Introduction. 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. Materials and Method. 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. Result. In mechanics test, the result of comparison between the contact pressure zones of zone 1–7, significant differences of contact pressure zones were identified between the Stovepipe group and Normal group in zone 3, 4 and 5. In zone 3 and 5, such significant differences were also identified between Champagne-fluted group and Normal group. In Stovepipe group, a significant difference of the contact pressure zone was observed at the proximal and distal. In Champagne-fluted group and the Normal group, a significant difference was observed in the contact pressure in distal femur (3, 4, 5 Zone) and (Zone1, 2, 6, 7) proximal femur. Discussion. Although in most studies Sawbone® is used for femoral models, the focus of this research is of those who possess a characteristic femur with marrow cavity form. Therefore, sodium chloride bone model was used instead. In comparison in terms of applicability between sodium chloride bone model and regular model, the failure of all 24 joints of sodium chloride bone model were unconfirmed in mechanics test. Moreover, the possibility that its performance in mechanics test is equivalent to Sawbone®is considered. The design concept for Zweymüller type achieves the ability to load distribute within a wide range of cortical bone across the middle position to distal femur. It's determined by the concept that a wide range of contact pressure was admitted at middle position and distal femur in the Champagne-fluted group and the Normal group. On the other hand, the contact pressure zone of Stovepipe was not able to meet the expected level at distal femur. The method of this research is control its stress condition within the stem design. By this point, it is considered possible that the stability of various stem design was able to be forecasted and the assessment of stableness was positive. Conclusion. On the basis of Noble's categories, 3 types of bone models were created by 3D prototyping technique, and pressure distribution measurement were performed. The result from the pressure distribution indicated that even in Zweymüller stem had anxiety of securing force in Champagne-fluted type and Stovepipe type canal. We believe the method of in vivo study can develop to assess the stability of implant preoperatively

Introduction. On the basis of a proposal by Noble, the marrow cavity form can be classified into three categories: normal, champagne-fluted and stovepipe. 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 stems. 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 stress distributioin and give feedback on future stem selection. Methods. As analyzing object, we selected SL-PLUS and BiCONTACT stems. To develop finite element models, two parts (cortical bone and stem) were constructed using four-node tetrahedral elements. The model consisted of about 60,000 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 was used as hardware and LS-DYNA Ver. 971 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 1500 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. Result. The maximum stress on femur implanted a SL-PLUS with marrow cavity form of normal, champagne-fluted and stovepipe were shown to be 90MPa, 90MPa and 45MPa. The maximum stress on a BiCONTACT with marrow cavity form of normal, champagne-fluted and stovepipe were shown to be 45MPa, 90MPa and 15MPa. Discussion. The design concept for aZweymüller-type stem can distribute load across a wide range of cortical bone from the middle position to the distal femur. It is determined using this concept that a wide range of stress was absorbed at the middle position and distal femur in the champagne-fluted and normal cases. On the other hand, the contact pressure zone of stovepipe could not meet the expected level at the distal femur. The method of this research involves controlling the stress conditions within the stem design. At this point, it is considered possible for the stability of various stem designs to be predicted and the stability to be assessed positively. On the basis of Noble's categories, three types of finite element model were made, and stress distribution measurement and finite element analyses were performed. The results indicate that Zweymüller stem has clinical validity for securing force in the champagne-fluted and stovepipe types from the stress distribution

Introduction. 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. Methods. 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. Result. The maximum stress at marrow cavity form of normal was shown to be 72 MPa. The stress of champagne-fluted was evenly distributed from proximal to distal, and the maximum stress was 67 MPa. For stovepipe, the maximum proximal stress was shown to be 120 MPa; moreover, stress concentration was observed. Discussion. The design concept for a Zweymüller-type stem can distribute load across a wide range of cortical bone from the middle position to the distal femur. It is determined using this concept that a wide range of stress was absorbed at the middle position and distal femur in the champagne-fluted and normal cases. On the other hand, the contact pressure zone of stovepipe could not meet the expected level at the distal femur. The method of this research involves controlling the stress conditions within the stem design. At this point, it is considered possible for the stability of various stem designs to be predicted and the stability to be assessed positively. On the basis of Noble's categories, three types of finite element model were made, and stress distribution measurement and finite element analyses were performed. The results indicate that Zweymüller stem has clinical validity for securing force in the champagne-fluted and stovepipe types from the stress distribution