Ex Vivo Evaluation of Cementless Acetabular Cup Stability Using Impact Analyses with a Hammer Instrumented with Strain Sensors

International audienceThe acetabular cup (AC) implant stability is determinant for the success of cementless hip arthroplasty. A method based on the analysis of the impact force applied during the press-fit insertion of the AC implant using a hammer instrumented with a force sensor was developed to assess the AC implant stability. The aim of the present study was to investigate the performance of a method using a hammer equipped with strain sensors to retrieve the AC implant stability. Different AC implants were inserted in five bovine samples with different stability conditions leading to 57 configurations. The AC implant was impacted 16 times by the two hammers consecutively. For each impact; an indicator I S (respectively I F) determined by analyzing the time variation of the signal corresponding to the averaged strain (respectively force) obtained with the stress (respectively strain) hammer was calculated. The pull-out force F was measured for each configuration. F was significantly correlated with I S (R 2 = 0.79) and I F (R 2 = 0.80). The present method has the advantage of not modifying the shape of the hammer that can be sterilized easily. This study opens new paths towards the development of a decision support system to assess the AC implant stability

Desempenho de sistema de monitorização capacitivo em implante ósseo instrumentado

Musculoskeletal disorders are becoming an ever-growing societal burden and, as a result, millions of bone replacements surgeries are performed per year worldwide. Although total joint replacements are recognized among the most successful surgeries of the last century, implant failure rates exceeding 10% are still reported. These numbers highlight the necessity of technologies to provide an accurate monitoring of the bone-implant interface state. This work aims to identify the performance of an instrumented implant to monitor implant stability using a planar capacitive technology. A 5x10x0.8 mm printed circuit with two 5x2 mm electrodes was fabricated to be integrated in an implantable device, with the objective of assessing the effect of a fully implantation into a biological specimen. The implant was fabricated with a conic geometry, to achieve a press-fit fixation, with 55 mm of length and a minimum/maximum diameters of 12 and 15 mm, respectively. After implantation, the system was put under compression and decompression cycles, so the bone-implant interface could be altered. In the compression cycle, the observed capacitance values decreased, indicating the sensor was moving away from the bone; and contrarily, in the decompression cycle, the capacitance increased with the progressive unloading. Values were obtained in intervals of [2.2090; 3.0764] pF for the compression and [1.9806; 3.1841] pF for the decompression. The mean percentage of capacitance change for the compression cycle was 3.67% and 5.06% for the decompression, indicating a greater change rate in the decompression cycle. Additional tests were carried where the implant and the sensor were rotated 90 and 180º, to show the influence of different interfaces in the measured capacitance. The latter tests allowed to support the results obtained without rotation, as different sensor positions provided different behaviors of the capacitance change. Further development is still needed related to the experimental setup, more specifically the in vitro specimens fixation and the environment control of the experiment room. In addition, energy harvesting to create self powering systems to avoid exernal links or finite-life alternatives are also a necessity for future instrumented implants. This work further demonstrated the potential of capacitive technologies to monitor the bone-implant fixation. Therefore, it also contributed towards the design of a new era of high-sophisticated implantable medical devices.Distúrbios musculares estão a tornar-se um fardo cada vez maior para a sociedade atual, e, como resultado, milhões de artroplastias são realizadas anualmente por todo o mundo. Apesar da artroplastia estar reconhecida entre os procedimentos mais bem sucedidos do último século, ainda se observa uma taxa de falha em implantes de cerca de 10%. Estes números realçam a necessidade das tecnologias conseguirem fornecer um diagnóstico preciso da interface osso-implante, podendo reduzir significativamente a necessidade de cirurgias de revisão. Este trabalho tem como objetivo avaliar o desempenho de um implante instrumentado para monitorizar a estabilidade em implantes, utilizando uma tecnologia capacitiva planar. De forma a verificar o efeito de uma inserção completa em espécimes biológicos, um circuito impresso de dimensões 5x10x0.8 mm com dois elétrodos de 5x2 mm foi fabricado com o objetivo de ser integrado dentro de um implante. O implante foi projetado com uma geometria cónica, de forma a obter uma fixação press-fit, com diâmetros mínimo/máximo de 12 e 15 mm, respetivamente, e um comprimento de 55 mm. Depois de implantado, o sistema foi posto sobre ciclos de compressão e de descompressão de forma a alterar a interface osso-implante. Nos ciclos de compressão, os valores observados da capacidade decresceram, indicando que o sensor se estava a afastar do osso; contrariamente, nos ciclos de descompressão, a capacidade tendia a aumentar com o descarregamento. Os valores foram obtidos no intervalo de [2.2090; 3.0764] pF para os ciclos de compressão e de [1.9806; 3.1841] pF para a descompressão. A percentagem média de variação da capacidade para os ciclos de compressão foi de 3.67% e de 5.06% para os de descompressão, indicando uma maior taxa de variação nos ciclos de descompressão. Adicionalmente, foram realizados testes em que o implante e o sensor foram rodados 90 e 180 de forma a verificar o efeito de interfaces diferentes na capacidade medida. Estes últimos testes permitiram também corroborar a validade dos testes de compressão e descompressão, visto que orientações diferentes do sensor deveriam dar tendências diferentes nas curvas de capacidade. No entanto ainda é necessário um desenvolvimento adicional relativamente ao setup experimental, mais concretamente na fixação dos espécimes biológicos durante os ensaios in vitro, assim como no controlo das condições ambiente do laboratório. Adicionalmente, o desenvolvimento de sistemas de energy harvesting são uma necessidade para o futuro dos implantes instrumentados de forma a ter um sistema auto-sustentável, evitando ligações com o exterior ou soluções de vida limitada. Este trabalho permitiu comprovar o potencial de tecnologias capacitivas para a monitorização do estado da interface osso-implante. Assim, também contribuiu para o desenvolvimento de uma nova era de dispositivos médicos implantáveis altamente sofisticados.Mestrado em Engenharia Mecânic

Dependence of the primary stability of cementless acetabular cup implants on their biomechanical environment

International audienc

Novel Research about Biomechanics and Biomaterials Used in Hip, Knee and Related Joints

Joint replacement is a very successful medical treatment. However, the survivorship of hip, knee, shoulder, and other implants is limited. The degradation of materials and the immune response against degradation products or an altered tissue loading condition as well as infections remain key factors of their failure. Current research in biomechanics and biomaterials is trying to overcome these existing limitations. This includes new implant designs and materials, bearings concepts and tribology, kinematical concepts, surgical techniques, and anti-inflammatory and infection prevention strategies. A careful evaluation of new materials and concepts is required in order to fully assess the strengths and weaknesses and to improve the quality and outcomes of joint replacements. Therefore, extensive research and clinical trials are essential. The main aspects that are addressed in this Special Issue are related to new material, design and manufacturing considerations of implants, implant wear and its potential clinical consequence, implant fixation, infection-related material aspects, and taper-related research topics. This Special Issue gives an overview of the ongoing research in those fields. The contributions were solicited from researchers working in the fields of biomechanics, biomaterials, and bio- and tissue-engineering

Development of Optimal Total Hip Joint Replacement

Total hip replacement (THR) is a surgical process in which the hip joint is replaced by a hip prosthesis. It is one of the most popular and cost effective surgery. In particular in 2014, 83,125 primary procedures were recorded. Some of these operations need to be carried out again for different reasons after sometime. These are called revision (replacement of the prosthesis) procedures. Important studies and statistics suggest that the number of THR procedures is projected to increase by almost 175% by 2030. Aseptic loosening appears to be the most significant cause of failure in THR. Aseptic loosening might lead to revision surgery and in turn can be avoided by enhancing the stability and durability of the hip replacement. Primary stability attained after surgery is a determinant issue for the long-term stability of cementless hip arthroplasty. Primary stability is the level of relative micromotion between the femur and the prosthesis induced via the physiological joint forces following the surgery. The hip prosthesis is also exposed to dynamic loadings and activities of daily living, which can induce the stress distribution on the prosthesis of the hip joint model and affect the durability of the implant. The aim of this study is to develop an optimal total hip replacement (THR) implant with new and improved design features to achieve stability and durability. The micromotion between bone and implant interface and the stress distribution on the prosthesis and femur assembly has been reviewed and investigated. The laboratory testing were carried out on the femur including the compression, torsion and Brinell hardness testing. A compression testing using strain gauge technique done on the hip implant. Finite element analysis software used to simulate all compression and torsion testing assuming the same boundary and loading conditions and subsequently the computational results were compared with the earlier experimental data to verify the experiments and models used. 7 The comparative micromotion studies and findings of other researchers were used beside the clinical follow-up reports on success or failure rates of related hip designs, to justify the best solutions for design factors. In this computational approach researchers usually use finite element methodology to calculate micromotion of elements, sometimes known as migration. The elements exceeding the threshold limit would simulate the migration and subsequently eliminated from the assembly. This procedure recurs until reaching the convergence that derives a stable mechanical equilibrium. One of the restrictions of micromotion analysis was the inability to divide the final results into axial and rotational components. Therefore it would have been inappropriate to eventually conclude the best femoral stem, without considering the sustaining torsional loadings. Another limitation was that the micromotion analysis would not reflect the stress distribution on the hip prosthesis and consequently would ignore the potential high stress concentration that is associated with post operative pain as well as low durability and long-term stability. For these reasons stress analysis was carried out under dynamic loadings of nine different activities to examine the von Mises stress, shear stress and principal stress distribution of a cementless hip implant. In each activity realistic boundary and loading conditions of a complete assembly of femur and hip implant were investigated which includes defining of many variables including different geometry, material properties, boundary conditions, forces and moments of varying magnitude and orientation over specific time intervals. The critical points and areas that were developed in the entire 3D model were evaluated and explained. The finite element analysis which verified by experimental testing and hold the clinical relevance were used to decide the best optimal hip stem design amongst different presented design concepts. This was accompanied and improved with further stress analysis of different design factors to get the final optimal model. High offset stem option is a unique feature that helps tightening the abductor and boosts the hip implant stability with the ability to adjust neck and offset. It gives a surgeon more options to fix the most accurate offset and do the operation more effectively. The final optimal design and its advantages were presented in the last chapter

Book of Abstracts 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering and 3rd Conference on Imaging and Visualization

In this edition, the two events will run together as a single conference, highlighting the strong connection with the Taylor & Francis journals: Computer Methods in Biomechanics and Biomedical Engineering (John Middleton and Christopher Jacobs, Eds.) and Computer Methods in Biomechanics and Biomedical Engineering: Imaging and Visualization (JoãoManuel R.S. Tavares, Ed.). The conference has become a major international meeting on computational biomechanics, imaging andvisualization. In this edition, the main program includes 212 presentations. In addition, sixteen renowned researchers will give plenary keynotes, addressing current challenges in computational biomechanics and biomedical imaging. In Lisbon, for the first time, a session dedicated to award the winner of the Best Paper in CMBBE Journal will take place. We believe that CMBBE2018 will have a strong impact on the development of computational biomechanics and biomedical imaging and visualization, identifying emerging areas of research and promoting the collaboration and networking between participants. This impact is evidenced through the well-known research groups, commercial companies and scientific organizations, who continue to support and sponsor the CMBBE meeting series. In fact, the conference is enriched with five workshops on specific scientific topics and commercial software.info:eu-repo/semantics/draf

Multiscale Biomechanics and Tribology of Inorganic and Organic Systems

This open access book gathers authoritative contributions concerning multiscale problems in biomechanics, geomechanics, materials science and tribology. It is written in memory of Sergey Grigorievich Psakhie to feature various aspects of his multifaceted research interests, ranging from theoretical physics, computer modeling of materials and material characterization at the atomic scale, to applications in space industry, medicine and geotectonics, and including organizational, psychological and philosophical aspects of scientific research and teaching as well. This book covers new advances relating to orthopedic implants, concerning the physiological, tribological and materials aspects of their behavior; medical and geological applications of permeable fluid-saturated materials; earthquake dynamics together with aspects relating to their managed and gentle release; lubrication, wear and material transfer in natural and artificial joints; material research in manufacturing processes; hard-soft matter interaction, including adhesive and capillary effects; using nanostructures for influencing living cells and for cancer treatment; manufacturing of surfaces with desired properties; self-organization of hierarchical structures during plastic deformation and thermal treatment; mechanics of composites and coatings; and many more. Covering established knowledge as well as new models and methods, this book provides readers with a comprehensive overview of the field, yet also with extensive details on each single topic