Li L P, Gu K B
Department of Mechanical and Manufacturing Engineering, University of Calgary, Alberta, Canada.
Proc Inst Mech Eng H. 2011 Sep;225(9):888-96. doi: 10.1177/0954411911412464.
Fluid pressurization in articular cartilages and menisci plays an important role in the mechanical function of the knee joint. However, fluid pressure has not been incorporated in previous finite element modelling of the knee, instead elastic models of the knee are widely used. It is believed that an elastic model can be used to predict the instantaneous load response of the knee as long as large effective moduli for the cartilaginous tissues are used. In the present study, the instantaneous response of the knee was obtained from a proposed model including fluid pressure and fibril reinforcement in the cartilaginous tissues. The results were then compared with those obtained from an elastic model using the effective modulus method. It was found that the deformations and contact pressures predicted by the two models were substantially different. An unconfined compression of a tissue disc was used to help understand the issue. It was clear that a full equivalence between the instantaneous and elastic responses could not be established even for this simple case. A partial equivalence in stress could be conditionally established for a given unconfined compression, but it was not valid for a different magnitude of compression. The instantaneous deformation of the intact tissues in the joint was even more difficult to determine using the effective modulus method. The results thus obtained were further compromised because of the uncertainty over the choice of effective modulus. The tissue non-linearity was one of the factors that made it difficult to establish the equivalence in stress. The pressurized tissue behaved differently from a solid material when non-linear fibril reinforcement was presented. The direct prediction of the instantaneous response using the proposed poromechanical model had the advantage of determining the fluid pressure and incompressible deformation.
关节软骨和半月板中的流体加压在膝关节的力学功能中起着重要作用。然而，以往膝关节的有限元建模中并未纳入流体压力，而是广泛使用膝关节的弹性模型。人们认为，只要使用软骨组织的大有效模量，弹性模型就可用于预测膝关节的瞬时载荷响应。在本研究中，膝关节的瞬时响应是从一个包含软骨组织中流体压力和纤维增强的模型中获得的。然后将结果与使用有效模量法从弹性模型中获得的结果进行比较。发现这两个模型预测的变形和接触压力有很大差异。使用组织圆盘的无侧限压缩来帮助理解这个问题。很明显，即使对于这个简单的情况，也无法在瞬时响应和弹性响应之间建立完全等效关系。对于给定的无侧限压缩，可以有条件地建立应力的部分等效关系，但对于不同大小的压缩则无效。使用有效模量法更难确定关节中完整组织的瞬时变形。由于有效模量选择的不确定性，由此获得的结果进一步受到影响。组织非线性是难以建立应力等效关系的因素之一。当存在非线性纤维增强时，受压组织的行为与固体材料不同。使用所提出的孔隙力学模型直接预测瞬时响应具有确定流体压力和不可压缩变形的优势。
