Eberle S, Bauer C, Gerber C, von Oldenburg G, Augat P
Institute of Biomechanics, Trauma Center Murnau, Murnau, Germany.
Proc Inst Mech Eng H. 2010;224(4):577-84. doi: 10.1243/09544119JEIM664.
The purpose of this study was to address the question of how the stability of a proximal hip fracture determines the fatigue and failure mechanism of an intramedullary implant. To answer this question, mechanical experiments and finite element simulations with two different loading scenarios were conducted. The two load scenarios differed in the mechanical support of the fracture by an artificial bone sleeve, representing the femoral head and neck. The experiments confirmed that an intramedullary nail fails at a lower load in an unstable fracture situation in the proximal femur than in a stable fracture. The nails with an unstable support failed at a load 28 per cent lower than the nails with a stable support by the femoral neck. Hence, the mechanical support of a fracture is crucial to the fatigue failure of an implant. The simulation showed why the fatigue fracture of the nail starts at the aperture of the lag screw. It is the location of the highest von Mises stress, which is the failure criterion for ductile materials.
本研究的目的是探讨近端髋部骨折的稳定性如何决定髓内植入物的疲劳和失效机制。为回答这个问题，进行了两种不同加载场景下的力学实验和有限元模拟。这两种加载场景在人工骨套筒对骨折的力学支撑方面存在差异，该人工骨套筒代表股骨头和股骨颈。实验证实，与稳定骨折相比，股骨近端不稳定骨折情况下髓内钉在较低载荷下失效。不稳定支撑的钉子在比有股骨颈稳定支撑的钉子低28%的载荷下失效。因此，骨折的力学支撑对植入物的疲劳失效至关重要。模拟显示了钉子的疲劳骨折为何始于拉力螺钉的孔处。它是等效应力最高的位置，而等效应力是韧性材料的失效准则。
