# Finite Element Model of Soliosis Brace with Increased Utility Characteristics
## 1 Introduction  
Idiopathic scoliosis is a complex, three-dimensional deformity of the spine and trunk that affects 1-3% of children, primarily between the ages of 10 and 16. For those with a Cobb angle of 20 to 40 degrees and who are still growing, the standard of care is a custom-made corrective brace used in conjunction with specialized physical therapy [1]. This brace, essentially a trunk brace or corset, is made of thermoplastic materials. The primary goal of such a brace is to halt the progression of spinal curvature while promoting thoracic and trunk symmetry. Typically, the brace is worn until the patient reaches skeletal maturity [2].  
Conventional Boston or Cheneau braces designed for the treatment of idiopathic scoliosis have an outer shell that envelops a large portion of the trunk, tailored to the specific type of scoliosis being treated. The shell, typically made of a 4 mm thick polypropylene sheet, is a rigid structure that is custom-fitted to the patient's torso. This rigid shell has several holes to facilitate checking the pressure exerted on the torso using internal corrective pads. These pads are strategically positioned inside the brace to align with the apex of the spinal curves. Given the complex design of standard braces, it is challenging to determine the specific areas of the shell that are responsible for the corrective action. This requires an understanding of how the rigid shell, tensioned by straps, effectively transfers loads to the internal pads. The focus of the current research builds on previously publishedwork [3] to further elucidate the operational mechanics of a Boston brace shell with proven therapeutic efficacy.  
The design intricacies of the orthosis have a significant impact on its utility characteristics. Factors such as heat and gas exchange between the body and the surrounding air through the brace, as well as the weight of the device, can adversely affect patient comfort and compliance [4]. Therefore, the goal of this work is to optimize brace design to use less material while maintaining corrective stiffness, which requires a comprehensive understanding of how corrective forces are distributed through the shell. An additional goal is to improve other important functional parameters of the corset including the patient's thermal comfort level, the level of gas exchange at the interface between the torso and the inner surface of the corset shell, and the degree of discretion in the use of the orthosis, related to its geometric size and shape.  
Finite element modeling (FEM) provides a tool for detailed stress analysis, although few studies have rigorously validated their simulations with empirical data [5; 6; 7]. [PERSON] and [PERSON] recently presented an FEM model of the Boston brace that was experimentally verified using electronic speckle pattern interferometry (ESPI) [3]. The ESPI system evaluated surface displacements of the brace under a three-point loading scheme that mimicked corrective forces. The minimal discrepancies between the experimental and FEM results indicated a high level of accuracy in the FEM model [3].  
The current study proposes an optimization strategy for brace design using numerical modeling through a previously validated FEM model [3] and a methodology centered on the concept of force flow lines. The result is a brace that maintains its corrective stiffness while significantly reducing its weight, thereby improving patient comfort and compliance, which in turn should improve clinical outcomes. This methodology can be extended to other thoracic-lumbar-sacral orthosis (TLSO) designs.