In the constant-brake-mean-effective-pressure experiments, at a brake mean effective pressure of 2.5 bar, diesel–propane and diesel–methane combustion behaved very similarly, the primary differences being in the preignition chemistry and the ignition delay trends. This study aims to investigate stress and strain distributions in the proximal tibia for full cementation and surface cementation of the Genesis II tibial component. A new concept of long stem with a distal polymeric (flexible material) tip reduces the magnitude of stresses at the end of the stem and therefore can theoretically contribute to reduce pain. Micromotion of each cup was measured in a custom made jig with linear variable differential transducers. Results suggested that cup geometry and proper surgical technique--in particular, proper sizing and depth of the acetabular cavity--are important in determining initial cup stability independent of adjuvant screw or spike fixation. For this material, the manufacturer specifies a compressive strength of 157MPa. Material and methods For diesel–propane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency increased to 39% as the percentage energy substitution was increased to 46%. Therefore it is suggested that higher energy strikes increase fracture risk, but do not offer large improvements to fixation or implant‐bone apposition. This experimental study investigated the effect of fins on the initial stability of the acetabular cup. Ten cavities produced during actual hip arthroplasty using debris-retaining reamers were replicated in dental alginate. Methods This project aims to provide a greater understanding of the six-axis biomechanics of the spine and the pre-clinical testing of spinal devices. Clinical studies using radiostereophotogrammetry have shown that those cemented hip prosthesis that migrate rapidly in the first two post-operative years are the ones that require early revision. A total of 16 specimens for each peg geometry were tested for two types of polyurethane foam blocks (Sawbones, Pacific Research Laboratories, Inc., WA) representing hard (40 PCF, 0.64 g/cm 3, 759 MPa, Sawbones #1522‐05) and soft (15 PCF, 0.24 g/cm 3, 123 MPa, Sawbones #1522‐02) bone. However, it does test peripheral fixation effectively, and has been shown to produce similar results to other fixation testing methods. Results Multi-pelvis characterisation of articular cartilage geometry, Acetabular Morphology: Implications for Joint-preserving Surgery, Initial stability of press-fit acetabular components: an in vitro biomechanical study, Press-fit acetabular cup fixation: Principles and testing, Alignment in total knee arthroplasty. We have shown that it is possible to measure the 3D relative translations and rotations of an acetabular cup inside the pelvis and simultaneously to measure the full‐field strain distribution in the bone surface. Acetabular defects were simulated in the Sawbones model. The range of subject-to-subject variations in the tibial slopes was substantive for males and females. The tri-spike fixation does not restrict motion at the ilium to the extent as the dome screws, but its effect at the ischium and pubis is much more pronounced. Objective: Their surface porosity is thought to promote the rapid osseointegration needed for stability and long-term mechanical support, because of reduced relative motion between components and native bone [7].This primary stability also depends on bone mineral density (BMD),"snug fit" between cup and acetabular bone when press-fit, and the surface porosity of components, The “Cervical Spine Injury Mechanism Analysis in Rugby Union” project is research programme funded by the RFU Injured Players Foundation (IPF). Exact fit conditions and two-millimeter press-fit were investigated. The architecture of the surrounding trabecular bone also was altered by the micromotion of the implant. graft (10 20 mm) (1522-04; Sawbones) (Figure 1). 2012;Small et al. Nevertheless, micromotions still apply as the golden standard and are preferred when high accuracy is necessary. Stem design does appear to impact the incidence of end-of-stem pain in revision total knee arthroplasty. The implants that had stable ingrowth of bone were surrounded by a zone of trabecular atrophy, whereas those that had unstable ingrowth of bone were surrounded by a zone of trabecular hypertrophy. An increase of press-fit from 0.7 mm to 1.2 mm did not significantly increase implant stability. The centers of each cube were marked and, in accordance with manufacturer recom-mendations, a 2.5-mm pilot hole was created for the 30 PCF cubes using a drill press. Such information is required to test and improve wear, strength and fixation stability of hip implants. In total, 79 patients (54 female) returned, with mean time since surgery of 12 years (10 to 14). Contact Us to create a custom product or solution that's ideal for your specific needs. The purpose of the present biomechanical investigation was to compare the in-vitro initial stability of a modular press-fit acetabular component using a polyethylene liner and using an alumina liner. On the basis of the good clinical results with the Monoblock cup, the upper limit of 100 µ of micromotion for osseointegation in macerated bone is probably set too low. Distal migration (called 'subsidence' in this paper) of up to 0.1 mm was measured; however the variability in absolute prosthesis migration was very high despite efforts to ensure that all extraneous factors were minimised. Cup designs use varied mechanisms for initial stability in bone; therefore, using different analogues and tests is appropriate. We observed a wide variation in the ability of the femoral prosthesis templates to reproduce normal femoral offset. The mechanical axis of the leg was significantly better in the computer-assisted group (96%, within +/- 3 degrees varus/valgus) compared with the conventional group (78%, within +/- 3 degrees varus/valgus). The follow-up was radiological and clinical. Measurement Stress relaxation in the bone caused a reduction in cup deformation of 13.52±4.06% after 1min and 29.34±5.11% after 10min. A device to measure prosthesis movement relative to bone was designed and fabricated. resultant torque: 1.5 Nm) and for ceramic-on-polyethylene (CoP: µ = 0.063; max. The peak strains were in the superior aspect of the acetabulum during Walking and in the superior-posterior aspect of the acetabulum and at the bottom of the posterior column during Standing-Up. Component seating was indexed by the distribution of bone-cup contact and the thickness of the gap between the component backing and the bone. Restoration of function is a goal of a different order and forms the scope of this book. The results do not contrast with those achieved using the same cup inserted with a polyethylene liner. Measuring relative micromotion between implant and bone is recognized as the golden standard for implant stability testing as this micromotion is directly linked to the long-term fixation of cementless implants. In vitro and in silico characterizations of augmented open-cell … This difference was more pronounced at low BMD, with the well-established PAC cup displaying less relative motion than the more porous GAC cup, consistent with better osseointegration than the more porous cup. In addition, bone remodeling simulations predict more extensive bone resorption under the baseplate for full cementation (43%) than for surface cementation (29%). This highlights the need to incorporate hip motion and measure all degrees of freedom when assessing cup micromotion. They allow good bone ingrowth, adequate implant contact and good stability. The results show a comparable behavior under load of tetrapods+coll and bone chips and suggest that tetrapods+coll could be an attractive alternative to bone chips. Part 1: Experimental simulation, A review of pre-clinical testing of femoral stem subsidence and comparison with clinical data, Total Knee Arthroplasty: A Guide to Get Better Performance, Acetabular options: Notes from the other side, Detailed characterization of diesel-ignited propane and methane dual-fuel combustion in a turbocharged direct-injection diesel engine, Initial Stability of Modular Acetabular Components. Two cemented tibial designs from two manufacturers and one porous metal monoblock cementless tibial design were studied. In 90% of the paired insertion tests, the screw identified by the surgeon as being easier to initially insert was the MS. The largest average differences were observed in the resistance to ultimate spin-out, with Ananova outperforming Exceed ABT and Plasmacup by 26 % and 17 % in the moderate and by 36 % and 38 % in the severe defect models, respectively. ... Sawbones blocks and sheets may be laminated or shaped for all your custom applications. Overall surface variation from hemispheric form in conventionally reamed cavities exceeded the experimental reamer's results (P < .005). There is a need for an experimental test which could ensure prostheses were not susceptible to aseptic loosening. Tilting moments determined with Method 1 ranged from 2.73 ± 0.24 Nm to 49.08 ± 1.50 Nm, and with Method 2, they ranged from 41.40 ± 1.05 Nm to 112.72 ± 5.33 Nm. Rapid migration of a cemented prosthesis relative to bone has been shown in vivo to correlate with early failure, and in this paper a method to make such migration measurements in vitro is described and tested. The MS was found to be easier to engage with the bone tunnel and initially insert than the CS while still achieving similar immediate postsurgical fixation strength. This effect was most pronounced in low-density bone at high strike velocities. Clinical and radiographic assessment was performed preoperatively, 6 and 12 months postoperatively, and annually thereafter. However, so far, this was found for one specific defect type and primary stability should be further investigated in additional/more severe defects. The acetabular opening plane was orientated in 21 degrees +/- 5 degrees for version, 48 degrees +/- 4 degrees for inclination and 19 degrees +/- 6 degrees for acetabular tilt with no gender differences. Results: The stability of the cup was assessed in two ways: (a) measurement of micromotion of the cup in 6 degrees of freedom under physiological loading and (b) uniaxial push-out tests. There were 58 cemented and 21 cementless tibial components. Kinematic results from the rigid body analyses were nearly identical to those from the fully deformable model, and the contact pressure and contact area correlation was acceptable given the great reduction in analysis time. Thirty-eight paired, size-matched, fresh-frozen cadaver acetabulae were used to study reamed surface topography and the seating of on-line versus oversized noncemented components. Evaluation consisted of a Knee Society clinical score and assessment of patient satisfaction. The force induced by the drop weight and cup seating after each impact was recorded. Impaired osseointegration in osteoporotic bone because of increased micromovement is not to be expected in the investigated cementless hip cups as no relevant differences in micromovement were found between normal and osteoporotic bone stock. This model was used in a previous study. All rights reserved. 2004;Jin et al. The experimentally assessed perception threshold followed the lowest excitation threshold of the modeled fibers. The loading profile simulated hip impingement at the extremes of motion and subluxation relocation of the hip joint. New porous implant designs attempt to improve outcomes due to improved osseointegration; however, sufficient primary stability is paramount for good osseointegration. Thereby, push-in force, lever-out moment, lever-out angle, and interface stiffness were determined. 1522-440, Sawbones Europe AB, Malmö, Sweden]. Widespread surveillance of existing implants is urgently needed alongside the carefully monitored introduction of new implant designs. We therefore determined (1) the spatial acetabular rim profile, (2) the topography of the articular lunate surface, and (3) the 3-D relationships of the acetabular opening plane comparing 66 bony acetabula from 33 pelves in female and male pelves. Static load testing revealed unacceptable micromovement over 150 microns (.150 mm) in most cups with 300-kg loads. Testing and Materials standard F1839-97 (Sawbones Solid Rigid Foam 1522-04; Pacific Research Laboratories, Figure 1. Explicit dynamic FE analyses have recently been used to efficiently predict TKR kinematics and contact mechanics during dynamic loading conditions. The press-fit cup was designed in two variants and manufactured using selective laser melting (SLM). Simulations reveal that both cementation techniques result in lower cancellous stresses under the baseplate compared to the intact tibia, with greater reductions being computed for full cementation. The objective of this study was to develop and experimentally validate an explicit FE TKR model that incorporates tibio-femoral and patello-femoral articulations. Both cemented all-polyethylene cups and cementless sockets have benefited from improvements in surgical techniques, cup designs, and bearing surfaces. The FE model described four horizontal layers; stratum corneum, epidermis, dermis, and hypodermal used to estimate the excitation threshold of Aβ-fibers terminating in dermis and Aδ-fibers terminating in epidermis. Most also rotated into varus. The model confirms that preferential excitation of Aδ-fibers may be achieved by small electrode stimulation due to higher current density in the dermoepidermal junction. Lateralization models with a 36mm glenosphere with neutral tilt and parallel screws. The varus/valgus alignment of the tibial components of 350 total knee arthroplasties was assessed radiologically. Different design solutions have been suggested for improvement of the initial stability of cementless acetabular cups, such as adding threads, spikes, or pegs to the hemispherical geometry, the pore structure of the surface; and screw fixation. Press-fit cup stability was tested in the following: firstly, polyurethane (PU) foam modelling cancellous support; secondly, glass-fibre reinforced epoxide (GFRE) tubes modelling acetabular cortical support; thirdly, cadaveric acetabula. Higher seating forces associated with the PSL design may result in inadequate seating and increased risk of component malpositioning or acetabular fracture in the intra-operative setting in high-density bone stock. The pull-out forces of the Ti-variant (complete-526 N, reduced-468 N) and the Ti-S variant (complete-548 N, reduced-526 N) as well as the lever-out moments of the Ti-variant (complete-10 Nm, reduced–9.8 Nm) and the Ti-S variant (complete-9 Nm, reduced–7.9 N) show no significant differences in the results between complete and reduced cups. The micromotion measurement device consisted of a 'target' of three spheres arranged in a cruciform structure. Developments for the future are improved delivery of care and training for surgeons and clinical teams. Depending on implant design, a different biomechanical behavior in osteoporotic bone and in bone with normal bone mineral density might be expected. The ability of the cups to withstand these critical impact forces indicates they are unlikely to fracture in normal clinical use and should meet the more challenging demands of active patients likely to receive this device. However inducible displacement trends provide a clinically comparable performance ranking. The determined lever-out moments range from 15.53 ± 1.38 Nm (intact cavity) to 1.37 ± 0.54 Nm (83%/50% defect). Copyright © 2018 Sawbones. Initial stability is an essential prerequisite to achieve osseointegration of press-fit acetabular cups in total hip replacements. Understanding the sensory and sympathetic innervation of bone should provide a better understanding of the mechanisms that drive bone pain and aid in developing therapeutic strategies for treating skeletal pain. In conclusion, Method 1 simulates the technique used by orthopedic surgeons to assess the correct fit of the trial cup, while Method 2 simulates the tilting of the cup in the acetabular bone cavity under in situ loading with the hip resultant force. Background Measures 130 mm x 180 mm x 40 mm. The aim of this study was to examine the influence of cup design and liner assembly on the deformation response during cup implantation. Initial stability has been identified as a crucial factor to achieve osseointegration and long-term survival. Aim of this study was to examine the influence of screw fixation on the primary stability of press-fit cups. But with increasing loads, the material became stiffer, and at high loads, the stress-strain curve became linear with a short-term tangent modulus of 1.9 MPa at a stress level of 0.5 MPa and a compressive strain level of 50%. None of the patients shown signs of aseptic augment or acetabular cup loosening. Results: Postoperatively, patients were monitored for two years on average period of 24-36 months. Because replacement is increasingly considered for patients younger than 55 years, improved decision making about whether a patient should undergo the procedure is needed. In order to ensure the best possible bone ingrowth of cementless acetabular cups, the primary stability of press-fit cups has been experimentally investigated and characterized in recent decades. A cadaver experiment was performed on 11 acetabuli implanted with a cementless acetabular cup. At a mean follow-up of two years (range 24-36 months) one patient had reinfection and one patient had infection. At the long-term follow-up, patients had supine RSA examinations to determine migration and loaded examinations (single leg stance) to determine inducible displacement. (B) Lateralization via bone graft. Full cementation results in greater stress reduction under the tibial baseplate than surface cementation, suggesting that surface cementation will result in less proximal bone resorption, thus reducing the possibility of aseptic loosening. 85% of the pushout fixation achieved using a 15 J impaction strike was attained by using a 7.5 J strike energy. Acetabular augments were used when preoperative and intraoperative findings indicated the presence of large acetabular defects that can hinder the stability of the revision implants. Whilst fixation of femoral stems achieves good clinical results, the fixation of acetabular components remains a challenge. Immediate postoperative stability of femoral stems is one of the key factors for the long-term success of total hip replacement. There were no significant associations between polar gap and any of the parameters considered. The surface structures consist of repeated open-porous, load-bearing elements orthogonal to the acetabular surface. Hyaluronan induces formation of a synovial lining like layer. Therefore, using a biomechanical cup block model, a press-fit cup design with a macro-structured surface was pushed into three cavity types (intact, moderate superior defect, and two-point-pinching cavity) made of 15 pcf and 30 pcf polyurethane foam blocks (n = 3 per cavity and foam density combination), respectively. The perception thresholds of 11 electrodes with diameters ranging from 0.2 to 20 mm were modeled and assessed on the volar forearm of healthy human volunteers by an adaptive two-alternative forced choice algorithm. All rights reserved. Principal cortical bone strains were measured experimentally in intact, surface cemented and fully cemented synthetic tibiae using strain gauges. Sympathetic fibers were labeled with an antibody raised against tyrosine hydroxylase. The elapsed time in training and test stage are 321.76 s and 5.69 s. To test the hypothesis that the acetabulum is non-spherical, a best-fit ellipsoid was also fitted to the geometry. The initial stability of cementless implants is one of the main concerns of these preclinical evaluations. The experimental cup was significantly more secure in most modes than other cups; the H-G II and Optifix cups showed similar stabilities, lower than that of the experimental cup but greater than that of the PCA cup (analysis of variance and Tukey's highly significant test; p < 0.001). The purpose of this study was to measure the structural properties of the latest design (fourth-generation) of composite femurs and tibias from Pacific Research Laboratories, Inc. Fourth-generation composite bones have the same geometries as the third-generation bones, but the cortical bone analogue material was changed to one with increased fracture and fatigue resistance, tensile and compressive properties, thermal stability, and moisture resistance. Original and simplified bone defect volume showed a conformity of 99%. When unstable implants were tested, motions were 1-2 order of magnitude higher. Each side was randomly implanted with one of the implants. To avoid the potential problems associated with screws that are often used to obtain initial stability of uncemented acetabular components, oversizing of the component has been recommended. A quantitative in vitro assessment of fit and screw fixation on the stability of a cementless hemispherical acetabular component, Areas of Contact and Extent of Gaps With Implantation of Oversized Acetabular Components in Total Hip Arthroplasty, Stem curvature and load angle influence the initial relative bone-implant motion of cementless femoral stems, Reamed surface topography and component seating in press-fit cementless acetabular fixation, In Vivo Skeletal Responses to Porous-Surfaced Implants Subjected to Small Induced Motions*, Inaccuracy of acetabular reaming under surgical conditions, Pain at the End of the Stem After Revision Total Knee Arthroplasty, Radiographic anatomic structure of the arthritic acetabulum and its influence on total hip arthroplasty, A comparison between automatically generated linear and parabolic tetrahedra when used to mesh a human femur, Measurement of the migration of cemented hip pros-thesis - An In vitro test, Initial stability of modular acetabular components. A long-term problem associated with total joint replacements is the formation of a fibrous tissue at the bone-cement interface which may compromise the fixation of the prosthesis. The cadaver test was used to establish the most suitable configuration of the foam model representing realistic support and geometrical conditions at the pelvis. For computational efficiency, we developed rigid body analyses that can reasonably reproduce the kinematics, contact pressure distribution, and contact area of a fully deformable system. However, the significant association between percentage bone yielding and interference fit (p < 0.0001) suggests a higher periacetabular fracture risk at higher interference fits. With a compressive strength of 18MPa 118 and a compressive modulus of 445MPa, in its solid test block form, the material has mechanical Six linear variable displacement transducers were aligned with the spheres so that motion of the prosthesis relative to the bone could be measured. The templates were then ranked according to their ability to reproduce the normal anatomical offset. Overview of the tested acetabular models; two single bone models (specimen 1 and 2) and four sets of three identical models (specimen [3][4][5][6]. On average it is 23% larger when going upstairs than during normal level walking. Cellular synthetic bones were used in this study because obtaining fresh human cadaver bones is difficult. At a brake mean effective pressure of 2.5 bar, the nitrogen oxide and smoke emissions were simultaneously reduced while the carbon monoxide and total unburned hydrocarbon emissions were increased. Stiff metal implants, which do not have the same elasticity as the surrounding bone, cause stress shielding. Preoperative templating is recommended to ensure that the size and orientation of implants is optimised. The most accurate was the CPS-Plus (Root Mean Square Error 2.0 mm) followed in rank order by: C stem (2.16), CPT (2.40), Exeter (3.23), Stanmore (3.28), Charnley (3.65), Corail (3.72), ABG II (4.30), Furlong HAC (5.08) and Furlong modular (7.14). The significant interference fit‐elastic modulus interaction suggests increasing the interference fit in patients with low bone quality leads to a greater reduction in micromotion than in patients with higher bone quality. The mechanical loading and function of the hip joint and proximal femur is thereby completely documented. The paper focuses on the loading of the femoral implant component but complete data are additionally stored on an associated compact disc. 3.0 Sawbones Scoundrel Overview ... 15:22. Biomechanical testing showed pullout strength of the anchor and tendon graft in a Sawbones model (Model 1522-04; Pacific Research Laboratories, Vashon, WA) to be 162 N. The density of these blocks was comparable to that of normal human cancellous bone (481 kg/m 3) (Sawbones; and ASTM International, West Conshohocken, PA). The pilot osteotomies were prepared using the pilot instrument (Supplementary Table S1) at 2000 rpm in a turning machine (TesT GmbH) to allow Most in vitro methods that assess cup stability do not reproduce physiological loading conditions and use simplified acetabular models with a spherical cavity. Acetabular components were seated with 0.8 mm to 2 mm interference fits in reamed polyethylene bone substrate of two different densities (0.22 g/cm(3) and 0.45 g/cm(3)). However, the ingrown bone was in continuity with the surrounding bone only in the groups of implants that had not been subjected to motion or that had been subjected to twenty micrometers of motion; in contrast, the implants that had been subjected to forty micrometers of motion were surrounded in part by trabecular bone but also in part by fibrocartilage and fibrous tissue, and those that had been subjected to 150 micrometers of motion were surrounded by dense fibrous tissue. Both axial and 15° flexion loading were considered. Porous metal augments show comparable excellent radiographic and clinical short-term outcomes, when combined with cemented or uncemented cups in revision hip arthroplasty. Eight cups from six manufacturers were press-fit into acetabular cavities prepared in two densities of Sawbones polyethylene foam and in bovine knee trabecular bone. Seating of the on-line hemispherical cups was best near the pole and poorest near the equator, whereas the converse was true for the 1-mm oversized dual-radius cups. While the periosteum is the most densely innervated tissue, when the total volume of each tissue is considered, the bone marrow receives the greatest total number of sensory and sympathetic fibers followed by mineralized bone and then periosteum. We see a clear influence of the cup wall thickness on the elastic deformability and accordingly on the primary stability of the examined cups. The experimental setup: the drop platen enabled repeatable hammer strikes to be applied with known energy. Micromotions resulting from CoC were statistically lower than those resulting from CoP (p < 0.05). The in vivo skeletal responses to the different magnitudes of relative motion were evaluated. Methods: Additionally, experimental and numerical deformation, push-out and lever-out tests of press-fit acetabular cups were carried out to assess the influence of the chosen material definition (linear elastic and CFP) on the numerical results. For a relatively thin cup with a wall thickness between 2.3 mm (equator) and 4 mm (pole) and with a modest nominal diametral interference of 1 mm, which corresponds to an actual interference of approximately 0.5 mm, the maximum diametral cup deflection (at the rim) was around 60 microm, compared with a diametral clearance of 80-120 microm between the femoral head and the acetabular cup, generally required for fluid-film lubrication and tribological performances. Relevance. The current move towards digitisation of X-rays may offer manufacturers an opportunity to improve template designs in certain instances, and to develop appropriate computer software. The coronal alignment of the femoral component was also more accurate in the computer-assisted group. It was found that a spherical cavity, with two identical areas relieved on opposite sides, was capable of creating a two-point pinching action of the ischeal and ilial columns on the cup as the worst-case scenario. The bone mineral density does have a significant influence on resultant relative motion (P = .0406), with higher bone mineral density correlating with less relative motion in both implants. The four designs are the Charnley (DePuy International Ltd., UK), the Exeter (Stryker Osteonics Howmedica Corp., USA), the Lubinus SPII (Waldemar-Link GmbH, Germany), and the Miiller Curved (JRI Ltd, UK). This paper proposes a discrete particle model based on the random-walk theory for simulating cement infiltration within open-cell structures to prevent osteoporotic proximal femur fractures. Aseptic loosening is the main reason for revision of total hip arthroplasty, and relative micromotions between cementless acetabular cups and bone play an important role regarding their comparatively high loosening rate. A high mallet mass with low strike velocity resulted in satisfactory implant stability and polar gap, while minimizing the risk of losing stability due to over-striking. For this reason two of these foams (Refs. End-of-stem pain was associated with solid cobalt chrome stems while a lower incidence of stem pain was associated with slotted titanium stems. They challenged them to define new thresholds of functional capacity after Total Knee Arthroplasty. It helps correct malalignment, restore satisfactory ligament tension and height of the joint line. Sufficient primary fixation stability is the basis for the osseointegration of cementless acetabular cups. Histological analysis demonstrated growth of bone into the porous coatings of all of the implants, including those that had been subjected to 150 micrometers of motion. Selection of acetabular shell and technique of implantation is an important factor as is the stem for a successful THA.
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