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      Large Diameter Femoral Heads Impose Significant Alterations on the Strains Developed on Femoral Component and Bone: A Finite Element Analysis

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          Abstract

          Total Hip Arthroplasty aims at fully recreating a functional hip joint. Over the past years modular implant systems have become common practice and are widely used, due to the surgical options they provide. In addition Big Femoral Heads have also been implemented in the process, providing more flexibility for the surgeon. The current study aims at investigating the effects that femoral heads of bigger diameter may impose on the mechanical behavior of the bone-implant assembly. Using data acquired by Computed Tomographies and a Coordinate Measurement Machine, a cadaveric femur and a Profemur-E modular stem were fully digitized, leading to a three dimensional finite element model in ANSYS Workbench. Strains and stresses were then calculated, focusing on areas of clinical interest, based on Gruen zones: the calcar and the corresponding below the greater trochanter area in the proximal femur, the stem tip region and a profile line along linea aspera. The performed finite elements analysis revealed that the use of large diameter heads produces significant changes in strain development within the bone volume, especially in the lateral side. The application of Frost’s law in bone remodeling, validated the hypothesis that for all diameters normal bone growth occurs. However, in the calcar area lower strain values were recorded, when comparing with the reference model featuring a 28mm femoral head. Along line aspera and for the stem tip area, higher values were recorded. Finally, stresses calculated on the modular neck revealed increased values, but without reaching the yield strength of the titanium alloy used.

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          Hip joint loading during walking and running, measured in two patients.

          The resultant hip joint force, its orientation and the moments were measured in two patients during walking and running using telemetering total hip prostheses. One patient underwent bilateral joint replacement and a second patient, additionally suffering from a neuropathic disease and atactic gait patterns, received one instrumented hip implant. The joint loading was observed over the first 30 and 18 months, respectively, following implantation. In the first patient the median peak forces increased with the walking speed from about 280% of the patient's body weight (BW) at 1 km h-1 to approximately 480% BW at 5 km h-1. Jogging and very fast walking both raised the forces to about 550% BW; stumbling on one occasion caused magnitudes of 720% BW. In the second patient median forces at 3 km h-1 were about 410% BW and a force of 870% BW was observed during stumbling. During all types of activities, the direction of the peak force in the frontal plane changed only slightly when the force magnitude was high. Perpendicular to the long femoral axis, the peak force acted predominantly from medial to lateral. The component from ventral to dorsal increased at higher force magnitudes. In one hip in the first patient and in the second patient the direction of large forces approximated the average anteversion of the natural femur. The torsional moments around the stem of the implant were 40.3 N m in the first patient and 24 N m in the second.
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            The elastic modulus for bone.

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              Clinical and radiographic evaluation of total hip replacement. A standard system of terminology for reporting results.

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                Author and article information

                Journal
                Open Orthop J
                TOORTHJ
                The Open Orthopaedics Journal
                Bentham Open
                1874-3250
                19 July 2011
                2011
                : 5
                : 229-238
                Affiliations
                [1 ]School of Mechanical Engineering, Mechanical Design & Control Systems Section, Laboratory of Dynamics and Structures, National Technical University of Athens, Greece
                [2 ]Department of Orthopaedic Surgery, University of Patras, Greece
                [3 ]First Department of Orthopaedics, University of Athens, ATTIKON University General Hospital, Athens, Greece
                Author notes
                [* ]Address correspondence to this author at the Department of Orthopaedic Surgery, University Hospital of Patras, Postal Code GR-26504, Rio, Greece; Tel: +302610999551; Fax: +302610994579, E-mail: panmegas@ 123456gmail.com
                Article
                TOORTHJ-5-229
                10.2174/1874325001105010229
                3141343
                21792381
                e3b7e3a8-c022-4433-a65e-9c8a1feda8ef
                © Theodorou et al.; Licensee Bentham Open.

                This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

                History
                : 26 January 2011
                : 10 May 2011
                : 25 May 2011
                Categories
                Article

                Orthopedics
                finite elements.,metal-on-metal,total hip arthroplasty,large diameter femoral heads

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