This preliminary study investigates the possibility of using a novel anisotropic brace to control spinal curvature. It has been already well established that in-brace correction is the initial factor that is used to evaluate the efficacy of new braces [13]. Studies about the reliability of Cobb’s angle measurement suggested that 5˚ is the standard error of measurement [13, 14]. In the current study, more than half of subjects obtained a greater than 5 ˚ change of Cobb’s angle, which is greater than the standard error of measurement. This result implicates that the intervention of propose brace had a positive effect on spinal curvature in certain cases.
Guo, et al. [15] conducted a randomized controlled study with scoliotic subjects who have a Cobb’s angle between 20°-30° to determine the efficacy of rigid braces and the SpineCor brace, and reported that the initial rate of in-brace correction for the rigid braces and SpineCor is 15.9% and 21.3% respectively. Karol [16] examined the effectiveness of several different types of rigid braces in male subjects with scoliosis who have a Cobb’s angle between 18°-45° and found that the initial rates of in-brace correction with the Milwaukee, Boston and Charleston braces are 17.4%, 35.6% and 62.2% respectively. The initial results of the anisotropic textile brace approximate those of some of the existing braces.
Lang, et al. [17] conducted a retrospective analysis with 112 AIS subjects who were undergoing rigid brace treatment and found that the Cobb’s angle, sagittal and coronal balances and lumbar-pelvis relationship affect in-brace correction. Nevertheless, the data in this study show that there is no relationship between in-brace correction and the Cobb’s angle.
Trunk asymmetry affects the self-confidence and feelings of sexual attractiveness of women with scoliosis. In addition to spinal correction, improving the brace aesthetics is also an important treatment outcome [18]. Kotwicki, et al. [19] investigated the external morphology of the trunk in a cross-sectional study of 24 girls who were wearing a brace versus 26 girls who were not undergoing bracing treatment and pointed out that there is no significant difference in the POTSI parameters between the two groups. This study further confirms the discrepancy between the Cobb’s angle and POTSI. A possible explanation is that the Cobb’s angle only attests to the tilt of the two end vertebrae of the curvature in the frontal plane [19].
The equilibrium of the artificial hinge bone is critical for the biomechanics of spinal correction as it is related to the pressure distribution of the brace. According to the equilibrium principle, the sum of the forces and the bending moments created must be zero to main stability. For Subject 2, pads were inserted at the right thoracic region, left lumbar region and right side of the pelvis. The intention was to apply the three-point pressure system in these three areas and correct the lumbar spinal curvature. However, as the pressure on the right side of the pelvis was increased due to the pad, the pressure from the corrective panel on the right side of the thoracic spine was reduced to maintain the balance of the artificial hinge bone. As a result, the forces exerted onto the right side of the thoracic spine were insufficient to counter the lumbar curve in the upper region, and thus an increase in the lumbar curve might be the result. To solve this issue, it is recommended that no pads are inserted at pelvis belt.
On the other hand, Subjects 1, 3, 4, and 5 show that the three-point pressure system can be effective with equilibrium of the artificial hinge bone. It was found that the location (left or right side) of the corrective panel that was placed against the lumbar/ thoracolumbar curve would influence the pressure distribution of the pelvis belt which holds the end point of the artificial hinge bone in place. After installing the corrective panel against the left lumbar/ thoracolumbar curve, the right of the pelvis belt was found to exert greater tension on the artificial hinge bone than the left side of the pelvis belt in order to maintain equilibrium of the hinge bone. In such cases, even if no pads were inserted at the right side of the pelvis belt, the right side of the pelvis belt also exerted a lower counter force against the lumbar curve when the corrective panel was placed against the left lumbar/ thoracolumbar curve.
Wong, et al. [20] investigated the biomechanics of rigid braces and reported that the pressure exerted by rigid braces ranges from 4.9 kPa to 9.34 kPa. Mac-Thiong, et al. [21] also conducted experimental measurements with rigid braces and found that the pressure induced by the Boston brace ranges between 10 kPa and 30 kPa. In this study, the interface pressure from the novel anisotropic textile brace ranges between 4.1 kPa and 25.6 kPa, which is very similar to the rigid braces. This shows that the textile brace also generates the same corrective forces as rigid braces against the torso. These results show the possibility of using elastic textile materials to provide adequate corrective pressure.
Another interesting finding in this study is that the pressure from the pad exerted onto the thoracic curve is significantly higher than that exerted onto the lumbar curve. This finding is consistent with those of a previous biomechanics study on rigid braces by Wong, et al. [20]. A possible explanation is that the ribcage directly absorbs the pressure from the pad exerted onto the thoracic curve, while the fat in the waist area might distribute the pressure exerted onto the lumbar curve.
Based on the law of mechanics, higher exerted forces would result in higher rates of in-brace correction. Adequate corrective forces are undoubtedly important to correct spinal curvature. However, our preliminary results agree with those [22] in that there is no significant correlation between interface pressure and in-brace correction, which might imply that after the corrective forces reach a certain level, any further increases in force will not increase spinal correction. However, further studies with a larger sample size are recommended to investigate the correlation between the interface pressure and in-brace correction.