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. 2018 Dec 4:5:2055668318809661.
doi: 10.1177/2055668318809661. eCollection 2018 Jan-Dec.

A mechanical analog thoracolumbar spine model for the evaluation of scoliosis bracing technology

Chloe L Chung  1 , Derek M Kelly  2 , Jack R Steele  3 , Denis J DiAngelo  1
Affiliations

A mechanical analog thoracolumbar spine model for the evaluation of scoliosis bracing technology

Chloe L Chung et al. J Rehabil Assist Technol Eng. .

Abstract

Introduction: Thoracolumbar braces are used to treat Adolescent Idiopathic Scoliosis. The objective of this study was to design and validate a mechanical analog model of the spine to simulate a thoracolumbar, single-curve, scoliotic deformity in order to quantify brace structural properties and corrective force response on the spine.

Methods: The Scoliosis Analog Model used a linkage-based system to replicate 3D kinematics of spinal correction observed in the clinic. The Scoliosis Analog Model is used with a robotic testing platform and programmed to simulate Cobb angle and axial rotation correction while equipped with a brace. The 3D force and moment responses generated by the brace in reaction to the simulated deformity were measured by six-axis load cells.

Results: Validation of the model's force transmission showed less than 6% loss in the force analysis due to assembly friction. During simulation of 10° Cobb angle and 5° axial rotation correction, the brace applied 101 N upwards and 67 N inwards to the apical connector of the model. Brace stiffness properties were 0.5-0.6 N/° (anteroposterior), 0.5-2.3 N/° (mediolateral), 23.3-26.5 N/° (superoinferior), and 0.6 Nm/° (axial rotational).

Conclusions: The Scoliosis Analog Model was developed to provide first time measures of the multidirectional forces applied to the spine by a thoracolumbar brace. This test assembly could be used as a future design and testing tool for scoliosis brace technology.

Keywords: Scoliosis; analog model; brace; loading/response model; spinal orthosis.

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Conflict of interest statement

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
Steps in designing the scoliosis analog model. (a) Coronal plane data, (b) critical anatomy corresponding to SAM components, and (c) SAM components. SAM: Scoliosis Analog Model. Note: Example EOS scan and parameters are shown, not the actual patient scan and data used for this study.
Figure 2.
Figure 2.
Test assembly. (a) The SAM mounted in the programmable robotic testing platform, (b) front view of the SAM showing anatomical coronal plane and reference plane, and (c) transverse view of the SAM showing anatomical coronal plane and reference plane. SAM: Scoliosis Analog Model.
Figure 3.
Figure 3.
Setup for validation of SAM force output. SAM: Scoliosis Analog Model.
Figure 4.
Figure 4.
Testing assembly. (a) SAM with single-curve thoracolumbar Boston brace and (b) tensiometer attached to strap. SAM: Scoliosis Analog Model.
Figure 5.
Figure 5.
Methodology for simulating a changing spinal curve using linkage components. (a) Corrected alignment and (b) deformed alignment.
Figure 6.
Figure 6.
Plotted brace force and moment response with derived stiffness properties. (a) Force–displacement curves of the upper load cell, (b) force–displacement curves of the lower load cell, and (c) moment–displacement curves of the upper load cell.
Figure 7.
Figure 7.
Free-body diagram of the SAM at 28° CA and 5° AR. SAM: Scoliosis Analog Model; CA: Cobb angle; AR: axial rotation.
See this image and copyright information in PMC

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