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Jonathan R T Jeffers - One of the best experts on this subject based on the ideXlab platform.
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Micromotion and push out evaluation of an additive manufactured implant for above the knee amputees
Journal of Orthopaedic Research, 2019Co-Authors: Spencer C Barnes, Anthony M. J. Bull, Jon C Clasper, Jonathan R T JeffersAbstract:In comparison to through-knee amputees the outcomes for above-the-knee amputees are relatively poor; based on this novel techniques have been developed. Most current percutaneous implant-based solutions for transfemoral amputees make use of high stiffness intramedullary rods for skeletal fixation, which can have risks including infection, femoral fractures, and bone resorption due to stress shielding. This work details the cadaveric testing of a short, cortical bone stiffness-matched subcutaneous implant, produced using additive manufacture, to determine bone implant Micromotion and push-out load. The results for the Micromotions were all <20 μm and the mean push-out load was 2,099 Newtons. In comparison to a solid control, the stiffness-matched implant exhibited significantly higher Micromotion distributions and no significant difference in terms of push-out load. These results suggest that, for the stiffness-matched implant at time zero, osseointegration would be facilitated and that the implant would be securely anchored. For these metrics, this provides justification for the use of a short-stem implant for transfemoral amputees in this subcutaneous application. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2104-2111, 2019.
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total ankle replacement design and positioning affect implant bone Micromotion and bone strains
Medical Engineering & Physics, 2017Co-Authors: Ran Sopher, Andrew A. Amis, James D F Calder, Jonathan R T JeffersAbstract:Abstract Implant loosening – commonly linked with elevated initial Micromotion – is the primary indication for total ankle replacement (TAR) revision. Finite element modelling has not been used to assess Micromotion of TAR implants; additionally, the biomechanical consequences of TAR malpositioning – previously linked with higher failure rates – remain unexplored. The aim of this study was to estimate implant-bone Micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses, and thereby identify fixation features and malpositioning scenarios increasing the risk of loosening. Finite element models simulating three of the most commonly used TAR devices (BOX ® , Mobility ® and Salto ® ) implanted into the tibia/talus and subjected to physiological loads were developed. Mobility and Salto demonstrated the largest Micromotion of all tibial and talar components, respectively. Any malpositioning of the implant creating a gap between it and the bone resulted in a considerable increase in Micromotion and bone strains. It was concluded that better primary stability can be achieved through fixation nearer to the joint line and/or while relying on more than a single peg. Incomplete seating on the bone may result in considerably elevated implant-bone Micromotion and bone strains, thereby increasing the risk for TAR failure.
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implant design and positioning affect the interface Micromotion in total ankle replacement
Journal of Bone and Joint Surgery-british Volume, 2016Co-Authors: Ran Sopher, Andrew A. Amis, James D F Calder, Jonathan R T JeffersAbstract:Introduction Survival rates of recent total ankle replacement (TAR) designs are lower than those of other arthroplasty prostheses. Loosening is the primary indication for TAR revisions [NJR, 2014], leading to a complex arthrodesis often involving both the talocrural and subtalar joints. Loosening is often attributed to early implant Micromotion, which impedes osseointegration at the bone-implant interface, thereby hampering fixation [Soballe, 1993]. Micromotion of TAR prostheses has been assessed to evaluate the stability of the bone-implant interface by means of biomechanical testing [McInnes et al. , 2014]. The aim of this study was to utilise computational modelling to complement the existing data by providing a detailed model of Micromotion at the bone-implant interface for a range of popular implant designs, and investigate the effects of implant misalignment during surgery. Methods The geometry of the tibial and talar components of three TAR designs widely used in Europe (BOX®, Mobility® and SALTO®; NJR, 2014) was reverse-engineered, and models of the tibia and talus were generated from CT data. Virtual implantations were performed and verified by a surgeon specialised in ankle surgery. In addition to the aligned case, misalignment was simulated by positioning the talar components in 5° of dorsi- or plantar-flexion, and the tibial components in ± 5° and 10° varus/valgus and 5° and 10° dorsiflexion; tibial dorsiflexed misalignement was combined with 5° posterior gap to simulate this misalignment case. Finite element models were then developed to explore bone-implant Micromotion and loads occurring in the bone in the implant vicinity. Results Micromotion and bone loads peaked at the end of the stance phase for both the tibial and talar components. The aligned BOX and SALTO demonstrated lower tibial Micromotion (with under 30% of bone-implant interface area subjected to Micromotion larger than 100µm, as opposed to > 55% for Mobility; Figure 1). Talar Micromotion was considerably lower for all designs, and no aligned talar component demonstrated Micromotion larger than 100µm. The aligned SALTO showed the largest talar Micromotion (Figure 2). Dorsiflexed implantation of all tibial components increased Micromotion and bone strains compared to the reference case; interestingly, the SALTO tibial component, which demonstrated the lowest Micromotion for the aligned case, also demonstrated the smallest changes in Micromotion due to malpositioning (Figure 3). The posterior gap between the tibia and implant further increased bone strains. Dorsi- or plantar-flexed implantation of all talar components considerably increased Micromotion and bone loads compared to the reference case (Figure 2), often resulting in Micromotion exceeding 100µm. The SALTO talar component demonstrated the smallest changes in Micromotion due to malpositioning. Discussion The aligned Mobility had greater tibial Micromotion than the SALTO and BOX, which agrees with higher revision rates reported in registry data ( e.g. NZJR, 2014). The increased Micromotion associated with dorsi- or plantar-flexion misalignment highlights the importance of aligning the implant correctly, and implies that SALTO can be more “forgiving” for malpositioning than the other TAR designs. Implant design and alignment are therefore important factors that affect the implant fixation and performance of the reconstructed ankle.
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IMPLANT DESIGN AND POSITIONING AFFECT THE INTERFACE Micromotion IN TOTAL ANKLE REPLACEMENT
Journal of Bone and Joint Surgery-british Volume, 2016Co-Authors: Ran Sopher, Andrew A. Amis, James D F Calder, Jonathan R T JeffersAbstract:Introduction Survival rates of recent total ankle replacement (TAR) designs are lower than those of other arthroplasty prostheses. Loosening is the primary indication for TAR revisions [NJR, 2014], leading to a complex arthrodesis often involving both the talocrural and subtalar joints. Loosening is often attributed to early implant Micromotion, which impedes osseointegration at the bone-implant interface, thereby hampering fixation [Soballe, 1993]. Micromotion of TAR prostheses has been assessed to evaluate the stability of the bone-implant interface by means of biomechanical testing [McInnes et al. , 2014]. The aim of this study was to utilise computational modelling to complement the existing data by providing a detailed model of Micromotion at the bone-implant interface for a range of popular implant designs, and investigate the effects of implant misalignment during surgery. Methods The geometry of the tibial and talar components of three TAR designs widely used in Europe (BOX®, Mobility® and SALTO®; NJR, 2014) was reverse-engineered, and models of the tibia and talus were generated from CT data. Virtual implantations were performed and verified by a surgeon specialised in ankle surgery. In addition to the aligned case, misalignment was simulated by positioning the talar components in 5° of dorsi- or plantar-flexion, and the tibial components in ± 5° and 10° varus/valgus and 5° and 10° dorsiflexion; tibial dorsiflexed misalignement was combined with 5° posterior gap to simulate this misalignment case. Finite element models were then developed to explore bone-implant Micromotion and loads occurring in the bone in the implant vicinity. Results Micromotion and bone loads peaked at the end of the stance phase for both the tibial and talar components. The aligned BOX and SALTO demonstrated lower tibial Micromotion (with under 30% of bone-implant interface area subjected to Micromotion larger than 100µm, as opposed to > 55% for Mobility; Figure 1). Talar Micromotion was considerably lower for all designs, and no aligned talar component demonstrated Micromotion larger than 100µm. The aligned SALTO showed the largest talar Micromotion (Figure 2). Dorsiflexed implantation of all tibial components increased Micromotion and bone strains compared to the reference case; interestingly, the SALTO tibial component, which demonstrated the lowest Micromotion for the aligned case, also demonstrated the smallest changes in Micromotion due to malpositioning (Figure 3). The posterior gap between the tibia and implant further increased bone strains. Dorsi- or plantar-flexed implantation of all talar components considerably increased Micromotion and bone loads compared to the reference case (Figure 2), often resulting in Micromotion exceeding 100µm. The SALTO talar component demonstrated the smallest changes in Micromotion due to malpositioning. Discussion The aligned Mobility had greater tibial Micromotion than the SALTO and BOX, which agrees with higher revision rates reported in registry data ( e.g. NZJR, 2014). The increased Micromotion associated with dorsi- or plantar-flexion misalignment highlights the importance of aligning the implant correctly, and implies that SALTO can be more “forgiving” for malpositioning than the other TAR designs. Implant design and alignment are therefore important factors that affect the implant fixation and performance of the reconstructed ankle.
Andrew A. Amis - One of the best experts on this subject based on the ideXlab platform.
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total ankle replacement design and positioning affect implant bone Micromotion and bone strains
Medical Engineering & Physics, 2017Co-Authors: Ran Sopher, Andrew A. Amis, James D F Calder, Jonathan R T JeffersAbstract:Abstract Implant loosening – commonly linked with elevated initial Micromotion – is the primary indication for total ankle replacement (TAR) revision. Finite element modelling has not been used to assess Micromotion of TAR implants; additionally, the biomechanical consequences of TAR malpositioning – previously linked with higher failure rates – remain unexplored. The aim of this study was to estimate implant-bone Micromotion and peri-implant bone strains for optimally positioned and malpositioned TAR prostheses, and thereby identify fixation features and malpositioning scenarios increasing the risk of loosening. Finite element models simulating three of the most commonly used TAR devices (BOX ® , Mobility ® and Salto ® ) implanted into the tibia/talus and subjected to physiological loads were developed. Mobility and Salto demonstrated the largest Micromotion of all tibial and talar components, respectively. Any malpositioning of the implant creating a gap between it and the bone resulted in a considerable increase in Micromotion and bone strains. It was concluded that better primary stability can be achieved through fixation nearer to the joint line and/or while relying on more than a single peg. Incomplete seating on the bone may result in considerably elevated implant-bone Micromotion and bone strains, thereby increasing the risk for TAR failure.
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implant design and positioning affect the interface Micromotion in total ankle replacement
Journal of Bone and Joint Surgery-british Volume, 2016Co-Authors: Ran Sopher, Andrew A. Amis, James D F Calder, Jonathan R T JeffersAbstract:Introduction Survival rates of recent total ankle replacement (TAR) designs are lower than those of other arthroplasty prostheses. Loosening is the primary indication for TAR revisions [NJR, 2014], leading to a complex arthrodesis often involving both the talocrural and subtalar joints. Loosening is often attributed to early implant Micromotion, which impedes osseointegration at the bone-implant interface, thereby hampering fixation [Soballe, 1993]. Micromotion of TAR prostheses has been assessed to evaluate the stability of the bone-implant interface by means of biomechanical testing [McInnes et al. , 2014]. The aim of this study was to utilise computational modelling to complement the existing data by providing a detailed model of Micromotion at the bone-implant interface for a range of popular implant designs, and investigate the effects of implant misalignment during surgery. Methods The geometry of the tibial and talar components of three TAR designs widely used in Europe (BOX®, Mobility® and SALTO®; NJR, 2014) was reverse-engineered, and models of the tibia and talus were generated from CT data. Virtual implantations were performed and verified by a surgeon specialised in ankle surgery. In addition to the aligned case, misalignment was simulated by positioning the talar components in 5° of dorsi- or plantar-flexion, and the tibial components in ± 5° and 10° varus/valgus and 5° and 10° dorsiflexion; tibial dorsiflexed misalignement was combined with 5° posterior gap to simulate this misalignment case. Finite element models were then developed to explore bone-implant Micromotion and loads occurring in the bone in the implant vicinity. Results Micromotion and bone loads peaked at the end of the stance phase for both the tibial and talar components. The aligned BOX and SALTO demonstrated lower tibial Micromotion (with under 30% of bone-implant interface area subjected to Micromotion larger than 100µm, as opposed to > 55% for Mobility; Figure 1). Talar Micromotion was considerably lower for all designs, and no aligned talar component demonstrated Micromotion larger than 100µm. The aligned SALTO showed the largest talar Micromotion (Figure 2). Dorsiflexed implantation of all tibial components increased Micromotion and bone strains compared to the reference case; interestingly, the SALTO tibial component, which demonstrated the lowest Micromotion for the aligned case, also demonstrated the smallest changes in Micromotion due to malpositioning (Figure 3). The posterior gap between the tibia and implant further increased bone strains. Dorsi- or plantar-flexed implantation of all talar components considerably increased Micromotion and bone loads compared to the reference case (Figure 2), often resulting in Micromotion exceeding 100µm. The SALTO talar component demonstrated the smallest changes in Micromotion due to malpositioning. Discussion The aligned Mobility had greater tibial Micromotion than the SALTO and BOX, which agrees with higher revision rates reported in registry data ( e.g. NZJR, 2014). The increased Micromotion associated with dorsi- or plantar-flexion misalignment highlights the importance of aligning the implant correctly, and implies that SALTO can be more “forgiving” for malpositioning than the other TAR designs. Implant design and alignment are therefore important factors that affect the implant fixation and performance of the reconstructed ankle.
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IMPLANT DESIGN AND POSITIONING AFFECT THE INTERFACE Micromotion IN TOTAL ANKLE REPLACEMENT
Journal of Bone and Joint Surgery-british Volume, 2016Co-Authors: Ran Sopher, Andrew A. Amis, James D F Calder, Jonathan R T JeffersAbstract:Introduction Survival rates of recent total ankle replacement (TAR) designs are lower than those of other arthroplasty prostheses. Loosening is the primary indication for TAR revisions [NJR, 2014], leading to a complex arthrodesis often involving both the talocrural and subtalar joints. Loosening is often attributed to early implant Micromotion, which impedes osseointegration at the bone-implant interface, thereby hampering fixation [Soballe, 1993]. Micromotion of TAR prostheses has been assessed to evaluate the stability of the bone-implant interface by means of biomechanical testing [McInnes et al. , 2014]. The aim of this study was to utilise computational modelling to complement the existing data by providing a detailed model of Micromotion at the bone-implant interface for a range of popular implant designs, and investigate the effects of implant misalignment during surgery. Methods The geometry of the tibial and talar components of three TAR designs widely used in Europe (BOX®, Mobility® and SALTO®; NJR, 2014) was reverse-engineered, and models of the tibia and talus were generated from CT data. Virtual implantations were performed and verified by a surgeon specialised in ankle surgery. In addition to the aligned case, misalignment was simulated by positioning the talar components in 5° of dorsi- or plantar-flexion, and the tibial components in ± 5° and 10° varus/valgus and 5° and 10° dorsiflexion; tibial dorsiflexed misalignement was combined with 5° posterior gap to simulate this misalignment case. Finite element models were then developed to explore bone-implant Micromotion and loads occurring in the bone in the implant vicinity. Results Micromotion and bone loads peaked at the end of the stance phase for both the tibial and talar components. The aligned BOX and SALTO demonstrated lower tibial Micromotion (with under 30% of bone-implant interface area subjected to Micromotion larger than 100µm, as opposed to > 55% for Mobility; Figure 1). Talar Micromotion was considerably lower for all designs, and no aligned talar component demonstrated Micromotion larger than 100µm. The aligned SALTO showed the largest talar Micromotion (Figure 2). Dorsiflexed implantation of all tibial components increased Micromotion and bone strains compared to the reference case; interestingly, the SALTO tibial component, which demonstrated the lowest Micromotion for the aligned case, also demonstrated the smallest changes in Micromotion due to malpositioning (Figure 3). The posterior gap between the tibia and implant further increased bone strains. Dorsi- or plantar-flexed implantation of all talar components considerably increased Micromotion and bone loads compared to the reference case (Figure 2), often resulting in Micromotion exceeding 100µm. The SALTO talar component demonstrated the smallest changes in Micromotion due to malpositioning. Discussion The aligned Mobility had greater tibial Micromotion than the SALTO and BOX, which agrees with higher revision rates reported in registry data ( e.g. NZJR, 2014). The increased Micromotion associated with dorsi- or plantar-flexion misalignment highlights the importance of aligning the implant correctly, and implies that SALTO can be more “forgiving” for malpositioning than the other TAR designs. Implant design and alignment are therefore important factors that affect the implant fixation and performance of the reconstructed ankle.
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Digital volume correlation and micro-CT: An in-vitro technique for measuring full-field interface Micromotion around polyethylene implants.
Journal of Biomechanics, 2015Co-Authors: Chamaiporn Sukjamsri, Diogo M. Geraldes, Thomas Gregory, Farah Ahmed, David Hollis, Samuel Schenk, Andrew A. Amis, Roger Emery, Ulrich HansenAbstract:Abstract Micromotion around implants is commonly measured using displacement-sensor techniques. Due to the limitations of these techniques, an alternative approach (DVC-μCT) using digital volume correlation (DVC) and micro-CT (μCT) was developed in this study. The validation consisted of evaluating DVC-μCT based Micromotion against known Micromotions (40, 100 and 150 μm) in a simplified experiment. Subsequently, a more clinically realistic experiment in which a glenoid component was implanted into a porcine scapula was carried out and the DVC-μCT measurements during a single load cycle (duration 20 min due to scanning time) was correlated with the manual tracking of Micromotion at 12 discrete points across the implant interface. In this same experiment the full-field DVC-μCT Micromotion was compared to the full-field Micromotion predicted by a parallel finite element analysis (FEA). It was found that DVC-μCT Micromotion matched the known Micromotion of the simplified experiment (average/peak error=1.4/1.7 μm, regression line slope=0.999) and correlated with the Micromotion at the 12 points tracked manually during the realistic experiment (R2=0.96). The DVC-μCT full-field Micromotion matched the pattern of the full-field FEA predicted Micromotion. This study showed that the DVC-μCT technique provides sensible estimates of Micromotion. The main advantages of this technique are that it does not damage important parts of the specimen to gain access to the bone–implant interface, and it provides a full-field evaluation of Micromotion as opposed to the Micromotion at just a few discrete points. In conclusion the DVC-μCT technique provides a useful tool for investigations of Micromotion around plastic implants.
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analysis of bone prosthesis interface Micromotion for cementless tibial prosthesis fixation and the influence of loading conditions
Journal of Biomechanics, 2010Co-Authors: Desmond Y R Chong, Ulrich Hansen, Andrew A. AmisAbstract:Abstract A lack of initial stability of the fixation is associated with aseptic loosening of the tibial components of cementless knee prostheses. With sufficient stability after surgery, minimal relative motion between the prosthesis and bone interfaces allows osseointegation to occur thereby providing a strong prosthesis-to-bone biological attachment. Finite element modelling was used to investigate the bone–prosthesis interface Micromotion and the relative risk of aseptic loosening. It was anticipated that by prescribing different joint loads representing gait and other activities, and the consideration of varying tibial–femoral contact points during knee flexion, it would influence the computational prediction of the interface Micromotion. In this study, three-dimensional finite element models were set up with applied loads representing walking and stair climbing, and the relative Micromotions were predicted. These results were correlated to in-vitro measurements and to the results of prior retrieval studies. Two load conditions, (i) a generic vertical joint load of 3×body weight with 70%/30% M/L load share and antero-posterior/medial-lateral shear forces, acted at the centres of the medial and lateral compartments of the tibial tray, and (ii) a peak vertical joint load at 25% of the stair climbing cycle with corresponding antero-posterior shear force applied at the tibial–femoral contact points of the specific knee flexion angle, were found to generate interface Micromotion responses which corresponded to in-vivo observations. The study also found that different loads altered the interface Micromotion predicted, so caution is needed when comparing the fixation performance of various reported cementless tibial prosthetic designs if each design was evaluated with a different loading condition.
Alexandre Terrier - One of the best experts on this subject based on the ideXlab platform.
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Effect of a collar on subsidence and local Micromotion of cementless femoral stems: in vitro comparative study based on micro-computerised tomography
International Orthopaedics, 2018Co-Authors: Valérie Malfroy Camine, Dominique Pioletti, Hannes A. Rüdiger, Alexandre TerrierAbstract:Purpose The aim of this study is to quantitatively compare the difference in primary stability between collarless and collared versions of the same femoral stem. Specifically, we tested differences in subsidence and Micromotion. Methods Collarless and collared versions of the same cementless femoral stem were implanted in two groups of six fresh-frozen cadaveric femurs. Each implanted femur was then subsequently tested for axial compressive and torsional loadings. A micro-CT based technique was applied to quantify implant subsidence and compute the map of local Micromotion around the femoral stems. Micromotion of collarless and collared stems was compared in each Gruen zone. Results Subsidence was higher but not significantly ( p = 0.352) with collarless (41.0 ± 29.9 μm) than with collared stems (37.0 ± 44.6 μm). In compression, Micromotion was lower ( p = 0.257) with collarless (19.5 ± 5 μm) than with collared stems (43.3 ± 33.1 μm). In torsion, Micromotion was also lower ( p = 0.476) with collarless (96.9 ± 59.8 μm) than collared stems (118.7 ± 45.0 μm). Micromotion was only significantly lower ( p = 0.001) in Gruen zone 1 and for compression with collarless (7.0 ± 0.6 μm) than with collared stems (22.6 ± 25.5 μm). Conclusions Primary stability was achieved for both stem designs, with a mean Micromotion below the osseointegration threshold. Under loading conditions similar to those observed in normal daily activity and with good press-fit, the collar had no influence on subsidence or Micromotion. Further studies are required to test the potential advantage of collar with higher loads, undersized stems, or osteoporotic femurs.
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Simultaneous and multisite measure of Micromotion, subsidence and gap to evaluate femoral stem stability
Journal of Biomechanics, 2012Co-Authors: Miguel Gortchacow, Michael Wettstein, Dominique Pioletti, Magdalena Müller-gerbl, Alexandre TerrierAbstract:The initial stability of cementless femoral components is crucial for the long-term success of total hip arthroplasty. This has been reported in animal and clinical studies. Until now, the stability was evaluated by the measurement of relative Micromotion on a few simultaneous locations around the stem in cadaveric experiments. This paper presents an extended experimental setup to measure simultaneously local Micromotion, subsidence and gap on hundreds of points at the bone–stem interface. This technique we applied to anatomical and straight stems in three pairs of cadaveric femurs. Measurements were in agreement with typically reported values. Conversely to other methods, which measure Micromotion between implant and bone anchoring points of the measuring device, our method provides local Micromotion between stem surface and adjacent bone surface. The observed variation of Micromotion at the peri-implant surface confirms the importance of this simultaneous measure on a lot of points around the implant.
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A new technique to measure Micromotion distribution around a cementless femoral stem
Journal of Biomechanics, 2011Co-Authors: Miguel Gortchacow, Michael Wettstein, Dominique Pioletti, Alexandre TerrierAbstract:The interfacial Micromotion is closely associated to the long-term success of cementless hip prostheses. Various techniques have been proposed to measure them, but only a few number of points over the stem surface can be measured simultaneously. In this paper, we propose a new technique based on micro-Computer Tomography (μCT) to measure locally the relative interfacial Micromotions between the metallic stem and the surrounding femoral bone. Tantalum beads were stuck at the stem surface and spread at the endosteal surface. Relative Micromotions between the stem and the endosteal bone surfaces were measured at different loading amplitudes. The estimated error was 10 μm and the maximal Micromotion was 60 μm, in the loading direction, at 1400 N. This pilot study provided a local measurement of the Micromotions in the 3 direction and at 8 locations on the stem surface simultaneously. This technique could be easily extended to higher loads and a much larger number of points, covering the entire stem surface and providing a quasi-continuous distribution of the 3D interfacial Micromotions around the stem. The new measurement method would be very useful to compare the induced Micromotions of different stem designs and to optimize the primary stability of cementless total hip arthroplasty.
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A micro CT technique to measure peri-implant Micromotions of cementless femoral stems
2010Co-Authors: Miguel Gortchacow, Michael Wettstein, Dominique Pioletti, Alexandre TerrierAbstract:The interfacial Micromotion is closely associated to the long-term success of cementless hip prostheses. Various techniques have been proposed to measure them, but only a limited number of points over the stem surface can be measured simultaneously. In this paper, we propose a new technique based on μCT to measure locally interfacial Micromotions between the metallic stem and the surrounding bone. Tantalum beads were spread and stuck at the stem and endosteal surfaces. Relative Micromotions were measured at different loading amplitudes. The error was 10 μm and the maximal Micromotion was 60 at 1400 N. This pilot study provided a local measurement of the Micromotion at 8 points simultaneously, but this technique could be easily extended to a couple of hundreds of points covering the entire stem surface. This new technique could be used to compare the primary stability of different cementless stem designs, and other implants.
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Feasibility of 3D Micromotion measurement around a loaded hip stem using micro-CT imaging.
2009Co-Authors: Miguel Gortchacow, Michael Wettstein, Dominique Pioletti, Shreya Saxena, Alexandre TerrierAbstract:It has been established that primary stability of femoral stems is a determinant of the clinical success of cementless total hip arthroplasty[1]. Excessive interface Micromotions may lead to a peri-implant fibrous tissue formation resulting in aseptic loosening of the implant [2]. The effect of Micromotion on the tissue outcome remains still unclear. However, it is becoming increasingly clear that interstitial fluid flow is the primary mechanism by which bone cells perceive changes in their mechanical environment [3]. Therefore, to estimate the interstitial peri-implant fluid flow, a detailed measurement of simultaneously normal and tangential Micromotion, is required. The objective of this study is to assess the feasibility of the Micromotion measurement on human cadaveric femur with micro computed tomography.
Clare K. Fitzpatrick - One of the best experts on this subject based on the ideXlab platform.
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FE analysis of the effects of simplifications in experimental testing on Micromotions of uncemented femoral knee implants
Journal of Orthopaedic Research, 2015Co-Authors: S. Berahmani, Dennis Janssen, David Wolfson, M.c. De Waal Malefijt, Clare K. Fitzpatrick, Paul J. Rullkoetter, Nicolaas Jacobus Joseph VerdonschotAbstract:Experimental testing of orthopaedic implants requires simplifications concerning load application and activities being analyzed. This computational study investigated how these simplifications affect Micromotions at the bone-implant interface of an uncemented femoral knee implant. As a basis, validated in vivo loads of the stance phase of gait and a deep knee bend were adopted. Eventually, three configurations were considered: (i) simulation of the complete loading cycle; (ii) inclusion of only tibiofemoral loads (ignoring patellofemoral loads); and (iii) applying only a single peak tibiofemoral force. For all loading conditions the largest Micromotions found at the proximal anterior flange. Without the patellofemoral force, peak Micromotions increased 6% and 22% for gait and deep knee bend, respectively. By applying a single peak tibiofemoral force Micromotions were overestimated. However, the peak Micromotions corresponded to the maximum tibiofemoral force, and strong Micromotion correlations were found between a complete loading cycle and a single peak load (R2 = 0.73 and R2 = 0.89 for gait and deep knee bend, respectively). Deep knee bend resulted in larger Micromotions than gait. Our study suggests that a simplified peak force can be used to assess the stability of cementless femoral components. For more robust testing, implants should be subjected to different loading modes.
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computationally efficient prediction of bone implant interface Micromotion of a cementless tibial tray during gait
Journal of Biomechanics, 2014Co-Authors: Clare K. Fitzpatrick, Pleun Hemelaar, Mark TaylorAbstract:Abstract Cementless tibial fixation in total knee replacement (TKR) has potential for improved fixation and ease of revision. Achieving primary stability in cementless TKR is critical to the performance of the components. Excessive Micromotion may prevent osseointegration at the bone–implant interface. Computational finite element (FE) studies have been used to predict Micromotion at the interface, but analysis of an entire activity cycle is computational expensive, prohibiting large numbers of analyses. Surrogate modeling methods can be used to train a numerical model to predict the response of an FE model. These models are computationally efficient and are suitable for high-volume or iterative analyses requiring probabilistic, statistical or optimization methods. The objective of this work was to train a surrogate model capable of predicting Micromotion over the entire bone–implant interface. A proximal tibial bone with mapped material properties was virtually implanted with a tibial tray. A FE model, with six-degree-of-freedom loads sampled from telemetric patients during walking, was used to generate training data for the surrogate model. The linear response surrogate model was evaluated for six full gait cycles; the average and peak Micromotion across the interface, and the percentage of bone–implant interface surface area experiencing Micromotions less than 50 and greater than 150 µm were calculated both as a function of the activity cycle and as the composite peak Micromotion throughout the cycle. Differences in root-mean-square (RMS) Micromotion between FE and surrogate models were less than 14 µm. FE analysis time for a complete gait cycle was 15 h, compared to 30 s for the surrogate model. Surrogate models have significant potential to rapidly predict Micromotion over the entire bone–implant interface, allowing greater range in loading conditions to be explored than is possible through conventional methods.
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Computationally-Efficient Prediction of Micromotion in a Cementless Tibial Tray
Journal of Bone and Joint Surgery-british Volume, 2013Co-Authors: Clare K. Fitzpatrick, Pleun Hemelaar, Mark TaylorAbstract:Introduction: Primary stability is crucial for long-term fixation of cementless tibial trays. Micromotion less than 50 μm is associated with stable bone ingrowth and greater than 150 μm causes the formation of fibrous tissue around the implant [1, 2]. Finite element (FE) analysis of complete activities of daily living (ADL9s) have been used to assess primary stability, but these are computationally expensive. There is an increasing need to account for both patient and surgical variability when assessing the performance of total joint replacement. As a consequence, an implant should be evaluated over a spectrum of load cases. An alternative approach to running multiple FE models, is to perform a series of analyses and train a surrogate model which can then be used to predict Micromotion in a fraction of the time. Surrogate models have been used to predict single metrics, such as peak Micromotion. The aim of this work is to train a surrogate model capable of predicting Micromotion over the entire bone-implant interface. Methods: A FE model of an implanted proximal tibia was analysed [3] (Fig. 1). A statistical model of knee kinetics, incorporating subject-specific variability in all 6-DOF joint loads [4], was used to randomly generate loading profiles for 50 gait cycles. A Latin Hypercube (LH) sampling method was applied to sample 6-DOF loads of the new population throughout the gait cycle. Kinetic data was sampled at 10, 50 and 100 instances and FE predictions of Micromotion were calculated and used to train a surrogate model capable of describing Micromotion over the entire bone-implant interface. The surrogate model was tested for an unseen gait cycle and the resulting Micromotions were compared with FE predictions. Results and discussion: Accuracy of the surrogate model increased with increasing sample size in the training set; with a LH sample of 10, 50 and 100 trials, the surrogate model predicted Micromotion at the bone-implant interface during gait with RMS accuracy of 61, 44 and 33 μm, respectively (Fig. 2). Similar range in Micromotion was measured in FE and surrogate models; although the surrogate model tended to over-predict Micromotion early in the gait cycle (Fig. 2). There was good agreement in location and magnitude of Micromotion at the interface surface through out the gait cycle (Fig. 3). Although encouraging, further work is required to optimize the number and distribution of the training samples to minimize the error in the surrogate model. Analysis time for the FE model was 15 hours, compared to 30 seconds for the surrogate model. The results suggest that surrogate models have significant potential to rapidly predict Micromotion over the entire bone-implant interface, allowing for a greater range in loading conditions to be explored than would be possible through conventional methods.
Nicolaas Jacobus Joseph Verdonschot - One of the best experts on this subject based on the ideXlab platform.
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the effect of assembly force and angle on contact pressures and Micromotions at the taper junction of modular hip implants
Journal of Bone and Joint Surgery-british Volume, 2016Co-Authors: Thom Bitter, D Janssen, B W Schreurs, T Marriot, Imran Khan, Nicolaas Jacobus Joseph VerdonschotAbstract:Introduction Recent reports implicate fretting corrosion at the head-stem taper junction as a potential cause of failure of some large diameter metal-on-metal (MOM) devices. Fretting observed at modular junctions is thought to be a type of ‘mechanically assisted’ corrosion phenomenon, initiated by mechanical factors that lead to an increase in contact stresses and Micromotions at the taper interface. These may include: intra-operative taper assembly, taper contamination by debris or body fluids, patient weight and ‘toggling’ of the head or increased frictional torque in a poorly functioning bearing. We adopted a finite element approach to model the head-taper junction, to analyze the contact mechanics at the taper interface. We investigated the effect of assembly force and angle on contact pressures and Micromotions, during loads commonly used to test hip implants. Materials and methods Models of the Biomet Type-1 taper, a 60 mm head and a taper adaptor were created. These models were meshed with a mesh size based on a mesh density convergence study. Internal mesh coarsening was applied to reduce computational cost. Elastic-plastic material properties based on tensile tests were assigned to all titanium components. The contact conditions used in the FE analyses were validated against push-on and pull-off experiments, resulting in a coefficient of friction of 0.5. To analyze Micromotions at the taper-adaptor connection, the models were loaded with 2300N (ISO 7206-4) and 5340N (ISO 7206-6), after being assembled with 2-4-15 kN, axially and under a 30o angle. This ISO standard is commonly used to determine endurance properties of stemmed femoral components. Micromotions and contact pressures were analyzed by scoring them to an average Micromotion and average contact pressure for the surface area in contact. Results For the higher loads (5340N) the average contact pressure decreased when a higher assembly force was used (Figure1a), as a result of the fact that the loads were distributed over a larger contact area. The average contact pressure increased when tested at the 30o angle. Figure1b shows that the average Micromotion decreased when a higher assembly load is applied, except when the adaptor is assembled at a 30o angle. When assembled at a 30o angle with 15 kN the average Micromotion is 1.5 times higher (11.1–7.4 µm). Discussion The location and patterns of the Micromotions were consistent with the patterns and locations of wear found on retrieved tapers described in the literature and those generated in an in vitro test model (Figure 2a-b). Increased impaction loads reduced the average amount of Micromotion and therefore, fretting. For more realistic results, we intend to apply more complex loading regimes in future analyses, enabling to study the effect of phenomena such as edge loading and frictional torque. Moreover, the mechanical outcome as presented here will be used in a wear model, to simulate volumetric wear.
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FE analysis of the effects of simplifications in experimental testing on Micromotions of uncemented femoral knee implants
Journal of Orthopaedic Research, 2015Co-Authors: S. Berahmani, Dennis Janssen, David Wolfson, M.c. De Waal Malefijt, Clare K. Fitzpatrick, Paul J. Rullkoetter, Nicolaas Jacobus Joseph VerdonschotAbstract:Experimental testing of orthopaedic implants requires simplifications concerning load application and activities being analyzed. This computational study investigated how these simplifications affect Micromotions at the bone-implant interface of an uncemented femoral knee implant. As a basis, validated in vivo loads of the stance phase of gait and a deep knee bend were adopted. Eventually, three configurations were considered: (i) simulation of the complete loading cycle; (ii) inclusion of only tibiofemoral loads (ignoring patellofemoral loads); and (iii) applying only a single peak tibiofemoral force. For all loading conditions the largest Micromotions found at the proximal anterior flange. Without the patellofemoral force, peak Micromotions increased 6% and 22% for gait and deep knee bend, respectively. By applying a single peak tibiofemoral force Micromotions were overestimated. However, the peak Micromotions corresponded to the maximum tibiofemoral force, and strong Micromotion correlations were found between a complete loading cycle and a single peak load (R2 = 0.73 and R2 = 0.89 for gait and deep knee bend, respectively). Deep knee bend resulted in larger Micromotions than gait. Our study suggests that a simplified peak force can be used to assess the stability of cementless femoral components. For more robust testing, implants should be subjected to different loading modes.
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Toward a more realistic prediction of peri-prosthetic Micromotions
Journal of Orthopaedic Research, 2011Co-Authors: B. Van Der Ploeg, Dennis Janssen, M. Tarala, Jasper Johan Homminga, Pieter Buma, Nicolaas Jacobus Joseph VerdonschotAbstract:The finite element (FE) method has become a common tool to evaluate peri-prosthetic Micromotions in cementless total hip arthroplasty. Often, only the peak joint load and a selected number of muscle loads are applied to determine Micromotions. Furthermore, the applied external constraints are simplified (diaphyseal fixation), resulting in a non-physiological situation. In this study, a scaled musculoskeletal model was used to extract a full set of muscle and hip joint loads occurring during a walking cycle. These loads were applied incrementally to an FE model to analyze Micromotions. The relation between Micromotions and external loads was investigated, and how Micromotions during a full loading cycle compared to those calculated when applying a peak load only. Finally, the effect of external constraints was analyzed (full model vs. diaphyseal fixation and reduced number of muscle loads). Relatively large Micromotions were found during the swing phase when the hip joint forces were relatively low. Maximal Micromotions, however, did concur with the peak hip joint force. Applying only a peak joint force resulted in peak Micromotions similar to those found when full walking cycle loads were applied. The magnitude and direction of the Micromotions depended on the applied muscle loads, but not on external constraints.