An axisymmetric and fully 3D poroelastic model for the evolution of hydrocephalus.

We formulate in general terms the equations for axisymmetric and fully 3D models of a hydrocephalic brain. The model is developed using small strain poroelasticity that includes non-linear permeability. The axisymmetric model is solved for four ventricle shapes, an ellipsoid, a 'peanut' shape, a 'cross' shape and a 'bone' shape. The distribution of fluid pressure, velocity and content in the deformed parenchyma for a blocked aqueduct provides new qualitative insight into hydrocepahlus. Some observations are offered for two forms of cerebrospinal fluid flow abnormality, normal pressure hydrocephalus and idiopathic intracranial hypertension. The model is extended to include a gravitational term in the governing equations and the effect of hydrostatic pressure variation is considered. Results of a fully 3D simulations are described for two horn-like lateral ventricles and one case with two lateral ventricles and a third ventricle.     

Numerical Modeling of Shockwave Treatment of Knee Joint

Arthritis is a degenerative disease that primarily affects the cartilage and meniscus of the knee joint. External acoustic stimulation is used to treat this disease. This article presents a numerical model of the knee joint aimed at the computer-aided study of the regenerative effects of shockwave treatment. The presented model was verified and validated. A numerical analysis of the conditions for the regeneration of the tissues of the knee joint under shockwave action was conducted. The results allow us to conclude that to obtain the conditions required for the regeneration of cartilage tissues and meniscus (compressive stresses above the threshold value of 0.15 MPa to start the process of chondrogenesis; distortional strains above the threshold value of 0.05% characterized by the beginning of the differentiation of the tissues in large volumes; fluid pressure corresponding to the optimal level of 68 kPa to transfer tissue cells in large volumes), the energy flux density of therapeutic shockwave loading should exceed 0.3 mJ/mm².     

Effect of non-linear permeability in a spherically symmetric model of hydrocephalus.

We examine a spherically symmetric model of the brain and apply non-linear permeability in a small strain poroelastic framework. Numerical solutions to the model show that non-linear effects tend to improve predictions of ventricle wall displacement and pressure increase in acute hydrocephalus in comparison with a constant permeability model. Our model is used to study different mechanisms for hydrocephalus: complete blockage of the aqueduct and normal pressure hydrocephalus (NPH), as well as offering observations on mechanical effects in idiopathic intracranial hypertension. In each situation it is possible to apply different parameter conditions to quantify mechanical effects that correspond to some observed symptoms. The results support and quantify ideas from Levine (2000, Ventricle size in pseudotumor cerebri and the theory of impaired CSF absorption. J. Neurol. Sci., 177, 85-94) on a poroelastic mechanism for some features of NPH and idiopathic intracranial hypertension.     

轴向振动时节段曲度对腰椎间盘应力演化的影响

研究人体腰椎运动节段承受长期轴向振动载荷时节段曲度对腰椎间盘应力演化的影响。基于人体腰椎L4～5节段CT扫描数据,建立人体腰椎L4～5节段的有限元模型。对腰椎间盘赋予多孔材料属性,并验证有限元模型的有效性。基于有限元模型,模拟L4～5节段以3种不同节段曲度(中立位、伸展2°、弯曲2°)承受时长为1 000 s的轴向振动的过程,得到这3种节段曲度下腰椎间盘的应力演化情况。各个曲度下腰椎间盘纤维环部分的峰值轴向应力均出现在其后外侧。在受载过程中,各个曲度下纤维环峰值轴向应力均呈非线性增大,且增速不断减小,至1 000 s时已趋于稳定。1 000 s时,伸展2°下纤维环峰值轴向应力比中立位下大39%,比弯曲2°下大109%。在受载过程中,各个曲度下髓核轴向应力亦呈非线性增长,增速不断减小。1 000 s时,伸展2°下髓核的轴向应力略小于其他两种情形。当L4～5节段以伸展2°的状态受载时,腰椎间盘受到的损伤最为严重;而当其以弯曲2°的状态受载时,腰椎间盘受到的损伤最小。当长时间处于全身振动条件下时,应尽量避免使腰椎处于向后伸展的姿态,而腰椎的小幅前屈可以保护腰椎间盘。