BACKGROUND:Prosthesis selection for total hip replacement is determined by geometrical matching with femoral medullary cavity of patients and the optimal biodynamics.It is of great significance for elevating outcomes of total hip replacement.OBJECTIVE:To evaluate the biomechanics of four groups of femoral stem prostheses matched with a femar and to get a stem whose mechanics distribution is similar to the normal femur.DESIGN:Controlled observation.SETTING:Department of Orthopaedics of Oriental Hospital Affiliated to Tongji University,Department of Orthopaedics of Changhai Hospital of Second Military Medical University of Chinese PLA,and Department of Mechanical and Power Engineering of Shanghai Jiao Tong University.MATERIALS:Experiments were performed at the Laboratory of Life Quality and Machinery Engineering of Department of Mechanical and Power Engineering of Shanghai Jiao Tong University from December 2004 to October 2005.A male volunteer aged 40 years with the normal proximal ferout(175 cm height and 78 kg weight),free from hip disease,were selected.X-ray image of the eutopic femar was shot and wrote into memory in the format of DICOM.The volunteer signed an infonned consent.The experiment was approved by Hospital Ethical Committee.No.Ⅰ prosthesis,Zimmer versys Fiber Metal Taperl 1#,No.Ⅱ prosthesis,Plus APL 2#,No.Ⅲ prosthesis,Welink Ribbed system cementless01#,and No.Ⅳprosthesis,Lima F2L 1# were used in this study.METHODS:The ezDICOM software was used to read files with DICOM format of femoral X-ray image,which was converted into files with bmp format.The image files with bmp format of the proximal femar X ray were introduced with Matlab software after regulation,and the two-dimensional contour data of femar were extracted.Prosthesis matched with the template was set in PhotoShop 7.0 software.The two-dimensional contour data of prosthetic femar were extracted in MATLAB software.The ANSYS software was used to establish the model of geometrical and two-dimensional nonlinearity finite element ncluding femur and femur-femoral stem.Stress distribution in the proximal femur was analyzed and compared by loading.MAIN OUTCOME MEASURES:Stress istribution of the proximal femur.RESULTS:Stress value and distribution of No.Ⅰ prosthesis and No.Ⅳ prosthesis in proximal femur were similar to the normal femar.Moreover,No.Ⅰ prosthesis was better than No.Ⅳ prosthesis.CONCLUSION:The biomechanics of femoral stem prostheses has been evaluated by analyzing and comparing the two-dimensional biomechanics of the femoral stem prostheses based on X-ray and template,which can offer support in optimal rosthesis selection.