According to proposal of Noble, the femoral bone marrow cavity form of patients who underwent Total Hip Arthroplasty (THA) can be classified under 3 categories; those are Stovepipe, Normal and Champagne-fluted. We developed typical sodium chloride femoral model was created by 3D prototyping technique. The purpose was to identify the relationship of pressure zone of the surrounding areas between femoral bone marrow cavity form and hip stem. As opponent clarified stem design concept Zweymüller type model was used. According to CT data with the patients who underwent THA, the sodium chloride femoral model was custom-made and selected as the representative model based on Noble's 3 categories. Eight models of each category were used to performed mechanical test.Introduction
Materials and Method
On the basis of a proposal by Noble, the marrow cavity form can be classified into three categories: stovepipe, normal, and champagne-fluted. In the present study, three typical finite element femoral models were created using CT data based on Noble's three categories. The purpose was to identify the relationship of stress distribution of the surrounding areas between femoral bone marrow cavity form and hip stem. The results shed light on whether the distribution of the high-stress area reflects the stem design concept. In order to improve the results of THA, researchers need to consider the instability of a stem design based on the pressure zone and give feedback on future stem selection. To develop finite element models, two parts (cortical bone and stem) were constructed using four-node tetrahedral elements. The model consisted of about 40,000 elements. The material characteristics were defined by the combination of mass density, elastic coefficient, and Poisson's ratio. Concerning the analysis system, HP Z800 Workstation(HP, Japan) was used as hardware and LS-DYNA Ver. 971 (Livermore Software Technology Corporation, USA) as software. The distal end of the femur was constrained in all directions. On the basis of ISO 7206 Part 4,8 that specifies a method of endurance testing for joint prostheses, the stem was tilted 10°, and a 500 N resultant force in the area around the hip joint was applied to the head at an angle of 25° with the long axis. Automatic contact with a consideration of slip was used. Von Mises stress during a 1.0 s period after loading was analyzed, and stress distribution in the stem and its maximum value were calculated.Introduction
Methods
