Wehner Tim, Penzkofer Rainer, Augat Peter, Claes Lutz, Simon Ulrich
Institute of Orthopaedic Research and Biomechanics, Ulm University, Germany.
Clin Biomech (Bristol). 2011 Feb;26(2):147-51. doi: 10.1016/j.clinbiomech.2010.09.009. Epub 2010 Oct 20.
The healing outcome of long bone fractures is strongly influenced by the mechanical environment. High interfragmentary movement at the fracture site is detrimental to the fracture healing process. Long bone fractures stabilized with thin intramedullary nails commonly used for unreamed intramedullary nailing might be very flexible in shear direction and therefore critical for the fracture healing outcome. The aims of this study were to simulate the shear interfragmentary movement during gait for a human tibia treated with intramedullary nailing and to investigate if this movement could be lowered by implant design modifications.
The shear movement was calculated with a 3D finite element model based on computer tomograph images of a cadaver bone-implant complex of a transverse tibia fracture treated with a Stryker T2 Standard Tibial Nail. This model was validated through in vitro test results under pure shear, axial, bending and torsional loading.
High shear movements of approximately 4mm were calculated during gait. These shear movements could be reduced by approximately 30% either by implant modifications or the use of a 1mm thicker nail. Combining the implant modifications with a 1mm thicker nail, the shear movements could be reduced by 54%.
The increase of the fixation stiffness by using an implant material with a high Young's modulus in combination with an angle-stable nail-screw fixation helps to reduce the shear movement during gait and possibly to lower the risk of a prolonged healing time with unreamed intramedullary nailing.
长骨骨折的愈合结果受力学环境的强烈影响。骨折部位的高骨折块间移动对骨折愈合过程不利。用常用于非扩髓髓内钉固定的细髓内钉固定长骨骨折时，在剪切方向可能非常灵活，因此对骨折愈合结果至关重要。本研究的目的是模拟髓内钉固定的人体胫骨在步态期间的剪切骨折块间移动，并研究这种移动是否可以通过植入物设计的改进而降低。
基于用史赛克T2标准胫骨钉治疗的胫骨横向骨折尸体骨-植入物复合体的计算机断层扫描图像，用三维有限元模型计算剪切移动。该模型通过在纯剪切、轴向、弯曲和扭转载荷下的体外测试结果进行验证。
计算出在步态期间约4mm的高剪切移动。通过植入物改进或使用1mm更厚的钉子，这些剪切移动可减少约30%。将植入物改进与1mm更厚的钉子相结合，剪切移动可减少54%。
使用具有高杨氏模量的植入材料结合角度稳定的钉-螺钉固定来增加固定刚度，有助于减少步态期间的剪切移动，并可能降低非扩髓髓内钉固定导致愈合时间延长的风险。
