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BACKGROUND: Aseptic loosening of the femoral prosthesis is one of the important issues affecting the life of knee joint replacement. Particles from tibial polyethylene component wear and stress shielding are the main causes of this loosening, which are all related to the femoral prosthesis materials. OBJECTIVE: To study the effects of femoral prosthesis materials on the stress of the distal femur of the knee joint and the contact pressure on the polyethylene component by finite element method. METHODS: Knee arthroplasty models with four materials, titanium alloy, cobalt-chromium alloy, titanium-hydroxyapatite functional gradient biomaterial (FGBM I), titanium-bioactive glass functional gradient biomaterial (FGBM II), were established; the prosthesis was endowed with different material properties in the Abaqus finite element software. The stress distribution of the important vulnerable path in the femur and the changes of contact pressure on the polyethylene component under different materials were studied. RESULTS AND CONCLUSION: (1) Compared with the currently used titanium alloy and cobalt-chromium alloy, functional gradient biomaterials could significantly increase the stress at the femoral-prosthetic interface and the stress in the pathway of an important vulnerable region of the femur. In those materials, FGBM I increased most significantly. (2) Maximum stress of FGBM I and FGBM II prostheses on polyethylene insert was 20.41% and 19.98% lower than cobalt-chromium alloy, 20.07% and 19.63% lower than titanium alloy. (3) The results showed that functionally gradient biomaterials could produce higher stress at the distal end of the femur and lower contact pressure on the polyethylene insert, reducing the wear and stress shield on polyethylene insert, and FGBM I has significant effects.
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Objective To study the characteristics of mouse-desktop and wrist-desktop contact pressure distributions during different mouse operations, and investigate the influence of desktop on the mouse and wrist during mouse operations, so as to obtain biomechanical references for musculoskeletal disorders of the hand and wrist. Methods The laser scanner and TekScan pressure measurement system were employed to measure contact area and contact pressure of the mouse and wrist during different mouse operations. Results The contact pressure, contact area, and contact force varied with time, and the peak contact pressure of the mouse and wrist with desktop were obtained. The peak contact pressure of the mouse in single clicking of left, right key and scrolling of middle key was 62.87, 33.83, 74.66 kPa, respectively, and for the wrist, the minimum contact pressure appeared in key clicking, being 23.25, 11.02, 16.26 kPa, respectively. Conclusions During mouse operations, the thenar, hypothenar as well as the ulnar and radial sides of the wrist are persistently subjected to the continuous pressure, therefore, repetitive and continuous mouse operation can lead to the development of carpal tunnel syndrome of wrist or other MSDs.
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Objective To study the characteristics of mouse-desktop and wrist-desktop contact pressure distributions during different mouse operations,and investigate the influence of desktop on the mouse and wrist during mouse operations,so as to obtain biomechanical references for musculoskeletal disorders of the hand and wrist.Methods The laser scanner and TekScan pressure measurement system were employed to measure contact area and contact pressure of the mouse and wrist during different mouse operations.Results The contact pressure,contact area,and contact force varied with time,and the peak contact pressure of the mouse and wrist with desktop were obtained.The peak contact pressure of the mouse in single clicking of left,right key and scrolling of middle key was 62.87,33.83,74.66 kPa,respectively,and for the wrist,the minimum contact pressure appeared in key clicking,being 23.25,11.02,16.26 kPa,respectively.Conclusions During mouse operations,the thenar,hypothenar as well as the ulnar and radial sides of the wrist are persistently subjected to the continuous pressure,therefore,repetitive and continuous mouse operation can lead to the development of carpal tunnel syndrome of wrist or other MSDs.
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Objective To study the distribution of stress, strain and effective surface pressure in the knee joint. Methods Based on CT/MR scan image data and using the Mimics/ANSYS software, a three-dimensional finite element model of the knee joint (including the upper/lower knee and the meniscus) was established with the principle of reverse engineering, and the treatment of articular cartilage and ligament was ignored in this model. The mechanical responses of the three models, i.e., the healthy knee joint, the knee joint with V-shape medial meniscal tears, the knee joint with longitudinal meniscal tears under axial loading were analyzed and compared. Results Under axial loading, the healthy knee joint would transfer the majority of the compressive stress loads, which were mainly concentrated in the lateral side of the middle part of the meniscus, and the maximum contact pressure appeared in the rear area of the middle part of the meniscus. When the meniscus was torn, the maximum stress appeared at the periphery of the tear, and the contact stress distribution of the meniscus was significantly changed due to the presence of the tear. Conclusions The meniscal tears have a significant influence on the stress distribution and peak stress of the knee joint. According to the shape of the meniscus, the doctor can determine the position of the stress concentration in the meniscus, and to determine the most important point in the treatment of the meniscus tear.
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Objective To compare contact mechanics of cartilage in normal hip and that in hip with Cam-type femoroacetabular impingement (FAI) using finite element method. Methods The 3D finite element models of normal hip and Cam-type FAI hip joints with varied Alpha angles were constructed. The contact pressures and stresses of intra-articular cartilages during routine daily activities, such as walking, sitting and standing, were calculated. Results During the whole gait cycle, the distribution of cartilage contact pressures on Cam-type FAI hip models with varied Alpha angles was similar to that in normal hip model, and no concentrated areas of high contact pressures and Von Mises stresses appeared. While during the motion of sitting and standing, the cartilage contact pressure on Cam-type FAI hip models was higher than that in normal hip model and increased with the Alpha angle increasing, and the contact area was mainly located at anterosuperior region of acetabular rim, where a concentration of high contact pressures and Von Mises stresses appeared. Conclusions Mode of motion is the key factor which causes changes of cartilage contact mechanics in Cam type FAI joints. Abnormally high cartilage contact pressures and Von Mises stresses might be the inducement to cartilage degeneration and eventually lead to osteoarthritis.
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El desgaste de los insertos de Polietileno de Ultra-Alto Peso Molecular (UHMWPE pos sus siglas en inglés) continúa afectando la longevidad de las prótesis totales de rodilla (PTR) junto con el aflojamiento aséptico, y ambos constituyen las dos principales causas de falla de las prótesis. Considerando esto, es necesario encontrar soluciones adecuadas para evitar el desgaste excesivo y hasta la ruptura de los insertos de polietileno. En este trabajo se realizó el estudio mediante simulación numérica de una PTR Scorpio II® Stryker®, la cual se retiró por desgaste del inserto de UHMWPE en el Hospital 1° de Octubre del ISSSTE en México. Se utilizaron las hipótesis de Bartel et al. (1995) y Chillag et al. (1991) para la validación del método numérico utilizado, las cuales establecen que el desgaste del polietileno puede reducirse utilizando insertos tibiales de mayor espesor, lo cual disminuye las presiones de contacto. Los análisis se realizaron mediante MEF variando el espesor del inserto de 6, 8, 10, 12 y 14 mm, suponiendo cargas axiales de tipo cuasi-estático en la articulación a cero grados de flexión, para 1.33 veces el peso de un individuo de 75 kg (736 N) empleando el ciclo normalizado de marcha. Los resultados obtenidos muestran similitud con los reportados por Bei et al. (2004) y Deen et al. (2006). Después de validar el método, se desarrolló el modelo de MEF de la PTR y se determinaron las curvas de esfuerzo y de áreas de contacto del inserto de UHMWPE, con lo que se obtuvo información importante para modificar el diseño y obtener una prótesis de geometría conforme en los planos coronal y sagital del inserto femoral y el inserto de polietileno, de acuerdo con el fenotipo mexicano.
Wear of UHMWPE inserts continues affecting the longevity of total knee replacements (TKR) together with septic loosening, and both constitute two main causes of prosthesis failure. It is necessary to find appropriate solutions to avoid excessive wear and failure of polyethylene inserts. In this work a study was carried out by means of numeric simulation of a Scorpio II® Stryker® TKR, which was retired due to wear of UHMWPE in the Hospital 1° de Octubre of ISSSTE in Mexico city. Hypotheses of Bartel et al. (1995) and Chillag et al. (1991) were used, which settle down that wear of polyethylene can decrease using thicker tibial inserts, which can be reduced contact pressures. Analyses of this work was carried out by means of FEM varying insert thickness of 6, 8, 10, 12 and 14 mm, considered quasi-static axial loads actuating on the articulation with zero degrees of flexion and loads equivalent to 1.33 times of bodyweight of a subject of 75 kg (736 N) was considered. Normalized gait cycle was employed and results obtained are similar to those reported by Bei et al. (2004) and Deen et al. (2006). After validating the method, a model of study case of TKR in FEM was developed and the curves of stress and contact areas of UHMWPE were determined, with which important information was obtained to modify the design, as well as to obtain a prosthesis of optimal conformity in both coronal and sagital planes of the femoral and UHMWPE inserts, in agreement with characteristics of the Mexican phenotype.
Subject(s)
Humans , Knee , Numerical Analysis, Computer-Assisted , Prostheses and Implants , Polyethylene , PressureABSTRACT
Objective To study the contact mechanics of metal-on-metal hip joint replacements under different walking conditions, particularly for the edge contact behavior between the cup and the head of the bearing due to large range movement. Methods The finite element model of a typical hip joint replacement with conformal spherical bearing was established to simulate the edge contact of hip joint replacement under the given cup inclination angles and vertical loads. Results The maximum contact pressure decreased slightly and the contact area increased when the cup inclination angles increased within the range of 0°~60°. When the cup inclination angles were more than 80°, the corresponding contact area moved to the cup edge, the maximum contact pressure and distribution range increased, but the position of the maximum contact pressure moved from the initial contact point to the new point with 6°~9° in the direction of the increasing cup inclination angle to balance the corresponding contact pressure distribution and the loaded human weight. Conclusions Different edge contact behavior of hip joint replacements tends to occur due to the bigger cup inclination angle. Therefore, much attention should be paid to the problem of edge contact for both the clinical surgery and the manufacturing of hip joint replacements.
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PURPOSE: A new method has been devised to determine contact pressures in prosthetic components. A real time analysis of the contact pressure distribution could help fine tuned implant positioning and ligament balancing during Total Knee Arthroplasty. MATERIALS AND METHODS: Posterior cruciate reserving type procedures were done with externally rotated femoral cut. Femorotibial contact pressure was measured in four compartments in both flexion and extension position. A LOAD CELL located beneath the tibial plate changes the contact pressure into electric signal and DP-41S transformed the electric sign into the pressure unit. Adjunctive fine-tuning operation was done to approximate the equilibrium among the four compartments of the tibial plate. RESULTS: Femorotibial contact pressure were distributed between 17.1 N (Newton) to 33.4 N (average 23.6 N). A peak contact pressure was exhibited in the anteromedial compartment in extended knee and in the posterolateral compartment in flexed knee. CONCLUSION: A LOAD CELL electronic transducer technique was introduced. This method was tried to get the balanced equilibrium of contact pressure between Femorotibial components during TKA.