[In vitro elution and mechanical properties of antibiotic-loaded SmartSet HV and Palacos R acrylic bone cements]

A Low Rate of Periprosthetic Infections after Aseptic Knee Prosthesis Revision Using Dual-Antibiotic-Impregnated Bone Cement

AIM

The incidence of periprosthetic joint infections (PJI) following aseptic knee revision arthroplasty lies between 3% and 7.5%. The aim of this study was to verify the hypothesis that the use of dual-antibiotic-impregnated cement in knee revision arthroplasty leads to a lower rate of periprosthetic joint infections.

METHODS

We retrospectively reviewed 403 aseptic revision knee arthroplasties performed between January 2013 and March 2021 (148 revisions of a unicompartmental prosthesis, 188 revisions of a bicondylar total knee arthroplasty (TKA), 41 revisions of an axis-guided prosthesis, and 26 revisions of only one component of a surface replacement prosthesis). The bone cement Copal G+C (Heraeus Medical, Wertheim, Germany) with two antibiotics-gentamycin and clindamycin-was used for the fixation of the new implant. The follow-up period was 53.4 ± 27.9 (4.0-115.0) months.

RESULTS

Five patients suffered from PJI within follow-up (1.2%). The revision rate for any reason was 8.7%. Survival for any reason was significantly different between the types of revision (p = 0.026, Log-Rank-test), with lower survival rates after more complex surgical procedures. The 5-year survival rate with regard to revision for any reason was 91.3% [88.2-94.4%] and with regard to revision for PJI 98.2% [98.7-99.9%], respectively.

CONCLUSION

The use of the dual-antibiotic-impregnated bone cement Copal G+C results in a lower rate of periprosthetic infections after aseptic knee prosthesis replacement than that reported in published prosthesis revisions using only one antibiotic in the bone cement.

Osteogenic and antibacterial dual functions of a novel levofloxacin loaded mesoporous silica microspheres/nano-hydroxyapatite/polyurethane composite scaffold

Lev/MSNs/n-HA/PU has been proved to be a novel scaffold material to treat bone defect caused by chronic osteomyelitis. We have previously identified that this material can effectively treat chronic osteomyelitis caused by Staphylococcus aureusin vivo. However, the potential mechanisms of antibacterial and osteogenic induction properties remain unclear. Thus, for osteogenesis property, immunohistochemistry, PCR, and Western blot were performed to detect the expression of osteogenic markers. Furthermore, flow cytometry and TUNEL were applied to analyze MC3T3-E1 proliferation and apoptosis. For antibacterial property, the material was co-cultivated with bacteria, bacterial colony forming units was counted and the release time of the effective levofloxacin was assayed by agar disc-diffusion test. Moreover, scanning electron microscope was applied to observe adhesion of bacteria. In terms of osteogenic induction, we found BMSCs adherently grew more prominently on Lev/MSNs/n-HA/PU. Lev/MSNs/n-HA/PU also enhanced the expression of osteogenic markers including OCN and COL1α1, as well as effectively promoted the transition from G1 phase to G2 phase. Furthermore, Lev/MSNs/n-HA/PU could reduce apoptosis of MC3T3-E1. Besides, both Lev/MSNs/n-HA/PU and n-HA/PU materials could inhibit bacterial colonies, while Lev/MSNs/n-HA/PU possessed a stronger antibacterial activities, and lower bacterial adhesion than n-HA/PU. These results illustrated that Lev/MSNs/n-HA/PU composite scaffold possess favorable compatibility in vitro, which induce osteogenic differentiation of MSCs, promote proliferation and differentiation of MC3T3-E1, and inhibit apoptosis. Moreover, clear in vitro antibacterial effect of Lev/MSNs/n-HA/PU was also observed. In summary, this study replenishes the potential of Lev/MSNs/n-HA/PU composite scaffold possess dual functions of anti-infection and enhanced osteogenesis for future clinical application.

Antibiotic elution and compressive strength of gentamicin/vancomycin loaded bone cements are considerably influenced by immersion fluid volume

The effect of doubling the immersion fluid (eluate) volume on antibiotic concentrations and on mechanical stability from vancomycin and gentamicin loaded bone cements was investigated in vitro. Antibiotic loaded bone cements containing premixed 1.34% gentamicin antibiotic concentration in the cement powder (wt), premixed 1.19% gentamicin wt and 4.76% vancomycin wt and premixed 1.17% wt gentamicin additionally manually blended with 4.68% wt vancomycin were tested. Six specimens per group were immersed in 4 ml and 8 ml for 6 weeks while the eluate was exchanged every 24 h. The antibiotic concentrations were repeatedly measured. Then the specimens were tested for compressive strength. Doubling the eluate volume significantly decreased gentamicin and vancomycin concentrations from 6 h and 24 h on, except for the gentamicin concentration of the additionally manually blended formulation after 3 weeks. The additionally manually blended vancomycin formulation produced significantly higher gentamicin concentrations in 8 ml compared to the other formulations. The reduction ratios of the vancomycin concentrations were significantly smaller than the reduction ratios of the gentamicin concentrations for the manually blended vancomycin formulation. Vancomycin containing formulations showed significantly lower compressive strengths than the vancomycin free formulation after immersion. Doubling the eluate volume lead to significant compressive strength reduction of the vancomycin containing formulations. Eluate volume change influences antibiotic elution dependent on the antibiotic combination and loading technique. The reducing effect is higher on vancomycin than on gentamicin elution. Compressive strength of gentamicin/vancomycin loaded bone cements after immersion is eluate volume dependent.

Elution Profiles of Two Methods of Antibiotic Tibial Nail Preparations

Interlocking nails coated with antibiotic-supplemented cement provide effective treatment of infected long bone nonunion, but the thicker coating on guidewires may provide greater antibacterial activity. This study compared the properties of cement cured on each construct by evaluating 2-cm segments of 8-mm interlocking nails and 3.5-mm guidewires coated with antibiotic-supplemented cement. Each construct (n=7 for each group) was coated with polymethylmethacrylate cement (Simplex; Stryker Orthopaedics, Mahwah, New Jersey) containing either 1 g tobramycin or 1 g vancomycin powder plus 2.2 g tobramycin powder. A No. 40 French polyvinyl chloride chest tube was used as a mold for all constructs. Segments were soaked in sterile phosphate-buffered saline, and entire aliquots were exchanged at various intervals over a 6-week period. Antibiotic concentration, antibacterial activity, cement curing temperature, and porosity were measured. At least half of the total elution of antibiotics occurred within the first 24 hours for all constructs. For the tobramycin-only cement, no differences between constructs were observed. For constructs containing both antibiotics, interlocking nails showed more antibiotic release than guidewires at most time points (P<.05-P<.001). Antibiotics were released for 6 weeks and continued to inhibit Staphylococcus aureus growth. Cement curing temperatures for interlocking nails were lower than those for guidewires (P<.05). Guidewires coated with cement containing tobramycin and vancomycin showed significantly greater porosity compared with the other 3 groups (P<.05), but the amount of antibiotic released did not directly relate to porosity for any construct type. Interlocking nails coated with antibiotic-supplemented cement may provide greater antibiotic delivery to infected long bone nonunion compared with guidewires. A thin mantle of cement may allow greater elution, possibly as a result of cooler exothermic reactions. [Orthopedics. 2017; 40(3):e436-e442.].

Carriers for the tunable release of therapeutics: etymological classification and examples

Introduction Physiological processes at the molecular level take place at precise spatiotemporal scales, which vary from tissue to tissue and from one patient to another, implying the need for carriers that enable tunable release of therapeutics. Areas covered Classification of all drug release to intrinsic and extrinsic is proposed, followed by the etymological clarification of the term 'tunable' and its distinction from the term 'tailorable'. Tunability is defined as analogous to tuning a guitar string or a radio receiver to the right frequency using a single knob. It implies changing a structural parameter along a continuous quantitative scale and correlating it numerically with the release kinetics. Examples of tunable, tailorable and environmentally responsive carriers are given, along with the parameters used to achieve these levels of control. Expert opinion Interdependence of multiple variables defining the carrier microstructure obstructs the attempts to elucidate parameters that allow for the independent tuning of release kinetics. Learning from the tunability of nanostructured materials and superstructured metamaterials can be a fruitful source of inspiration in the quest for the new generation of tunable release carriers. The greater intersection of traditional materials sciences and pharmacokinetic perspectives could foster the development of more sophisticated mechanisms for tunable release.

Evaluation of Elution and Mechanical Properties of High-Dose Antibiotic-Loaded Bone Cement: Comparative "In Vitro" Study of the Influence of Vancomycin and Cefazolin

Use of antibiotic-loaded bone cements is one of the most effective methods for the prevention and treatment of prosthetic joint infection. However, there is still controversy about the optimal combination and doses of antibiotics that provide the maximum antimicrobial effect without compromising cement properties. In this study, vancomycin and cefazolin were added to a bone cement (Palacos R+G). Antibiotic release, fluid absorption, and mechanical properties were evaluated under physiological conditions. The results show that the type of antibiotic selected has an important impact on cement properties. In this study, groups with cefazolin showed much higher elution than those containing the same concentration of vancomycin. In contrast, groups with cefazolin showed a lower strength than vancomycin groups.

Increased antibiotic release and equivalent biomechanics of a spacer cement without hard radio contrast agents

We compared a novel calcium carbonate spacer cement (Copal® spacem) to well-established bone cements. Electron microscopic structure and elution properties of the antibiotics ofloxacin, vancomycin, clindamycin, and gentamicin were examined. A knee wear simulator model for articulating cement spacers was established. Mechanical tests for bending strength, flexural modulus, and compressive and fatigue strength were performed. The electron microscopic analysis showed a microporous structure of the spacer cement, and this promoted a significantly higher and longer antibiotic elution. All spacer cement specimens released the antibiotics for a period of up to 50days with the exception of the vancomycin loading. The spacer cement showed significantly less wear scars and fulfilled the ISO 5833 requirements. The newly developed spacer cement is a hydrophilic antibiotic carrier with an increased release. Cement without hard radio contrast agents can improve tribological behaviour of spacers, and this may reduce reactive wear particles and abrasive bone defects.

Study of the Influence of Bone Cement Type and Mixing Method on the Bioactivity and the Elution Kinetics of Ciprofloxacin

The objectives of this study were to examine ciprofloxacin release from three trademarks of bone cements (Simplex®, Lima® and Palacos®) and its bioactivity using as variables, the mixing method, the chemical form of the antibiotic and the antibiotic combination. The antibiotic amount released in base form represents 35% of antibiotic amount released when hydrochloride form is incorporated. Moreover, the combination (vancomycin and ciprofloxacin) shows a stronger release (132%) than hydrochloride ciprofloxacin alone. Three cements show equal drug release profile (P > 0.05). A bioactivity simulation exercise showed that until 72 hours post-surgery, ciprofloxacin concentrations in the implant would be higher than 0.1 μg/mL in 100% of the patients. After drain removal, it is expected that bioactivity would increase since drug clearance from implant would decrease.

Effects of vancomycin, cefazolin and test conditions on the wear behavior of bone cement

Antibiotic cement has been recommended in the treatment of prosthetic infections. The purpose of this study was to investigate the mechanical behavioral changes in cement loaded with two antibiotics, vancomycin and cefazolin, in dry and liquid medium. Six groups and four study conditions were established according to the doses of antibiotic used and the ageing (immersion in phosphate buffered saline) of the samples. Properties evaluated were friction coefficient and wear. Samples in dry medium showed higher wears than in liquid. Antibiotic selection did not influence wear properties tested in dry conditions, however, in liquid medium, there were higher frictional coefficients and wear for cefazolin loaded cement after one week and for vancomycin and cefazolin after one month. The results suggest that antibiotic cements behave differently in liquid and that the molecular characteristics of antibiotics are essential for determining this influence.

Microhardness of bi-antibiotic-eluting bone cement scaffolds

Bi-antibiotic-impregnated bone cements (BIBCs) are widely used in orthopaedics as a prophylactic agent (depot) to address post-surgical infections. Although hardness is widely considered a viable index to measure the integrity of the cement structure, there are few specific studies involving changes in hardness characteristics of BIBCs post elution of high doses of two widely used antibiotics: tobramycin and gentamicin. Increased doses of antibiotics and increased duration of elution may also decrease the hardness of polymethyl methacrylate (PMMA) bone cement, thus increasing the chances of shattering, scratching, and deformation.

In this project, we have investigated the changes in surface hardness of five different antibiotic-loaded specimens: 0.5 g tobramycin and 0.5 g gentamicin together, 1 g tobramycin, 1 g gentamicin, 5 g tobramycin and 5 g gentamicin together, and 10 g tobramycin (each added to 40 g of PMMA), post elution for various time periods (1, 3, and 21 days). The effect of hydration on the hardness of bone cement was studied to replicate in vivo conditions. The micro-indentation tester (Buehler m5103) was utilized to determine if the increased antibiotic loads would compromise the integrity of the bone cement matrix.

The results demonstrated that the amount of drug initially incorporated determined the hardness of the cement post elution. As compared to the control (no antibiotic), specimens containing 1 and 10 g of antibiotic exhibited over 50% and 73% decrease in hardness, respectively. The different treatment durations (post 1 day) as well as the hydration conditions had insignificant effect on the hardness of the cement.

High rate of infection control with one-stage revision of septic knee prostheses excluding MRSA and MRSE

BACKGROUND

The rate of infection control for one-stage revision of infected knee arthroplasties is unclear as are the factors influencing infection control. Such factors include duration of infection and the type of infected prosthesis.

QUESTIONS/PURPOSES

We therefore determined: (1) the rate of infection control with one-stage revision of septic knee prostheses, (2) the clinical knee scores that can be achieved, (3) whether the duration of infection or the type of prosthesis influence the level of infection control, and (4) whether different types of prostheses influence the knee scores.

METHODS

We retrospectively reviewed prospectively collected data from 63 patients who underwent one-stage revisions of septic knee endoprostheses (six unicondylar, 37 primary total knee replacement prostheses, and 20 hinged knee endoprostheses) between 2004 and 2006. All were treated locally and systemically with microorganism-specific antibiotics. For this study we excluded patients with Methicillin-resistant Staphylococcus aureus and Methicillin-resistant Staphylococcus epidermidis or unknown microorganisms. The patients were examined for infection every 3 months and Oxford and Knee Society scores were assessed at the same time. The minimum followup was 24 months (mean followup, 36 months; range, 24-70 months).

RESULTS

None of the patients with replacement unicondylar and primary total knee replacement prostheses had recurrence of infection. Three of the 20 patients with the hinged infected knee prostheses had recurrences; these three patients had chronic infections and had undergone two to three revision operations during at least a 5-year period. The likelihood of infection control was influenced by the duration of infection. The mean Knee Society knee score 24 months after surgery was 72 points (range, 20-98 points), the Knee Society function score was 71 points (range, 10-100 points), and the Oxford-12 knee score was 27 points (range, 13-44 points).

CONCLUSIONS

One-stage revision of septic knee prostheses achieved an infection control rate of 95% and higher knee scores than reported for two-stage revisions. Higher rates of recurrent infection appeared to be associated with long-term chronic infections of hinged prostheses.

Sufficient release of antibiotic by a spacer 6 weeks after implantation in two-stage revision of infected hip prostheses

BACKGROUND

Although antibiotic-loaded spacers are commonly used to treat periprosthetic infections, it is unclear whether spacers continue to release bactericidal levels of antibiotic 6 weeks after implantation.

QUESTIONS/PURPOSES

We asked whether an antibiotic can be detected in the tissue surrounding the spacer 6 weeks after implantation and whether the concentration is higher than the minimal inhibition concentration (MIC) previously determined for pathogens that are responsible for most periprosthetic infections.

METHODS

We removed 14 spacers used in two-stage septic revisions of infected hip prostheses 6 weeks after the primary implantations and determined the concentration of the antibiotics in the membrane formed between the spacer and the neighboring bone on the acetabular and the femoral sides. In seven cases Copal cement with gentamicin and clindamycin were used, and in seven other cases vancomycin was added to the Copal cement. Concentrations of the spacer antibiotics in the neighboring tissue were determined by tandem mass spectroscopy.

RESULTS

All three antibiotics were detected in concentrations higher than their MIC. There were no differences between the groups regardless whether vancomycin was added to the cement, or whether the cement was applied with the acetabular cup spacer or with the stem spacer.

CONCLUSIONS

We concluded that, using the spacer technique described in this study, 6 weeks after spacer implantation, the concentrations of antibiotic are sufficient to treat a periprosthetic infection.

Antibiotic-loaded cement in orthopedic surgery: a review

Infections in orthopaedic surgery are a serious issue. Antibiotic-loaded bone cement was developed for the treatment of infected joint arthroplasties and for prophylaxes in total joint replacement in selected cases. Despite the widespread use of the antibiotic-loaded bone cement in orthopedics, many issues are still unclear or controversial: bacterial adhesion and antibiotic resistance, modification of mechanical properties which follows the addition of the antibiotic, factors influencing the release of the antibiotic from the cement and the role of the surface, the method for mixing the cement and the antibiotic, the choice and the effectiveness of the antibiotic, the combination of two or more antibiotics, and the toxicity. This review discusses all these topics, focusing on properties, merits, and defects of the antibiotic loaded cement. The final objective is to provide the orthopaedic surgeons clear and concise information for the correct choice of cement in their clinical practice.

Gentamicin release from commercially-available gentamicin-loaded PMMA bone cements in a prosthesis-related interfacial gap model and their antibacterial efficacy

Background

Around about 1970, a gentamicin-loaded poly (methylmethacrylate) (PMMA) bone cement brand (Refobacin Palacos R) was introduced to control infection in joint arthroplasties. In 2005, this brand was replaced by two gentamicin-loaded follow-up brands, Refobacin Bone Cement R and Palacos R + G. In addition, another gentamicin-loaded cement brand, SmartSet GHV, was introduced in Europe in 2003. In the present study, we investigated differences in gentamicin release and the antibacterial efficacy of the eluent between these four cement brands.

Methods

200 μm-wide gaps were made in samples of each cement and filled with buffer in order to measure the gentamicin release. Release kinetics were related to bone cement powder particle characteristics and wettabilities of the cement surfaces. Gaps were also inoculated with bacteria isolated from infected prostheses for 24 h and their survival determined. Gentamicin release and bacterial survival were statistically analysed using the Student's t-test.

Results

All three Palacos variants showed equal burst releases but each of the successor Palacos cements showed significantly higher sustained releases. SmartSet GHV showed a significantly higher burst release, while its sustained release was comparable with original Palacos. A gentamicin-sensitive bacterium did not survive in the high gentamicin concentrations in the interfacial gaps, while a gentamicin-resistant strain did, regardless of the type of cement used. Survival was independent of the level of burst release by the bone cement.

Conclusions

Although marketed as the original gentamicin-loaded Palacos cement, orthopaedic surgeons should be aware that the successor cements do not appear to have the same release characteristics as the original one. Overall, high gentamicin concentrations were reached inside our prosthesis-related interfacial gap model. These concentrations may be expected to effectively decontaminate the prosthesis-related interfacial gap directly after implantation, provided that these bacteria are sensitive for gentamicin.

Enhancement of antibiotic elution from acrylic bone cement

Antibiotic-loaded acrylic bone cement is a well-established tool in the prophylaxis and treatment of orthopedic infections. Numerous studies about its pharmacokinetic properties have demonstrated that only a small part of the incorporated antibiotic amounts can be released, mostly over the first 8-10 weeks. Therefore, in the past 10 years, several attempts have been made for enhancement of the drug elution from bone cement. This article reviews this experience and pays special attention on biantibiotic combinations, additives other than antimicrobial agents, as well as the effect of ultrasound on the antibiotic elution characteristics.

Revision of late periprosthetic infections of total hip endoprostheses: pros and cons of different concepts

Many concepts have been devised for the treatment of late periprosthetic infections of total hip prostheses. A two-stage revision with a temporary antibiotic-impregnated cement spacer and a cemented prosthesis appears to be the most preferred procedure although, in recent times, there seems to be a trend towards cementless implants and a shorter period of antibiotic treatment. Because of the differences in procedure, not only between studies but also within studies, it cannot be decided which period of parenteral antibiotic treatment and which spacer period is the most suitable. The fact that comparable rates of success can be achieved with different treatment regimens emphasises the importance of surgical removal of all foreign materials and the radical debridement of all infected and ischaemic tissues and the contribution of these crucial procedures to the successful treatment of late periprosthetic infections.

The compressive properties of bone cements containing large doses of antibiotics

The addition of large amounts of antibiotics to bone cement provides a convenient local delivery, but may influence the compressive properties of the cement. Flucloxacillin and vancomycin were added to Simplex P (Stryker, Limerick, Ireland) and VersaBond (Smith & Nephew) cements. Tripling the antibiotic dose from 2 to 6 g had little effect on the static compressive properties 24 hours after curing. After 4 weeks in phosphate-buffered saline, there was marked decrease in properties with the addition of antibiotics. Compressive strength of cements with 6 g of antibiotic was reduced to near or below the ASTM and ISO minimum of 70 MPa after 4 weeks in phosphate-buffered saline. Microcomputer tomography revealed increased porosity and clumping of the radiopacifier with the addition of antibiotics.

Orthopaedic bone cement: do we know what we are using?

Bone cements produced by different manufacturers vary in their mechanical properties and antibiotic elution characteristics. Small changes in the formulation of a bone cement, which may not be apparent to surgeons, can also affect these properties. The supplier of Palacos bone cement with added gentamicin changed in 2005. We carried out a study to examine the mechanical characteristics and antibiotic elution of Schering-Plough Palacos, Heraeus Palacos and Depuy CMW Smartset bone cements. Both Heraeus Palacos and Smartset bone cements performed significantly better than Schering-Plough Palacos in terms of mechanical characteristics, with and without additional vancomycin (p < 0.001). All cements show a deterioration in flexural strength with increasing addition of vancomycin, albeit staying above ISO minimum levels. Both Heraeus Palacos and Smartset elute significantly more gentamicin cumulatively than Schering-Plough Palacos. Smartset elutes significantly more vancomycin cumulatively than Heraeus Palacos. The improved antibiotic elution characteristics of Smartset and Heraeus Palacos are not associated with a deterioration in mechanical properties. Although marketed as the 'original' Palacos, Heraeus Palacos has significantly altered mechanical and antibiotic elution characteristics compared with the most commonly-used previous version.

[Finite element analysis of a cemented ceramic femoral component for the assembly situation in total knee arthroplasty]

The femoral components of the total knee replacements are generally made of metal. In contrast, ceramic femoral components promise improved tribological and allergological properties. However, ceramic components present a risk of failure as a result of stress peaks. Stress peaks can be minimised through adequate implant design, proper material composition and optimum force transmission between bone and implant. Thus, the quality of the implant fixation is a crucial factor. The objective of the present study was to analyse the influence of the cement layer thickness on stress states in the ceramic femoral component and in the femur. Two- and three- dimensional finite element analyses of an artificial knee joint with cement layers of different thickness and with an unbalanced cement layer thickness between the ceramic femoral component and the femur were performed. Higher stress regions occurred in the area of force transmission and in the median plane. The maximum calculated stresses were below the accepted tensile strength. Stresses were found to be lower for cement layer thickness of <2.0 mm.