic injectable ceramic bone substitute. The study shows initial high targeted local vancomycin levels, sustained and complete release at three weeks, and systemic concentrations well below toxic levels. The plain ceramic bone substitute has been proven to regenerate bone but should also be useful in preventing bone infection. Cite this article: M. Stravinskas, M. Nilsson, A. Vitkauskiene, S. Tarasevicius, L. Lidgren. Vancomycin elution from a biphasic ceramic bone substitute. Bone Joint Res 2019;8:49–54. DOI: 10.1302/2046-3758.82.BJR-2018-0174.R2

Abstract. Background. The aim of the present experimental study was to analyse vancomycin elution kinetics of nine bone fillers used in orthopaedic and trauma surgery over 42 consecutive days. Methods. Two allograft bone chips (carriers 1 and 2), a calcium-sulfate matrix (carrier 3), a hydroxyapatite/calcium-sulphate composite (carrier 4), four bone cements (carriers 5-8) and a pure tricalcium phosphate matrix (carrier 9), either already contained vancomycin, or were mixed with it following manufacturer's recommendations. Over 42 days, half of elution medium was substituted by the same amount of PBS at 9 distinct time points. Vancomycin concentration in obtained samples were measured with a kinetic microparticle immunoassay, and masses consecutively calculated. To enhance comparability between carriers analysed, vancomycin mass released related to overall mass within each probe was determined. Notably, elution kinetics of carriers 1 to 4 have been published previously. Results. All carriers initially released high vancomycin masses, followed by constant reduction later into the experiment. Mean initial vancomycin masses released after 4 hours were highest for carriers 1 (337.7 ± 76.2 mg), 9 (68.4 ± 4.9 mg), and 2 (49.0 ± 54.6 mg). From prefinal (35 days) to last measurement (42 days) carriers 2 (8.6 ± 4.8 mg), 1 (2.4 ± 1.0 mg), and 5 (0.1 ± 0.1 mg) had released highest vancomycin masses. Notably, all five bone cements tested only released a small percental amount of their total mass up to the last measurement (42 days; 2.1% – 9.3%), whilst allografts and resorbable synthetic bone fillers discarded high percental values (22.5% – 79.2%). Conclusions. Elution kinetics differ between 9 antibiotic-loaded bone fillers, with high vancomycin masses released by allografts and resorbable bone fillers over time. Transferred to clinical practice, these may be favoured over bone cements in case prolonged and high antibiotic release is warranted rather than mechanical stability

Introduction. Vancomycin is commonly added to acrylic bone cement during revision arthroplasty surgery. Proprietary cement preparations containing vancomycin are available but significantly more expensive. We investigated whether the antibiotic elution and mechanical strength of ‘home-made’ vancomycin containing bone cement was comparable to commercial vancomycin-impregnated cement. Methods. A total of 18 cement discs of constant size, containing either proprietary CopalG+V. ®. ; or ‘home-made’ CopalR+G. ®. with vancomycin added by hand, were made. Each disc contained the same antibiotic quantities (0.5g gentamycin, 2g vancomycin) and was immersed in ammonium acetate buffer in a sealed container. Fluid from each container was sampled at eight time points over a two week period. The concentration of gentamicin and vancomycin in the fluid was analysed using high performance liquid chromatography mass spectrometry. The impact strength of each PMMA cement preparation was measured using a Charpy-type impact tester. Results. Highest peak antibiotic concentrations were observed from the ‘home-made’ vancomycin containing cement, added as in the operating theatre. Overall antibiotic elution was, five-fold (vancomycin) and two-fold (gentamicin), greater from the ‘home-made’ mix compared to commercially mixed cement. However the ‘home-made’ cements showed greater variation in elution kinetics compared to the commercial mix. Use of a vacuum during mixing had no significant effect on antibiotic elution in any of the samples. Impact strength testing showed no significant differences between the groups. Discussion. Our findings suggest the addition of 2g vancomycin powder to gentamicin-impregnated bone cement in theatre, significantly increases elution of both antibiotics, with no significant loss of strength, compared to commercially prepared cement. Conclusion. We have found no significant advantages of expensive off-the-shelf vancomycin-impregnated bone cement and recommend the addition of vancomycin powder by hand when making cement beads and spacers

AIM: Chronic osteomyelitis is a difficult to treat infection requiring prolonged antimicrobial therapy and involving systems of local antimicrobial delivery. Linezolid is a new antimicrobial agent with well documented in vitro activity against gram positive cocci when resistance to other antistaphylococcal agents is present. Few data are present regarding its embedding in local antimicrobial delivery systems and subsequent elution. The elution of linezolid by a polylactic acid (PLA) system was studied. METHODS: Linezolid was dry-mixed with PLA at a ratio of 1:9, ie 50mg of linezolid were mixed with 450mg PLA. The mixture was diluted with 0,5mL of methanol and placed at the bottom of a cylindrical vial. Two replicas were created and one mL of Mueller-Hinton broth was added over the free solid surface of each mixture. Vials were transferred to a 37°C incubator and broth was replaced every 48h for 11 days. Concentration of linezolid was determined by an HPLC method using a Zorbax Eclipse XDB-C8 column and UV detection. RESULTS: Mean linezolid concentration at days 1, 3, 5, 7, 9 and 11 was 2778.54 mg/L, 2456.22 mg/L, 668.63 mg/L, 324.86 mg/L, 390.10 mg/L, and 155.28 mg/L respectively. CONCLUSION: Elution of linezolid by a PLA local delivery system remains very high throughout the period studied. The results are promising for the therapy of staphylococcal chronic osteomyelitis with the use of a PLA local antimicrobial delivery system employing linezolid

Introduction: It is common practice to use additional antibiotics in bone cement for revision hip surgery. Ideally antibiotic elution would initially be rapid and then reduce to zero in order to reduce the risk of antibiotic resistance developing. There is evidence that the addition of antibiotics to bone cement leads to deterioration in mechanical properties. We have carried out a study to see if the addition of vancomycin to Palacos R40G and Smartset GHV affects their in-vitro antibiotic elution and mechanical properties. Methods: Palacos R40G (contains 0.5g gentamycin per 40g mix) and Smartset GHV (contains 1g gentamycin per 40g mix) were used. 40g samples of the two cements with no additional vancomycin, 1g and 2g vancomycin were prepared by a standard method using vacuum mixing in a syringe. Antibiotic elution over a five week period was measured using an immunoassay method. Standard mechanical testing was carried out according to methods defined in ISO 5833. Results: Smartset GHV eluted double the quantity of gentamycin as Palacos R40G, as would be expected. Both cements eluted more gentamycin when vancomycin was added. Smartset appears to elute more vancomycin than Palacos initially and then shows a more rapid tailing off. The mechanical properties of the two cements were the same with no statistical differences found between them. Both showed deterioration in flexural strength with addition of increasing vancomycin. Discussion: Smartset may have improved qualities of antibiotic elution as compared with Palacos with similar mechanical properties. The presence of higher initial quantities of gentamycin does not lead to reduced mechanical properties

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

The use of polymethylmethacrylate (PMMA) bone cement loaded with antibiotics has become increasingly common in orthopaedic surgery. However, bacterial resistance in antibiotics is an increasing and emerging problem. PMMA bone cements containing different antibiotics, such as gentamicin plus vancomycin may be effective in prevention and treatment of infections (particularly from MRSA and MRSE). The purpose of this study was to determine the in vitro elution characteristics of gentamicin and vancomycin when combined in acrylic cement. Three groups of ten cement disks were prepared. Group I (control group) contained 0.5g of gentamicin per 40-g packet of Palacos-R+G powder. Group II contained 0.5g of gentamicin and 1g of powdered vancomycin and group III contained 0.5g of gentamicin and aqueous solution of vancomycin. Each cement disc (25mm x 20mm) was immersed in a 50-mL bath of normal saline at 37oC. Samples were taken at specific sampling intervals (1, 3, 7, 15, 30, 60, 90, 120, 150, 180 days). Antibiotic concentrations were measured using fluorescence polarisation immunoassay. With regards to gentamicin release, high but rapidly decreasing antibiotic levels were detected within the first week and low concentration after the first month. Samples from Group II eluted significantly more gentamicin (120%–20% during the first month). The influence on the gentamicin release was significant but minor when aqueous solution of vancomycin (Group III) was added. With regards to vancomycin release, high antibiotic levels were detected within the first 3 days and low concentrations after the first week. Cement samples from Group II eluted significantly more antibiotic in comparison with samples from Group III. Bone cements loaded with combinations of gentamicin and vancomycin are more effective in releasing gentamicin than bone cements with gentamicin as a single drug. Powdered vancomycin in cement samples has better elution characteristics in comparison with aqueous solution of vancomycin

Prosthetic joint infections are difficult to treat due to bacterial biofilm. Our group has developed a linezolid elution system by human cancellous bone delivering high concentrations the first 48 hours (Giannitsioti et al. 53rd ICAAC, 2013: A-1050). We tested the activity of this system to inhibit growth of one ica expressing isolate of Staphylococcus epidermidis (MRSE). At a first step, sterile mesh cylinders containing bone particles of the femoral head of healthy volunteers (MCB) were impregnated into 3mg/ml linezolid for 1, 24 and 48 hours. Then log-phase inocula of 103, 105 and 107cfu/ml were exposed to MCB at 370C for 8 days with regular readings of bacterial growth. MCB were transferred into fresh Muller-Hinton Broth (MHB) every 24h to avoid material corrosion. At a second step, to simulate the ability of the system against biofilm-coated MCB, MCB without linezolid were incubated with 103 and 105 cfu/ml for 1 and 24h. MCB were daily transferred into fresh MHB containing 100μg/ml on day 1, 15 μg/ml on day 2, 3 μg/ml on day 3 and 0.5 μg/ml on day 4. 24h linezolid impregnated MCB achieved rapid bacterial killing of the 105 cfu/ml bacterial suspension followed by re-growth (Figure, n= 5). Similar results were observed for 1h and 48h impregnation and for both tested inocula. When biofilm-coated MCB generated by 24h exposure to 105 cfu/ml were exposed to linezolid, rapid bacterial killing was achieved followed by re-growth. Linezolid local elution may inhibit biofilm-producing MRSE only when locally eluted concentrations exceed 10μg/ml

Aim: To compare the in-vitro elution characteristics of CMW1 and Palacos R bone cements containing gentamicin or teicoplanin or a combination of both. Materials & Methods: Four types of bone cement discs (28x22mm) were prepared. Disc 1(control) contained Palacos R or CMW1 cement without any added antibiotic. Disc2 contained Palacos R or CMW1 with gentamicin. Disc 3 contained Palacos R or CMW1 with teicoplanin. Disc 4 contained Palacos R or CMW1 with gentamicin and teicoplanin powder. The discs containing teicoplanin were prepared by adding teicoplanin powder (2gm) to the respective cement powder (40 gm with or without 0.5gm of gentamicin) and then adding the monomer (vacuum mixing). All the discs were immersed in 50 ml normal saline bath in a sterile pot and maintained at temperature of 37 deg Celsius. 24 hours later a 5ml sample was taken from each pot for assay, to measure the amount of antibiotic eluted, using fluorescence polarization immuno-assay technique. The discs were then removed from the pots, washed with normal saline and reimmersed in a fresh 50 ml saline pot. This procedure was repeated at hours 48, 72, 120 and week 1, 2, 3 & 6 for all discs. Results: All discs and assays were done in triplicate and average total value at 6 weeks (μ gm/ml) taken for statistical analysis. CMW1:. Gentamicin eluted from disc4 was higher than disc2 (94.9 v 34.37. p< 0.0003). Teicoplanin eluted from disc4 was higher than disc3 (202.1 v 147.57. p< 0.004). PALACOS R:. Gentamicin eluted from disc4 was higher than disc2 (144.17 v 86.43. p< 0.0004). Teicoplanin eluted from disc4 was less than disc3 (140.17 v 213.73. p< 0.008). Conclusion: Palacos R cement elutes more antibiotic than CMW1 and antibiotic combination in bone cement resulted in, mostly, synergistic effect of increased elution of individual antibiotic

Vitamin E (alpha-tocopherol) is a free-radical stabilizing agent used to maintain oxidative stability in radiation crosslinked UHMWPE for total joint replacements. Diffusion of vitamin E into UHMWPE after irradiation is one method of incorporation, while an alternative is blending vitamin E with UHMWPE resin powder and subsequently irradiating the consolidated mixture. With the latter method, it is possible for the antioxidant properties of Vitamin E to be exhausted in blends during irradiation, leading to oxidation. We report on the relative oxidative resistance of both irradiated (100kGy, 150kGy, 200kGy) vitamin E blends (0.02 wt%, 0.05 wt% and 0.1wt%) and post-irradiation vitamin E-diffused UHMWPE after three years of real-time aging in an aqueous environment at 40°C. Blocks of each type, including irradiated virgin UHMWPE, were also accelerated aged per ASTM F2003. Oxidation was measured with FTIR per ASTM F2102. Oxidation potential was determined through nitric oxide staining of hexane extracted thin sections, FTIR analysis and calculated using the height of the nitrate peak (1630 cm^-1). Our results showed that unstabilized samples exhibited substantial oxidation and oxidation potential throughout the surface and bulk with both types of aging. Post-irradiation diffused UHMWPE showed no detectable oxidation and decreasing oxidation potential with both aging methods. The vitamin E concentration at the surface of the diffused blocks decreased and the initial non-uniform profile with high surface concentration (3.4 wt%) shifted towards a uniform profile, equilibrating at an index of 0.1 or 0.7 wt% vitamin E. Samples showed a reduction in their initial vitamin E content by 47%– 61% over 36 months, but oxidative stability was not compromised. The non-uniform profile presumably created a driving force for elution into the aqueous environment, while the difference in solubility of vitamin E at 40°C, compared to the initial diffusion temperature at 120°C, may have also contributed. After six months of real-time aging, all irradiated blends showed surface oxidation, while 0.02 wt% blends additionally showed subsurface oxidation potential. However, oxidation was not induced by accelerated aging Methods: in any blended, irradiated samples. In conclusion, real-time aging resulted in greater differentiation in the relative oxidative stability of vitamin E-stabilized, radiation crosslinked UHMWPEs than accelerated aging. Irradiated blends with vitamin E concentrations as high as 0.1 wt% showed surface oxidation after 3 years; higher vitamin E concentrations cannot address this shelf oxidation as that will also reduce the crosslinking efficiency and increase wear. Post-irradiation diffused UHMWPE, which was not limited by the amount of incorporated vitamin E, showed oxidative resistance up to 3 years with a reduction in oxidative potential

Introduction: The use of polymethylmethacrylate (PMMA) bone cement loaded with antibiotics has become increasingly common in the treatment of infected knee and hip arthroplasties and also as prophylaxis in primary joint replacement. However bacterial resistance in antibiotics is an increasing and emerging problem. PMMA bone cements containing different antibiotics, such as gentamicin plus vancomycin may be effective in prevention and treatment of infections (particularly from MRSA and MRSE). The purpose of this study was to determine the in vitro elution characteristics of gentamicin and van-comycin when combined in acrylic cement. Material and methods: Three groups of six cement disks were prepared. Group I (control group) contained 0.5g of gentamicin sulphate per 40-g packet of Palacos-R+G powder. Group II contained 0.5g of gentamicin sulphate and 1g of finely powdered vancomycin and Group III contained 0.5g of gentamicin sulphate and aqueous solution of vancomycin (containing 2mL water for injection and 1g vancomycin). All discs were prepared using vacuum mixing technique. Each cement disc (25mm diameter × 20mm thick) was fully immersed in a 50-mL bath of normal saline at 37o C temperature in a covered beaker. At specific sampling intervals (1, 3, 7, 15, 30, 60, 90, 120, 150, 180 days) the discs were removed and placed in fresh 50 ml bath for 24 hours. Then a 2 mL sample of each solution was taken. Samples were frozen at −60° C until they were analyzed. Gentamicin and vancomycin concentrations were measured using fluorescence polarization immunoassay. Results: With regards to gentamicin release, high but rapidly decreasing antibiotic levels were detected within the first week, resulting in an almost steadily low concentration by the end of the first month. Cement samples eluted significantly more gentamicin (120%-20% during the first month) when powdered vancomycin (Group II) was added. The influence on the gentamicin release was significant but minor when aqueous solution of vancomycin (Group III) was added (40%-20% during the same period). With regards to vancomycin release, high antibiotic levels were detected within the first 3 days and low concentrations after the first week. Cement samples from Group II eluted significantly more antibiotic (80%–100%) in comparison with samples from Group III during the first days. Gentamicin and vancomycin are detectable in measurements at 150 and 180 days samples. Conclusions: Bone cements loaded with combinations of gentamicin and vancomycin are more effective in releasing gentamicin than bone cements with gentamicin as a single drug. The presence of powdered vancomycin in cement samples has major influence on the total gen-tamicin release in comparison with cements containing aqueous solution of vancomycin

Aim. In vivo studies have shown a preventive and curative effect of using an injectable vancomycin containing biphasic ceramic in an osteomyelitis model. No clinical long term pharmacokinetic release study has been reported. Inadequate concentration in target tissues results in treatment failure and selection pressure for antibiotic-resistant organisms. Our hypothesis was that vancomycin in the first week would reach high local concentrations but with low systemic levels. Method. 9 patients (6 women, 3 men) with trochanteric hip fractures classified as A1 and A2 according to the AO-classification all had internal fixations. The mean age was 75.3 years (± S.D. 12.3 years, range 44–84y). An injectable ceramic with hydroxyapatite embedded in a calcium sulphate matrix containing 66mg vancomycin per mL augmented the fixation. A mean of 9.7 mL (± S.D. 0.7 mL, range 8–10mL) was used. The elution of vancomycin was followed by collecting drain fluid, blood (4 days) and urine (4 weeks). Results. The concentration of antibiotics in the drain showed an important burst during the first 12h after surgery, with a mean value of 709.9 µmol/L (± S.D. 383.9), which decreased linearly to a mean value of 60.9 µmol/L at 2.5 days. In the urine, the vancomycin concentration reached 68.9 µmol/L (± S.D. 34.4) during the first day, which was decreased logarithmic over the first two weeks to reach zero at 20 days (see Figure). The systemic concentration of vancomycin was constantly low, not exceeding 2.6 µmol/L. Conclusions. This is the first long term pharmacokinetic study reporting vancomycin release from a biphasic injectable ceramic bone substitute. The study shows initial high targeted local vancomycin levels (wound drainage), sustained and complete release at three weeks (verified by the urine concentrations), and systemic concentrations well below toxic levels. This system should be useful in preventing and treating bone infection

Purpose: Previous studies have shown the utility of the bisphosphonate zoledronic acid (ZA) by systemic administration and local delivery for enhancing local bone formation with porous implants. The purpose of this study was to quantify the long term effect of local delivery of ZA on bone growth within and around porous tantalum implants one year after surgery. Method: Hydroxyapatite coated porous tantalum (Trabecular Metal. ™. , Zimmer Inc) implants measuring 9 mm in diameter and 90 mm in length were used in a canine bilateral femoral intramedullary model. Commercially pure ZA (Novartis Pharma) of either 0.05 mg or 0.20 mg ZA was applied to implants. Bilateral surgery was performed on 10 dogs – all 10 with a control implant on one side and 5 each with either a 0.05 mg or 0.20 mg ZA-dosed implant on the contralateral side. After one year, the femora were harvested and processed for undecalcified thin section histology and backscattered scanning electron microscopy. Statistical analysis was done using the student’s t tests and multiple two-level hierarchical models. Results: The 160 histologic sections revealed that compared with controls, there was more intramedullary bone around implants dosed with both 0.05 mg ZA (+91%, p< 0.001) and 0.20 mg ZA (+115%, p< 0.001). Bone ingrowth was present in all sections and was more abundant within 1.5mm of the implant periphery. The 0.20 mg ZA dose resulted in more net intramedullary bone formation than the 0.05 mg dose (+41%, p< 0.006). The mean extent of bone ingrowth for implants dosed with 0.20 mg ZA was significantly greater than controls (+32%, p< 0.003) and also greater than for implants dosed with 0.05 mg ZA (+47% for the area within 1.5 mm of the periphery, p< 0.002). Conclusion: This study demonstrated that the enhanced net bone formation that occurs due to local elution of ZA from porous implants was sustained out to 1 year after surgery. A notable dose response was also demonstrated. The peri-implant response was confined to within a few millimeters of the implant suggesting that ZA elution remains localized. This study supports the concept of using ZA-dosed implants for enhancing net bone formation within and around noncemented implants

Purpose: The bisphosphonate Zoledronic acid (ZA) is effective for increasing net bone formation within and around implants when directly eluted from implants. The extent to which this occurs or whether ZA is more widely distributed through diffusion into the circulation is unknown. The purpose of this study was to utilize 14C-labeled ZA to quantify the localization and skeletal distribution of ZA in a canine intramedullary implant model. Method: A solution of 100μg 14C-labeled ZA was evenly distributed onto each implant surface of three hydroxyapatite coated porous tantalum (Trabecular Metal. ™. , Zimmer Inc) implants measuring 5 mm in diameter and 50 mm in length. The implants were inserted within the left femoral intramedullary canal of an adult mongrel dog and left in situ for 6 weeks. The 3 femora with implants and all the other long bones were harvested, dried, pulverized into a fine powder and disolved in HCl. This solution was then placed in a scintillation cocktail (Ultima Gold AB, Perkin Elmer USA) and analyzed with a Packard Tri-Carb 2100TR liquid scintillator spectrometer. Data were analyzed with student’s t tests and nested analyses of variance with p=0.05. Results: Very high amounts of ZA were present within the bone samples immediately adjacent to the implants – range 243 – 1487 ng ZA/g of bone, mean of 800 ng ZA/g. By 1 cm proximal or distal to the implant, the values diminished by up to an order of magnitude. All other bone samples contained very low amounts of 14C, (range, 0.8 – 22.6 ng ZA/g; mean 6.5 ng ZA/g), indicating diffusion of ZA into the circulation and a level of systemic distribution. This is about 11-fold less in magnitude (p< 0.0001). Conclusion: Local elution of ZA directly from an implant results in half of the ZA being distributed locally in the femur with the rest being distributed throughout the skeleton, at levels that are much less than the therapeutic dose required to appreciably affect bone remodeling or cause complications. postoperative time periods

Infection poses one of the greatest medical challenges, one further complicated by bacterial biofilm formation that renders the infection antibiotic insensitive. The goal of this investigation was to covalently link the antibiotic vancomycin (VAN) to a bone allograft so as to render the tissue inhospitable to bacterial colonization and the subsequent establishment of infection. We could achieve uniform tethering of the antibiotic to the allograft with minimal disruption of the underlying bone structure. The tethered VAN remained active against gram-positive organisms with no detectable S.aureus colonization. Additionally, the grafted VAN prevented biofilm formation, even in protected topographical niches. Attachment of the antibiotic to the allograft surface was robust-the stabilized VAN remained active for long time periods. Osteoblasts cultured on the VAN-allograft evidenced no changes in cellular phenotype. We opine that this new chimeric construct represents a superior transplantable substrate with a plethora of applications in medicine, dentistry and surgery.

Aim. Local antibiotics released through a carrier is a commonly used technique to prevent infection in orthopaedic procedures. An interesting carrier in aseptic bone reconstructive surgery are bone chips impregnated with AB solution. Systemically administered Cefazolin (CFZ) is used for surgical site infection prophylaxis however in vitro study showed that fresh frozen and processed bone chips impregnated with CFZ solution completely release the CFZ within a few hours. On the other hand irradiated freeze-dried bone chips, treated with supercritical CO2 (scCO2) have been shown to be an efficient carrier for the antibiotics vancomycine or tobramycine. With this pilot study we wanted to investigate if CFZ solution impregnation of bone chips treated with scCO2 shows a more favorable release pattern of CFZ. Method. The bone chips were prepared using the standard scCO2 protocol and were impregnated with 100 mg/ml cefazolin at different timepoints during the process: before freeze drying (BC type A), after freeze drying (BC type B) and after gamma-irradiation. 0.5g of the impregnated bone grafts were incubated with 5ml of fetal calf serum (FCS) at 37°C. At 2, 4, 6, 8 and 24h of incubation 200µl of eluate was taken for analysis. After 24h the remaining FCS was removed, bone grafts were washed and new FCS (5ml) was added. Consecutive eluate samples were taken at 48, 72 and 96h of incubation. The concentration of CFZ in the eluates was measured with the validated UPLC-DAD method. Analysis was performed in triplicate. Results. The mean concentration of CFZ in the eluate obtained from BC type A incubated for 2h was higher compared to BC type B, respectively 581 mg/l and 297 mg/l. However, the elution profile is the same for both types: the CFZ concentration in the eluates drops within the first 24h from 581 mg/l to 365 mg/l (37%) for BC type A and from 297 mg/l to 132 mg/l (56%) for BC type B. After 24h no further significant CFZ release is seen. Impregnation of the bone chips before or after gamma irradiation did not affect this elution profile. Conclusions. Bone chips treated with scCO2 show a comparable elution pattern compared to non-scCO2 treated bone chips. AB release depends on the properties of the AB, making it impossible to copy the same impregnation protocol for different antibiotics. The stability of CFZ in solution at 37°C and its release are a major concern when establishing an impregnation protocol with CFZ

Aims. There is a lack of biomaterial-based carriers for the local delivery of rifampicin (RIF), one of the cornerstone second defence antibiotics for bone infections. RIF is also known for causing rapid development of antibiotic resistance when given as monotherapy. This in vitro study evaluated a clinically used biphasic calcium sulphate/hydroxyapatite (CaS/HA) biomaterial as a carrier for dual delivery of RIF with vancomycin (VAN) or gentamicin (GEN). Methods. The CaS/HA composites containing RIF/GEN/VAN, either alone or in combination, were first prepared and their injectability, setting time, and antibiotic elution profiles were assessed. Using a continuous disk diffusion assay, the antibacterial behaviour of the material was tested on both planktonic and biofilm-embedded forms of standard and clinical strains of Staphylococcus aureus for 28 days. Development of bacterial resistance to RIF was determined by exposing the biofilm-embedded bacteria continuously to released fractions of antibiotics from CaS/HA-antibiotic composites. Results. Following the addition of RIF to CaS/HA-VAN/GEN, adequate injectability and setting of the CaS/HA composites were noted. Sustained release of RIF above the minimum inhibitory concentrations of S. aureus was observed until study endpoint (day 35). Only combinations of CaS/HA-VAN/GEN + RIF exhibited antibacterial and antibiofilm effects yielding no viable bacteria at study endpoint. The S. aureus strains developed resistance to RIF when biofilms were subjected to CaS/HA-RIF alone but not with CaS/HA-VAN/GEN + RIF. Conclusion. Our in vitro results indicate that biphasic CaS/HA loaded with VAN or GEN could be used as a carrier for RIF for local delivery in clinically demanding bone infections. Cite this article: Bone Joint Res 2022;11(11):787–802