EVALUATION AND ENHANCEMENT OF THERMAL AND MECHANICAL PERFORMANCE OF POSTURE CORRECTION GIRDLE FOR ADOLESCENT IDIOPATHIC SCOLIOSIS (AIS)

Student thesis: PhD

Abstract

The posture correction girdle is a newly developed flexible orthosis to treat preteen and teenage girls between the ages of 10 and 13 who are in the early stages of scoliosis (Liu, 2015). The aim of this girdle is to enhance the physical and psychological comfort of patients in order so that there is more compliance with treatment which would increase the treatment efficacy. The girdle also enhances posture control and reduces the possibility of spinal curve progression in scoliosis. However, this functional intimate apparel still has limitations. For example, compliance is poor in the summer as the posture correction girdle is a multi-layered functional garment. If the breathability of the textile materials is inadequate, body heat and moisture cannot pass through the fabric, which would cause physiological discomfort during wear. In addition, there is little control of the spine as the girdle is very flexible, which means that the corrective forces are inadequate for the correction of spinal curvature. In the study by Liu et al. (2014) on the construction of the girdle, their subjects have a Cobb’s angle that is between 6° and 20°. This means that their girdle is only suitable for those with mild scoliosis. However, there could be the need to treat scoliosis patients with more severe spinal deformities. Therefore, the girdle in Liu et al. (2014) would need to be modified to improve the thermal and mechanical properties which would extend the benefits of the treatment to those with a more severe spinal curvature.
Apart from the limitations of the girdle design, there is no systematic method used to determine the most effective amount of pressure exertion and evaluate the effect of the pressure exertion on the correction of spinal deformity by the girdle. This means that Liu et al. (2014) only based their results on observation of the spinal curvature by using radiography. However, exposure to radiation may pose risks to human health. Also, the efficiency of the flexible girdle in preventing the progression of scoliotic deformity is not known after the adolescent participants wore the girdle. There is the risk that the magnitude of the spinal curvature may even increase after the wear trial. Therefore, new prediction or evaluation methods would be useful to assess the effectiveness of the modified girdle in this study.
This study consists of different components, including: (a) enhancing the thermal comfort of an existing posture correction girdle in Liu et al. (2014), (b) enhancing the mechanical properties of the existing posture correction girdle, (c) a clinical study of a modified posture correction girdle with newly sourced materials, and (d) the development of prediction models including a soft mannequin with a scoliotic spine and a biomechanical model.
In order to improve the thermal comfort of the existing posture correction girdle, 15 types of cool-touch fabrics in the market have been newly sourced which are then subjected to different types of physical testing, including measuring the thermal conductivity, air and water vapor permeabilities, and peak heat flux. The thermal properties of the fabrics that are already used in the existing girdle and the newly sourced fabrics are compared to determine the most suitable combination of fabric layers. After determining the fabrics that are best suited for the modified girdle, the modified girdle is fabricated and then evaluated through the preliminary wear trial. The wear trial consists of 2 parts - objective and subjective assessments. In the objective assessment, IRT and temperature and humidity sensors are used, while an interview is conducted for the subjective assessment. All of the results in the preliminary wear trial show the same trend in that the modified posture correction girdle provides better thermal comfort. Therefore, the new composition of the posture correction girdle might potentially improve the thermophysiological comfort of the wearer and encourage patients to comply with the entire length of the treatment.
In order to enhance the mechanical properties of the existing posture correction girdle, 4 different types of supporting struts in the market are newly sourced and along with the struts used in the original girdle in Liu et al. (2014), subjected to bending and recovery tests to compare their mechanical properties. The most suitable material that would improve the efficacy of spinal correction treatment with a girdle should be adequately stiff with a good recovery property. A preliminary wear trial which includes pressure measurements and radiographic examination is also conducted to determine the effect of the girdle with different types of struts. Based on the findings, modified versions of the girdle with moulded SMA struts have been developed since the SMA struts have the best recovery and a high degree of stiffness. However, they cannot exert pressure evenly because they do not easily bend to conform to the curves of the body. For orthoses that require an even pressure distribution, moulding in accordance with the body shape is recommended.
A clinical study is also carried out to further study the efficacy of the modified posture correction girdle. In total, 16 female subjects with AIS have participated in this study, among which 6 wore the original posture correction girdle while 10 wore the modified girdle. Among the 10 subjects in the group who wore the modified girdle, 5 of them wore the girdle with curved SMA struts on one side and the other 5 wore the girdle with curved SMA struts on both sides. The results show that the insertion method with curved SMA struts inserted into both sides of the girdle provides the best corrective effect while the girdle with curved SMA struts on one side has the poorest corrective effect among the three experimental groups. The result proves that the hard brace mechanism which is adopted in the girdle with curved SMA struts on one side is not feasible. On the other hand, the perceived comfort of the girdles are assessed by conducting a questionnaire and interviews. The results indicate that the girdle inserted with curved SMA struts on one side is problematic in terms of psychological and physiological comfort. This girdle seems to be unbalanced at the waist and is a concern because the wearers might be the object of scrutiny and curiosity due to their appearance. Therefore, the girdle might increase the stress level of the subjects. Also, straight SMA struts cause pain and pose difficulties of stretching and fixing the waistband into the correct position. Therefore, the perceived comfort of the girdle inserted with curved SMA struts on one side is the lowest while the girdle inserted with RB struts is highest in perceived comfort due to the high flexibility, lightness in weight and minimal restriction of body movement.
After obtaining the clinical data, prediction models are developed to simulate the treatment with a girdle on a scoliotic patient. In order to validate the biomechanical model, a soft mannequin is first developed and validated. The soft mannequin is a moulded silicone rubber torso which contains 3D printed vertebrae and intervertebral discs. These components are the same as those in the finite element model (FEM) formulated in this study. Two prototypes are constructed. The validation of the soft mannequin is done by pressure measurements and spinal curve changes which are compared to the clinical results. The results show that the soft mannequin made of softer silicone rubber (Shore 00 hardness of 10) produces similar pressure results as those of the real life cases. Similar to the clinical study, there are greater shifts in the spine when the girdle with SMA struts is worn, so that it can be concluded that the corrective effect of the girdle with SMA struts excels that of the girdle with RB struts.
With regard to the FEM, two models have been constructed to simulate the posture correction girdle with SMA and RB struts. Both models consist of five geometric models: the torso, posture correction girdle, supportive struts, vertebrae of the lumbar spine and intervertebral discs. The FEM is validated by using the interface pressure and spinal corrective effects measured from the validated soft mannequin model. The output of the FEM shows extremely low stress values compared to the measured pressure of the soft mannequin. Although the pressure values obtained from the FEM and soft mannequin differ at the pelvis, they show the same trend in that the interface pressure on the left side of the underbust is higher than that at the right side of the underbust, the interface pressure at the right side of the waist is higher than that at the left side of the waist and the left side of the pelvis is higher than that of the right side of the pelvis for the girdle with RBs. However, in terms of the spinal corrective effects, the FEM results are not comparable with those of the soft mannequin model. The model contains many sharp edges and small meshes which might have affected the calculations.
The research results and findings provide useful information on the effects including the thermal and mechanical performances since the flexible scoliotic brace (girdle) is constructed of different types of materials. In addition, the relationship between material stiffness and interface pressure is useful for future developments in flexible orthoses. The modified version of the posture correction girdle shows better thermal comfort and corrective effect than the original design. Although the efficacy of the modified girdle is not comparable with conventional hard brace treatment, this study provides a reference for improving the flexible brace treatment. The soft mannequin can also be used to predict the pressure distribution and corrective effect of the posture correction girdle. Finally, the outputs of this project can extend to the development of a flexible brace that provides wear comfort and good corrective effects on scoliotic patients.
Date of Award2019
Original languageEnglish
Awarding Institution
  • The Hong Kong Polytechnic University
SupervisorYiu Wan Yip (Chief supervisor), Kit Lun Yick (Co-supervisor) & Dr NG Sun Pui Zerance (Co-supervisor)

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