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PubMed1993

Microstructural pathway of fracture in poly(methyl methacrylate) bone cement.

Mechanical failure of poly(methyl methacrylate) (PMMA) bone cement is linked to failure of cemented total joint prostheses. An essential step to minimize, if not eliminate, cement fracture is to understand the material characteristics controlling fracture resistance. At least four phases of bone cement can be identified that may affect the damage zone formation: pre-polymerized beads, interbead matrix polymer, BaSO4, and porosity. Gel permeation chromatography (GPC) was used to determine the molecular weight (MW) distributions of the two polymer phases. Mechanical testing, scanning electron microscopy and light microscopy were used to analyse fracture mechanisms. Fatigue crack propagation of bone cement was distinctly different from rapid crack propagation. Microcracks defined the damage zone for fatigue fracture. The microcracks developed in the interbead matrix and not through the pre-polymerized beads. Light microscopy revealed evidence of craze formation on surfaces of fractured beads during rapid fracture, but not on fatigue surfaces. GPC analysis indicated an increase in MW from the bead phase alone to the fully cured bone cement, indicating a greater MW in the interbead matrix polymer. Increases of 36 and 176% were measured for two different bone cements, but the bulk of the polymer has an MW of less than 1 x 10(6). Three factors were suggested to explain why the microcracks seem to prefer to grow in the interbead matrix: the presence of BaSO4, shrinkage during the curing process, and the different polymerization processes of the bead and the interbead polymers.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1979

The morphology of polymethylmethacrylate (PMMA) bone cement: surface structures and causes of their origin.

This study deals with the correlation between the polymerizing bone cement and the surrounding tissue. The surface structures of bone cements, polymerized in air, in tissue medium (in vitro) and in human bone during implantation were investigated and compared with the contours of the tissue of the implant bed. Basing on the dimensional differences it was differentiated between contours of 1st order and 2nd order: contours of 1st order are within the macroscopic range, contours of 2nd order within the microscopic range. The surface of bone cement polymerized in living human tissue differed essentially from samples polymerized under laboratory conditions. The differences are to be seen macroscopically in the coarse relief as well as microscopically in the shape and the connection of the superficial methylmethacrylate beads. Bone cements, polymerized in air show an ideal, even and closed surface. Bone cements, polymerized in tissue medium exhibit macroscopically some wrinkles, in the microscopic range their contours are either closed (samples prepolymerized at 22 degrees C) or partly open and partly closed (samples prepolymerized at 24 degrees C). The surface of bone cement implants, retrieved from human bones are characterized macroscopically by a marked wrinkled and papillary relief, microscopically by flattened beads, and most often by an irregular, rough and open surface with isolated beads giving almost the impression of a porous surface structure. The character of the surface of the bone cement originates from external, mechanical influences, from changes in the volume of the bone cement and from effects of the surrounding tissues. The surface of the bone cement implanted in human bone conforms exactly with the contour of the adjacent tissue; the tissue contour is infact a negative of the cement surface. The incomplete connection between the superficial PMMA beads seems to be of some practical value: In areas, where the PMMA beads are largely isolated, the mechanical stressability of the "polymer composite" is relatively low. Under high load, beads and bead-clusters may break off the surface. Shattering of bone cement implants possibly may start from such an open, porous surface area where PMMA beads are extensive isolated.

Acrylic Resins↗
PubMed1997

In-situ polymerization behaviour of bone cements.

The polymerization behaviour of bone cements during total hip replacements is characterized by a fast and highly non-isothermal bulk reaction. In the first part of this paper the reaction kinetics are analysed by calorimetric analysis in order to determine the rates of polymerization in isothermal and non-isothermal conditions. A phenomenological kinetic model, accounting for the effects of autoacceleration and vitrification, is presented. This model, integrated with an energy balance, is capable of predicting the temperature across the prosthesis, the cement and the bone and the degree of reaction in the cement, during in situ polymerization. The temperature and the degree of reaction profiles are calculated, as a function of the setting time, taking into account the system geometry, the thermal diffusivity of bone, prosthesis and cement, and the heat rate generated by the reaction according to the kinetic model. Material properties, boundary and initial conditions are the input data of the heat transfer model. Kinetic and heat transfer models are coupled and a numerical solution method is used. The model is applied in order to study the effects of different application procedures on temperature and degree of reaction profiles across the bone-cement-prosthesis system.

Journal Article↗
PubMed1991

The release of gentamicin after total hip replacement using low or high viscosity bone cement. A prospective, randomized study.

Low viscosity bone cement is expected to give improved long term fixation of prosthetic components by increased intrusion into cancellous bone. Fixation is more difficult to achieve after revision for infection because of the inferior quality of the bone. We have compared the amount of gentamicin released from high viscosity and low viscosity bone cements in 41 patients undergoing total hip replacement. The concentration of gentamicin in serum and the wound secretion, and the amount recovered from the urine, was about three times higher for low viscosity cement. A possible explanation for this is an increase in surface area of the cement body because of improved intrusion of cement into bone. The improved mechanical fixation and the high concentration of gentamicin of the bone cement interface favours the use of low viscosity cement, especially in revision for deep infection.

Aged↗
PubMed2004

The characteristics of a hydroxyapatite-chitosan-PMMA bone cement.

In this study, we propose a new bioactive bone cement (BBC), composed of natural bone powder (hydroxyapatite; HA), chitosan powder, and the currently available polymethylmethacrylate (PMMA) bone cement, for use in orthopedic surgeries such as vertebroplasty or as bone filler. Three types of BBCs (BBC I, BBC II, and BBC III) were prepared with different composition ratios. In vitro tests and animal studies were performed with the new BBCs, and with a currently available commercial PMMA bone cement. Surface morphology, chemical composition, changes in pH over time, exothermic temperatures, intrusion, and cellular responses were investigated in vitro. Scanning electron microscopy (SEM) and radiological and histological examinations were performed in animal studies. The results showed that the major components of the BBCs were C, O, Ca, P, Cl, Si, S, Ba, and Mg. The pH values of the BBCs decreased after 1 day, but eventually recovered to 7.2-7.4. The water absorbency, weight loss, and porosity of the BBCs were higher than those of pure PMMA, but the compressive Young's modulus and the ultimate compressive strength (UCS) of the BBCs were lower than those of pure PMMA. The exothermic temperatures of the BBCs were considerably lower than that of pure PMMA. BBC II and III required longer times to solidify than did pure PMMA. Intrusion tests showed that the BBCs were more intrusive than was pure PMMA. Cell proliferation tests demonstrated that BBC II was preferable to pure PMMA for cell attachment and proliferation. No cytotoxic characteristics were found associated with any of the BBCs. In animal tests, BBC II was more biocompatible and osteoconductible than was pure PMMA. The results of in vitro and animal studies indicated that the proposed BBCs have potential clinical application as replacements for the pure PMMA bone cements currently in use.

Animals↗
PubMed2001

Mixing systems and the effects of vacuum mixing on bone cement.

The aim of a good cement mix is to produce bone cement that has the best mechanical properties possible in order that it can carry out its load transfer role successfully over the lifetime of the implant. The data presented shows that vacuum mixing reduces the cement porosity, which results in improved strength, and resistance to creep deformation and fatigue failure in the bone cement. It seems, however, that eliminating a high degree or all of the cement porosity may be detrimental because it leads to greater shrinkage and cracking in the material. A moderate vacuum level will improve the mechanical properties, but reduce the risk of thermal shrinkage and cracking which is seen at higher vacuum levels. In addition, the mixer design has a significant influence on the quality of the cement produced, affecting porosity, unmixed powder and subsequently the mechanical properties of the material. In the next issue we will be concluding this series of articles by covering the importance of temperature and its effects on the phases of the cement polymerisation process. Bone cement training courses are being run within hospitals by Summit Medical as part of our commitment to enhancing the skills of the perioperative practitioner and to ensuring the best long-term outcome for the patient.

Biomechanical Phenomena↗
PubMed1997

Influence of delayed injection time on the creep behavior of acrylic bone cement.

It has been proposed that creep of acrylic bone cement may contribute to loosening of cemented total joint replacements. If true, it is important that factors affecting creep of bone cement are identified. The objective of this study was to evaluate the effect of an operator-controlled variable, injection time, on the creep behavior of acrylic bone cement. Results from this investigation showed that injection time significantly (p < 0.0001) influenced creep behavior of bone cement. "Delayed" injection time of acrylic bone cement increased creep by approximately 5 times in 24 h compared to specimens prepared according to standard injection procedures.

Acrylates↗
PubMed2006

Strontium-containing hydroxyapatite bioactive bone cement in revision hip arthroplasty.

Clinical outcome of cemented implants to revision total hip replacement (THR) is not as satisfactory as primary THR, due to the loss of bone stock and normal trabecular pattern. This study evaluated a bioactive bone cement, strontium-containing hydroxyapatite (Sr-HA) bone cement, in a goat revision hip hemi-arthroplasty model, and compared outcomes with polymethylmethacrylate (PMMA) bone cement. Nine months after operation, significantly higher bonding strength was found in the Sr-HA group (3.36+/-1.84 MPa) than in the PMMA bone cement group (1.23+/-0.73 MPa). After detached from the femoral component, the surface of PMMA bone cement mantle was shown relatively smooth, whereas the surface of the Sr-HA bioactive bone cement mantle was uneven, by SEM observation. EDX analysis detected little calcium and no phosphorus on the surface of PMMA bone cement mantle, while high content of calcium (14.03%) and phosphorus (10.37%) was found on the surface of the Sr-HA bone cement mantle. Even higher content of calcium (17.37%) and phosphorus (10.84%) were detected in the concave area. Intimate contact between Sr-HA bioactive bone cement and bone was demonstrated by histological and SEM observation. New bone bonded to the surface of Sr-HA cement and grew along its surface. However, fibrous tissue was observed between PMMA bone cement and bone. The results showed good bioactivity of Sr-HA bioactive bone cement in this revision hip replacement model using goats. This in vivo study also suggested that Sr-HA bioactive bone cement was superior to PMMA bone cement in terms of bone-bonding strength. Use of bioactive bone cement may be a possible solution overcoming problems associated with the use of PMMA bone cement in revision hip replacement.

Animals↗
PubMed2000

Validation and in vitro characterization of antibiotic-loaded bone cement release.

Antibiotic-loaded polymeric bone cement is used in orthopedic surgery to deliver local high concentrations of antibiotics to the tissues. The precise mechanism by which antibiotic is released from the polymeric matrix is still not very well known. This research was conducted to investigate the in vitro drug release behavior of antibiotic from acrylic bone cement. A spectrophotometric method for the quantitative analysis of gentamicin sulfate using o-phtaldialdehyde as a derivatizing reagent was thoroughly validated, in order to assure a minimum quality level of the measures. The method proved to be quick, reliable, less expensive than methods such as polarization fluorescence immunoassay and others, and therefore more convenient for the routine analysis of the numerous samples generated during in vitro liberation assays. The release of gentamicin from commercial CMW1 acrylic bone cement samples was investigated following proposed in vitro release experiments.

Algorithms↗
PubMed1994

Failure of the cement-bone interface. A consequence of strengthening the cement-prosthesis interface?

We report the early failure, at a mean of 37 months, of 17 femoral prostheses due to aseptic loosening at the cement-bone interface. In every case the prosthesis had been manufactured with a surface coating designed to enhance the strength of the cement-prosthesis interface. It is postulated that improving the bond at the cement-prosthesis interface may transfer increased stress to the cement-bone interface and cause early failure at that interface.

Adult↗
PubMed2004

Methyl-methacrylate bone cement surface does not promote platelet aggregation or plasma coagulation in vitro.

Leakage of viscous bone cement into venous blood possibly resulting in pulmonary embolism may occur during percutaneous vertebroplasty. Our aim was to study if bone cement surface or cement liquid component could induce platelet aggregation or plasma coagulation in vitro. Two types of commonly used methyl-methacrylate bone cement, Palacos (Heraeus Kulzer, Germany) and Vertebroplastic (DePuy, Acro Med, England), were smeared on thin glass slides that were inserted over the bottom of cuvettes immediately or after 24 h, and platelet aggregation was recorded over 10 min. Bone cement liquid component, containing methyl-methacrylate monomer and N,N-dimethyl-p-toluidine, was tested in 2% and 4% final concentration. Partial thromboplastin time (PTT) was determined by the hook method in the presence of bone cement-smeared glass slides or 6% bone cement liquid. Both types of bone cement, either fresh or aged, did not promote platelet aggregation, whereas collagen-coated glass slides induced substantial platelet aggregation (65 +/- 37%). On the other hand, bone cement liquids reduced platelet aggregation induced by collagen solution to an average of less than 15% (p < 0.01). Bone cement, fresh or aged, had no effect on PTT, but bone cement liquids significantly prolonged PTT: median and 1st-3rd interquartile range 149 (96-171) s for Vertebroplastic and 132 (99-194) s for Palacos, p = 0.03 for both comparisons with normal pool plasma without additives that had PTT of 69 (62-71) s. We conclude that the surface of fresh or aged bone cement is not thrombogenic in vitro. The bone cement liquid inhibits platelet aggregation and plasma clotting in relatively high concentrations that cannot be expected in vivo.

Blood Coagulation↗
PubMed1981

[A study on the mechanical properties of bone cement (methylmethacrylate) and its strength alteration in vivo (author's transl)].

UNLABELLED: Bone cement (Methylmethacrylate) is now extensively used for the fixation of various endoprostheses in orthopaedic surgery. Although considerable number of works have been accumulated on the use of this material, relatively little is known about its basic characteristics such as inherent physical properties and the strength alteration in vivo. In recent years, loosening of the prosthesis has become one of the major problems, jeopardizing the use of the prosthesis in conjunction with the bone cement. The aim of this study is to investigate the mechanical properties of the commonly available bone cements and, particularly, to see any chronological deterioration of the material in vivo. METHODS: 1. For the study of the mechanical properties, dumbbell-shaped test pieces were made of three different types of commercially available bone cement (Surgical Simplex, CMW and Palacos R) and tested under tension load using Shimazu Autograph in a temperature and moisture controlled room (Experiment I). 2. The same test pieces (Surgical Simplex and CMW) were imbedded in the paravertebral muscle of rabbits for one, six and sixteen months and, then, tested in the same fashion as in Experiment I (Experiment II). 3. The fracture surface of the test piece after the tension load testing was examined under a scanning electron-microscope to find any changes before and after the imbedding (Experiment III). RESULTS: 1. The bone cement showed a viscoelastic behavior under the tension load in vitro. 2. The modulus of elasticity was the smallest in Palacos R which showed the greatest amount of viscoelastic deformation in vitro. 3. The longer was the imbedded period, the weaker was the tensile strength. The amount of viscoelastic deformation tended to decrease with time, which resulted in the decrease of the total amount of deformation. The modulus of elasticity was the smallest in the sixteen week group in both Surgical Simplex and CMW. 4. The scanning electromicroscopic studies failed to reveal any significant changes on the fracture surface after the imbedding. CONCLUSION: In view of this considerable strength alteration of the bone cement in vivo, the author considers this would be an important factor leading the prosthesis into loosening other than the hitherto proposed various factors such as chemical damage of the bone by the monomer, thermal bone necrosis by the polymerization heat and fatigue fracture of the bone adjacent to the bone cement. While the improved technique in the use of the bone cement is mandatory, the author stressed the importance of further research into the better material or method for the interface between the bone and the prosthesis.

Animals↗
PubMed1992

[Results of using bone cement and phenol lavage in the surgical management of giant cell bone tumors].

Authors report on experiences gained with phenol lavage used as adjuvant and filling with bone cement in the surgical treatment of giant cell tumors of the bone. The effect of the adjuvant therapy was a considerable decrease in the rate of relapses: in 11 patients 1 relapse was found only in contrary to the 15 relapses in the control material (41 per cent) after 36 excochleations. They think that with adequate indications both the phenol lavage and filling with bone cement are useful supplements to the surgical therapy.

Adolescent↗
PubMed2004

Investigation of fatigue crack growth in acrylic bone cement using the acoustic emission technique.

Failure of the bone cement mantle has been implicated in the loosening process of cemented hip stems. Current methods of investigating degradation of the cement mantle in vitro often require sectioning of the sample to confirm failure paths. The present research investigates acoustic emission as a passive experimental method for the assessment of bone cement failure. Damage in bone cement was monitored during four point bending fatigue tests through an analysis of the peak amplitude, duration, rise time (RT) and energy of the events emitted from the damage sections. A difference in AE trends was observed during failure for specimens aged and tested in (i) air and (ii) Ringer's solution at 37 degrees C. It was noted that the acoustic behaviour varied according to applied load level; events of higher duration and RT were emitted during fatigue at lower stresses. A good correlation was observed between crack location and source of acoustic emission, and the nature of the acoustic parameters that were most suited to bone cement failure characterisation was identified. The methodology employed in this study could potentially be used as a pre-clinical assessment tool for the integrity of cemented load bearing implants.

Acoustics↗
PubMed1975

Dimensional behavior of curing bone cement masses.

The curing of bone cements is accompanied by release of polymerization heat and, hence, by a temperature rise of the curing cement mass. This temperature rise causes expansion of enclosed air bubbles and evaporation of the volatile monomer. An overall expansion of 3 to 5 vol % has been mentioned in the literature. It has often been stated that this expansion favours the fixation of metal endoprostheses in the marrow cavity of bone. To check for the influence of this expansion on linear dimensions of the cured cement mass we filled stainless steel cylinders with a precision bore of 22,000 +/- 0,005 mm and a length of 120 mm with bone cement. After curing of the cement in a environment of 37 degrees C the resulting cement rod was released from the cylinder and the diameter of the rod was measured at 37 degrees C. The influence of the "foaming effect" on the transverse dimensions of the rods was studied by curing the cement at 37 degrees C and 2 atm air pressure in a high-pressure-vessel. This method of curing eliminates porosity in the cement almost completely, so that curing shrinkage is to be expected rather than expansion of the cement mass. The results indicate that a volumetric expansion of the cement during curing of cylindrical rods in laboratory experiments, can be accompanied by a linear diametrical shrinkage of the cement mass. The explanation of this phenomenon is to be sought in the fact that the volumetric expansion takes place at a time when the cement is still plastic; by the formation of gas bubbles, the cement is forced in longitudinal direction into the cylinder and when the temperature of the mass has passed through a maximum, the cooling of the cement mass results in a thermal shrinkage of approximately 0.4% linearly. Extrapolating this laboratory result to clinical situation one might doubt whether the overall expansion of bone cements during curing will result in a permanent positive pressure on the walls of marrow cavity and whether it will contribute to a better fixation of endoprostheses than in the case of a, still hypothetical, nonporous cement.

Bone Cements↗
PubMed1990

Porosity of various preparations of acrylic bone cements.

The total porosity and mean pore sizes of various bone cement preparations were measured using image analysis. The porosity in different commercial bone cements varied from 5% to 16% when these cements were prepared in the usual fashion. Centrifugation for 30 seconds resulted in a substantial reduction in the overall porosity of Simplex P, AKZ, Zimmer Regular, and CMW bone cements by reducing both the mean pore size and the number of pores per unit area. In contrast, the porosity of LVC, Palacos R, and Palacos R with gentamicin bone cements was not significantly decreased by centrifugation. Chilling the monomer before mixing resulted in higher porosity of both the centrifuged and uncentrifuged Simplex P, Zimmer Regular, and CMW bone cements. Simplex P mixed with chilled monomer and centrifuged for 120 seconds has one of the lowest porosities of the various cements, while retaining good handling characteristics and excellent fatigue strength.

Acrylic Resins↗
PubMed1998

Performance of adhesive bone cement containing hydroxyapatite particles.

A new acrylic bone cement which can adhere to both bone and prostheses was developed based on a methyl methacrylate (MMA) monomer containing 4-methacryloyloxyethyl trimellitate anhydride (4-META) as adhesion promoting agent. Moreover, hydroxyapatite (HA) particles were introduced into the 4-META cement as a bone compatible filler. The mechanical strengths of an acrylic bone cement without 4-META decreased drastically with an increase in the percentage of HA particles in the cement. However, the mechanical strengths of the HA-containing 4-META cement did not change in the same way as that of the 4-META cement without HA due to adhesion between the cement HA particles and matrix. The HA particles did not affect the adhesion of the 4-META cement to bone and metals. Implantation of the 4-META cement and the HA-containing 4-META cement in animals demonstrated that these cements did not disturb bone ingrowth and the new bone was able to contact the cement directly. The 4-META cements, with and without HA particles, could adhere to bone in vivo.

Biocompatible Materials↗
PubMed2002

The static and cyclic strength of a bone-cement bond.

Four-point bending static and fatigue tests were carried out on bone-cement bonds. The effects of the pressurization and the washing of the bone joint face on the bond strength were investigated. The results are summarized as follows. When the bond surface of cancellous bone is washed prior to the application of the bone cement, both the static and fatigue strengths of the bond are increased relative to the corresponding properties of unwashed bone-cement bonds. From observations of bone-cement interfaces as well as the fracture surfaces of bone-cement specimens, it has been determined that bone cement was able to infiltrate into fine holes present in washed cancellous bone. However, such infiltration occurred to a much lesser degree in the case of unwashed cancellous bone. Increasing the molding pressure during the time of cement application to the bone from 39200 to 117600 Pa had a beneficial effect on the bending strength and fatigue properties, particularly in the case of washed bone cement specimens. An increase in molding pressure also resulted in a reduction in the amount of scatter in test results.

Journal Article↗