Helwig P, Faust G, Hindenlang U, Kröplin B, Eingartner C
Department Orthopädie und Traumatologie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.
Technol Health Care. 2006;14(4-5):411-9.
Static analysis with finite element of a realistic femur nail bone-implant system in a typical proximal femoral fracture under physiological load bearing situations provides results for stress, displacement and strain. The question to be answered is, if simulation with the finite element analysis is able to explain biomechanically clinical observed patterns of failure. Surface-Reconstruction with CT database of a proximal femur and reconstruction with CT based density data was done. Next steps were to unite the bone structure with the Proximal Femoral Nail and to model two relevant fractures (31-A2.2 and A2.3 according AO). After modelling of geometry, isotropic material behaviour and load application numeric calculation of the femur-nail system with FE-software was performed. FE simulation mainly shows an axial dislocation of the femoral head screw with nearly no dislocation of the antirotation screw. This so-called z-effect therefore means: (1) Tilting of the proximal main fragment around the sagittal axis between the screws and (2) relative movement of both screws in the frontal plane. Relative movement of the two screws against each other could be the reason for implant failure, the so called cut out. Furthermore simulation shows different gliding of the screws explaining the so called z-telescoping. The analyzed stress patterns have to be relativized, because isotropic material behaviour of cancellous bone was assumed. Further examinations for this issue are necessary.
在生理负荷情况下，对典型股骨近端骨折中逼真的股骨钉骨植入系统进行有限元静态分析，可得出应力、位移和应变的结果。需要回答的问题是，有限元分析模拟是否能够从生物力学角度解释临床上观察到的失效模式。利用近端股骨的CT数据库进行表面重建，并基于CT密度数据进行重建。接下来的步骤是将骨骼结构与股骨近端钉结合，并对两种相关骨折（根据AO分类为31 - A2.2和A2.3）进行建模。在对几何形状、各向同性材料特性和载荷施加进行建模后，使用有限元软件对股骨钉系统进行数值计算。有限元模拟主要显示股骨头螺钉的轴向移位，而抗旋转螺钉几乎没有移位。因此，这种所谓的z效应意味着：（1）近端主要骨折块围绕螺钉之间的矢状轴倾斜；（2）两个螺钉在额平面内的相对运动。两个螺钉相互之间的相对运动可能是植入物失效（即所谓的穿出）的原因。此外，模拟还显示了螺钉的不同滑动，这解释了所谓的z形伸缩。由于假设松质骨具有各向同性材料特性，所以所分析的应力模式必须进行相对化处理。对此问题还需要进一步研究。
