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2 Acta of Bioengineering and Biomechanics

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Evaluation of contact characteristics of a patient-specific artificial dysplastic hip joint

Mutlu I., Ugur L., Celik T., Buluc L., Muezzinoglu U. S., Kisioglu Y.

Acta of Bioengineering and Biomechanics

2014

Vol. 16, no. 2

111--120

This study addresses the results of the experimental measurements for the contact surface areas and contact pressure distributions of a dysplastic hip joint. The hip joint consists of pelvis, proximal femur and artificial cartilages for both acetabulum and femoral head. The dysplastic hip joint is modeled in three dimensional (3D) form using the computerized tomography (CT) images obtained in vivo of an adult female patient. The modeled hip joint components are manufactured as a non-natural dysplastic hip joint using different materials and manufacturing processes. The dysplastic hip joint produced is subjected to compression forces experimentally to measure the contact surface area and contact pressure distributions between the femoral head and acetabulum using the pressure sensitive Fuji film. Different types of specific fixtures and molds are designed and manufactured to produce the dysplastic hip joint components and perform the experimental studies. The measured results using a non-natural dysplastic hip joint are compared with relevant results reported in current literature considering the peak and mean contact pressure values. Therefore, the obtained results showed that the non-natural dysplastic hip models can be generated and replaced to determine the contact characteristics for an elusive cadaveric model. In conclusion, the artificial models might be useful to understand the contact pressure distributions and potential changes in surface pressure contours and their effects on the stress distributions.

Stress distribution comparisons of foot bones in patient with tibia vara : a finite element study

Özkan A., Atmaca H., Mutlu I., Celik T., Ugur L., Kisioglu Y.

Acta of Bioengineering and Biomechanics

2013

Vol. 15, no. 4

67--72

Blount’s disease, or tibia vara, is the most common cause of pathologic genu varum in children and adolescents. Changes in the loading of knee structures such as tibial articular cartilage, menisci and subcondral bone are well documented in case of genu varum. But the mechanical effects of this condition on foot bones are still questionable. In this study, the authors hypothesized that stress distributions on foot bones might increase in patients with tibia vara when compared with patients who had normal lower extremity mechanical axis. Three-dimensional (3D) finite element analyses of human lower limb were used to investigate and compare the loading on foot bones in normal population and patient with tibia vara. The segmentation software, MIMICS was used to generate the 3D images of the bony structures of normal and varus malalignment lower extremity. Except the spaces between the adjacent surface of the phalanges fused, metatarsals, cuneiforms, cuboid, navicular, talus and calcaneus bones were independently developed to form foot and ankle complex. Also femur, tibia and fibula were modeled utilizing mechanical axis. ANSYS version 14 was used for mechanical tests and maximum equivalent stresses (MES) were examined. As a result of the loading conditions, in varus model MES on talus, calcaneus and cuboid were found higher than in normal model. And stress distributions changed through laterally on middle and fore foot in varus deformity model.