| Author: | Liu, Shan |
| Title: | A comprehensive study of the whole orthotic treatment period in adolescent idiopathic scoliosis with the consideration of force application, patient’s clinical features, and treatment compliance |
| Advisors: | Wong, Man Sang (BME) |
| Degree: | Ph.D. |
| Year: | 2026 |
| Subject: | Scoliosis in children Scoliosis -- Treatment Spine -- Abnormalities Orthopedic apparatus Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Biomedical Engineering |
| Pages: | 1 volume (various pagings) : color illustrations |
| Language: | English |
| Abstract: | Adolescent idiopathic scoliosis (AIS) is a three-dimensional spinal deformity that may progress rapidly during puberty, leading to pain, functional limitations, and psychosocial burden if left untreated. Thoracolumbosacral orthoses (TLSOs) represent the primary nonoperative intervention for moderate AIS in skeletally immature patients; however, treatment outcomes remain highly variable. Despite decades of clinical use, orthotic force application is still largely empirical. A critical gap lies in the lack of integrated evidence explaining how controlling force direction, its relationship to spinal deformity, patient-specific clinical features, and treatment compliance jointly influence orthotic effectiveness. This limitation constrains the development of evidence-based and personalized orthotic strategies. Accordingly, this doctoral thesis investigates the multifactorial determinants of orthotic treatment effectiveness in AIS through five interrelated sub-studies, with a particular focus on the biomechanics of controlling force direction (CFD) and its interaction with structural and patient-related factors. The first sub-study developed a computer vision-based method to quantitatively estimate controlling force direction from CAD/CAM orthotic models and examined its association with treatment outcomes. When considered independently of structural orientation, CFD was not significantly associated with either immediate in-orthosis correction or long-term stabilization, indicating that force direction alone is insufficient to capture the complexity of corrective biomechanics. The second sub-study introduced the concept of CFD-PMC alignment, defined as the angular difference between CFD and the plane of maximum curvature (PMC). Closer alignment, particularly within 15°–20°, was associated with significantly greater improvements in PMC-specific curvature, especially among patients with milder deformities. These findings support the premise that effective orthotic correction requires force application to be guided by individual structural orientation. The third sub-study evaluated spinal flexibility, quantified by the reduction in Cobb angle from standing to supine radiographs, as a biomechanical moderator of treatment response. Flexibility demonstrated a modest association with in-orthosis correction and interacted with CFD-PMC alignment, suggesting that long-term outcomes depend on how intrinsic flexibility translates into mechanical responsiveness under structure-guided force application. The fourth sub-study examined body habitus using body mass index (BMI) and BMI-for-age Z-scores. Contrary to previously reported U-shaped associations, no significant relationships were identified between BMI and either in-orthosis correction or long-term outcomes. These results indicate that BMI contributes minimally to outcome variability, further emphasizing the central roles of force-structure alignment and compliance. The fifth sub-study assessed orthotic compliance using both objective sensor-based wear-time data and subjective self-reports. Higher compliance was consistently associated with superior outcomes. Notably, among patients with comparable wear time, those with better CFD-PMC alignment achieved greater improvements, underscoring the combined importance of orthosis design and patient adherence. Together, these findings establish an integrated biomechanical and clinical framework for understanding orthotic treatment in AIS. Rather than being driven by any single factor, treatment effectiveness emerges from the combined influence of force application, structural deformity, spinal flexibility, BMI, and compliance. This thesis advances the concept of structure-guided force alignment and highlights the potential for future CAD/CAM orthoses to optimize controlling force vectors relative to individualized spinal deformity, thereby enabling more personalized, reliable, and evidence-based scoliosis management. |
| Rights: | All rights reserved |
| Access: | open access |
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