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PubMed1991

A method for bone-cement interface thermometry. An in vitro comparison between low temperature curing cement Palavit, and Surgical Simplex P.

Previous temperature measurements at the bone-cement intreface have all shown large variations. To evaluate more precisely the temperature profiles during cement curing, a new experimental model was developed. Eight thermocouple electrodes at the bone-cement interface for each test specimen were used for continuous temperature recordings. Temperature profiles of Palavit was compared with those of Surgical Simplex P in an in vitro model using isolated pig femurs. Defects of 12 x 17 mm in the femoral metaphysis were filled with cement. In six tests with each type of cement, Palavit peaked at a temperature of 50 +/- 0.5 degrees C, whereas Surgical Simplex P peaked at 60 +/- 0.7 degrees C. Core temperatures reached peak values of 70 +/- 0.8 degrees C and 95 +/- 2.2 degrees C for Palavit and Surgical Simplex P, respectively.

Animals↗
PubMed1997

Hydroxyapatite impregnated bone cement: in vitro and in vivo studies.

Hydroxyapatite (HA) particle impregnated polymethylmethacrylate (PMMA) bone cement was fabricated in order to induce bony tissue ingrowth into the pores left behind by resorption of the HA. The amount of HA was 0%, 10%, and 30% by weight. After mixing the HA with bone cement it was cast in a 4 mm inside diameter glass tube (10 mm long). Each specimen was cut into half and used for in vitro and in vivo experiment. Diametral tensile and flexural bend tests were made to evaluate its mechanical properties. SEM (scanning electron microscope) and ESCA (electron spectroscopy for chemical analysis) were used to evaluate the surface characteristics of the specimen. Push-out test and histology studies were made after implanting the specimens for six weeks in the distal portion of rabbit femur. The mechanical test results showed significant decrease of the flexural and diametral tensile strength linear with the increased amount of HA (p < 0.05). The SEM and ESCA analyses showed no definite exposure of HA particles on the surface of the specimens due to the covering by PMMA. The interfacial shear strength of the implanted specimens showed significant increases in the 30% HA specimens compared with the 0% ones but the 10% specimens did not show any difference. Histological observation showed little HA particle apposition to new bone in 10% specimens but more in the 30% ones. In conclusion, this study showed the decreased mechanical properties both by increasing the amount of HA particles and with the bone particles impregnated bone cement. In vivo study showed much lower interfacial shear strength due to implant site compared to other studies but the 30% HA specimens showed statistically significant increase in the push-out strength after implanting into the distal end of rabbit femora.

Animals↗
PubMed1999

No biological advantage with a low temperature curing versus a conventional bone cement: an experimental, mechanical and histomorphometrical study in the rabbit tibia.

Both tibial marrow cavities of 12 rabbits were evacuated and filled with curing bone cement. In one of the tibias conventional curing bone cement (Simplex P) was injected, while the other tibia of the same animal was filled with a low temperature curing bone cement (Boneloc). Three titanium implants were inserted along the proximal metaphysis of each tibia. Eight weeks after insertion the most distal implant in each tibia was removed while recording the removal torque. The implant was then once again screwed home into its bone bed. The animals were sacrificed 16 weeks after implant insertion. The previously removed implant and another implant in each tibia were then both removed while recording the removal torque. The third implant in each tibia was cut out en bloc with surrounding tissue and processed for ground section. We found no statistical differences in the mechanical or the histomorphometric evaluation of implant integration between the two cements, indicating that the low temperature curing bone cement does not result in a significantly different bone response from that of a conventional acrylic cement.

Journal Article↗
PubMed2004

[Antibiotic-loaded bone cements: from laboratory studies clinical evaluation].

Antibiotic-loaded bone cements (ALBC) were initially used empirically, both for the treatment of infected prostheses and for antibioprophylaxis. We conducted in vitro and animal studies as a prerequisite for proper clinical evaluation. We measured gentamicin diffusion from methacrylate bone cement, and found that the concentration in surrounding fluid was significantly above the minimal inhibitory concentration (MIC). We then implanted ALBC in the proximal femora of 100 ewes, in conditions close to those of total hip replacement (THR). Antibiotic concentrations in bone were above 4 x MIC for more than 6 months. We subsequently measured antibiotic concentrations in drainage fluid, blood and urine samples from 50 patients undergoing THR. Concentrations were over 20 x MIC in periprosthetic fluid, but were below the detection limit in blood after 24 hours and in urine after one week. The blood concentration was less than 1 mg/l--far below the ototoxic and nephrotoxic threshold (8 mg/l). Having established antibiotic bioavailability, we then examined the clinical efficacy of ALBC. We participated in several studies, including a French multicentric review of 342 THR procedures (direct and two-stage exchanges). ALBC was beneficial in both settings, with an 85% infection control rate. This included patients with very severe infections (multiresistant strains, severe osteolysis) treated with two-stage exchanges; and moderate infections treated by direct exchange. (This latter procedure offers fewer complications, more durable functional results, a shorter hospital stay and lower treatment costs.) We also used ALBC for antibioprophylaxis in over 2000 THR procedures, and noted no complications. This method is now being assessed in more than 200 000 cases contained in the Swedish THR Register. The experimental methods that we developed (laboratory studies, animal implantation, clinical pharmacokinetics) set the groundwork for clinical studies of gentamicin ABLC, and also allowed us to develop other ALBC formats, containing vancomycin, for example (restricted to salvage therapy). We also used these methods to evaluate antibiotic-loaded bone substitutes (calcium and carbon phosphates), designed not only to control infectious osteitis but also to replace osteolytic bone.

Anti-Bacterial Agents↗
PubMed1983

Evaluation of bone cement failure criteria with applications to the acetabular region.

A Strain energy density (SED) criterion based on a fracture mechanics approach was used to assess the possible failure of acetabular bone cement after total hip replacement. Stress distributions in the cement at the bone-cement interface were calculated using two-dimensional finite element analyses. The results indicate that increasing the thickness of bone cement reduces the risk of cement fracture. The addition of a metal backing to the polyethylene cup and retention of the subchondral bone further reduces the risk of failure. The SED criterion was found to predict the same critical regions as zones of possible cement failure as the von Mises' criterion. Although either criterion can be used for predicting failure in this acetabular analysis both criteria are excessively conservative in predicting failure in regions where high principal compressive stresses are present. Further development of cement failure criteria are indicated.

Acetabulum↗
PubMedDate not supplied

The influence of temperature and specimen size on the flexural properties of PMMA bone cement.

A three-stage investigation was undertaken to examine the influence of specimen size and polymerization environment on the flexural properties of PMMA. In the first stage, specimens were cut from large pieces of commercially cast acrylic (lucite) and self-curing dental acrylic. The material properties of the cast acrylic as calculated from the results of flexural testing were not influenced by specimen size in the range of 1 X 10 X 30 to 3 X 10 X 60 mm, whereas 1-mm thick dental cement specimens had 12% (p less than 0.001) higher stress and 24% (p less than 0.001) higher strain to failure than 3-mm specimens cut from the same sample. In the second stage, self-curing dental cement and Simplex P bone cement were molded in different thicknesses. These experiments demonstrated that molding thin 1.6-mm specimens resulted in increases of 14% (p less than 0.001) in stress and 30% (p less than 0.001) in strain to failure as compared with 3.2-mm specimens, which were greater differences than those due to the specimen thickness effects alone. In the third stage, temperatures of cement were monitored during polymerization, and cements were molded at different temperatures. These results demonstrated that thicker cement samples reached higher temperatures and that cement samples polymerized at lower temperatures (21 versus 37 degrees C) had 12% (p less than 0.001) greater stress and 105% (p less than 0.001) greater strain to failure.

Bone Cements↗
PubMed1991

Glass ceramic approach to controlling the properties of a glass-ionomer bone cement.

Glass-ionomer dental cements have potential as bone cements in joint replacement surgery. However, commercially available glasses used in dental cements suffer from the loss of fluorine during the melting procedure and from phase separation of the glass upon quenching, giving rise to inter- and intra-batch variation. A model glass was examined in which minimal loss of fluorine is observed. This results in a glass whose composition is reproducible between batches. This glass will crystallize both above and below the glass transition temperature following heat treatments. Cements can be produced whose properties vary with the degree of crystallinity of the glass-ceramic. A commercial glass was also examined and was found to crystallize to an apatite phase.

Bone Cements↗
PubMed2006

The combination of ultrasound with antibiotics released from bone cement decreases the viability of planktonic and biofilm bacteria: an in vitro study with clinical strains.

OBJECTIVES: Antibiotic-loaded bone cements are used for the permanent fixation of joint prostheses. Antibiotic-loaded cements significantly decrease the incidence of infection. The objective of this study was to investigate whether the viability of bacteria derived from patients with a prosthesis-related infection could be further decreased when antibiotic release from bone cements was combined with application of pulsed ultrasound. METHODS: Escherichia coli ATCC 10798, Staphylococcus aureus 7323, coagulase-negative staphylococci (CoNS 7368 and CoNS 7391) and Pseudomonas aeruginosa 5148 were grown planktonically in suspension and as a biofilm on three different bone cements: Palacos R without gentamicin as control, gentamicin-loaded Palacos R-G and gentamicin/clindamycin-loaded Copal. The viability of planktonic and biofilm bacteria was measured in the absence and presence of pulsed ultrasound for 40 h. RESULTS: Ultrasound itself did not affect bacterial viability. However, application of pulsed ultrasound in combination with antibiotic release by antibiotic-loaded bone cements yielded a reduction of both planktonic and biofilm bacterial viability compared with antibiotic release without application of ultrasound. CONCLUSIONS: This study shows that antibiotic release in combination with ultrasound increases the antimicrobial efficacy further than antibiotic release alone against a variety of clinical isolates. Application of ultrasound in combination with antibiotic release in clinical practice could therefore lead to better prevention or treatment of prosthesis-related infections.

Anti-Bacterial Agents↗
PubMed1986

The effect of centrifugation on the fracture properties of acrylic bone cements.

In this study, centrifugation did not alter the static or cyclic fracture properties of bone cement. Tests of fracture toughness and fatigue-crack propagation of centrifuged specimens of commercial cements (with and without antibiotic additions) demonstrated no significant difference from control values. Among the cements tested, Palacos (with and without antibiotic) was found to have a significantly higher fracture toughness than either Simplex or Zimmer. We attributed this difference in fracture toughness to the higher molecular weight measured for the Palacos cements. For the tested cements, only Simplex had a significantly greater volume contraction on setting due to centrifugation. The results of our study demonstrate that centrifugation of bone cement does not improve the cement's resistance to fracture in the presence of surface imperfections, such as those found at the bone-cement interface.

Bone Cements↗
PubMed2002

Preoperative identification of a bone-cement allergy in a patient undergoing total knee arthroplasty.

Allergy to polymethyl methacrylate bone-cement or its components is unusual. Because of the potential for an inflammatory response in an allergic patient and the possibility of pain and loosening if a cemented implant is used, it is imperative to identify patients with this allergy to modify their treatment. We report the case of an otherwise healthy 60-year-old woman who needed a total knee arthroplasty and who had an allergy to methyl methacrylate bone-cement identified preoperatively. The appropriate evaluation for a patient who is suspected to have an allergy to bone-cement or its components is reviewed.

Arthroplasty, Replacement, Knee↗
PubMed2001

In vitro adherence and accumulation of Staphylococcus epidermidis RP 62 A and Staphylococcus epidermidis M7 on four different bone cements.

Bacterial resistance of Staphylococcus epidermidis, a serious pathogen of implant-related infections, to antibiotics is related to the production of a glycocalyx slime that impairs antibiotic access and the killing by host defense mechanisms. In vitro studies of different bone cements containing antibiotics, developed for the prevention of biomaterial-associated infection, could not always demonstrate complete eradication of biomaterial-adherent bacteria. We have investigated four different bone cements in regard to bacterial accumulation of a slime-producing strain RP 62 A and its isogenic mutant M7 lacking the ability to produce exopolysaccharide slime using a bacterial adhesion assay and modified Kirby-Bauer technique. A significant effect of exopolysaccharide production for the accumulation on bone cement could be demonstrated. The gentamicin/clindamycin bone cement was the only tested biomaterial that produced a large zone of bacterial inhibition in the inoculated area adjacent to the biomaterial. The bacterial adhesion was not reduced significantly and there was no correlation between zones of inhibition on blood agar plates and the quantitative adhesion assay. The clinical efficacy of the gentamicin/clindamycin bone cement must be proven in vivo.

Analysis of Variance↗
PubMed2004

In vitro testing of antimicrobial activity of bone cement.

The purpose of this study was to establish a reliable and cost-effective microplate proliferation assay for in vitro antimicrobial testing of bone cement samples. Cement samples devoid of antimicrobial agents, loaded with 2% gentamicin or with different concentrations of high-porosity silver, were incubated in a 96-well microplate with several staphylococcal, Pseudomonas aeruginosa, and Enterococcus faecium isolates exhibiting different susceptibilities to gentamicin. After being rinsed, the samples were brought into a soy medium in which adherent cells on the cement surface either were killed by the antimicrobial surface or started to release clonal counterparts. The medium was monitored in real time by recording a time proliferation curve for each well. Microplate testing revealed no antibacterial effect of plain bone cement. The antibacterial activity of gentamicin-loaded bone cement was shown by the microplate test to depend on the gentamicin susceptibilities of the strains. The effect of high-porosity silver was dose dependent. Bactericidal activity against all tested strains was found for bone cement loaded with 1% high-porosity silver. The accuracy of this new proliferation assay was shown by the high correlation between the types of proliferation curves and antibiotic susceptibility. In contrast to routine agar diffusion testing, it assesses the dynamic response of microorganisms to antimicrobial agents in biomaterials and allows high-throughput screening and detection of antimicrobial properties of poorly water-soluble compounds like silver.

Anti-Bacterial Agents↗
PubMed2000

A controlled-notch specimen to study fatigue crack initiation in bone cement.

Despite the extensive literature on the mechanical characteristics and failure properties of poly(methyl methacrylate) bone cement, little is known of its fatigue crack initiation process. The most likely in vivo bone cement fatigue crack initiation sites are internal flaws and irregularities on the bone cement surface. The stress concentration created by a flaw, and subsequently the stress state at that flaw, depends on the flaw geometry. To model the fatigue crack initiation process of a flaw, it is necessary to reproduce the stress state at that flaw. In this study, a special mold was designed to introduce notches with specific tip radii into fatigue specimens. The notch was molded into the specimen to simulate the in vivo flaw formation process. The molding method allows control of the stress concentration by specifying the notch tip radius. We created notched specimens where the tip radii of the notches ranged from "sharp" (< 3 microm) to 400 microm. The results demonstrated that notched specimens created by the special mold satisfied two necessary requirements for fatigue crack initiation studies: (1) the material microstructure at the notch tip must not be disrupted by the notching process, and (2) the notch tip stress field, determined by the notch tip geometry, must be reproducible.

Biocompatible Materials↗
PubMed2002

Predicting the failure response of cement-bone constructs using a non-linear fracture mechanics approach.

A non-linear fracture mechanics approach was used to predict the failure response of complex cement-bone constructs. A series of eight mechanical tests with a combination of tensile and shear loading along the cement-bone interface was performed. Each experiment was modeled using the finite element method with non-linear constitutive models at the cement-bone interface. Interface constitutive parameters were assigned based on the quantity of bone interdigitated with the cement. There was a strong correlation (r2 = 0.80) between experimentally measured and finite element predicted ultimate loads. The average error in predicted ultimate load was 23.9 percent. In comparison to the ultimate load predictions, correlations and errors for total energy to failure (r2 = 0.24, avg. error = 38.2 percent) and displacement at 50 percent of the ultimate load (r2 = 0.27, avg. error = 52.2 percent) were poor The results indicate that the non-linear constitutive laws could be useful in predicting the initiation and progression of interface failure of cemented bone-implant systems. However improvements in the estimation of post-yield interface properties from the quantity of bone interdigitated with cement are needed to enhance predictions of the overall failure response.

Bone Cements↗
PubMed1990

[A quantitative analysis for determining porosity of pre-compressed and vacuum-mixed bone cement].

The porosity and the mechanical strength of 64 bone cement specimens were investigated. Different types of mixing procedures were tested: 1) hand, 2) compression, 3) vacuum and 4) the combination of vacuum stirring and compression. The differences in porosity and mechanical stability are remarkable. In relation to hand-mixed bone cement all techniques are leading to a reduction in the number of cavities. Specimens made by compression are showing a confluence of several small cavities to a few large. There is only a change in the distribution of the embedded gas volume, but not a reduction. The lowest porosity is seen in vacuum mixed specimens.

Bone Cements↗
PubMed1996

Elution characteristics of vancomycin and tobramycin combined in acrylic bone-cement.

Combining two antibiotics in antibiotic-loaded bone-cement is common in clinical practice. As the effect this has on elution characteristics is unknown, an in vitro quantitative elution study was carried out. Three groups of five antibiotic-loaded cement disks were prepared and placed in individual saline baths for 5 weeks. The elution of tobramycin from the disks in the study group (containing 2.4 g tobramycin and 1.0 g vancomycin per 40-g packet of Palacos-R cement powder [Smith & Nephew Orthopaedics, Memphis, TN]) was increased by 68% over that of the tobramycin control disks (2.4 g tobramycin only) (P = .024). The release of vancomycin from the study group disks was increased by 103% over the vancomycin control disks (1.0 g vancomycin only) (P = .007). Combining two antibiotics in bone-cement improves elution of both antibiotics in vitro and may translate into enhanced elution in vivo.

Anti-Bacterial Agents↗
PubMed2004

[Stress levels in bones and bone cement in the thoracolumbar spine afer kyphoplasty. Finite element study].

The study quantified the stress levels in treated and untreated vertebral bodies following kyphoplasty. Three-dimensional FE models of treated and untreated T11, T12, L1, and L2 vertebral bodies were evaluated to examine the stress levels within the bone and bone cement. A validated T12-L1 model was used to investigate the effect of kyphoplasty treatment on adjacent vertebral stresses and strains. Using the single vertebral models, bone cement modulus changes had minimal effect on the stresses in the bone or the cement. The presence of bone cement had a minimal effect on the stress magnitudes or distribution in the adjacent T12 vertebra. This study provides quantification of the stress levels in bone cement and bone in vertebral bodies treated with kyphoplasty under in vivo-like loading conditions. The presence of bone cement immediately following kyphoplasty has only a slight effect on the stress magnitudes or distributions in adjacent vertebrae.

Biomechanical Phenomena↗
PubMed2000

Mechanical evaluation of a bio-active bone cement for total hip arthroplasty.

A new bio-active bone cement, known as CAP, has been developed as an alternative to acrylic bone cement. CAP has improved mechanical properties, with a high modulus that is over five times that of PMMA. The effects of this high modulus are examined by finite element analysis, when the CAP is used in place of PMMA to fix the femoral component in total hip prostheses. The results show a higher tensile stress of 8.76 MPa in the CAP cement, compared with 1.99 MPa in the PMMA cement. However, it is also shown that CAP has a superior fatigue strength of approximately 40 MPa, obtained from a cyclic loading test.

Arthroplasty, Replacement, Hip↗