BackgroundFor the treatment of low back pain, the following three scenarios of posterior lumbar interbody fusion (PLIF) were usually used, i.e., PLIF procedure with autogenous iliac bone (PAIB model), PLIF with cages made of PEEK (PCP model) or titanium (Ti) (PCT model) materiel. But the benefits or adverse effects among the three surgical scenarios were still not fully understood.MethodFinite element analysis (FEA), as an efficient tool for the analysis of lumbar diseases, was used to establish a three-dimensional nonlinear L1-S1 FE model (intact model) with the ligaments of solid elements. Then it was modified to simulate the three scenarios of PLIF. 10 Nm moments with 400 N preload were applied to the upper L1 vertebral body under the loading conditions of extension, flexion, lateral bending and torsion, respectively.ResultsDifferent mechanical parameters were calculated to evaluate the differences among the three surgical models. The lowest stresses on the bone grafts and the greatest stresses on endplate were found in the PCT model. The PCP model obtained considerable stresses on the bone grafts and less stresses on ligaments. But the changes of stresses on the adjacent discs and endplate were minimal in the PAIB model.ConclusionsThe PCT model was inferior to the other two models. Both the PCP and PAIB models had their own relative merits. The findings provide theoretical basis for the choice of a suitable surgical scenario for different patients.

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The age distribution of corneal diseases in the Chinese population is distinct from other countries. The corneal diseases tend to increase in prevalence in middle age, especially for infectious corneal disease. The prevalence of corneal tumor is high in early and late life. Corneal degenerative disease occurs predominately in seniors.

Object: To establish a non-linear finite element (FE) model for human L4-L5 lumbar segment and verify its reliability. Method: A FE model of human L4-L5 lumbar segment was established. Some empirical expressions were used to simulate the mechanical properties of vertebral body. The annulus fibrosus and nucleus were assigned hyper-elastic material. The surrounding ligaments were assigned be unsymmetric spring elements. The FE model was developed in ABAQUS software under the loading conditions of axial compression, lateral bending, extension, torsion, and flexion. Result: The result curves of different loading conditions all represent a similar nonlinear curve. The axial force and displacement curve of L4-L5 FE model was closely correlated with the published results of in vitro experimental study. The relationship between moment and degrees also showed a good agreement with the experimentally determined in vitro data during the loading condition of lateral bending, extension, torsion, and flexion. Conclusion: The FE model established in this paper can effectively reflect the actual mechanical properties of human L4-L5 lumbar spine. It can be used as the basis for further research on lumbar degenerative diseases and related treatments.