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Research Papers

The Effect of Boundary Condition on the Biomechanics of a Human Pelvic Joint Under an Axial Compressive Load: A Three-Dimensional Finite Element Model

[+] Author and Article Information
Zhixiu Hao1

 Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Building 9003, Tsinghua University, Beijing 100084, China email: haozx@tsinghua.edu.cnDivision of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology,  Tsinghua University, Beijing 100084, ChinaMusculoskeletal Tumor Center, People’s Hospital,  Peking University, Beijing 100044, China

Chao Wan, Xiangfei Gao, Tao Ji

 Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Building 9003, Tsinghua University, Beijing 100084, China email: haozx@tsinghua.edu.cnDivision of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology,  Tsinghua University, Beijing 100084, ChinaMusculoskeletal Tumor Center, People’s Hospital,  Peking University, Beijing 100044, China

1

Corresponding author.

J Biomech Eng 133(10), 101006 (Oct 31, 2011) (9 pages) doi:10.1115/1.4005223 History: Received January 10, 2011; Revised September 26, 2011; Published October 31, 2011; Online October 31, 2011

The finite element (FE) model of the pelvic joint is helpful for clinical diagnosis and treatment of pelvic injuries. However, the effect of an FE model boundary condition on the biomechanical behavior of a pelvic joint has not been well studied. The objective of this study was to study the effect of boundary condition on the pelvic biomechanics predictions. A 3D FE model of a pelvis using subject-specific estimates of intact bone structures, main ligaments and bone material anisotropy by computed tomography (CT) gray value was developed and validated by bone surface strains obtained from rosette strain gauges in an in vitro pelvic experiment. Then three FE pelvic models were constructed to analyze the effect of boundary condition, corresponding to an intact pelvic joint, a pelvic joint without sacroiliac ligaments and a pelvic joint without proximal femurs, respectively. Vertical load was applied to the same pelvis with a fixed prosthetic femoral stem and the same load was simulated in the FE model. A strong correlation coefficient (R2=0.9657) was calculated, which indicated a strong correlation between the FE analysis and experimental results. The effect of boundary condition changes on the biomechanical response depended on the anatomical location and structure of the pelvic joint. It was found that acetabulum fixed in all directions with the femur removed can increase the stress distribution on the acetabular inner plate (approximately double the original values) and decrease that on the superior of pubis (from 7 MPa to 0.6 MPa). Taking sacrum and ilium as a whole, instead of sacroiliac and iliolumber ligaments, can influence the stress distribution on ilium and pubis bone vastly. These findings suggest pelvic biomechanics is very dependent on the boundary condition in the FE model.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

The experiment of the pelvis in vitro for obtaining strain values on the measure points

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Figure 2

The Finite Element model of human pelvic with main bone structures (proximal femur, sacrum and pelvis bone) and main ligaments (Sacroiliac, Sacrospinous, Iliolumbar, Superior pubic and Arcuate pubic ligaments). In the FE model, the bones were meshed by modified 10-node, 60 degree-of-freedom quadratic tetrahedral elements and ligaments were represented by groups of linear spring elements (purple lines in the figure).

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Figure 3

The Young’s modulus distribution of pelvic FE model based on the Gray value of CT data: (a) the front view; (b) the vertical sectional view of the ilium. The material Young’s modulus range of sacrum, left pelvis and right pelvis were from 3.045 MPa to 23,856.1 MPa, from 9.883 MPa to 23,621.5 MPa and from 16.915 MPa to 24,564.8 MPa, respectively.

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Figure 4

The linear regression analyses of the FE analysis results and experimental results. The x- and y- axis corresponded to experimental and FE analysis strain results, respectively. The regression equation showed that the FE analysis results had a strong correlated relationship with the experimental results (R2=0.9657).

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Figure 5

The comparison of equilibrium strain values on seven measure points in the experiment and the FE models under different loads (a) under 150 N; (b) under 350 N;(c) under 550 N

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Figure 6

The comparison of von Mises stress on seven measure points in three FE cases: (a) under 150 N; (b) under 350 N; (c) under 550 N

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Figure 7

The contour of von Mises stress in three FE cases under an 550 N load. The stress distribution along the iliopectineal line, on the inferior part of the sacrum and on the superior ramus of the pubis changed significantly in the comparison of three FE cases. (a) and (b): case 1 (anterior and posterior views); (c) and (d): case 2 (anterior and posterior views), (e) and (f); case 3 (anterior and posterior views).

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