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Understanding the relationship between the changes in the axonal transport of the optic nerve (ON) and lamina cribrosa (LC) deformation will be helpful to estimate the degree of axonal transport block by measuring the LC deformation in vivo. First, the changes in the axonal transport of the ON were studied using an acute high intraocular pressure (IOP) model, which was established by perfusing saline water into the anterior chamber of cats. The IOP of cat was unilaterally elevated to and maintained at 30, 40, and 50 mmHg. The axonal transport of the ON was examined by confocal laser scanning microscope. Then the deformations and stress distributions of the LC and ON were calculated using a three-dimensional finite element model of the LC microstructure including ON. The results showed axonal transport changes of ON increased with elevation of the IOPs. While Young's modulus of the LC and ON were assumed as 0.1 MPa and 0.03 MPa, the numerical simulation results showed that LC had displacements of 0.02, 0.03, and 0.04 mm backward at the IOPs of 30, 40, and 50 mmHg, respectively. The calculated compressive strain applied to the ON were 0.0425, 0.0567, and 0.0709 under 30, 40, and 50 mmHg IOP, respectively. The results of strain and stress analysis of LC and ON showed that the deformation of LC would compress the ON. The axonal transport abnormalities could be inferred by measuring the LC deformation in vivo. [ABSTRACT FROM AUTHOR]

Background: The complicated basilar invagination and atlantoaxial dislocation (BI-AAD) can cause a variety of neurological symptoms. Active treatment should be given. The main method of surgical treatment is to relieve the compression of the ventral bone of the brain stem and to fix the unstable spinal segments for fusion. At present, more surgical methods choose modified posterior cervical reduction and internal fixation fusion. Objective: The clinician has preliminarily designed an internal occipital fixation system capable of restoring both horizontal and vertical AADs, and proposed a new compression and distraction reduction (CDR) technique. The feasibility and effectiveness of posterior AAD reduction surgery using CDR techniques for different types of patients were studied in this paper. Methods: First, according to the CT scan sequence images of the congenital BI-AAD patient's cervical vertebra, the software Materialize Mimics 13.1 was imported to reconstruct 3D geometric model of cervical spine (C0-C7). Then the geometric topology model was carried out in Geomagic2012 software, and surrounding soft tissue was established using SpaceClaim 14.0. The 3D finite element model (FEM) of cervical vertebra for congenital BI-AAD patients was obtained by assigning material attributes, setting contacts and mesh in ANSYS 14.0. To simulate the physiological activities of the spine under two conditions of forward flexion and backward extension, preoperative verification was carried out with the maximum displacement parameter. According to the postoperative CT data of the patient, the position and degree of freedom (DOF) of the occipitocervical internal fixation system were determined. The FEM of the occipitocervical internal fixation system was established by dividing unit grid in ANSYS. Using multiple loading step of statics analysis method, the CDR technology of posterior AAD reduction surgery was simulated. When the atlantoaxial horizontal and vertical reductions were satisfactory, the displacement data were obtained and verified using the post-operative data. Results: The cervical spine (C0-C7) FEM of congenital BI-AAD patients was established. For some lateral atlantoaxial articulation abnormal ossification II, we simulated the CDR technique for the AAD reduction surgery and proposed using the vertical traction instead of vertical reduction. Conclusion: This study confirms the feasibility and effectiveness of posterior AAD reduction surgery using CDR techniques and proposes the different reduction optimization scheme for the patients with lateral atlantoaxial articulation abnormal ossification II of congenital BI-AAD. The results of this study provide a biomechanical theoretical basis for improving the reliability of simple posterior reduction surgery and optimizing the surgical treatment of BI-AAD. [ABSTRACT FROM AUTHOR]

The elevated intraocular pressure (IOP) is one of the important risk factors of glaucomatous optic nerve damage. The deformations of glaucomatous optic nerve head (ONH) due to the elevated IOP might lead to further damage to the optic nerve. The ONH deformations due to the elevated IOP depend on their geometry. Therefore, it is meaningful to investigate the relationship between geometrical parameters and the deformation of ONH. Firstly, the geometrical parameters of ONH were obtained by in vivo using spectral domain optical coherence tomography. Then, individual-specific three-dimensional (3D) models of ONH for glaucoma and normal subjects were established and the deformations of ONH were acquired by using finite element method. Furthermore, the thickness changes of retina and lamina cribrosa were calculated under different IOPs. Finally, correlations between geometrical parameters and the relative deformations of the human ONH were researched by using Spearman correlation. It was found that the relative thickness change of patient's retina was larger than that of normal subjects under the same condition. The correlation of several parameters, including cup area, and lamina cribrosa depth, with relative deformations of ONH had statistical significance. [ABSTRACT FROM AUTHOR]

Background: Determining the viscoelastic properties of cornea is important in the fields of understanding of the tissue's response to mechanical actions and the accurate numerical simulation of corneal biomechanical behavior under the effects of keratoconus and refractive surgery. To address this need, we present an approach to model the viscoelastic response of rabbit cornea from uniaxial test data. Methods: The corneal strip samples from six rabbits were obtained to perform cyclic uniaxial tension tests and stress relaxation tests. We investigated the suitability of six constitutive models, including empirical models and hyperelastic models, by a quasi-linear viscoelastic law. Applying non-linear optimization techniques, we found material parameters for each different strip sample. Results and conclusions: The model gave a better fit to loading data with , and predicted the unloading data in the cyclic uniaxial tests with errors-of-fit ranging from 0.03 to 0.06. The results indicate that the best model is the power of the first invariant of strain with Prony form relaxation model, and that the method to identify the material parameters are valid for modeling the visoelastic response of cornea from uniaxial test data. [ABSTRACT FROM AUTHOR]

The sclera is an important connective tissue that protects the sensitive layers within the eyeball. Identifying the mechanical properties of the sclera near the posterior pole is necessary to analyze the deformation of the sclera and stresses changing in the optic nerve head tissues. We propose a method to determine the mechanical properties of the sclera using dimensional analysis, finite element method and the indentation test. The elastic moduli of the sclera for different indentation depths and positions were identified. We found that the elastic moduli of the sclera varied with indentation depth. This was due to the effect of the mechanical properties of the substrate tissues inside the sclera. The elastic modulus of the choroid had the biggest effect on the determination of elastic modulus of the sclera, whereas that of the vitreous body could be ignored when the ratio of the indentation depth to the thickness of the sclera was less than 0.5. The effects of mechanical properties of the substrate tissues become more pronounced at greater indentation depths. [ABSTRACT FROM AUTHOR]

When performing anterolateral foraminotomy for the treatment of cervical spondylotic radiculopathy, the extent of uncinate process resection affects the stability of the cervical spine. The aim of this study was to determine the stability of the cervical spine after resection of various amounts of the uncinate process. Based on computed tomography (CT) scans of an adult male volunteer, a three-dimensional geometric model of the cervical spine (C4-C6) was established using Mimics 13.1, SolidWorks 2012, and ANSYS 15.0 software packages. Next, the mechanical parameters of the tissues were assigned according to their different material characteristics. Using the tetrahedral mesh method, a three-dimensional finite element model of the cervical spine was then established. In modeling uncinated process resection, two excision protocols were compared. The first excision protocol, protocol A, mimicked the extent of resection used in current clinical surgical practice. The second excision protocol, protocol B, employed an optimal resection extent as predicted by the finite element model. Protocols A and B were then used to resect the left uncinate process of the C5 vertebra to either 50% or 60% of the total height of the uncinate process. The stability of the cervical spine was assessed by evaluating values of deformation and maximum equivalent stress during extension, flexion, lateral bending, and rotation. After protocol A resection, the total deformation was increased as was the maximum equivalent stress during left and right rotation. After protocol B resection, the total deformation was little changed and the maximum equivalent stress was visibly decreased during left and right rotation. As evidenced by these results, protocol B resection had relatively little effect on the stability of the cervical spine, suggesting that resection utilizing the limits proposed in protocol B appears to better maintain the stability of the cervical spine when compared with current clinical surgical practice as replicated in protocol A. [ABSTRACT FROM AUTHOR]

To investigate the differences of mechanical responses between pulmonary artery and aorta to different biaxial loading conditions, we simulated the process of human pulmonary artery and aorta subjected to biaxial loading based on four-family fiber strain density function model determined from uniaxial extension data of arterial walls. It was shown that different stress-strain curves of pulmonary artery and aorta under biaxial loading conditions: different loading ratios between the loads in two perpendicular directions and displacement-controlled equibiaxial stretch. Tissue stiffness, defined as the first derivative of the stress-strain response at a strain point, of human pulmonary artery and aorta were obtained when they were subjected to biaxial loads (systemic pressure). The two-dimensional mechanical response of artery can be acquired by determination of the four-family fiber strain density function model of the tissue based on uniaxial extensile data. There are differences between material properties of pulmonary artery and aorta: aorta is stiffer circumferentially than longitudinally, and pulmonary artery is more compliant circumferentially than longitudinally. [ABSTRACT FROM AUTHOR]