Volokh K Y, Yoshida H, Leali A, Fetto J F, Chao E Y S
Department of Orthopedic Surgery, Johns Hopkins University, Baltimore, MD, USA.
J Biomech Eng. 2006 Jun;128(3):467-70. doi: 10.1115/1.2187050.
The femoral head deteriorates in osteonecrosis. As a consequence of that, the cortical shell of the femoral head can buckle into the cancellous bone supporting it. In order to examine the buckling scenario we performed numerical analysis of a realistic femoral head model. The analysis included a solution of the hip contact problem, which provided the contact pressure distribution, and subsequent buckling simulation based on the given contact pressure. The contact problem was solved iteratively by approximating the cartilage by a discrete set of unilateral linear springs. The buckling calculations were based on a finite element mesh with brick elements for the cancellous bone and shell elements for the cortical shell. Results of 144 simulations for a variety of geometrical, material, and loading parameters strengthen the buckling scenario. They, particularly, show that the normal cancellous bone serves as a strong supporting foundation for the cortical shell and prevents it from buckling. However, under the development of osteonecrosis the deteriorating cancellous bone is unable to prevent the cortical shell from buckling and the critical pressure decreases with the decreasing Young modulus of the cancellous bone. The local buckling of the cortical shell seems to be the driving force of the progressive fracturing of the femoral head leading to its entire collapse. The buckling analysis provides an additional criterion of the femoral head collapse, the critical contact pressure. The buckling scenario also suggests a new argument in speculating on the femoral head reinforcement. If the entire collapse of the femoral head starts with the buckling of the cortical shell then it is reasonable to place the reinforcement as close to the cortical shell as possible.
在股骨头坏死中，股骨头会发生退变。因此，股骨头的皮质骨壳可能会向支撑它的松质骨内塌陷。为了研究这种塌陷情况，我们对一个逼真的股骨头模型进行了数值分析。该分析包括髋关节接触问题的求解，以提供接触压力分布，以及基于给定接触压力的后续塌陷模拟。通过用一组离散的单侧线性弹簧近似软骨来迭代求解接触问题。塌陷计算基于一个有限元网格，其中松质骨采用砖块单元，皮质骨壳采用壳单元。对各种几何、材料和载荷参数进行的144次模拟结果证实了塌陷情况。特别地，这些结果表明正常的松质骨为皮质骨壳提供了强大的支撑基础，防止其塌陷。然而，在股骨头坏死发展过程中，退变的松质骨无法阻止皮质骨壳塌陷，且临界压力随着松质骨杨氏模量的降低而减小。皮质骨壳的局部塌陷似乎是股骨头逐渐骨折直至完全塌陷的驱动力。塌陷分析提供了股骨头塌陷的一个额外标准，即临界接触压力。塌陷情况还为推测股骨头强化提供了一个新的论据。如果股骨头的完全塌陷始于皮质骨壳的塌陷，那么将强化物尽可能靠近皮质骨壳放置是合理的。
