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PubMed2004

Quantitative measurement of the stresses induced during polymerisation of bone cement.

When bone cement cures, residual stresses due to bulk and thermal shrinkage will result. Present finite element (FE) simulations of implanted constructs often do not account for these stresses as an initial condition; this may lead to overestimations of the fatigue life of the cement. In the present study, an instrumented stem equipped with strain gauges and a thermocouple was employed to experimentally quantify the residual stresses induced as a result of bone cement curing within a simulated bone/cement/stem construct. Residual stresses as high as 10 MPa were observed in the cement mantle. Residual stresses of this magnitude are potentially high enough to initiate damage within the cement mantle or at the stem/cement interface immediately post-implantation. The acoustic emission technique has demonstrated that cracking and sliding mechanisms are occurring during curing, resulting in partial relaxation of these stresses. The implications for FE simulations of the implanted construct are discussed.

Bone Cements↗
PubMed2004

Bone cement treatment for aneurysmal bone cyst in a dog.

An eighteen month old female Doberman pinscher dog was referred to teaching hospital of Adnan Menderes University, Faculty of Veterinary Medicine with the complaint of right forelimb lameness for a month. On the basis of clinical, radiographical, scintigraphical, computed tomographical and histopathological findings, aneurysmal bone cyst was diagnosed. Surgical curettage and bone cement treatment were applied. The patient recovered after 12 months. This case proves that aneurysmal bone cyst, without osteolysis and/or damages to the surrounding tissues, may result in a good prognosis if curettage and treatment with bone cement are done.

Animals↗
PubMed1995

Pullout strength of fixation screws from polymethylmethacrylate bone cement.

Polymethylmethacrylate bone cement is often used to fill voids and increase the strength of osteoporotic and pathological bone. However, it is unclear as to which method of cement augmentation provides optimal screw fixation. This study was conducted to determine which of the current cement augmentation techniques provides the strongest construct when used in association with orthopaedic fixation screws. Pullout strength was determined for screws placed in sawbones with no cement, soft cement, doughy cement and hard cement after drilling and tapping. All cement-screw constructs were significantly stronger than the no cement group. Screws placed in doughy cement had a significantly higher pullout force than those placed in hard cement. Pullout strength of screws placed in soft cement was intermediate between the other cement techniques but not significantly different from either group.

Biocompatible Materials↗
PubMed2007

Hollow bone cement filled with impacted cancellous bone as a substitute for bone grafts in cervical spine fusion.

Autogenous iliac crest bone is the gold standard for graft material in cervical spinal fusion, but a high incidence of donor site morbidity has been reported. Therefore, to achieve a better fusion rate and decrease the rate of donor site morbidity, we used a novel method whereby hollow bone cement filled with impacted cancellous bone is used as a substitute for bone graft in cervical interbody fusion. From 2003 to 2004, 21 patients with cervical spinal disorders who were treated using this method were included in this study. Fourteen patients underwent single-level grafts and seven underwent two-level grafts. Evaluation included a monthly clinical and X-ray examination for the first 3 months, and then follow-up every 3 months thereafter. Multiple-slice computed tomography (CT) scan with reconstruction to evaluate the viability of the bone graft was performed when evidence of bone fusion was found on X-ray. The mean age of the patients was 59 years (range 27-79). The mean follow-up period was 19 months (13-24 months). Evidence of impacted cancellous bone bridging the adjacent vertebral body was observed in all patients at the 6-month follow-up based on X-rays and reconstructive CT scans. No severe donor site morbidity occurred. One patient experienced hardware failure due to screw fracture, but a reconstructive CT scan revealed well-bridged cancellous bone between the vertebral bodies. Hollow bone cement filled with impacted cancellous bone could be an alternative material for cervical spine interbody fusion. Using this method, we found not only satisfactory growth of cancellous bone in the holes of the bone cement, but also low morbidity in the donor site. However, for this method, the long-term stability, potential complications, and the necessity of instrumentation all require further investigation.

Adult↗
PubMed1990

Effect of vacuum mixing on the mechanical properties of antibiotic-impregnated polymethylmethacrylate bone cement.

Polymethylmethacrylate bone cement, containing either no added antibiotic, 0.5 g of Vancomycin, 1.0 g of Vancomycin, or 1.0 g of Tobramycin, was mixed either in air or a vacuum chamber. Following storage in a water bath at 37 degrees C for 48 h, the specimens were tested in four-point bending. The porosity of the specimens was assessed radiographically, and their antibacterial activity was monitored for 21 days. The bending strength of the vacuum mixed specimens containing no antibiotic was 40% greater than that of similar air-mixed specimens. However, there were no significant differences in the bending strength of either the air- or vacuum-mixed specimens when any of the antibiotic dosages were added. The bending modulus of the vacuum-mixed specimens, containing no antibiotic, was significantly greater than the moduli of all the other specimen groups which did not differ from each other. Vacuum mixing reduced the apparent porosity of the specimens fivefold, and while the addition of antibiotic did not effect porosity of the air-mixed specimens, that of the vacuum-mixed specimens was doubled. Although initial rapid decreases were seen, leaching of antibiotic from the cement and antibacterial activity continued through the 21-day monitoring period.

Biomechanical Phenomena↗
PubMedDate not supplied

Dependence of curing time, peak temperature, and mechanical properties on the composition of bone cement.

Commercial bone cements usually contain hydroquinone as the polymerization inhibitor and N,N-dimethyl-p-toluidine as the accelerator in the benzoyl peroxide-initiated redox polymerization. The former compounds have certain shortcomings in their biocompatibility profile. Measurements of the setting times, polymerization exotherms, and postpolymerization strengths of the cured monomer-polymer compositions show that the hydroquinone can be replaced by food grade di-tert-butyl-p-cresol (BHT). The more reactive 4-N,N-(dimethylamino)phenethanol can replace 4-N,N-dimethyl-p-toluidine, yielding cements with shorter setting times and increased strengths. Excessive heat liberated on polymerization can be reduced by partial substitution of higher-molecular-weight methacrylates, e.g., dicyclopentenyloxyethyl methacrylate for methyl methacrylate, but there is a decrease in strength of the resulting polymer. More successful has been the addition to the monomer of 1% or 2% of the chain transfer agent pentaerythritol tetra(3-mercaptopropionate), which lowers the peak temperature without changing the physical properties of the cement. Compositions with short curing times, lower exotherms, and mechanical properties that exceed those of a commercial material have been formulated.

Acrylates↗
PubMed1990

The influence of curing time and environment on the fracture properties of bone cement.

Fracture of bone cement at the bone-cement interface is considered to be of significance in the aseptic loosening of orthopaedic implants. The characterisation of the fracture properties of bone cement is influenced by the time and environment in which it is cured. Cement samples stored in air and water at 21 and 37 degrees C for 7 and 21 days were tested using the 'Chevron' test to determine the work of fracture. It was found that the storage temperature and environment had important influences on the fracture resistance of bone cement. In a physiological environment cement appears to take longer to attain a fracture resistance equivalent to that of cement stored at room temperature.

Bone Cements↗
PubMed2002

Flexural strength distribution of a PMMA-based bone cement.

Polymethylmethacrylate bone cement containing either no added antibiotic or 0.5 g of Gentamicin was prepared and stored either in air at room temperature or in a 37 degree C water bath for 48 h. An additive-free cement stored in air at room temperature was also tested for purposes of comparison. Following storage the specimens were tested in flexure. Weibull statistics demonstrated to fit the flexural strength distribution of all the materials tested with regression coefficients of at least 0.98. The presence of a BaSO(4) radiopacifier markedly reduced the mean flexural strength and increased the data scatter in the air-stored specimens. On the other hand, the flexural strength of both impregnated and nonimpregnated antibiotic increased when those materials were stored in water at 37 degree C, compared with the same material stored in air, as a consequence of the water ingress. The water-stored antibiotic-impregnated cement displayed lower flexural strength, increased data scatter, and a remarkably higher number of weak specimens compared with the antibiotic-free cement. The influence of the load type on the flexural behavior was studied by testing the air-stored specimens in three-point bending and four-point bending. Cements tested in four-point bending resulted in lower flexural strength than that tested in three-point bending. The ratio of mean strength measured in the different load arrangements was satisfactory, as predicted by the Weibull model.

Anti-Bacterial Agents↗
PubMed2004

The effect of surface treatment of hydroxyapatite on the properties of a bioactive bone cement.

Bioactive bone cements based on a paste-paste system for orthopaedic applications have been developed. They consist of hydroxyapatite (HA) filler particles in a methacrylate matrix comprising urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA). To improve the interface between inorganic filler and organic matrix the HA particles were subjected to two different surface treatment methods, using polyacrylic acid (PAA) and gamma-methacryloxypropyltrimethoxy silane (gammaMPS). The aim of the present study was to determine the influence of surface treatment on the mechanical properties, namely compressive strength (CS), diametral tensile strength (DTS) and three-point flexural strength (FS) of the cements and the effect of ageing in simulated body fluid (SBF). Comparing the mechanical properties of the two cements after fabrication, the gammaMPS-HA cement showed higher strength values for all tests conducted (CS = 185+/-19.6 MPa, DTS = 27+/-2.5 MPa, FS=50.2+/-4.9 MPa), whereas PAA-HA containing cement had strength values around 20% lower. However, poly(acrylic acid) surface treatment was found to be more effective in improving the interface, and PAA-HA cements maintained their mechanical properties after immersion in SBF whereas gammaMPS-HA cement showed a reduction in strength values post ageing. From the results of this study, it is concluded that PAA treatment of the HA filler is a viable alternative to silanation with gammaMPS which may provide increased durability in aqueous environments.

Acrylic Resins↗
PubMed2000

The fixation of the cemented femoral component. Effects of stem stiffness, cement thickness and roughness of the cement-bone surface.

After cemented total hip arthroplasty (THA) there may be failure at either the cement-stem or the cement-bone interface. This results from the occurrence of abnormally high shear and compressive stresses within the cement and excessive relative micromovement. We therefore evaluated micromovement and stress at the cement-bone and cement-stem interfaces for a titanium and a chromium-cobalt stem. The behaviour of both implants was similar and no substantial differences were found in the size and distribution of micromovement on either interface with respect to the stiffness of the stem. Micromovement was minimal with a cement mantle 3 to 4 mm thick but then increased with greater thickness of the cement. Abnormally high micromovement occurred when the cement was thinner than 2 mm and the stem was made of titanium. The relative decrease in surface roughness augmented slipping but decreased debonding at the cement-bone interface. Shear stress at this site did not vary significantly for the different coefficients of cement-bone friction while compressive and hoop stresses within the cement increased slightly.

Alloys↗
PubMed1989

Effect of posterior cruciate sacrifice on durability of the cement-bone interface. A nine-year survivorship study of 100 total condylar knee arthroplasties.

This article presents a survivorship analysis of the second conservative 100 primary total-condylar knee arthroplasties in 75 patients performed between 1979 and 1980, with a maximum follow-up of 9 years. With this type of knee arthroplasty, the posterior cruciate ligament is routinely sacrificed. Survivorship results revealed that 98.9 per cent of the knees had good outcome at 9 years of follow-up, using revision surgery for aseptic and septic loosening and radiographic evidence of global radiolucency or shift of the component as endpoint. Radiographic survivorship analysis showed well-fixed components in 87 per cent of implants, using endpoint criteria of appearance and progression of radiolucency under tibial component. Sacrificing the posterior cruciate ligament does not adversely affect durability of fixation of the total-condylar knee arthroplasty. Bone cement provides an excellent fixation of total knee implant.

Adult↗
PubMed1998

Bisphosphonates in bone cement inhibit PMMA particle induced bone resorption.

OBJECTIVE: Wear particle induced bone resorption is thought to be one of the mechanisms that contribute to implant loosening. It has previously been shown that macrophages, in response to polymethylmethacrylate (PMMA) particles, differentiate into bone resorbing osteoclasts, and that this process is inhibited by a bisphosphonate, etidronate (EHDP). The aim of this study was to determine whether incorporating EHDP in bone cement could reduce PMMA associated bone resorption. METHODS: Two concentrations of EHDP were mixed with PMMA monomer before polymerisation. Particles of PMMA (1-10 microns) were generated then added to mouse monocytes cocultured with UMR106 rat osteoblast-like cells and the extent of osteoclast differentiation was determined by assessing the extent of tartrate resistant acid phosphatase (TRAP) staining and measuring the amount of lacunar bone resorption. RESULTS: The addition of PMMA to monocyte-UMR106 cocultures resulted in a marked increase in the number of TRAP positive osteoclast-like cells and a significant increase in the number of lacunar resorption pits compared with control cultures to which no particles had been added. After the addition of particles of PMMA + 20 mg EHDP, significantly fewer lacunar pits (p = 0.00006) and fewer TRAP positive cells were noted compared with cocultures containing PMMA particles alone. CONCLUSIONS: These results indicate that by mixing a bisphosphonate with bone cement, it is possible to inhibit PMMA particle induced bone resorption. This bisphosphonate inhibition of PMMA biomaterial wear particle containing macrophage-osteoclast differentiation and bone resorption may provide a possible therapeutic strategy to prevent or to control the osteolysis of aseptic loosening.

Animals↗
PubMed2004

The effect of moisture absorption on the fatigue crack propagation resistance of acrylic bone cement.

In vivo, bone cement is subject to cyclic loading in a fluid environment. However, little is known about the effect of moisture absorption on the fatigue crack propagation resistance of bone cement. The effect of moisture absorption at 37 degrees C on the fatigue crack propagation resistance of a common bone cement (Endurance, DePuy, Orthopaedics, Inc.) was examined. Preliminary fracture toughness tests were conducted on disk-shaped, vacuum-mixed cement specimens (compact tension type) that were cyclically pre-cracked. Plain-strain fracture toughness K(IC) (MPa square root(m)) was determined. To study the effect of moisture absorption four treatment groups, with different soaking periods in Ringer's at 37 degrees C, of Endurance cement were tested. The specimens weights prior to and following soaking showed a significant increase in mean weight for specimens soaked for 8 and 12 weeks. Linear regression analysis of log(da/dN) vs. log (deltaK) was conducted on the combined data in each fatigue test group. Soaking bone cement in Ringer's at 37 degrees C for 8 and 12 weeks lead to an improvement in fatigue crack propagation resistance, that may be related to water sorption that increases polymer chain mobility, with enhanced crack tip blunting. It may be more physiologically relevant to conduct in vitro studies of fatigue and fracture toughness of bone cements following storage in a fluid environment.

Absorption↗
PubMed2002

Curing characteristics of acrylic bone cement.

Commercial acrylic bone cements are supplied as two components, a polymer powder and a liquid monomer. Mixing of the two components is followed by a progressive polymerization of the liquid monomer to yield a solid mass, a high level of heat being generated during this exothermic reaction. The exposure of bone to high temperatures has led to incidences of bone necrosis and tissue damage, ultimately resulting in failure of the prosthetic fixation. The aim of this study was to determine the thermal properties of two acrylic bone cements as they progress through their polymerization cycles. It was also felt that there was a need to quantify the variations in the curing characteristics as a function of preparing bone cement by different techniques, hand mixing and vacuum mixing. A number of parameters were calculated using the data gathered from the investigation: peak temperature, cure temperature, cure time, and the cumulative thermal necrosis damage index. The results show the temperature profile recorded during polymerization was lowest when the cement was prepared using the Howmedica Mix-Kit I system: 36 degrees C for Palacos R and 41 degrees C for CMW3 respectively. When the acrylic cements were prepared in any vacuum mixing system there was evidence of an increase in the cure temperature. The main factor that contributed to this rise in temperature was an imbalance in the polymer powder : liquid monomer ratio, there was a high incidence of unmixed powder visible in the mixing barrel of some contemporary vacuum mixing devices. Observing the thermal characteristics of the polymethyl methacrylate (PMMA) bone cements assessed, it was found that particular formulations of bone cements are suited to certain mixing methodologies. It is vital that a full investigation is conducted on a cement mixing/delivery system prior to its introduction into the orthopaedic market.

Journal Article↗
PubMed1998

Isothermal and non-isothermal polymerization of a new bone cement.

A new bone cement based on poly(ethylmethacrylate) (PEMA), hydroxyapatite powder (HA) and n-butylmethacrylate monomer (n-BMA) has been studied using isothermal and non-isothermal polymerization. Methacrylate monomers are highly reactive and release a considerable amount of heat during polymerization. A quantitative understanding of the methacrylate polymerization is necessary because the thermal history of the polymerization has considerable influence on the final properties of a bone cement. In the first part, polymerization kinetics are analysed by means of differential scanning calorimetry (DSC). DSC data are used to evaluate a phenomenological model describing the cure kinetics of this new bone cement. In the second part, a kinetic model coupled with the energy balance is used to obtain temperature and degree of conversion profiles in the bone-cement-prosthesis system, under non-isothermal conditions, as function of initial temperature and thickness of the cement. Material properties, boundary and initial conditions and the kinetic behaviour are the input data for the numerically solved heat-transfer model. The temperature at the bone/cement interface, can be considered as a weak point, often responsible for total joint replacement failure. For this particular bone cement exhibiting a low exotherm and low glass transition temperature, the interfacial temperature is lower than the threshold level for thermal tissue damage (50 degrees C). The conversion occurs almost completely, avoiding problems with unreacted monomers that can be released by the cement, giving rise to tissue damage.

Journal Article↗
PubMed2001

Influence of mixing techniques on the physical properties of acrylic bone cement.

Palacos R bone cement was prepared using three commercially available mixing techniques, first generation, second generation and third generation, to determine the mechanical properties and porosity contents of the bone cement. The compressive strengths, bending strengths and flexural moduli were expressed as a function of void content. The volume of pores within the cement structure was found to be a contributing factor to the physical properties of acrylic bone cement. The lower the volume of voids in the cement the better the compressive and flexural properties, hence stronger bone cement. It was found that the best results were obtained from cement that had been mixed using the Mitab Optivac or Summit HiVac Syringe systems at a reduced pressure level of between -72 and -86 kPa below atmospheric pressure, resulting in cement of porosity 1.44-3.17%; compressive strength 74-81 MPa; flexural modulus 2.54-2.60 GPa; and flexural strength 65-73 MPa.

Acrylates↗