Finite element calculation of head and neck lag screws in different placement positions for intertrochanteric fracture

Wang Dong-dong; Gao Feng; Cheng Jie-ping; Miao Wei-wei; Xu Chun-hua; Zhu Wei-min

doi:10.3969/j.issn.2095-4344.2014.17.008

Abstract：BACKGROUND:Our team summarized and found that in addition to a smal part due to the intertrochanteric comminuted and individual existence of the reset problem in the postoperative cases of coxa vara, radiograph of the vast majority of patients with complications after review revealed:two head and neck lag screws were positioned in the upper and middle femoral neck. <br> OBJECTIVE:To verify the biomechanical properties of lag screws in different points of the neck of proximal femur using finite element calculation so as to guide the implantation of proximal femoral intramedul ary nail and to reduce the occurrence of complications. <br> METHODS:Three dimensional models of fracture undergoing intramedul ary nail implantation in the proximal femur were established by using Boolean operation in MIMICS. This experiment contained two groups:in the lower and middle group, the lag screw was placed in the 1/3 lower and middle neck of femur;in the upper and middle group, the lag screw was placed in the 1/3 upper and middle neck of femur. The stress distribution of femur and proximal femoral intramedul ary nail was calculated using finite element software when lag screw was implanted at different directions. <br> RESULTS AND CONCLUSION:Results of the stress distribution of the fracture broken ends showed that the stress of the smal trochanter was less in the lower and middle group than that in the upper and middle group. Moreover, mean value of maximal stress of intramedul ary nail in the proximal femur was larger in the lower and middle group than that in the upper and middle group. Results of the opening angle of the fracture surface demonstrated that the opening angle of the fracture surface after loading was smal er in the lower and middle group than that in the upper and middle group. Analysis results of the relationship between load and displacement displayed that the total displacement of the top of the femur after loading was smal er in the lower and middle group than that in the upper and middle group. These results confirmed that two head and neck lag screws in the 1/3 lower and middle femoral neck showed perfect biomechanical property, stable structure, and reasonable stress, which has important reference values in the clinic.