Failure of the cement-bone interface.
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Bone Cements↗
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Fluoroscopy-based 3-D reconstruction of femoral bone cement: a new approach for revision total hip replacement.
In revision total hip replacement the removal of the distal femoral bone cement can be a time consuming and risky operation due to the difficulty in determining the three-dimensional (3-D) boundary of the cement. We present a new approach to reconstruct the bone cement volume by using just a small number of calibrated multiplanar X-ray images. The modular system design allows the surgeon to react intraoperatively to problems arising during the individual situation. When encountering problems during conventional cement removal, the system can be used on demand to acquire a few calibrated X-ray images. After a semi-automatic segmentation and 3-D reconstruction of the cement with a deformable model, the system guides the surgeon through a free-hand navigated or robot-assisted cement removal. The experimental evaluation using plastic test implants cemented into anatomic specimen of human femoral bone has shown the potential of this method with a maximal error of 1.2 mm (0.5 mm RMS) for the distal cement based on just 4-5 multiplanar X-ray images. A first test of the complete system, comparing the 3-D-reconstruction with a computed tompgraphy data set, confirmed these results with a mean error about 1 mm.
Arthroplasty, Replacement, Hip↗
Ex vivo degradation of a poly(propylene glycol-fumarate) biodegradable particulate composite bone cement.
We have developed a biodegradable particulate composite bone cement consisting of a poly(propylene glycolfumarate)-(methylmethacrylate) matrix mixed with calcium carbonate and tricalcium phosphate particulates. Previous ex vivo studies suggest that this system provides sufficient strength for a number of potential clinical applications including structural reinforcement of osseous defects, internal fixation devices for age-related fractures, and delivery of antibiotics to treat osteomyelitis. As a first step toward investigating in vivo responses to this material, we studied the influence of varied concentrations of crosslinker, accelerator, and free radical on the mechanical properties of the cement. We then developed an ex vivo degradation assay and correlated the mechanical properties of degrading cement with the temporal changes in chemical properties of both the cement and the bathing medium. The optimal cement formulation was composed of one-third poly(propylene glycolfumarate)-(methylmethacrylate), one-third calcium carbonate, and one-third tricalcium phosphate, and provided initial compressive strengths of up to 30 MPa and compressive moduli of up to 300 MPa. Degradation rates, measured by a decline in mechanical properties, dissolution of calcium from the cement, and change in pH of the bathing medium, could be controlled by changing the concentration of reactants in the matrix. Specifically, an increase in methylmeth-acrylate or increase in both methylmethacrylate and benzoyl peroxide was inversely proportional to the rate of degradation and directly proportional to the initial mechanical properties. The degradation products and environmental changes appear to be compatible with physiologic remodeling and therefore justify examination of the in vivo response to implantation of this material.
Analysis of Variance↗
Osteoconductivity and bone-bonding strength of high- and low-viscous bioactive bone cements.
A study was conducted to evaluate the osteoconductivity and bone-bonding ability of two types of bioactive bone cement, both consisting of apatite and wollastonite containing glass-ceramic powder (AW-P), fused silica glass powder (SG-P), submicron fumed silica as an inorganic filler, and bisphenol-a-glycidyl methacrylate (Bis-GMA) based resin as an organic matrix. The cements had two kinds of formulas: one (dough-type cement; designated DTC) composed of 85% (w/w) filler and 15% resin, which was developed for fixation of the acetabular component in total hip arthroplasty and could be handled manually; and one (injection-type cement; designated ITC) composed of 79% (w/w) filler and 21% resin. ITC was developed for fixation of the femoral component and, because it had a lower viscosity than DTC, could be injected. The DTC and ITC both contained 73% AW-P, 25% SG-P, and 2% fumed silica in the weight ratio of the filler component. Two other types of cement, both of which consisted of 83.3% AW-P or SG-P, 1.7% fumed silica, and 15% resin, were used as reference material (designated AWC or SGC) for a detaching test. Following the packing of bone defects in the rat tibiae with either DTC or ITC, histological examination revealed that the DTC and ITC had both directly contacted the bone and were almost completely surrounded by bone by 16 weeks after the surgery and that no marked biodegradation had occurred at 52 weeks postimplantation. Rectangular plates (2 x 10 x 15 mm) of AWC, DTC, ITC, and SGC were implanted into the metaphysis of the tibia of male rabbits and the failure load was measured by a detaching test at 10 and 25 weeks after implantation. The failure loads of AWC, DTC, ITC, and SGC were 3.65, 2.21, 2.44, and 0.04 kgf at 10 weeks and 4.87, 2. 81, 2.82, and 0.13 kgf at 25 weeks, respectively. Observation of the bone-implant interface by scanning electron microscopy and energy dispersive X-ray microanalysis revealed that all the samples except SGC formed direct contact with the bone and that only AWC-implanted tibiae had a layer of a low calcium and phosphorus level at the bone-implant interface. Results showed that DTC and ITC have excellent osteoconductivity and bone-bonding ability under non-weight-bearing conditions.
Animals↗
The effect of ethanol on acrylic bone cement.
Prosthesis loosening is a major problem associated with the use of poly(methyl methacrylate) (PMMA) bone cement that may be related to a peri-implant vacuolisation commonly observed at bone-cement interface. Methyl methacrylate (MMA) monomer may be one of the cement components partly responsible for the mentioned vacuolisation due to a cytotoxic effect associated to this compound. Alcoholism has been related to bone necrosis in predisposed individuals. Furthermore, ethanol has been shown to clean material with adherent cement debris during cleaning procedure in laboratory. Consequently, we have decided to study whether ethanol will also be related to an increased liberation of MMA from the polymer matrix. 'In vitro' release studies using PMMA plates were conducted to access the role of ethanol on the liberation of the monomer. Contact angle measurements and surface tension estimation were also carried out in order to find a possible effect of ethanol on surface cement properties. Results suggest that ethanol, even in small quantities, enhances the leaching of the monomer from the polymer matrix, but does not considerably change the wettability properties of the cement surface.
Acrylic Resins↗
[Standardization of implant materials shown by "bone cement". Comparative investigations in consideration of antibiotic admixtures (author's transl)].
Test methods for acrylic based bone-cements proposed by a draft international standard are approved by investigation of different bone cements. The cements showed different qualities and different mechanical properties. Added antibiotics slow down the polymerisation, possible influences to mechanical properties are covered by handlingcaused deviations. Pressure test and impact test are leading to different strength statements.
Anti-Bacterial Agents↗
Bioactive bone cement: effect of surface curing properties on bone-bonding strength.
The fact that bisphenol-a-glycidyl methacrylate (bis-GMA)-based cements contain an uncured surface is believed to play an important role when determining the surface curing properties of the cements. Therefore, in the present study, the bone-bonding strength of cement plates having an uncured surface on one side and a cured surface on the other side has been evaluated. These cement plates were composites of a bis-GMA-based resin with either an apatite- and wollastonite-containing glass-ceramic (AW-GC) powder or a hydroxyapatite (HA) powder, respectively designated AWC and HAC. The amount of each of these powders in a composite cement was 70 wt %. We formulate the hypothesis that the uncured surface of a cement plate is bioactive having bone-bonding properties. The goal of the present study was to indicate the bone-bonding strength of the uncured surfaces of AWC and HAC and compare the strength with the respective cured surfaces by a detaching in vivo test, as well as to histologically examine the bone-cement interface. Each plate has been implanted into the tibiae of male Japanese white rabbits, taking care to retain the surface properties, and the so-called "failure load has been measured using a detaching test followed 8 weeks after implantation. The failure load for AWC-plates at the uncured surface (2.05 +/- 1.11 kgf, n = 8) was significantly higher than AWC at its cured surface side (0.28 +/- 0.64 kgf, n = 8). The failure load for HAC-plates at the uncured surfaces (1.40 +/- 0.68 kgf, n = 8) was significantly higher than HAC at its cured surface (0.00 +/- 0.00 kgf, n = 8). Failure loads for AWC at its uncured and cured surfaces were both higher than for HAC, although not significantly. Direct bone formation has been observed histologically for both AWC and HAC on the uncured surfaces, and a Ca-P-rich layer was observed only at the uncured surface of AWC. These findings strongly suggest that uncured surfaces are useful for exposing a bioactive filler on a surface of composites, being very effective in inducing bone bonding.
Animals↗
In vitro measurement and computer modelling of the diffusion of antibiotic in bone cement.
The diffusion coefficient for a particular antibiotic (benzyl penicillin) in various types of bone cement has been calculated from direct measurement of the passage of radio-labelled penicillin through thin sections of cement at intervals over a period of 90 days, assuming the transport processes to be Fickian. Since the concentration gradient across the test sample is not uniform in the earlier stages of the experiment, a finite-difference approximation to the diffusion equation was used to take account of the transient behaviour in determining the coefficient. This method of analysis may also be used to predict the release, as a function of time, from the surface of antibiotic-loaded bone cement and from implanted pre-loaded PMMA beads used to provide antibiotic cover following bone or joint surgery. Our computer-generated predictions appear to agree very well with previously published figures arising from in vivo and in vitro studies and we conclude therefore, that Fick's Law accurately describes the process, even when the cement mix is inhomogeneous. We have by this means a reliable method by which the diffusion coefficients for various combinations of cement, antibiotic and other additives may be retrospectively determined and compared.
Anti-Bacterial Agents↗
Mechanical influences on tissue differentiation at bone-cement interfaces.
Retrieval studies have shown that tissue at the bone-cement or bone-implant interface can develop into fibrous tissue, fibrocartilage, and bone, and that tissue differentiation appears to be mechanically influenced. A prior histologic analysis of retrieved interface tissues supporting cemented Marmor unicondylar knee components found that beneath the central portion of these implants, a thick, mature layer of fibrocartilage consistently developed, whereas fibrous tissue formed beneath the prosthesis periphery and adjacent to the bone beneath the tibial spine. Finite-element analysis was used to model the interface tissue supporting a cemented Marmor tibial component and interpreted patterns of stress and strain generated in the interface according to a mechanically based tissue differentiation theory. Distortional strain and hydrostatic stress, mechanical stimuli that are hypothesized to be associated with fibrous matrix and cartilaginous matrix production, respectively, were found to correlate well with the previous histologic findings. Given the biologic environments in which the retrieved interface tissues developed, frequently applied hydrostatic stress of approximately 0.7 MPa may be sufficient to stimulate cartilaginous extracellular matrix production in the interface tissue, and frequently applied distortional strain of 10% may be sufficient to stimulate fibrous extracellular matrix production.
Biomechanical Phenomena↗
Antibiotic-impregnated bone cement: an in vitro comparative analysis.
This manuscript examines the in vitro antibacterial activity of eight different antibiotics when mixed with polymethyl methacrylate. Two different parameters are presented as being important considerations in the choice of antibiotic. One parameter is the bacterial inhibition created by the direct contact of the antibiotic-impregnated bone cement. The second parameter is the bacterial inhibition produced by diffusion of antibiotic from the bone cement into the surrounding liquid medium. These two experimental models were created to establish the contiguous and remote antimicrobial effects of antibiotic-impregnated bone cement.
Anti-Bacterial Agents↗
Strain-controlled fatigue of acrylic bone cement.
Monotonic tensile tests and tension-compression fatigue tests were conducted of wet acrylic bone cement specimens at 37 degrees C. All testing was conducted in strain control at a strain rate of 0.02/s. Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress. The number of cycles to fatigue failure was also more strongly controlled by strain amplitude than stress amplitude. Specimen porosity distribution played a major role in determining the tensile and fatigue strengths. The degree of data scatter suggests that Weibull analysis of fatigue data may be useful in developing design criteria for the surgical use of bone cement.
Acrylic Resins↗
Hydroxyapatite granules interposed at bone-cement interface in total hip replacements: histological study of retrieved specimens.
The effect of hydroxyapatite (HA) granules interposed between bone and polymethylmethacrylate (PMMA) bone cement in total hip replacement was histologically evaluated. The technique consisted of smearing 2-5 g of HA granules (straight phi = 100-300 microm) onto the bone surface just before cementing. Four specimens containing well-fixed bone-cement interface were retrieved at 1, 2, 6, and 10 years postoperatively and examined with back-scattered electron microscopy and light microscopy. The majority of HA granules were incorporated into remodeled trabeculae, and highly convoluted bone-cement interface was maintained up to 10 years. The presence of active remodeling in the adjacent bone was observed. There were no significant inflammatory or foreign body reactions against interposed HA granules. In one specimen retrieved from a patient with rheumatoid arthritis, bone formation around HA granules was limited after 1 year. These results have provided histological evidence for the significantly reduced incidence of radiolucent lines in total hip replacement with this cementing technique, reported elsewhere.
Aged↗
Plain radiographs inadequate for evaluation of the cement-bone interface in the hip prosthesis. A cadaver study of femoral stems.
To determine whether plain radiographs accurately represent the true cement-bone interlock, a comparison was made between radiographs and macroscopic morphology on cross sections of 11 human femora into which a cemented endoprosthesis had been inserted. Four femora had been retrieved postmortem from patients with a hip arthroplasty, and seven cadaver femora were cemented under varying conditions. All the femora were radiographed and then cut for macroscopic inspection of the cement-bone interface with respect to gross interposition, depth of cement penetration, integrity of the bone bed, and lamellation of the cement.
Bone Cements↗
Fatigue testing and performance of acrylic bone-cement materials: state-of-the-art review.
Over the past three decades or so, a very large volume of literature has been generated on the impact of an assortment of variables on the fatigue lifetimes of a large number of acrylic bone-cement formulations. In the present article, this literature is examined critically to reveal areas of agreement, areas of disagreement, as well as a welter of underexplored and unexplored topics. For example, there is unanimity of support for the notion that an increase in the molecular weight of the powder constituents or the fully cured cement leads to an increase in the cement's fatigue life, whereas there is disagreement as to whether vacuum mixing the cement constituents leads to an increase in the fatigue life of the fully cured cement (relative to the hand-mixed counterpart). Among the underexplored topics is systematic study of the effect of test frequency on the fatigue results, whereas determination of the optimal concentration of the antibiotic in an antibiotic-loaded cement is an example of the unexplored topics. It is pointed out that resolving the controversies, addressing the underexplored topics, and filling the lacunae will allow comprehensive evaluations of acrylic bone-cement materials to be made. This enhanced body of knowledge will prove invaluable in the continued use of acrylic bone cement as the anchoring agent in cemented arthroplasties.
Animals↗
In vitro testing of the potential for orthopedic bone cements to cause apoptosis of osteoblast-like cells.
The purpose of this study was to investigate in vitro the apoptosis- and/or necrosis-inducing potential of polymethylmethacrylate (PMMA)-based bone cements for prosthetic surgery. Four bone cements widely used in orthopedics were tested as extracts onto osteoblast-like MG-63 cells and for comparison, HL-60 cells, which are remarkably sensitive to apoptotic stimuli. Neutral red uptake (NRU) was used to measure cell viability while Hoechst 33258 staining was used to detect DNA content. Apoptosis was characterized using a BrdU-based ELISA assay for DNA fragmentation and examined by fluorescence microscopy using acridine orange and propidium iodide staining of nuclei. The generation of reactive oxygen species (ROS), which could mediate apoptosis, was verified using dichlorofluorescein-diacetate (DCFH-DA) oxidation to DCF. After 24 h of challenge of the cells with the four cement extracts, the viability of either MG-63 or HL-60 cells was found to be unaltered, as recorded by NRU. Apoptotic cell death was induced by three cements in HL-60, whereas MG-63 cells were significantly affected by the four cements tested: the finding of DNA fragments both in the cytoplasm and supernatants of MG-63 after 24 h demonstrated that these cells underwent late-apoptosis secondary necrosis. Fluorescent staining of the nuclei confirmed the results obtained with the ELISA test. Oxygen free radicals were elicited by two cements in HL-60 cells, while MG-63 did not generate ROS in response to cements. This study helps to gain more insight into the mechanism of cell death induced by PMMA-based cements and suggests apoptosis of osteoblasts as a part of the tissue reaction around cemented prostheses.
Apoptosis↗
Effect of intramedullary bone cement fixation on fracture healing.
The effect of bone cement implanted in the marrow cavity on the fracture healing process was assessed in rabbits with an experimentally induced transverse fracture of the tibia. In the cement treated animals external callus formation occurred slowly, due to poor bone-forming capacity of the endosteum and a failure to form a bridge at the fracture site. Numerous resorption cavities then occurred in the cortical bone. The microangiogram revealed a lack of blood supply from the marrow in the cement treated group. Thus, the histological changes were probably due to obstruction of the marrow blood supply to cortical and endosteal bone.
Animals↗
Antibiotic impregnated bone cement in total hip arthroplasty. An in vivo comparison of the elution properties of tobramycin and vancomycin.
A prospective in vivo quantification was performed to measure the elution of tobramycin and vancomycin antibiotics from two commonly used bone cements. Forty patients were divided into four groups: Group I, tobramycin-Simplex; Group II, tobramycin-Palacos-R; Group III, vancomycin-Simplex; and Group IV, vancomycin-Palacos-R. Antibiotic levels were measured from hemovac wound drainage, urine, and serum and compared with control groups who received either intravenous tobramycin or vancomycin. There were no significant differences in daily mean tobramycin levels in hemovac samples between Groups I and II. Tobramycin hemovac levels from Groups I and II were significantly higher than the tobramycin control group. Similarly, no differences were seen in daily mean vancomycin levels of the hemovac samples between Group III and IV; however, the intravenous vancomycin control group had significantly higher levels in the hemovac fluid than Groups III or IV. Tobramycin in the hemovac fluid from Groups I and II was highly bioactive against the control organism. Vancomycin in the hemovac fluid from Groups III and IV had variable bioactivity against the control organism. In 30% of the cases, no vancomycin was detected in the hemovac fluid, and in these cases, the hemovac fluid had no effect on the control organism. Tobramycin elutes to give adequate local tissue levels and releases antibiotic effects when used in an antibiotic bone cement combination. Vancomycin has variable elution properties and is not a predictable additive for the bone cements tested.
Bone Cements↗
The osteolytic response of macrophages to challenge with particles of Simplex P, Endurance, Palacos R, and Vertebroplastic bone cement particles in vitro.
The capacity of clinically relevant wear particles from Simplex P, Endurance, Vertebroplastic and Palacos R bone cements to activate macrophages to produce cytokines and bone resorbing activity in vitro was compared. Cement particles were generated aseptically by using a pin on plate rig. The particles were irregular in shape, and there were no significant differences in the particle characteristics of the different bone cement types (mean equivalent circle diameter range 0.225--0.36 mum, mean area range 0.048--0.063 microm(2), mean aspect ratio range 1.481--1.593, and mean length 0.412--0.523 microm). The volumetric concentration of particles in the 0.1- to 1.0-microm size range was 85% Palacos R, 82% Endurance, 80% Simplex P, and 77% Vertebroplastic. Particles were cultured with C3H macrophages at 100 microm(3) per cell for 24 h. Cytokines were determined by enzyme-linked immunosorbent assay and bone resorption (BR) measured by Ca(45) release from murine calvarias. Particles of Palacos R and Endurance stimulated enhanced production of TNF-alpha, IL-1-beta, and IL-6 (p<0.05; ANOVA). Simplex P particles only stimulated IL-1-beta (p<0.05; ANOVA). Vertebroplastic particles did not stimulate production of any of the cytokines. Particles of Palacos R generated the highest BR (1.38), but this did not reach statistical significance. The BRs for the other bone cements were no greater than the control. Hence, compared with the same volumetric concentrations, particles of Palacos R and Endurance were the most, and particles of Vertebroplastic were the least biologically reactive.
Animals↗