Tensile properties of a bone cement containing non-ionic contrast media

A Three-Parameter Weibull Distribution Method to Determine the Fracture Property of PMMA Bone Cement

Poly (methyl methacrylate) (PMMA) bone cement is an excellent biological material for anchoring joint replacements. Tensile strength ft and fracture toughness KIC have a considerable impact on its application and service life. Considering the variability of PMMA bone cement, a three-parameter Weibull distribution method is suggested in the current study to evaluate its tensile strength and fracture toughness distribution. The coefficients of variation for tensile strength and fracture toughness were the minimum when the characteristic crack of PMMA bone cement was αch∗=8dav. Using the simple equation αch∗=8dav and fictitious crack length Δαfic=1.0dav, the mean value μ (= 43.23 MPa), minimum value ftmin (= 26.29 MPa), standard deviation σ (= 6.42 MPa) of tensile strength, and these values of fracture toughness (μ = 1.77 MPa⋅m1/2, KICmin = 1.02 MPa⋅m1/2, σ = 0.2644 MPa⋅m1/2) were determined simultaneously through experimental data from a wedge splitting test. Based on the statistical analysis, the prediction line between peak load Pmax and equivalent area Ae1Ae2 was obtained with 95% reliability. Nearly all experimental data are located within the scope of a 95% confidence interval. Furthermore, relationships were established between tensile strength, fracture toughness, and peak load Pmax. Consequently, it was revealed that peak load might be used to easily obtain PMMA bone cement fracture characteristics. Finally, the critical geometric dimension value of the PMMA bone cement sample with a linear elastic fracture was estimated.

Wear Behaviour of the Pair Ti–6Al–4V–UHMWPE of Acrylic Bone Cements Containing Different Radiopaque Agents

The objective of this study was to improve the wear behaviour of acrylic bone cements by substituting the conventional inorganic radiopaque agents (BaSO4, ZrO2) for different iodinated radiopaque monomers which can co-polymerize with the methyl methacrylate monomer, MMA. To this aim, the wear behaviour of the pair Ti–6Al–4V–UHMWPE (ultra high molecular weight polyethylene) was studied in the absence and in the presence of cement particles (the third body).

Comparison of two methods of fatigue testing bone cement

Two different methods have been used to fatigue test four bone cements. Each method has been used previously, but the results have not been compared. The ISO 527-based method tests a minimum of 10 samples over a single stress range in tension only and uses Weibull analysis to calculate the median number of cycles to failure and the Weibull modulus. The ASTM F2118 test regime uses fewer specimens at various stress levels tested in fully reversed tension-compression, and generates a stress vs. number of cycles to failure (S-N) or Wöhler curve. Data from specimens with pores greater than 1mm across is rejected. The ISO 527-based test while quicker to perform, provides only tensile fatigue data, but the material tested includes pores, thus the cement is closer to cement in clinical application. The ASTM regime uses tension and compression loading and multiple stress levels, thus is closer to physiological loading, but excludes specimens with defects obviously greater than 1mm, so is less representative of cement in vivo. The fatigue lives between the cements were up to a factor 15 different for the single stress level tension only tests, while they were only a factor of 2 different in the fully reversed tension-compression testing. The ISO 527-based results are more sensitive to surface flaws, thus the differences found using ASTM F2118 are more indicative of differences in the fatigue lives. However, ISO 527-based tests are quicker, so are useful for initial screening.

Alternative acrylic bone cement formulations for cemented arthroplasties: present status, key issues, and future prospects

All the commercially available plain acrylic bone cement brands that are used in cemented arthroplasties are based on poly (methyl methacrylate) and, with a few exceptions, have the same constituents. It is well known that these brands are beset with many drawbacks, such as high maximum exotherm temperature, lack of bioactivity, and volumetric shrinkage upon curing. Furthermore, concerns have been raised about a number of the constituents, such as toxicity of the activator (N,N,dimethyl-p-toluidine) and possible involvement of the radiopacifier (BaSO(4) or ZrO(2) particles) in third-body wear. Thus, over the years, many research efforts have been expended to address these drawbacks, culminating in a large number of alternative formulations, which may be grouped into 16 categories. Although there are a number of reviews of the large literature that now exists on these formulations, each covers only some of the categories and none contains a detailed discussion of the germane issues. The objective of the present work, therefore, was to present a comprehensive and critical review of the whole field. In addition to succinct descriptions of the cements in each category, there are explicative summaries of literature reports, a detailed discussion of several key issues surrounding the potential for use of these cements in cemented arthroplasties, and a presentation of numerous ideas for future studies.

Effect of iodixanol particle size on the mechanical properties of a PMMA based bone cement

Iodixanol (IDX) is a water soluble opacifier widely used in radiographical examinations of blood vessels and neural tissue, and it has been suggested as a potential contrast media in acrylic bone cement. The effect of the iodixanol particle size on the polymerisation process of the bone cement, the molecular weight, and the quasi-static mechanical properties have been investigated in this article. The investigation was performed using radiolucent Palacos powder mixed with 8 wt% of iodixanol with particle sizes ranging from 3 to 20 microm MMD, compared with commercial Palacos R (15 wt% ZrO2) as control. Tensile, compressive and flexural tests showed that smaller particles (groups with 3, 4, and 5 microm particles) resulted in significantly lower mechanical properties than the larger particles (groups with 15, 16, and 20 microm particles). There was no difference in molecular weight between the groups. The thermographical investigation showed that the IDX cements exhibit substantially lower maximum temperatures than Palacos R, with the 4 microm IDX group having the lowest maximum temperature. The isothermal and the constant rate differential scanning calorimetry (DSC) did not show any difference in polymerisation heat (DeltaH) or glass transition temperature (Tg) between radiolucent cement, or cement containing either IDX, or ZrO2. The findings show that the particle size for a bone cement containing iodixanol should be above 8 microm MMD.

Palamed G compared with Palacos R with gentamicin in Charnley total hip replacement. A randomised, radiostereometric study of 60 HIPS

We performed a randomised, radiostereometric study comparing two different bone cements, one of which has been sparsely clinically documented. Randomisation of 60 total hip replacements (57 patients) into two groups of 30 was undertaken. All the patients were operated on using a cemented Charnley total hip replacement, the only difference between groups being the bone cement used to secure the femoral component. The two cements used were Palamed G and Palacos R with gentamicin. The patients were followed up with repeated clinical and radiostereometric examinations for two years to assess the micromovement of the femoral component and the clinical outcome. The mean subsidence was 0.18 mm and 0.21 mm, and the mean internal rotation was 1.7 degrees and 2.0 degrees at two years for the Palamed G and Palacos R with gentamicin bone cements, respectively. We found no statistically significant differences between the groups. Micromovement occurred between the femoral component and the cement, while the cement mantle was stable inside the bone. The Harris hip score improved from a mean of 38 points (14 to 54) and 36 (10 to 57) pre-operatively to a mean of 92 (77 to 100) and 91 (63 to 100) at two years in the Palamed G and Palacos R groups, respectively. No differences were found between the groups. Both bone cements provided good initial fixation of the femoral component and good clinical results at two years.

In vitro and in vivo biological responses to a novel radiopacifying agent for bone cement

Iodixanol (IDX) and iohexol (IHX) have been investigated as possible radiopacification agents for polymethylmethacrylate (PMMA) bone cement, to replace the currently used barium sulphate and zirconia. IDX and IHX are both water-soluble iodine-based contrast media and for the last 20 years have been used extensively in clinical diagnostic procedures such as contrast media enhanced computed tomography, angiography and urography. One of the major reasons to remove the current radiopacifying agents is their well-documented cytotoxicity and their potential to increase bone resorption. Using in vitro bone resorption assays, the effect of PMMA particles plus IDX or IHX to induce osteoclast formation and lacunar resorption on dentine slices has been investigated. These responses have been compared with the in vitro response to PMMA particles containing the conventional radiopacifying agents, that is, barium sulphate and zirconia. In parallel, the in vivo reaction, in terms of new bone formation, to particles of these materials has been tested using a bone harvest chamber in rabbit tibiae. In vitro cell culture showed that PMMA containing IHX resulted in significantly less bone resorption than PMMA containing the conventional opacifiers. In vivo testing, however, showed no significant differences between the amounts of new bone formed around cement samples containing the two iodine-based opacifying agents in particulate form, although both led to fewer inflammatory cells than particles of PMMA containing zirconia. Our results suggest that a non-ionic radiopacifier could be considered as an alternative to the conventional radiopacifying agents used in biomaterials in orthopaedic surgery.

Influence of the radiopacifier in an acrylic bone cement on its mechanical, thermal, and physical properties: Barium sulfate-containing cement versus iodine-containing cement

In all acrylic bone cement formulations in clinical use today, radiopacity is provided by micron-sized particles (typical mean diameter of between about 1 and 2 microm) of either BaSO(4) or ZrO(2). However, a number of research reports have highlighted the fact that these particles have deleterious effects on various properties of the cured cement. Thus, there is interest in alternative radiopacifiers. The present study focuses on one such alternative. Specifically, a cement that contains covalently bound iodine in the powder (herein designated the I-cement) was compared with a commercially available cement of comparable composition (C-ment3), in which radiopacity is provided by BaSO(4) particles (this cement is herein designated the B-cement), on the basis of the strength (sigma(b)), modulus (E(b)), and work-to-fracture (U(b)), under four-point bending, plane-strain fracture toughness (K(IC)), Weibull mean fatigue life, N(WM) (fatigue conditions: +/-15 MPa; 2 Hz), activation energy (Q), and frequency factor (ln Z) for the cement polymerization process (both determined by using differential scanning calorimetry at heating rates of 5, 10, 15, and 20 K min(-1)), and the diffusion coefficient for the absorption of phosphate-buffered saline at 37 degrees C (D). For the B-cement, the values of sigma(b), E(b), U(b), K(IC), N(WM), Q, ln Z, and D were 53 +/- 3 MPa, 3000 +/- 120 MPa, 108 +/- 15 kJ m(-3), 1.67 +/- 0.02 MPa check mark m, 7197 cycles, 243 +/- 17 kJ mol(-1), 87 +/- 6, and (3.15 +/- 0.94) x 10(-12) m(2) s(-1), respectively. For the I-cement, the corresponding values were 58 +/- 5 MPa, 2790 +/- 140 MPa, 118 +/- 45 kJ m(-3), 1.73 +/- 0.11 MPa check mark m, 5520 cycles, 267 +/- 19 kJ mol(-1), 95 +/- 9, and (3.83 +/- 0.25) x 10(-12) m(2) s(-1). For each of the properties of the fully cured cement, except for the rate constant of the polymerization reaction, at 37 degrees C (k'), as estimated from the Q and ln Z results, there is no statistically significant difference between the two cements. k' for the I-cement was about a third that for the B-cement, suggesting that the former cement has a higher thermal stability. The influence of various characteristics of the starting powder (mean particle size, particle size distribution, and morphology) on the properties of the cured cements appears to be complex. When all the present results are considered, there is a clear indication that the I-cement is a viable candidate cement for use in cemented arthroplasties in place of the B-cement.

Bone cement X-ray contrast media: A clinically relevant method of measuring their efficacy

It is important to compare different contrast media used in bone cement according to their ability to attenuate X-rays and thereby produce image contrast between bone cement and its surroundings in clinical applications. The radiopacity of bone cement is often evaluated by making radiographs of cement in air at an X-ray tube voltage of 40 kV. We have developed a method for ranking contrast media in bone cement simulating the clinical situation, by (1) choosing the same X-ray tube voltage as used in clinical work, and (2) using a water phantom to imitate the effects of the patients' soft tissue on the X-ray photons. In clinical work it is desirable to have low radiation dose, but high image contrast. The voltage chosen is a compromise, because both dose and image contrast decrease with higher voltage. Three contrast media (ZrO(2), BaSO(4), and Iodixanol) have been compared for degree of "image contrast." Comparing 10 wt % contrast media samples at an X-ray tube voltage of 40 kV, ZrO(2) produced higher image contrast than the other media. However, at 80 kV, using a water phantom, the results were reversed, ZrO(2) produced lower image contrast than both BaSO(4) and Iodixanol. We conclude that evaluations of contrast media should be made with voltages and phantoms imitating the clinical application.

Water uptake and release from iodine-containing bone cement

Water uptake and release characteristics of PMMA cement containing the water-soluble contrast media iohexol or iodixanol have been investigated. The water uptake study revealed that iohexol had the highest uptake of water (3.7%) and that iodixanol had an uptake close to that of Palacos R (2.3% and 1.9%). The curves obtained showed the materials to follow classic diffusion theory, with an initial linearity with respect to t(1/2) making it possible to calculate the diffusion coefficients. This showed iohexol to have the lowest diffusion coefficient, Palacos R the highest, and iodixanol close to that of Palacos R. The release study showed that more iohexol than iodixanol was released from the bone cement; the long-term release was above 25 microg/mL for iohexol compared to slightly above 10 microg/mL for iodixanol. A microCT investigation showed that the risk of developing an observable radiolucent zone is negligible.

A radiopaque polymeric matrix for acrylic bone cements

As part of the search for an alternative to inorganic radiopaque agents, this work studies the possibility of modifying bone cement formulations by incorporating a radiopaque monomer, that is, 4-iodophenol methacrylate (IPMA), in the liquid phase. The monomer was synthesized in the laboratory, and cements were prepared by the standard method. The influence on the different cement characteristics of various monomer concentrations was studied. It was seen that the setting time decreased as the percentage of monomer increased. The radiopacity attained in the 15 vol.% IPMA formulations was about the same as that for a cement containing 10 wt.% barium sulphate. Dynamic and static mechanical properties were measured. The materials did not show significant differences in the glass transition temperature. However, static mechanical properties showed enhanced compressive strength, tensile strength, and elastic modulus with respect to conventional cements formulated with barium sulphate. Histological studies showed a good response of muscular tissue to implanted specimens.