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PubMed2001

A simple method of determining the modulus of orthopedic bone cement.

Accurate determination of the elastic modulus of surgical bone cements is of primary importance, when evaluating the stresses within the cement mantle in Total Joint Arthroplasty. This article presents a new method of determining the modulus of surgical bone cements from the biaxial flexural test. The biaxial flexural test is not currently employed in mainstream orthopedic mechanical testing, which is surprising because most loading in orthopedic applications is biaxial in nature. Nor has this method been utilized for dental materials, even though the biaxial flexure test has been used for many years in this field. It has been demonstrated that the modulus of surgical bone cements can be determined from the biaxial flexural test, and these results are in agreement with results from compressive and bending tests.

Bone Cements↗
PubMed1994

Sodium fluoride sustained-release bone cement: an experimental study in vitro and in vivo.

A new "low temperature" bone cement, consisting of polymethylmethacrylate (PMMA) and 6% sodium fluoride, was developed for use in orthopedics. Fluoride is a well-known agent that may stimulate osteoblast activity and differentiation in vitro and in vivo; for this reason fluoride has been used for 30 years in the treatment of osteoporotic diseases of the bone. A local effect obtained with a slow release of fluoride from bone cement at the interface between bone and prosthetic implants could potentially enhance new bone formation around the prosthesis. This material was investigated both "in vitro", by establishing the kinetics of fluoride release from the acrylic bone cement and its maximal compressive strength, and "in vivo", by fitting 24 rabbits, which were then killed after 4, 12 and 16 weeks, with femoral implants, following labelling with fluorescent stains to allow the histologic evaluation of bone remodelling. The "in vitro" study revealed the release kinetics of fluoride from bone cement and the compressive strength of PMMA, that is not affected by the addition of fluoride. The "in vivo" investigation showed considerable healing ability after surgical and heat trauma, and new bone formation that appears larger on the surface in contact with fluoridated cement.

Animals↗
PubMed2006

Effects of bone cement particles on the function of pseudocapsule-derived fibroblasts.

BACKGROUND: Despite the wide clinical use of bone cement, little is known about cellular responses to the debris from this material. We thus investigated the effects of bone cement particles on the secretion of soluble osteotropic factors in prosthetic pseudomembrane-derived fibroblasts. METHODS: Bone cement particles were added to fibroblasts maintained in tissue culture. The secretions of soluble receptor activator for nuclear factor kappa B ligand and osteoprotegerin together with interleukin-6 and tumor necrosis factor-alpha were assessed by enzyme-linked immunosorbent assays. The fibroblasts were also co-cultured with osteoclast precursors in the presence and absence of particles, and we assessed osteoclast formation and bone resorption. RESULTS: The particles produced an increase in the secretion of soluble receptor activator for nuclear factor kappa B ligand, interleukin-6 and tumor necrosis factor-alpha, but not osteoprotegerin. At a concentration of 88 particles/cell, bone cement particles yielded a 2-fold increase (327 pg/mL) in soluble receptor activator for nuclear factor kappa B ligand secretion, a 5-fold (239 pg/mL) increase in interleukin-6 secretion and 4-fold (129 pg/mL) increase in tumor necrosis factor-alpha secretion. The particles also enhanced bone resorption in the co-culture group. Both the increase in soluble receptor activator for nuclear factor kappa B ligand secretion and the increase in bone resorption were inhibited by the addition of neutralizing antibodies to the proinflammatory cytokines. INTERPRETATION: Our findings show that bone cement particles are capable of stimulating the secretion of soluble receptor activator for nuclear factor kappa B ligand in pseudocapsule-derived fibroblasts by increasing the secretion of proinflammatory cytokines, and may also promote implant loosening.

Aged↗
PubMed2005

Dynamic creep and mechanical characteristics of SmartSet GHV bone cement.

The restrained dynamic creep behaviour and mechanical properties of SmartSet GHV bone cement have been investigated at both room temperature and body temperature. It was found that the bone cement behaves significant differently at room temperature from that at body temperature. The test temperature had a strong effect on the creep performance of the bone cements with a higher creep rate observed at body temperature at each loading cycle. For both temperatures, two stages of creep were identified with a higher creep rate during early cycling followed by a steady state creep rate. The relationship between creep deformation and loading cycle can be expressed by a Hyperb 1 model. As a visco-elastic material, the sensitivity of bone cement to the temperature change was evident during mechanical testing. Compared to the mechanical strength at room temperature, a decreased value was demonstrated at body temperature. The bending modulus was very sensitive to the change in testing temperature, where a reduction of 52% was recorded. A significant reduction in compressive and bending strength, 31 and 23% were recorded respectively. The effect of temperature on bending strength was less apparent, where only 13% reduction was exhibited at body temperature compared to room temperature.

Bone Cements↗
PubMed2003

Structural degradation of acrylic bone cements due to in vivo and simulated aging.

Acrylic bone cement is the primary load-bearing material used for the attachment of orthopedic devices to adjoining bone. Degradation of acrylic-based cements in vivo results in a loss of structural integrity of the bone-cement-prosthesis interface and limits the longevity of cemented orthopedic implants. The purpose of this study is to investigate the effect of in vivo aging on the structure of the acrylic bone cement and to develop an in vitro artificial aging protocol that mimics the observed degradation. Three sets of retrievals are examined in this study: Palacos brand cement retrieved from hip replacements, and Simplex brand cement retrieved from both hip and knee replacement surgeries. In vitro aging is performed using oxidative and acidic environments on three acrylic-based cements: Palacos, Simplex, and CORE. Gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR) are used to examine the evolution of molecular weight and chemical species within the acrylic cements due to both in vivo and simulated aging. GPC analysis indicates that molecular weight is degraded in the hip retrievals but not in the knee retrievals. Artificial aging in an oxidative environment best reproduces this degradation mechanism. FTIR analysis indicates that there exists a chemical evolution within the cement due to in vivo and in vitro aging. These findings are consistent with scission-based degradation schemes in the cement. Based on the results of this study, a pathway for structural degradation of acrylic bone cement is proposed. The findings from this investigation have broad applicability to acrylic-based cements and may provide guidance for the development of new bone cements that resist degradation in the body.

Acrylates↗
PubMed2003

Fatigue strength of PMMA bone cement mixed with gentamicin and barium sulphate vs pure PMMA.

Barium sulphate is added to polymethylmethacrylate (PMMA) bone cement as a radiopacifier. Gentamicin is an antibiotic added to bone cement to treat or prevent infection in arthroplasty. This study investigated the combined effect of barium sulphate and gentamicin sulphate on the fatigue strength of PMMA bone cement. Three different formulations were studied: pure PMMA, PMMA with barium sulphate added and PMMA with barium sulphate and gentamicin sulphate added. Before testing all specimens were stored in water at 37 degrees C for at least 15 days to season the PMMA and to elute the antibiotic. Fatigue tests were performed following a previously validated procedure. The slope part of the Wöhler diagram was obtained and a rough endurance limit was estimated for all three formulations. The experimental data showed that the addition of barium sulphate to PMMA bone cement affected the fatigue strength of the material, whereas addition of gentamicin sulphate to the radiopaque PMMA had no effect on the fatigue properties of the bone cement. While PMMA with barium sulphate added was confirmed to have a reduced fatigue strength when compared with plain PMMA, no detrimental effect was found for the addition of gentamicin sulphate to radiopaque PMMA.

Anti-Bacterial Agents↗
PubMed1983

Strain-rate dependence of the compressive properties of normal and carbon-fiber-reinforced bone cement.

Normal and carbon-fiber-reinforced (1 wt. %) bone cement samples were tested in compression at various strain rates. Both the compressive strength and proportional limit increased in general with increasing strain rate. Similar strain-rate sensitivity was also shown by the carbon-fiber-reinforced bone cement. The mechanical properties, namely the modulus of elasticity, the proportional limit, and the compressive strength of the carbon-fiber-reinforced bone cement showed highly significant positive correlations with the strain rate.

Bone Cements↗
PubMed1984

Osseous penetration rate into implants pretreated with bone cement.

The titanium bone growth chamber consists of two titanium disks held together by two screws. At the level of the intersection between the disks, a 1 mm wide canal penetrates the implant. After implantation, in e.g. the rabbit, tibial metaphysis bone and vessels will grow through this canal, the contents of which are collected four weeks after surgery. Microradiography and a computer-based analysis give a numerical representation of the amount of newly formed bone in the canal. When the bone ingrowth into two identical titanium implants, one inserted in the left and the other in the right tibia, was compared, only small and insignificant differences were found in the same animal. However, when one animal was compared to another, greater differences in the bone-forming capacity were found, in spite of the fact that the rabbits were controlled with respect to race, age and sex. The osseous penetration rate into titanium canals was compared to the bone ingrowth in equally sized pipes of polymerized acrylic cement which had been inserted in the titanium chamber. In these cases there was significantly less bone formed in the cement pipes compared to the titanium controls. Poor biocompatibility of the cement compared to titanium is suggested to be one factor responsible for the reduced bone formation in the cement environment. This may be one reason for the fibrous tissue capsule generally seen around cemented implants.

Animals↗
PubMed2007

The role of cement viscosity on cement-bone apposition and strength: an in vitro model with medullary bleeding.

We compared the mechanical and morphological characteristics of cement-bone structures created with either standard- or low-viscosity cement using a human cadaver model that simulated intramedullary bleeding. The goal is to determine if the viscosity of the cement would affect the strength of the cement-bone interface and the degree of apposition between the cement and bone. The tensile strength of cement-bone constructs with standard-viscosity cement (2.42 +/- 1.55 MPa) was 21% stronger than with low-viscosity cement (2.00 +/- 1.51 MPa, P = .034). Cement-bone apposition was positively correlated (r2 = 0.29, P <. 0001) with the strength of the interface. There was 15% greater apposition between cement and bone (P = .036) for standard-viscosity cement. Low-viscosity cement may be less effective in displacing bone marrow and in preventing hemodynamic backflow, resulting in less apposition and a weaker interface.

Aged, 80 and over↗
PubMed2004

Flexural properties of crosslinked and oligomer-modified glass-fibre reinforced acrylic bone cement.

The flexural properties of oligomer-modified bone cement with various quantities of crosslinking monomer with or without glass fibre reinforcement were studied. The flexural strength and modulus of acrylic bone cement-based test specimens (N=6), including crosslinked and oligomer-modified structures with or without glass fibres, were measured in dry conditions and after immersion in simulated body fluid (SBF) for seven days (analysis with ANOVA). One test specimen from the acrylic bone cement group containing 30 wt % crosslinking monomer of its total monomer content was examined with scanning electron microscope (SEM) to evaluate signs of the semi-interpenetrating polymer network (semi-IPN). The highest dry mean flexural strength (130 MPa) was achieved with the bone cement/crosslinking monomer/glass fibre combination containing 5 wt % crosslinking monomer of its monomer content. The highest flexural modulus (11.5 GPa) was achieved with the bone cement/crosslinking monomer/glass fibre combination containing 30 wt % crosslinking monomer of its monomer content. SBF storage decreased the flexural properties of the test specimens, as did the addition of the oligomer filler. Nevertheless, the addition of crosslinking monomer and chopped glass fibres improves considerably the mechanical properties of oligomer-modified (i.e. porosity-producing filler containing) acrylic bone cement. In addition, some signs of the semi-IPN structure were observed by SEM examination.

Acrylic Resins↗
PubMed2000

Prophylaxis of implant-related staphylococcal infections using tobramycin-containing bone cement.

In a rabbit model, premixed tobramycin-containing bone cement was studied for its efficacy to prevent infections with two frequently encountered staphylococcal species in arthroplasty surgery. After intramedullary inoculation with staphylococci, either standard or premixed tobramycin-containing Simplex-P bone cement was injected in the right femur of 120 rabbits. Development of infection was examined by culture of femoral bone after 7 or 28 days. Loss of body weight and elevated erythrocyte sedimentation rate in the control rabbits inoculated with Staphylococcus aureus were seen in the first postoperative week, returning to normal in 28 days. Inoculation with Staphylococcus epidermidis resulted only in a low-grade infection. All rabbits receiving premixed tobramycin-containing bone cement were free of signs of infection, and all their cultures were negative. Culture yield from Staphylococcus aureus controls increased with time and inoculum dose. Staphylococcus epidermidis controls needed higher inoculum doses to establish an infection, while culture yield decreased in time. These differences in mode of prosthesis-related infection are explained by differences in virulence factors.

Animals↗
PubMed2003

Preparation of epoxy-SiO2 hybrid sol-gel material for bone cement.

An organic-inorganic hybrid material, epoxy-SiO(2), was prepared by incorporating epoxy structure units covalently into a SiO(2) glass network via the sol-gel approach. The precursor was obtained by the reaction of diglycidyl ether of bisphenol A (DGEBA) with 3-aminopropyl trimethoxysilane (APTS). The precursor was then hydrolyzed and co-condensated with tetraethyl orthosilicate (TEOS) in tetrahydrofuran (THF) at room temperature to yield epoxy-SiO(2) hybrid sol-gel material having a 50 wt % SiO(2) content. Thermal properties of the hybrid material were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The hybrid sol-gel material epoxy-SiO(2) was the solid, powder component of bone cement. The liquid component contains bis-phenol-A glycidyl methacrylate (Bis-GMA), triethyleneglycol dimethacrylate (TEGDMA), and methyl methacrylate (MMA) with 25, 55, and 20 vol %, respectively. We discuss the comparison between the new epoxy-SiO(2) bone cement and the commercial Simplex P bone cement. Mechanical properties such as Young's modulus, compressive strength, hardness, and impact strength of the new epoxy-SiO(2) bone cement exceeded those of Simplex P bone cement. The tensile and bending strengths of the new epoxy-SiO(2) bone cement were approximately the same as those of Simplex P bone cement. In order to evaluate the biocompatibility of the new bone cement, an MTT test and optical microscopy were conducted in cell culture. Results indicated that the new epoxy-SiO(2) bone cement exhibits very low cytotoxicity compared with Simplex P bone cement.

Animals↗
PubMed2006

Controlled release of gentamicin from calcium phosphate-poly(lactic acid-co-glycolic acid) composite bone cement.

Modification of a self setting bone cement with biodegradable microspheres to achieve controlled local release of antibiotics without compromising mechanical properties was investigated. Different biodegradable microsphere batches were prepared from poly(lactic-co-glycolic acid) (PLGA) using a spray-drying technique to encapsulate gentamicin crobefate varying PLGA composition and drug loading. Microsphere properties such as surface morphology, particle size and antibiotic drug release profiles were characterized. Microspheres were mixed with an apatitic calcium phosphate bone cement to generate an antibiotic drug delivery system for treatment of bone defects. All batches of cement/microsphere composites showed an unchanged compressive strength of 60 MPa and no increase in setting time. Antibiotic release increased with increasing drug loading of the microspheres up to 30% (w/w). Drug burst of gentamicin crobefate in the microspheres was abolished in cement/microsphere composites yielding nearly zero order release profiles. Modification of calcium phosphate cements using biodegradable microspheres proved to be an efficient drug delivery system allowing a broad range of 10-30% drug loading with uncompromised mechanical properties.

Animals↗
PubMed2001

The preparation of bone cement.

The hip joint is subjected to large, repetitive loads. It is therefore clear that the bone cement, which allows the transfer of load across the new joint, must be able to withstand the everyday loads that it will be subjected to. Improving the mechanical properties of the cement to withstand high stresses, fatigue and creep loading will reduce the chances of failure, ultimately increasing the longevity of the joint replacement. To date, work in this area has concentrated on improving the mechanical properties of bone cement through improved bone cement mixing techniques. In the next issue we will be covering the effect that the design of the mixer and vacuum mixing has on improving the mechanical properties, such as the strength, fatigue and creep resistance, of the bone cement.

Arthroplasty, Replacement↗
PubMed2001

[Effect of ultrasonic shock waves on the bone-bone cement interface].

PURPOSE OF THE STUDY: Identification of the impact of ultrasound shock wave on the integration of bone cement in the bone and the examination of a potential application of this method in order to facilitate the extraction of cemented implants, mainly femoral component of total hip arthroplasty. MATERIAL: We used pig proximal femurs from which we made fragments involving approximately one third to one half of the profile of the bone and Palacos bone cement. METHOD: We made a groove in the cancellous bone, pressed bone cement with a wire loop in the cavity and let it harden. The samples were divided by random selection into two groups. Samples from A group were exposed to ultrasound shock waves and group B served as a control group. Then we measured the force needed for the extraction of the cement plug from the bone. RESULTS: Our measuring has shown an evident decrease of the force necessary for the extraction of the bone cement after the application of ultrasound shock wave. We did not find out any macroscopically evident damage of the bone cement or of the surrounding cortical bone. DISCUSSION: The results of our measuring are influenced by a different shape and size of the examined samples which also substantially differ from the situation when a stem of the endoprosthesis is implanted in the femoral canal and is surrounded by a cement mantle. As concerns risks associated with the application of the shock wave in this indication there is a risk of a fracture of the cortical bone around THR stem (the literature does not mention this complication) and a risk of the increase of pressure in the medullary cavity of the femur combined with a risk of fat embolism. In our view this increase of pressure is comparable with the effect of the implantation of femoral component. This method cannot be used for releasing cementless implants as the surrounding cortical bone gets damaged before the implant is released. CONCLUSION: Ultrasound shock wave is still used rarely in orthopaedics, however, the existing results are promising in many aspects. Of great importance is the fact that it is a non-invasive method. The field dealt with by this work covers only experiments in vitro but the results provide hope for a future clinical use.

Animals↗
PubMed2006

Surface and chemical properties of surface-modified UHMWPE powder and mechanical and thermal properties of its impregnated PMMA bone cement, IV: effect of MMA/accelerator on the surface modification of UHMWPE powder.

In our previous study, we manufactured a reinforced poly(methylmethacrylate) (PMMA) bone cement with 3 wt% of the surface-modified ultra high molecular weight polyethylene (UHMWPE) powder to improve its poor mechanical and thermal properties resulting from unreacted methylmethacrylate (MMA), the generation of bubble and shrinkage, and high curing temperature. In the present study, the effect of ratios of MMA and N,N'-dimethyl-p-toluidine (DMPT) solutions in redox polymerization system was investigated for the surface modification of UHMWPE powder. We characterized physical and chemical properties of surface-modified UHMWPE powder and reinforced bone cements by a scanning electron microscope, ultimate tensile strength (UTS) and curing temperature (Tmax). It was found that UTSs (41.3-51.3 MPa) of the reinforced PMMA bone cements were similar to those (44.5 MPa) of conventional PMMA bone cement (control), as well as significantly higher (P < 0.05) than those (33.8 MPa) of 3 wt% unmodified UHMWPE powder-impregnated bone cement. In particular, the UTS of redox polymerization system using MMA/DMPT solution was better than that of radical system using MMA/xylene solution. Also, Tmax of the reinforced PMMA bone cements decreased from 103 to 72-84 degrees C. From these results, we confirmed that the surface-modified UHMWPE powder can be used as reinforcing agent to improve the mechanical and thermal properties of conventional PMMA bone cement.

Biomechanical Phenomena↗
PubMed1980

Antibiotics and bone cements. Experimental and clinical long-term observations.

Comparing several antibiotics and different bone cements, the mixture of Palacos R (polymethylmethacrylate, PMMA) with gentamicin proved to be the most suitable one as far as a high and sustained release of the antibiotic from the artificial resin is concerned. A continuous leaching of gentamicin was observed for more than 5 years. Gentamicin proved to be stable in Palacos R for the whole period of time. The release of 12 antibiotics from Palacos R was evaluated in vitro. Four other bone cements were included in this study as well, in order to evaluate the leaching of gentamicin from these materials. The combination Gentamicin-Palacos R (GP) showed a 2--3 fold higher and much more prolonged release than did the other mixtures. From this investigation, which also included studies of commercially available antibiotic bone cement mixtures, it is quite obvious that there exist distinct differences in the various bone cements as well as in the various antibiotics as regards their qualification for use in alloarthroplasty. Pharmacokinetic studies in patients after implantation of GP showed low gentamicin concentrations in serum (on average 1.8 microgram/ml) and urine. However, in wound exudate, derived directly from the vicinity of the implanted cement, gentamicin concentrations up to 150 micrograms/ml were observed. Also in tissue samples from the vicinity of the implant, high concentrations were measurable for a long period of time (up to 5 1/2 years).

Acrylic Resins↗
PubMed1994

Polymerization kinetics, glass transition temperature and creep of acrylic bone cements.

Sulfix-6 and Zimmer LVC 60/30 bone cements were selected and the polymerization kinetics and resulting glass transition temperature Tg; creep behaviour in the dry or water-saturated state; and sorption and diffusion of water were studied. The calculation of conversion was based on a comparison of the residual polymerization heat measured by differential scanning calorimetry and the corresponding theoretical value. The conversion reached 99% after 90 min of quasi-adiabatic polymerization starting at 23 degrees C or after 10 min of isothermal polymerization at 37 degrees C. The Tgs of the cements prepared in the former way were about 82 and 100 degrees C, respectively. Creep rate of the bone cements at 37 degrees C decreased with the time of creeping. Sorbed water enhanced the compliance, but reduced the creep rate for long times so that water sorption during the service time may not have detrimental effects on the creep resistance of the cements. Both types of cements contained about 1% of low molar mass substances extractable by water. Measurements of the sorption kinetics of water showed that the diffusion coefficient is 0.14 x 10(-11) and 0.22 x 10(-11) m2/s and 1 yr sorption achieves 2.11% and 2.89% for Sulfix and Zimmer, respectively.

Adsorption↗