Author: Wu, Huidong
Title: Estimation of plane of maximum curvature for enhancement of orthotic management of adolescent idiopathic scoliosis (AIS)
Advisors: Wong, Man-sang (BME)
He, Cheng-qi (BME)
Degree: Ph.D.
Year: 2022
Subject: Scoliosis -- Patients
Orthopedic apparatus
Spine -- Abnormalities
Hong Kong Polytechnic University -- Dissertations
Department: Department of Biomedical Engineering
Pages: xxiii, 176 pages : color illustrations
Language: English
Abstract: Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional (3D) spine deformity in adolescents with unknown causes. Coronal-Cobb angle (coronal-Cobb) measured from radiograph serves as the golden standard in assessing patients with AIS.. However, it may underestimate the severity of AIS and not fully reflect the 3D features of spinal deformity. Therefore, 3D descriptors, including the best-fit plane (BFP), end-apical-end plane (EAEP), and plane of maximum curvature (PMC), were proposed. However, these descriptors were not commonly used in assessing AIS due to the complexity of their acquisition methods. The BFP and EAEP are regarding the three axes of the human coordinate system, and the PMC only uses the vertical axis. By comparison, the PMC seems closer to the coronal-Cobb as both reveal the spinal curvature in a vertical plane. The PMC is a vertical plane between the sagittal and coronal planes and presents the maximum spinal curvature. Its parameters include the maximum Cobb angle (PMC-Cobb) and PMC orientation (PMC-orientation, the angle between the sagittal plane and PMC).
Radiographic and ultrasound techniques have been applied for PMC assessments. However, they are operated with special software/skills (e.g., 3D reconstruction), further validations are being explored. Therefore, Part I of this study was to develop a more user-friendly computational method (CM) for estimating the PMC (PMC-Cobb; PMC-orientation) and verify its results with computed tomography (CT). In the proposed CM, PMC was estimated via an anti-trigonometric function based on the 3D coordinates of 8 points located at the upper-end vertebra's superior endplate and the lower-end vertebra's inferior endplate of the spinal curve in the coronal and sagittal CT images. The users identified the 8 points manually. In the CT method, the PMC was determined via rotating a vertical plane, where the scoliotic spine was projected onto, with 5° increments, and measuring the Cobb angle in each rotated plane. Twenty-nine subjects with AIS were recruited, and two well-trained raters collected the data. The results of this study demonstrated high intra- & inter-rater reliability for the PMC obtained using the CM (intra- & inter-rater intraclass correlation coefficient ≥0.87). The PMC acquired using the CM was strongly correlated with those obtained using the CT method (ICC ≥0.84, Pearson correlation coefficient (r) ≥0.72, linear regression analysis (R2) ≥0.69). To conclude, the CM provided reliable and valid PMC information for patients with AIS. The contribution of PMC in 3D assessment and classification of AIS was reported earlier. Compared with the coronal-Cobb, the PMC appeared to be more informative since it provides both the maximum curve magnitude (PMC-Cobb) and the rotation of the spinal curve towards the coronal plane (PMC-orientation). In the sagittal plane of a normal spine, curves are present in the thoracic and lumbar regions. However, the thoracic and/or lumbar curve(s) are/is abnormally rotated towards the coronal plane in a scoliotic spine, accompanying with or without changes in the original curvature. This indicates that the coronal-Cobb was only a component of the spinal curvature. In orthotic treatment, if only the correction of coronal-Cobb is considered, the sagittal curve may go beyond physiological range, likely causing thoracic hyper-kyphosis and lumbar hyper-lordosis. Thus, employing the PMC as a supplement of the coronal-Cobb in managing AIS would be necessary. Due to the complexity of the PMC method, it was not considered in managing AIS in the past. The CM has been developed and converted into comprehensible software in this study. A preliminary study demonstrated high reliability of the PMC obtained using this software (ICC ≥0.91), and further study is going on. With continuous effort, it believes that the CM would potentially serve as a useful tool for the 3D assessment of AIS. Additionally, Part I of this study was first to investigate CT usage in assessing the PMC and the prone-standing difference/correlation of PMC. The results could establish a foundation for future relevant studies.
In current practice, spinal orthosis was designed empirically. The pressure-pad shape and correcting-force direction vary among orthoses designed by different orthotists. There were 5 most common pressure-pad shapes (A, B, C, D, and E) applied inside orthoses according to Society on Scoliosis Orthopedic and Rehabilitation Treatment (SOSORT) investigation. It is ambiguous what pressure-pad shape and correcting-force direction would provide an optimal correction. The PMC could be a promising descriptor for reflecting 3D characteristics of AIS, which may make it valuable for orthosis design. Thus, Part II of this study was to investigate (I) what pressure-pad shape and (II) correcting-force direction could produce a better clinical efficacy, and (III) whether the PMC concept would improve the clinical efficacy of orthosis designed (correcting force in the PMC zone, PMC-orientation ±15° of the thoracic curves or perpendicular to the plane located in the PMC zone of the thoraco/lumbar curves). The pressure-pad shape and correcting-force direction would be estimated based on the modified models of patients' trunks in the Computer-Aided Design /Computer-Aided Manufacturing system (CAD/CAM). The PMC was estimated using the CM proposed in part I based on patients' EOS images (biplanar X-rays). The optimal correcting-force direction was analysed by evenly diving the left and right posterior quadrants into 4 zones, respectively: zone 1(0° to ±22.5°), zone 2 (22.5° to 45.0° or -22.5° to -45.0°), zone 3 (45.0° to 67.5° or -45.0 to -67.5°), and zone 4 (67.5° to 90° or -67.5° to -90°) (the sagittal plane=0° and coronal plane=+/-90°; clockwise and counter-clockwise rotation from the sagittal plane to coronal plane was recorded as "+" and "-", respectively, in top view). The outcome measurements included PMC (PMC-Cobb; PMC-orientation), coronal-Cobb, thoracic kyphosis, and lumbar lordosis at the pre-orthosis, immediate in-orthosis, and follow-up off-orthosis (6-12 months). The clinical efficacy was analysed using the immediate in-orthosis correction and the success rate of progression control. Based on the inclusion and exclusion criteria proposed by the Scoliosis Research Society (SRS), 81 consecutive patients with AIS were selected from the database of a local hospital. This study's results suggested that pressure-pad shape A appeared superior clinical efficacy for the spinal curves accompanied by the thoracic hyper-kyphosis. In contrast, shape E produced superior clinical efficacy for the curves combined with thoracic hypo-/normal kyphosis. The correcting force with the direction in zone 2 could provide superior correction of curves combined with thoracic hyper-kyphosis. By comparison, those with direction in zone 3 were more effective for controlling curves accompanied by thoracic hypo-/normal kyphosis. The orthoses designed with the PMC concept did not show superior to those designed without the PMC concept in correcting the spinal curvature. It may be because of some confounding factors. For instance, only considering correcting-force direction on the convex side of the spinal curve was involved in analysis while neglecting correcting-force level and counter-forces. Still, it first applied the PMC for enhancing orthotic design and would create a base for continuous study. Based on the biomechanical analyses of all results, correcting force with direction at 30°-40° regarding the sagittal plane may be more effective in controlling curves with thoracic hyper-kyphosis; correcting force with direction over 50°may be more helpful for controlling curves with thoracic hypo-/normal kyphosis. Additionally, rotation of the spinal curve (PMC-orientation) was not significantly corrected after orthosis fitting, which was in line with the earlier reports. This may be associated with the correcting forces and anatomical structures of the spine and rib cage. A primary limitation should be noted. This study only involved the correcting-force direction on the convex side of the spinal curve in analysis while ignoring some potential confounding factors, such as correcting-force level and counter-forces. Nevertheless, this study initiated a starting point in understanding the 3D correction of orthoses designed with different pressure-pad shapes, correcting-force directions, and the PMC concept, which would help optimize the orthotic management of AIS. A future prospective study with more potential confounding factors controlled was suggested to further confirm the findings of this study.
Rights: All rights reserved
Access: open access

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