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Research Papers

The Patient-Specific Brace Design and Biomechanical Analysis of Adolescent Idiopathic Scoliosis

[+] Author and Article Information
Wen-Zhong Nie, Ming Ye, Cheng-Tao Wang

School of Mechanical Engineering, Shanghai Jiaotong University, Shanghai 200240, China

Zu-De Liu

Renji Hospital, Shanghai Jiaotong University, Shanghai 200127, China

J Biomech Eng 131(4), 041007 (Feb 03, 2009) (7 pages) doi:10.1115/1.3049843 History: Received November 11, 2007; Revised September 29, 2008; Published February 03, 2009

Brace application has been reported to be an effective approach in treating mild to moderate idiopathic adolescent scoliosis. However, little attention is focused on the biomechanical study of patient-specific brace treatment. The purpose of this study was to propose a design method of personalized brace and to analyze its biomechanical behavior and to compare the brace forces with the I-Scan measurement system. Based on a three-dimensional patient-specific finite element model of the spine, rib cage, pelvis, and abdomen, a parametric patient-specific model of a thoracolumbosacral orthosis was built. The interaction between the torso and the brace was modeled by surface-to-surface contact interface. Three standard strap tensions (20 N, 40 N, and 60 N) were loaded on the back of the brace to simulate the strap tension. The I-Scan distribution pressure measurement system was used to measure the different region pressures, and the equivalent forces in these regions were calculated. The spinal curve changes and the forces acted on the brace generated by the strap tension were evaluated and compared with the measurement. The reduction in the coronal curvature was about 60% for a strap tension of 60 N. The sacral slope and the lordosis were partially reduced in this case, but the kyphosis had no obvious change. The brace slightly modified the axial rotation at the apex of the scoliotic curve. The forces generated in finite element analysis were approximately in good agreement with the measurement. The design and biomechanical analysis methods of patient-specific brace should be useful in the design of more effective braces.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

The patient CT scout images (a) and geometrical model (b)

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Figure 2

(a) Positions of the generative curves; (b) definition of the generative curves

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Figure 3

The geometrical and FE models of the patient-specific brace ((a) the geometry model in brace (AP view), (b) the FE model with strap tension (PA view), (c) the abdominal FE model, (d) the brace FE model, (e) the rib cage FE model, and (f) the T1-S1 FE model)

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Figure 4

(a) Comparison of the motion angle on the lumbar spine for loading with pure moments of 3.75 N m in experimental studies (30) and FE analyses (31) and this study; (b) comparison of the intradiscal pressure changes in the four disk levels for loading pure flexion bending moments of 3.75 N m in the sagittal plane in experimental studies (30) and FE analyses (31) and this study

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Figure 5

Spine curve of the patient from the simulation with strap tensions of 20 N (filled square), 40 N (filled triangle), 60 N (filled cross), and without brace (filled diamond). All data are in millimeters.

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Figure 6

Force (N) acting on the brace for the three strap tensions (“Sim” presents simulation result, “Mea” presents our measurement result, and “Mac” is the experiment result measured by Mac-Thiong (14))

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