Vertebroplasty is a minimal invasive surgical procedure for treatment of vertebral compressive fractures, whereby cement is injected percutaneously into a vertebral body. Cement viscosity is believed to influence injectability, cement wash-out and leakage. Altering the liquid to powder ratio can affect the viscosity, level of cohesion and extent cement fill within the vertebral body and the ultimately strength and stiffness of the cement-vertebra composite. The association of these combined factors remains unclear. The aim of this study was to determine the relationship between cement viscosity and the potential augmentation of strength and stiffness in a model simulating in-vitro prophylactic vertebroplasty of osteoporotic vertebral bodies. Samples of synthetic bone (Sawbone) representing osteoporotic bone were manually injected with 1mL of calcium phosphate cement using a 11G cannulated needle. Calcium phosphate cement was produced by mixing alpha-tricalcium phosphate, calcium carbonate and hydroxyapatite with an aqueous solution of 5 wt% disodium hydrogen phosphate. Three liquid to powder ratio (LPR) representing different viscosity levels were used; i.e. 0.5mL/g (low viscosity), 0.45mL/g (medium viscosity) and 0.35mL/g (high viscosity). Cement filled samples were then placed in an oven (37oC) for 20 min and then immersed in Ringer's solution (37oC) for 3 days. Samples of synthetic bone without cement injection were used as controls. Potential for leakage and wash-out was determined using gravimetric analysis. Extent of cement fill was determined using computer tomography (CT). Samples were tested under axial compression at a rate of 1 mm/min and the strength and stiffness determined. Statistical significance against controls was determined using a one-way analysis of variance (p<0.05). Low viscosity cement showed more cement leakage (p=0.512) and increased cement wash-out after 3 days in Ringer's solution (p=0.476). Qualitative assessment of cement fill within the vertebral body using CT imaging supported the wash-out results. The strength (p<0.05-0.01) and stiffness (p<0.01) of samples significantly increased by cement injection in comparison to control, the extent of this increase was greater with increasing cement viscosity. Linear correlation analysis showed a definite association between the mechanical properties and viscosity of injected cement and was dependent on the amount of cement retained within the synthetic bone post-setting

Introduction: The failure rate of cemented hip replacements is about 1% per year, mainly due to aseptic loosening. PMMA acts as a grout, therefore high pressure is needed to ensure fixation. Various plug designs are used to increase pressure. No data is available on their ability to occlude the canal. Factors including canal size, canal shape and cement viscosity may affect performance. The two aims of this study are (I) to determine the effect of cement viscosity, canal shape and canal size on the ability of cement restrictors to withstand cementation pressures, and (II) to determine which of the currently commercially available designs of cement restrictor is able to withstand cementation pressures, regardless of values of other potentially influential factors. Methods: Artificial femoral canals were drilled in oak blocks. Circular canals had diameters of 12 or 17.5 mm. Oval canals had short axes equal to the diameter of the circular canals and long axes 1.3 times longer. This ellipticity of 1.3 is average for human femoral canals. One of four types of cement plugs (Hardinge, DePuy, UK; Exeter, Stryker, UK; Amber Flex, Summit Medical, UK; and OptiPlug, Scandimed, Sweden) was inserted. A pressure transducer was fitted in the canal just proximal to the plug. Bone cement (Palacos LV-40 low viscosity or Palacos R-20 high viscosity, both Schering Plough, UK) was prepared in a mixing device for 1 min at 21°C, and inserted in the artificial canal after 4 minutes. A materials testing machine was used to generate pressure in the cement. Cement pressure and plug position were measured. All combinations of canal size and shape, plug design and cement viscosity were pre-selected according to a D-optimal experimental design which was optimised to perform a four-way ANOVA to analyse the four main factors plus the interactions between plugs and the other three factors. A total of 23 experiments was performed. Results: Average cement pressures achieved differed between implants (OptiPlug 448±66 kPa, Hardinge 142±66, Exeter 705±66, Amber Flex 475±72; p=0.002, all mean±SEM). They also differed between canal sizes (12 mm 529±49, 18 mm 356±47; p=0.03), canal shapes (Round 631±45, Oval 254±51; p=0.004) and cement viscosity (High 535±54, Low 350±43; p=0.03). No significant interaction between factors was found. Discussion and Conclusion: All plugs resisted lower pressures in large canals, oval canals or with low viscosity cement. When comparing plugs, these different circumstances should therefore be taken into account. Of the four tested, the Exeter plug performed best in all adverse circumstances. The OptiPlug and AmberFlex, which are both resorbable, had an intermediate performance. The Hardinge plug performed worse

The advantages of high viscosity Simplex AF cement (PMMA) compared to low viscosity Simplex P are the low porosity, the high fatigue strength, the lower polymerization time, and the lower maximum polymerization temperature. A prospective, randomized, double-blind clinical study was conducted to assess the in vivo effects of viscosity of bone cement on the micromotion of a polished tapered stem and UHMWP-cup (Exeter, Stryker-Howmedica). Roentgen Stereophotogrammetric Analysis (RSA-CMS, Medis, The Netherlands) was used to measure micromotion. Twenty patients were included in a Simplex AF group (70 ± 4.3 years), and twenty patients were included in a Simplex P group (71 ± 7.3 years). No significant differences in body mass index and clinical hip scores were observed between the two studied groups. There was no significant difference of the subsidence of both high and low viscosity cemented Exeter stems. The subsidence was according to the literature and showed that the viscosity of the bone cement did not influence the cement-implant bond of this polished tapered stem design. The total migration of the cups and the migration along the medial-lateral axis were significantly larger for the Simplex AF cemented cups compared to the Simplex P cemented cups (p=0.037). This can be explained by the higher cement mantle thickness in acetabular Gruen zone 2 (p=0.003) and 3 (p=0.004) of the Simplex AF cemented cups. We conclude from this study that the viscosity of the bone cement has no effect on the subsidence of polished tapered stems and that a high cement mantle thickness around an UHMWP-cup has a negative effect on fixation

Introduction

While fixation on the acetabular side in resurfacing implants has been uncemented, the femoral component is usually cemented. The most common causes for early revision in hip resurfacing are femoral head and or neck fractures and aseptic loosening of the femoral component. Later failures appear to be more related to adverse soft-tissue reactions due to metal wear. Little is known about the effect of cementing techniques on the clinical outcome in hip resurfacing, since retrieval analysis of failed hip resurfacing show large variations. Two cementing techniques have dominated. The indirect low viscosity (LV) technique as for the Birmingham Hip resurfacing (BHR) system and the direct high viscosity (HV) technique as for the Articular Surface replacement (ASR) system. The ASR was withdrawn from the market in 2010 due to inferior short and midterm clinical outcome. This study presents an in vitro experiment on the cement mantle parameters and penetration into ASR resurfaced femoral heads comparing both techniques.

Modern cementation techniques in hip arthroplasty are enhanced by the use of a cement restrictor. Failure of cemented hip replacements is commonly caused by aseptic loosening. Cement plugs which occlude the medullary canal are widely used to increase cementation pressures. Many plug types with variable performance exist. Ideally, plug performance should be sufficient regardless of other factors. All plug designs are circular in cross section, yet the vast majority of human femora are of oval section, the average ellipticity for human femora being 1.3. This study aims to determine (I) the effect of cement viscosity, canal shape and canal size on plug performance and (II) which designs of cement restrictor are able to withstand cementation pressures, regardless of values of other potentially influential factors. Methods: Artificial femoral canals were drilled in oak blocks. Canals had diameters of 12 or 17.5 mm and oval or circular cross section. Four synthetic plug types (Hardinge, Exeter, Summit and OptiPlug.) and a bone plug (human allograft, Sulzer instrumentation) were tested. The effect of canal diameter, canal shape and low or regular cement viscosity was assessed. Results: Maximal pressures achieved varied significantly between plugs. (OptiPlug 448±66 kPa, Hardinge 142±66, Exeter 705±66, Amber Flex 475±72, Bone plug 502±97 kPa; p=0.002, all mean±SEM). Al plugs performed worse in canals of increased size and of elliptical canal cross section (12 mm 529±49, 18 mm 356±47; p=0.03), canal shapes (Round 631±45, Oval 254±51; p=0.004). Cement viscosity had no statistical effect. Discussion: Elliptical canal cross section and increased canal diameter adversely affects performance of all plug designs. Of the five tested, the Exeter and bone plugs performed best in all adverse circumstances. The Opti-Plug and AmberFlex, which are both resorbable, had an intermediate performance. The Hardinge plug performed worse. These factors should be considered when selecting plug design

Absorbable cement restrictors have been in use over the last few years. They have been shown to be as effective as the standard non-absorbable cement restrictors in achieving cement pressurisation and stopping distal cement migration in in vitro studies. The aim of this study is to compare in vivo, the effectiveness of absorbable with non-absorbable cement restrictors. One hundred and thirty-six consecutive patients who had total hip replacement performed using charnley cemented femoral prosthesis were selected and randomly divided in to two groups pre operatively. One group received Hardinge TM non-absorbable cement restrictor and the second group received Biostop TM absorbable cement restrictor. Type of the prosthesis, the surgical approach, the time from start of mixing of the cement to insertion of the cement (measure of viscosity of the cement), the cementing technique and the distance at which the cement restrictor was inserted were noted intraoperatively, the canal diameter was measured from the preoperative AP radiograph of the hip. The distance at which the cement restrictor was inserted was measured on the AP radiograph of the hip taken twenty-four hours postoperatively. All the above factors were statistically assessed as to their effect in the distal migration on cement restrictor using multiple regression analysis. There was no statistical difference between the two types of cement restrictors (P= 0.44). Surgeon, Surgical approach, femoral canal diameter P> 0.2 cementing technique P> 0.1 and Cement viscosity P= 0.082 had no effect on the degree of distal migration of the cement. In conclusion Biostop TM absorbable cement restrictor is as effective as Hardinge TM non-absorbable cement restrictor. We could not show any relationship between femoral canal diameter cementing technique and cement viscosity and distal cement migration which leads us to conclude that in the presence of adequate cement restriction these factors have little effect in distal migration of cement mantle

Background. Aseptic loosening of cemented femoral stems results from migration of wear particles along the bone-cement interface, producing a foreign body reaction. After cement insertion, blood back pressure can disrupt the bone-cement interface, enabling this spread of wear particles. Our study investigates whether altering timing and speed of stem insertion can reduce this risk. Methods. We inserted mock “C-Stem” femoral components (De Puy-Synthes), using Smartset HV cement (De Puy-Synthes) into artificial femora, fitted with proximal and distal pressure transducers. Cement insertion began two, three or four minutes after mixing. Cement pressures were then allowed to settle for one minute and the stems were then inserted over durations of 25, 60 or 90 seconds. Results. Quicker insertion led to high peak pressures; however insertion over 90 seconds at 4 and 5 minutes achieved more sustained pressures above blood back pressure. Slower insertion particularly improved proximal pressurisation. Furthermore when the stem was inserted over 90 seconds at 5 minutes then the cement pressures remained high after full insertion of the stem. Conclusions. Commonly, femoral stems are inserted rapidly. Our study demonstrates that by inserting the femoral stem more slowly, cement pressure can be maintained above blood back pressure for longer. We believe that after slower stem insertion, the higher cement viscosity enables the surgeon to maintain cement pressure, via the stem, sufficient to resist blood back pressure without inadvertently over inserting the stem. This safe and simple modification of cementing technique generates higher and more sustained cement pressures. Level of evidence. 3. Disclosures. Depuy-Synthes kindly provided the equipment used in the study. None of the authors received any payment or other benefits

Background: Several factors can alter a cements viscosity and hence it’s handling characteristics. An in vitro study was performed to ascertain whether anecdotal observations of differences in handling between batches of the same cement brand existed. Methods: 3 batches of Simplex P Tobramycin (SPT), Refobacin Bone Cement (RBC), SmartSet GHV (SSG) and Palacos R+G (PRG) were tested. 6 replicates of each batch were vacuum mixed and their viscosity in relation to time was measured in laboratory conditions (50 ±5% humidity and 23 ±1°C) using a rheometer. 6 replicates of each batch had their handling characteristics examined after they were hand mixed in theatre conditions. Results: Inter and intra-batch variability was seen in the viscosity of all brands of cements tested. Inter-batch calculations were influenced by high intra-batch viscosity variability. The viscosity of RBC cement was very similar to SSG, but significantly different to PRG (p = 0.01 at 5N and p = 0.009 at 40 N). Interpretation: Our results suggest that in clinical practice extrinsic factors such as preparation conditions and methods probably play a more important role than the cements intrinsic variability. However, variability in handling and viscosity will exist in all brands of cement prepared in theatre conditions and the surgeon needs to be aware why they may act differently

Introduction: Vertebroplasty is increasingly used in the treatment of painful osteoporotic vertebral fractures, and involves transpedicular injection of bone cement into the fractured vertebral body. Effective infiltration of the vertebral body cancellous bone by the cement is determined by the cement viscosity, and by the permeability of the bone. However, it is unclear how permeability is influenced by regional variations in porosity and architecture of bone within the vertebral body. The aim of the present study was to investigate how permeability is influenced by porosity and architecture of cancellous bone mimics. Methods: Cylindrical polyamide mimics of two types of cancellous bone structures were fabricated using selective laser sintering (SLS) techniques. Structure A had the rod-like vertical and horizontal trabeculae typical of the anterior vertebral body, while structure B had oblique trabeculae typical of the posterior-lateral vertebral body. Structure B had fewer trabeculae than A. Porosities of 80 and 90% were represented for both structures. Golden syrup, which has a viscosity similar to bone cement. 1. , was injected into the mimics at a constant speed using a ram driven by a materials testing machine. Pressure drop measurements across the mimic, made using a differential pressure transducer, were obtained at five different injection speeds. Permeability of each mimic was calculated from these measurements. 2. Two more repeat permeability measurements were performed on each mimic. Results: Repeat measurements were always within 12% of the mean value. For structure A the mean permeabilities were 1.26×10-7 and 1.82×10-7m2 for the 80 and the 90% porosity mimics respectively. The corresponding mean permeabilities for structure B were 1.92×10-7 and 2.86×10-7m2. Discussion: These preliminary results indicate that higher permeabilities occur in structures with higher porosities, and with structures containing fewer trabeculae that are arranged obliquely. Since permeability is a determinant of cement infiltration, taking into account patient-specific bone architecture parameters may improve the safety and clinical outcome of vertebroplasty. Future experiments will clarify in more detail the architectural parameters that have greatest effect on permeability

Acrylic bone cements are used rather extensively in orthopedic and spinal applications. The incorporation of calcium phosphate additives to bone cements, to induce osteoconductivity, have typically resulted in increased cement viscosity, decreased handling, and detrimental effects of the mechanical performance of the cement. Additionally, bioactive bone cements are offered at a premium cost, which limits clinical use of these materials. The goal of this study was to examine and characterize an alternative two-solution poly (methyl Methacrylate) (PMMA) bone cement (referred to as TSBC), after incorporation of several calcium phosphate additives and antimicrobials. These bioactive and antimicrobial two-solution cements were designed to have adjustable properties that meet specific requirements of orthopedic applications. The addition of a bioactive agent would lead to increased levels of bone reformation after surgery, while an antibiotic within the cement would decrease the ability for pathogens to grow in the interface between the bone and new implant. TSBC is a pre-mixed bone cement that exhibits a combination of attractive properties including high strength, adjustable viscosity, adequate exothermal properties, as well as offering the possibility of using the same batch multiple times. The addition of antibiotics has not been previously explored in two-solution bone cements. Therefore, it is desirable to induce antibacterial activity with this formulation. Hydroxyapatite (Ca5(PO4)3(OH)), Brushite (CaHPO4•2H2O), and Tricalcium Phosphate (Ca3(PO4)2)(TCP) were incorporated into the TSBC in varying concentrations (25 and 50 wt%), and the rheological characteristics were examined to verify the feasibility of adding high concentrations of fillers to this cement formulation. Results demonstrated that unlike commercial powder-liquid formulations, calcium phosphate additives in TSBC do not detrimentally affect handling and the rheological properties of the material, while also providing maintenance of cement strength and other physical properties. TSBC material spends a dramatically increased amount of time in the swelling phase, as compared to powder-liquid formulations and thus is better suited to incorporate additives fully into its polymer matrix. Current two-solution bone cements do not contain any osteoconductive or antimicrobial agents. This study investigated the effects of addition of these bioactive agents in the physical and mechanical properties of the cement. Cement porosity was investigated to ensure that the porous nature of the bioactive cement does not damage the mechanical stability of the material. Further imaging will be conducted to demonstrate the improved osteointegration of these bioactive cement with osteoblasts (Figure 1). Degradation studies have been conducted to validate the biodegradable properties of the bioactive components and antibiotics release profile. It is further hypothesized that the degradation time will correlate to the antimicrobial activity. As the cement is replaced with natural bone, more and more antimicrobial will become exposed to the physiologic environment causing a continuous antimicrobial release as the material is partially replaced with new bone over time. Antimicrobial effectiveness and antimicrobial release studies are under-way to illustrate the cements ability to restrict growth at the cement surface, as well as show the antimicrobial release profile over time

Introduction and Aims: Bone cement (Polymethylmethacrylate) is commonly used to augment internal fixation in osteoporotic bone. An inconsistency exists among surgeons regarding the appropriate mixing time for bone cement to achieve optimal screw purchase. The study addresses the effect of cement viscosity on fixation augmentation in both healthy and simulated osteoporotic canine bone. Method: Fourteen canine femora were plated using eight-hole DC plates and 3.5mm screws, repairing transverse diaphyseal osteotomies with and without a gap. In the left femora, cement was mixed for one minute (liquid) prior to injection into drilled and tapped holes that were either properly sized (2.5mm) or over-drilled (3.2mm) to simulate osteoporotic bone. In the right femora, cement was mixed for five minutes prior to injection (thick paste). Four-point bending stiffness for each plated construct was normalised to baseline stiffness, followed by failure loading. Results: Within the properly sized holes, there were no significant differences in bending stiffness with or without a gap at the fracture site. The liquid cement had a force to failure 77% greater than that of cement as a paste (p< 0.05). Within the over-sized holes simulating osteoporotic bone, there was no difference between liquid and paste without a gap. With a gap, liquid cement demonstrated an increased bending stiffness of 24% (p< 0.05) and force to failure was 92% higher (p< 0.05). Bone cement in its liquid state may provide increased structural support in the setting of an osteoporotic fracture, possibly due to increased interdigitation of the cement with the screw threads and bone. Conclusion: In a canine diaphyseal fracture model, screw insertion into liquid cement achieves greater bending stiffness and resists a greater load to failure than insertion into cement with the consistency of a paste

Background: Inadequate proximal femoral pressures obtained during a cemented, primary hip replacement may lead to poor stem fixation. Proximal occlusion during stem insertion,may help in achieving a uniform and sustained rise in intra-medullary pressures, distally and proximally. High intra-medullary pressures correlate with better cement penetration and increased cement-bone interface push-out strength. Methodology: An In-vitro analysis of femoral pressures was performed. A femoral medullary cavity was created in plaster of Paris constrained in an aluminium cylinder. Intramedullary pressures were measured via pressure transducers. High viscosity bone cement (Palacos-R) was gunned into the medullary cavity. No.3 Exeter stem was inserted with no proximal occlusion, with thumb occlusion over the calcar and with the Exeter Horse-collar. Experiments were repeated by delaying the timing of insertion and with lower viscosity cement (Simplex-P). A small series of experiments were done to ensure that that the stem insertion was performed at standard cement viscosity. The experiments were carried out with the same viscosity of Palacos-R at 4 minutes and Simplex-P at 6 minutes. Palacos-R at 4 minutes 30 seconds had a higher viscosity. Results: A total of 54 experiments were performed. Of these 18 experiments were done with Palacos R cement, with the stem inserted early on in the curing phase and 18 with a delayed time of insertion. The last 18 experiments were performed with Simplex P cement with the stem inserted early on in its curing phase. Intramedullary pressures were better in all zones, for all cement modes, with proximal occlusion. The highest pressures were seen with Palacos-R at 4 minutes 30 seconds with proximal thumb occlusion. Stem insertion into Palacos-R at 4 minutes or 4 minutes 30 seconds, gave higher pressures than Simplex-P, with or without any form of occlusion. With Simplex-P, intramedullary pressures were higher, with Collar rather than thumb occlusion. Conclusion: Occluding the medial cal car area during stem insertion, is an effective way of achieving and sustaining high-pressures in the proximal and distal femur. The highest pressures are obtained with stem inserted into Palacos-R at 4 minutes 30 seconds, with proximal thumb occlusion. Collar occlusion may be better in achieving higher pressures, with lower viscosity, Simplex-P

Aims

The Exeter short stem was designed for patients with Dorr type A femora and short-term results are promising. The aim of this study was to evaluate the minimum five-year stem migration pattern of Exeter short stems in comparison with Exeter standard stems.

Study Design: Comparative, prospective follow-up study. Objective: Comparison of outcome between patients treated with Percutaneous VertebroPlasty (PVP) using low viscosity PolyMethylMetAcrylate (PMMA) bone cement and patients treated with PVP using medium viscosity PMMA bone cement. Summary of background data. Viscosity is the characterizing parameter of PMMA bone cement, currently the standard augmentation material in PVP, and influences interdigitation and cement distribution inside the vertebral body, injected volume and extravasation, thereby affecting the clinical outcome of PVP. In PVP, low, medium and high viscosity PMMA bone cements are used interchangeably. However, effect of viscosity of cement on clinical outcome in patients with Osteoporotic Vertebral Compression Fractures (OVCFs) has not yet been explicit subject of investigation. Methods: Follow-up was conducted using a 0–10 Pain Intensity Numerical Rating Scale (PI-NRS) and the Short Form 36 (SF-36) Quality of Life (QoL) questionnaire before PVP and at 7 days (PI-NRS only), 1 month, 3 months and 12 months after PVP. Cement leakage was analyzed on direct post-operative CT-scanning. Injected cement volume was measured using a calibrated DICOM-viewer and the degree of interdigitation was assessed. At six and 52 weeks and at suspicion, patients were analyzed for the incidence of new fractures. Results: Thirty consecutive patients received PVP using low viscosity PMMA bone cement (OsteoPal-V. ®. ) for 62 OVCFs, followed by 34 patients who received PVP using medium viscosity PMMA bone cement (Disc-O-Tech. ®. ) for 67 OVCFs. Baseline characteristics were comparable between groups. Viscosity qualification was stated by the manufacturer. results regarding PI-NRS and SF-36 were comparable between both groups. Postoperative comparison of injected cement volume, degree of interdigitation, proportion of bipedicular procedures, incidence of new vertebral fractures and complications revealed no substantial differences between both groups. In the low viscosity group a significantly greater proportion of vertebrae showed cement extravastion (81,0% versus 71,6%, p = 0,029). Multiple logistic analysis revealed no definitive predictive factors for the occurrence of cement leakage (yes/ no) (Odds Ratio [95% CI], P):. Severity (acc to Genant et al): 1.82 [0,69 – 4.89], 0.229. Fracture Type (Genant et al): 1.22 [0.64 – 2.32], 0.550. Injected Volume: 0.98 [0.76 – 1.27], 0.875. Spinal Region: 0.87 [0.48 – 1.55], 0.628. Cement Viscosity: 0.42 [0.16 – 1.10], 0.076. Conclusion: No major differences in clinical outcome after PVP in OVCFs using low and medium viscosity PMMA bone cement were found. Viscosity of PMMA bone cement is likely to influence cement extravastion, although this could not be confirmed

Introduction: Aseptic loosening is a long-term complication of many cemented arthroplasty procedures. The integrity of the fixation interface, in particular the level of interdigitation between cement and bone, is crucial to sustaining the stability of arthroplasty components[. 1. ]. Studies have shown that the viscosity of cement at the time of application is a significant parameter in determining this level of interdigitation[. 2. ]. However, the rheological properties of cement at key stages in arthroplasty procedures have not been quantified, and it is unclear if current operative techniques achieve optimum cement delivery properties. Furthermore, because the cure process of bone cement is highly dependent on environmental conditions, it is extremely difficult to accurately predict the time to curing. Oscillatory shear rheometry can be used to characterise the viscoelastic properties of bone cement. However, most commercial rheometers used for this purpose are too large, expensive and delicate for peri-operative use. The aim of this work is to develop a new laboratory method for measuring the viscoelastic properties of bone cement at the time of application and to investigate the relationship between these properties and the level of cement interdigitation. Methods: A simple, inexpensive electromagnetic rotary actuator has been developed to provide accurate measurements of force, displacement and velocity without the use of sensors. These parameters can be used to continually monitor both viscous and elastic properties of curing bone cement. To consider subjective cementation techniques, a method has been devised where a surgeon indicates early and late doughing stages for a PMMA bone cement within a clinical environment. A computer interface has been developed to plot the real-time properties of the cement that are measured using the self-sensing device concurrently. The range of practical variability of cement delivery properties is then established. In order to investigate the effect of cement viscosity on the level of interdigitation a rig has been developed in which cement is applied to a standardised bone analogue under controlled conditions. The open pore ceramic analogue has been shown through microCT scanning to have a structure that is representative of the trabecular structure in human bone. CMC solution is used to represent back bleeding. Once set, the sample is evaluated using microCT to measure the level of interdigitation. Results: Preliminary results show that bone cement has largely viscous properties following mixing and largely elastic properties towards setting. Values of dynamic viscosity obtained show the cement to have a low viscosity following mixing, then as polymer beads begin to dissolve in the monomer, the viscosity rapidly increases. The rate of viscosity increase then slows as polymer chains are created, before a final rapid increase in viscosity indicating the onset of setting. Conclusion: A validated method has been developed to measure the viscoelastic properties of curing bone cement at key stages in arthroplasty procedures and to investigate the effect of these viscoelastic properties using a simple standardised bone model

Aims

Periprosthetic hip fractures (PPFs) after total hip arthroplasty are difficult to treat. Therefore, it is important to identify modifiable risk factors such as stem selection to reduce the occurrence of PPFs. This study aimed to clarify differences in fracture torque, surface strain, and fracture type analysis between three different types of cemented stems.

Bone cement with an antibiotic additive is currently widely available, gentamicin being the most common type. However, the high resistance of such organisms as staphylococci to gentamicin has popularised the practice of adding additional antibiotic powders to the cement mix. This study aims to quantify the effects of adding 1g active of seven antibiotics on the viscoelastic properties of the cement from mixing to set time using a robust rheometer, developed at the University of Leeds. CMW1 Radiopaque cement was the base cement selected for its widespread familiarity. Viscosity and elasticity were recorded at two rates of shear until the cements set. Viscosity was found to decrease with shear rate, but the cements were found to have a significant elastic component that greatly increased with shear rate. This indicates that for maximum cement penetration, maintained pressure would be more effective than “hammering”. It should be noted that the effects described above are small compared to other theatre variables, especially temperature and humidity

Introduction: The viscosity of bone cement used in total joint arthroplasty is an important for determining the proper handling characteristics of the cement and its interlock with bone. The degree of penetration and, therefore, the integrity of the arthroplasty are dependent on the viscosity of the bone cement system. As yet there is still no standard measurement of the efficacy of each bone/cement system with regard to the ability of the cement to penetrate the interstices of the bone. Aim: To quantify the rheological properties of bone cement systems with the view to assisting in cement selection for orthopaedic purposes. Material & Methods: The rheological properties of a variety of current bone cements were determined using a novel apparatus developed at the CSIRO called the Micro Fourier Rheometer (MFR). This device measures the complex viscosity and complex modulus by subjecting a sample to small amplitude oscillatory squeezing between two parallel plates. The force transmitted through the sample is detected by a dynamic load cell and the complete signal spectrum is then analysed using Fourier Techniques. The bone cement is mixed according to manufacturers’ instructions and placed between the plates and is then subjected to a random displacement. Subsequent Fourier analysis lends itself to rheological parameters such as real and imaginary modulus, viscosity and phase (1–100 Hz). Results: Consistent with earlier studies, it was found that the viscosity increased with time in an almost linear manner due to the progression of the polymerisation reaction of the cement. Thereupon the cement mass began its exothermic phase and the viscosity increased exponentially until fully set. The complex modulus at this time, when extrapolated to zero frequency, corresponded to the static modulus (as in conventional mechanical testing). The viscosity was highly dependent upon the shear rate (or frequency). As the cement was sheared the viscosity reduced, establishing the pseudo-plastic or shear-thinning nature of these materials. The phase provided an accurate measure of the setting and working time of the cement brands corresponding with studies by Krause (1982) and Ferracane (1981). Conclusions: The results supported the conclusion that rapid insertion of the prosthesis is recommended, creating high shear stresses, thus decreasing the cement’s viscosity and allowing better cement penetration and mechanical interlock. The study highlights the differences between the major brands of bone cement

There exists a lot literature referring to the cementing technique of hip replacements, but when talking about longevity of knee prostheses only seldom the cementing technique is mentioned even though 90% of the knees are cemented. Especially the tibial component, that has to cope with different forces such as pressure, rotation, tilt and sliding, is said to last longer when cemented. Cementing Technique: There are many aspects that need to be thought of when cementing knee prostheses:. The preparation of the bone: The preparation of the surface of the bone is of great importance, as the-bond of the cement with the bone is by the shape of the surfaces and not by a chemical reaction. A good penetration of the cement into the cancellous-bone enlarges the connecting surface and optimizes the power transmission. The pulse-lavage is the most effective to open the spongy bone. Sclerotic bone needs to be penetrated. Selection of cement: PMMA-cement (Polymeth-ylmetacrylat) is used with proven effectiveness since 1958 (Charnley). Very Similar to the well known cement Palacos (BiometMerck) is the new SmartSet GHV (DePuy) but it provides a longer time for processing, which is useful when cementing all components in one go. Mixing and hardening time are therefore shorter. Mixing of the cement: Mixing is mostly done manually even though it is known that the quality of the cement is minor than with a vacuum system. The advances of such a system are better microporosity, no air bubbles, and safety for the staff, who breathe less fumes. Application of cement – viscosity: The cement can be applied to the prosthesis or directly onto the bone. If the implant is precoated, the viscosity of the cement should be low to achieve better joint. The bone should in any case be dry to avoid mixing with blood. Pressure: During implantation a short high pressure is of importance for the depth of penetration. Some implants have an edge to guarantee better distribution of the pressure. During the hardening of the cement the pressure has to b ekept at a certain level as the volume of the cement changes a bit during the polimerisation. Hardening: The pressure needs to be controlled avoiding small movements. When cementing all components at once the ligaments have to be balanced, otherwise unnoticed deviations might occur. The leg should not be hyperextended to avoid tilting of the components. Temperature of polimerisation: The temperature can be reduced in vivo by cooling of the bone or the cement and by good spongy bone that transports the temperature away. If the cement penetrates more than 5 mm or its homogeneous thickness is more than 3mm osteonecrosis is likely to occur. Thickness of cement layer: Several authors and the finite element measurements found out, that acement layer from 2–5 mm ensures good stability for the tibial component. Cementing the shaft does not lead to significant better results but may lead to atrophy of the bone underneath the tibial plateau. Femoral components show good results also uncemented. Excess of cement: Cement that juts out must be removed especially in the dorsal parts, where an impingement can be produced. Bits in the soft tissue must also be removed with care. Cement should not touch the polyethylene during the whole procedure. Antibiotics: The quality and longevity of the cement is reduced by adding antibiotics because of resulting higher porosity. A special management for risk patientsis necessary. When cementing knee prostheses one should give high attention to the cementing technique as especially a good anchorage of the tibial component will lead to longevity of the implant