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Scoliosis and Spinal Disorders

Volume 10 Supplement 1

IRSSD 2014 Meeting Abstracts

Oral presentation
Open Access

Comparison of biomechanical behavior between a cast material torso jacket and a polyethylene based jacket

  • Robert Rizza1,
  • XueCheng Liu2,
  • John Thometz2 and
  • Channing J Tassone2
Scoliosis201510(Suppl 1):O71

https://doi.org/10.1186/1748-7161-10-S1-O71

©  Rizza et al; licensee BioMed Central Ltd. 2015

Published: 19 January 2015

Keywords

Shear ModulusFinite Element ModelPoisson RatioBase DesignMaterial Cost

Introduction

Numerous designs are often used in the treatment of early onset of scoliosis. A Thoraco-Lumbo-Sacral Orthosis (TLSO) is constructed using Polyethylene (PE). A series of casting is implemented using cast material. The Cast material is less dense, allows the skin to breathe, and is made of a biodegradable water based resin (3M, BSN Medical). TLSO braces provide correction mechanically through constraint forces, which are minimized with excessive lateral defection.

Objectives

This study was motivated by goal to compare the biomechanical behavior of the cast based jacket with a PE based design.

Materials and methods

Samples of cast material (Delta-Cast Soft, BSN Medical) were tested for mechanical properties (Young’s Moduli, Poisson ratio and shear modulus). The cast material is a composite material with properties varying in different directions (Figure 1). A finite element model of a patient’s brace was created using an optical scan of the brace. The number of layers in the cast model was varied to determine the number of optimal layers. For the PE, a thickness of 4 mm was used. Loads applied to the brace by the torso were held constant and the lateral defection determined.
Figure 1

Figure 1

Results

The simulations indicate that the cast jacket with 6 layers will generate at most 4.7 mm deformation. The PE brace will generate a deformation of 2 mm (Figure 2). The structural factor of safety (FOS) for the cast brace was found to be 5.71 and 2.70 for the PE design. The mass of the cast design was 0.175 kg compared to 0.643 kg for the PE design. Material costs for the cast design would be $25.95 and for the PE design $51.90.
Figure 2

Figure 2

Conclusions

Both designs will generate the proper constraint forces to maintain spinal correction. Based on the design parameters (thickness, mechanical properties, FOS and cost) the brace made of cast material, though slightly thicker (6.6 mm compared to 4 mm) would be 3.5 times lighter and cost half as much (based on material costs). Furthermore the cast brace has double the strength. Thus, from the biomechanical point of view, the cast brace is more efficient than the PE brace.

Authors’ Affiliations

(1)
Dept. of Mechanical Engineering, Milwaukee School of Engineering, Milwaukee, USA
(2)
Department of Orthopaedic Surgery, Medical College of Wisconsin, USA

Copyright

© Rizza et al; licensee BioMed Central Ltd. 2015

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Scoliosis and Spinal Disorders

ISSN: 2397-1789

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