Abstract
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Objective
Contact casting with plaster bandages is a standard technique for thoraco-lumbo-sacral orthosis (TLSO) fabrication. However, this hands-on process depends on the operator’s skill as well as requires a close physical contact, involving potential risks of coronavirus and influenza virus infection and the patient’s personal space violation. Recently, noncontact, highly accurate molding technology using 3-dimensional (3D) digital scanning has been developed. Although 3D scanning is widely applied for limb orthosis, its spinal application mainly focuses on pediatric scoliosis. Comparative studies across diverse body types remain limited. Therefore, this study aimed to clarify the adaptability, accuracy, and fabrication time of TLSO produced using noncontact 3D digital scanning, comparing with conventional contact plaster-bandage casting.
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Methods
TLSO was fabricated using both contact and noncontact techniques for mannequins with 4 different body types. High-precision scanner and computed tomography (CT) were used to assess the shape reproducibility by quantifying the gap area between the orthosis and mannequin. In addition, total fabrication time was compared between the 2 techniques.
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Results
High-precision scanner identified that 3D scanning showed a higher shape reproducibility than conventional casting, particularly in curvilinear areas (all p<0.001). In CT measurement, 3D scanning demonstrated a smaller gap area in all the body types (all p<0.001). Fabrication time was also shorter during 3D scanning (54.9±0.9 minutes) than during conventional casting (100.0±5.5 minutes) (p<0.001).
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Conclusion
Noncontact 3D digital scanning facilitates a rapid, accurate, and reproducible TLSO fabrication across diverse body types, providing a safer and more efficient alternative to conventional contact plaster-bandage casting.
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Keywords: Thoraco-lumbo-sacral orthosis, Contact plaster-bandage casting, Noncontact three-dimensional imaging, Adult spinal deformity, Scoliosis, Vertebral fracture
INTRODUCTION
Orthotic treatment has a long history as a conservative approach for supporting or correcting spinal and limb deformities [
1-
3]. Thoraco-lumbo-sacral orthosis (TLSO) provides a nonsurgical treatment option for spinal deformity including adolescent idiopathic scoliosis [
1] and vertebral fracture [
4,
5]. Traditional plaster-bandage method is still widely used for its fabrication [
6]. However, casting technique using plaster bandages for spinal orthosis requires a hands-on physical contact with the patient, which involves potential risks of personal space violation, such as feelings of anxiety, discomfort, and stress, as well as of the spread of infectious diseases, e.g., coronavirus and influenza virus. Moreover, other potential problems of this conventional technique include plastic waste, prolonged working time, and more importantly, variability in the final outcomes of orthosis quality, largely depending on the orthotist’s skill levels [
6,
7].
Three-dimensional (3D) digital scanning method typically uses the structured light or infrared depth sensing to capture the accurate surface geometry without any physical contact [
8]. This technology allows the accurate capture of the body contour and the generation of digital models which can be immediately integrated with a computer-aided design/computer-aided manufacturing (CAD/CAM) system for the orthotic design [
9,
10]. These recent advances in 3D scanning technology have led to a frequent use of customized orthotics through faster and more efficient fabrication [
10-
12]. The application of a noncontact 3D digital scanner for spinal orthosis molding reduces major issues of conventional plaster-bandage casting, such as the need for physical contact, operator-dependent variability, and associated risks of infection, by enabling more accurate and consistent data acquisition [
12].
Several reports on the use of 3D digital scanners to create prosthetics and orthotics in the limbs have shown advantages in the shape reproducibility, accuracy, and fabrication time [
13-
15]. Improving the orthosis accuracy and reproducibility does not only enhance the patient’s comfort and adherence but also contributes to better biomechanical corrections and clinical outcomes. Regarding the torso orthosis, such as TLSO fabricated using 3D scanning, many prior studies focused on pediatric idiopathic scoliosis, reporting improved corrective effects compared with conventional plaster-based methods [
16,
17]. However, few studies have compared and clarified the utility of 3D digital scanning technique with the traditional casting technique across a wide range of body types, including adults, children, and plus-sized individuals. Therefore, we designed a preclinical study for the body size and shape-dependent difference in the adaptability of TLSO designed by a conventional contact casting technique with plaster bandages versus a new noncontact 3D digital scanning technique.
MATERIALS AND METHODS
1. Ethics Statement
This study did not involve human participants or live animals. Therefore, approval from the institutional review board or animal care and use committee was not required.
2. Mannequin Models and Molding Techniques
We purchased commercially available Japanese mannequins to simulate 4 different body types, which comprised an adult man (height, 185 cm), adult woman (height, 173 cm), plus-sized adult woman (height, 168 cm), and kid (height, 113 cm) (
Fig. 1A). For each of 4 mannequins, 2 TLSOs were molded and actually fabricated using a plaster-bandage technique and using a 3D digital scanning technique, and their fitting adaptability was compared (total 8 TLSOs were tested). Conventional plaster-bandage orthoses were prepared by 2 certified orthotists, each with more than 10 years of experience, to ensure the reliability of the applied contact molding technique (
Fig. 1B). 3D digital scanner (Structure Sensor Mark II; Occipital Inc., USA) [
18] connected to an iPad Air (Apple Inc., USA) was used for body scanning (
Fig. 1C). This scanner device captures from all 4 sides the target object with the placement of 6 scale markers on the sternum, xiphoid process, bilateral anterior superior iliac spines, pubic symphysis, and sacrum; consequently, total scan time of the mannequin takes approximately 30 seconds only (
Fig. 1D). To ensure reproducible scanning conditions, the scanner was positioned 50 cm from the mannequin, aligned horizontally, and operated under consistent ambient lighting. Scan data were obtained using the Scanner–Structure SDK application (ver. 3.5.2; XRPro LLC, USA).
The following steps were taken to compare the reproducibility of body shape in the mannequin (
Fig. 1E). In the conventional method, negative model was first created by taking a cast using plaster bandages on the mannequin. Subsequently, this model’s surface was scanned using a handheld scanner (Spectra; Vorum Co., Canada) to acquire digital 3D data. Collected data were imported into a CAD/CAM system (Canfit Design; Vorum Co.). Then, positive model was carved from a polyurethane block. Meanwhile, in the 3D digital scanning method, mannequin itself was directly scanned using the 3D digital scanner (Structure Sensor Mark II) to obtain 3D data, which was read into the same CAD/CAM system and carved out of a polyurethane block for positive model development. Finally, polyurethane models and the corresponding mannequins were scanned using a high-precision 3D measurement system (FARO Edge ScanArm ES equipped with Laser Line Probe V5 ES; FARO Japan Co., Japan). Surface geometric data were analyzed using a shape comparison software (Geomagic Control 2014; 3D Systems, USA). Automatic alignment function was applied to accurately superimpose each orthosis model onto its corresponding mannequin. Thereafter, color deviation map was generated to visualize these regional differences. Warm colors (e.g., red) indicate “loose” areas where the model exceeded the mannequin, intermediate colors (e.g., green) indicate “fit” areas where the model was nearly identical with the mannequin, and cool colors (e.g., blue) indicate “tight” areas where the model was smaller than the mannequin. In this system, deviation was classified into thirteen color-graded levels (1 [blue]–7 [green]–13 [red]), the distribution of which was compared between the 2 fabrication methods.
To understand not only computational virtual data but also real accuracy data of 3D shape, corseted mannequins in the supine position were scanned with computed tomography (CT) (Revolution EVO; General Electric, USA) under the settings: exposure time, 25 seconds; tube voltage, 120 kV; tube current, 200 mA; field of view, 450 mm, slice thickness, 1.00 mm (
Fig. 1F). CT images were analyzed using the ImageJ software (
https://imagej.net/ij/, accessed on January 1, 2025). In each of 4 different body segments—bust, underbust, torso, and waist, the gap area between the orthosis inner surface and the mannequin’s outer surface was manually measured and shown as the percentage relative to the mannequin’s surface on 4 consecutive axial CT slices. Then, their average was determined as the corresponding segment value. Finally, mean percentage of 4 segments developed from 2 TLSOs created by conventional contact casting and 3D digital scanning in 4 different body types—adult man, adult woman, plus-sized adult woman, and kid—was compared (total n=32, each n=4). Subsequently, to identify effects of the body contour for TLSO molding, body segment-specific shape reproducibility was assessed using individual data from 4 consecutive CT images (total n=16–32, each n=4). All measurements were performed twice at a 1-week interval by 2 investigators blinded to this study, and the mean value was used for statistical analysis.
Time required for the entire orthotic fabrication process to complete was recorded during conventional contact and noncontact 3D digital scanning techniques. Total processing time, measured from the start of molding to the completion of orthosis fabrication, was compared between both methods (total n=8, each n=4).
6. Statistical Analysis
As descriptive statistics, continuous variables are presented as the mean±standard deviation and categorical variables are presented as the frequency (percentage).
Statistical comparisons were applied to the quantitative accuracy evaluation of TLSO fabrication by the conventional contact plaster-bandage and noncontact 3D digital scanning techniques. Chi-square test with residual analysis was used to compare the distribution of shape reproducibility measured by a high-precision scanner. One-way or 2-way analysis of variance with Tukey post hoc test was applied to compare the area of the gap between the mannequin and orthosis in CT. Time required to complete TLSO fabrication was also compared using unpaired Welch t-test. Comparison of sample means is shown as the mean difference (%), p-value (95% confidence interval [CI], lower limit to upper limit). p-value <0.05 was considered statistically significant. In addition, intraobserver and interobserver reliability for CT measurement was calculated using the intraclass correlation coefficient (ICC).
RESULTS
1. 3D Digital Scanning Shows a Higher TLSO Shape Reproducibility Measured by a High-Precision Scanner Than Plaster-Bandage Casting Across All 4 Body Types
To assess the shape reproducibility, surface data of the fabricated TLSO and original mannequin were obtained using a high-precision optical scanner. Scanned TLSO data were then superimposed onto those of the corresponding mannequin to analyze the surface difference.
In the adult man model, TLSO fabricated by the conventional plaster-bandage method was particularly “loose” along the midline of the body, both anteriorly and posteriorly, whereas that produced using the 3D digital scanner more precisely reproduced the mannequin’s shape (
Fig. 2A). Similar trend was observed in the adult woman model, but it was more pronounced because of the greater body undulation (
Fig. 2B). Similarly, 3D digital scanner showed a more precise reproducibility in the plus-sized adult woman model (
Fig. 2C). In the kid model, 3D digital scanner was able to create a nearly identical shape (
Fig. 2D).
Histogram analysis identified significant differences in the deviation distribution of shape reproducibility between the 2 molding techniques across all 4 body types, statistically presenting a consistently higher percentage of “well-fit” 6–8 categories in 3D digital scanning than conventional plaster-bandage casting (all p<0.001). Additional residual analysis revealed that the “perfectly fit” category 7 appeared significantly more often in the 3D digital scanning group of all 4 body types (all p<0.001), indicating a consistently accurate distribution by noncontact molding technology (
Fig. 2E).
To evaluate the fitting accuracy, CT axial images were obtained. Then, the gap area ratio was quantitatively calculated between the inner surface of TLSO and the outer surface of mannequin. CT measurement presented that the intraobserver and interobserver reliability by ICC for the gap scale was 0.913–0.936 and 0.915, respectively, both indicating a high reproducibility (
Fig. 3A).
In the adult man model, the gap area was significantly reduced with TLSO created using the 3D digital scanner than with that created by the plaster-bandage method (12.0%±0.2% vs. 8.4%±0.3%, p<0.001). Consistently in the adult woman model (17.2%±0.5% vs. 10.9%±0.3%, p<0.001), plus-sized adult woman model (9.5%±0.5% vs. 5.4%±0.6%, p<0.001), and kid model (12.0%±0.5% vs. 7.8%±1.0%, p<0.001), the gap area was significantly smaller with 3D digital scanning-created TLSOs. Regardless of the body shape, TLSOs created by noncontact 3D scanning provided a higher fitting accuracy than those created by conventional contact plaster-bandage casting (
Fig. 3B).
Focusing on TLSO models developed using the plaster-bandage technique, comparison displayed that the adult woman model (17.2%) had a significantly larger gap area than the adult man model (12.0%) (5.3%, p<0.001; 95% CI, 4.1–6.5), plus-sized adult woman model (9.5%) (7.7%, p<0.001; 95% CI, 6.5–9.0), and kid model (12.0%) (5.2%, p<0.001; 95% CI, 4.0–6.5), possibly because of the pronounced body curvature (
Fig. 3C).
Furthermore, even using the 3D digital scanning technique, similar trend still exists, although the differences were much smaller than TLSOs with the plaster-bandage method. Adult woman model (10.9%) exhibited a larger gap area than the adult man model (8.4%) (2.5%, p<0.001; 95% CI, 1.3–3.8), plus-sized adult woman model (5.4%) (5.5%, p<0.001; 95% CI, 4.3–6.7), and kid model (7.8%) (3.1%, p<0.001; 95% CI, 1.9–4.4) (
Fig. 3D). Even in body areas with strong curvatures that tended to produce the gap, noncontact 3D digital scanning technology achieved more accurate fitting than the conventional contact casting method.
Additional body segment-specific analysis using individual data from 4 consecutive CT images was performed. Across all 4 segments—bust, underbust, torso, and waist, the gap area was consistently smaller with TLSOs created by 3D digital scanning than with plaster-bandage casting (all p<0.001) (
Fig. 4A). Within each mannequin, particularly in the adult woman model, contact plaster-bandage casting showed pronounced gaps at the underbust and torso segments (p<0.001 to p=0.006), reflecting greater difficulty in capturing the complex body contour with contact molding, whereas 3D digital scanning reached no substantial segment-specific differences in the plus-sized adult woman and kid models with a relatively smooth body surface (
Fig. 4B).
Adoption of 3D scanning led to a considerable improvement in production efficiency. In the conventional contact plaster-bandage technique, the process required 15.0±0.8 minutes for molding, 10.0±1.3 minutes for creating a positive model from the negative cast, and 44.8±3.4 minutes for modifying the positive model, which resulted in approximately 70 minutes to complete the positive model. In contrast, with the noncontact 3D scanning technique, whole body scanning took 30 seconds, followed by 5 minutes for data processing, 9.9±0.9 minutes for CAD-based data editing, and 10.0±0.9 minutes for CAM-based cutting of the positive model. Minimal labor was required because the latter step was automated. This process resulted in a total of approximately 25 minutes to complete the positive model. Subsequent plastic molding and trimming processes took 15 minutes each, regardless of the fabrication method, which resulted in a total production time of 100.0±5.5 minutes with contact plaster-bandage casting and 54.9±0.9 minutes with noncontact 3D scanning (-45.1 minutes, p<0.001; 95% CI, -61.7 to -28.5) (
Fig. 5).
DISCUSSION
To the best of our knowledge, this is the first study to compare the adaptability of TLSO created using the conventional contact plaster-bandage technique versus using the more modern noncontact 3D digital scanning technique for various body types. Relative to plaster-bandage casting, 3D scanning provided a superior adaptability to the patient’s body figure with a broader applicability to all the tested 4 body types. In clinical practice, orthosis is frequently prescribed for various disease conditions, such as conservative treatment, postoperative stabilization, and osteoporotic vertebral fracture. Although several studies have reported limited or no clinical benefits of TLSO bracing for vertebral fracture [
20,
21], it is still commonly prescribed because TLSO provides psychological reassurance and short-term stability to the patients [
22-
24]. In most facilities, conventional plaster-bandage casting remains a standard molding method. However, prolonged bed rest before orthotic fabrication, pain during the molding process, and then a close physical contact can occasionally become clinical challenges. Then, TLSO quality, largely depending on the orthotist’s skill and experience, is still problematic. Therefore, the development of faster, safer, and more accurate molding technologies is required, particularly for the elderly patients with limited mobility.
3D digital scanning technology has attracted increasing attention in more recent years. Several studies have applied 3D scanning with CAD/CAM systems to the fabrication of spinal orthosis for pediatric scoliosis, and most of these investigations have reported an improved correction rate and clinical usefulness compared with conventional plaster-based methods [
25,
26]. Regarding safety and ethical concerns, 3D digital scanning offers substantial advantages by minimizing the need for a direct contact with the patient, allowing the maintenance of social distancing. During the coronavirus disease 2019 pandemic, orthotic fabrication workflows were drastically modified to avoid direct patient–clinician contact with the risk of infection [
27]. Our 3D scanning method enables the minimization of any physical contact with the patient, thereby maintaining social distance and reducing the spread of infectious diseases. Moreover, nonbody contact procedures do not only enhance the patient’s comfort but also help prevent inappropriate or uncomfortable interactions during the molding process, which is beneficial for the orthotist as well. Another important advantage of 3D digital scanning is the absence of deformation risk of the negative model after measurement, unlike the conventional plaster-bandage method. During conventional casting, molded negative model for the orthosis must be transported to the workshop, during which journey deformation may occur. However, digital data can be easily stored, modified, and shared, facilitating immediate improvements and feedbacks for the orthotist. As shown in this study, digital workflows further contribute to the improvement of working efficiency with the reduced total fabrication time [
12,
28].
Although costs may represent a practical limitation, long-term efficiency of 3D digital scanning technique offers potential advantages. In this study, running costs of the plaster-bandage technique primarily consisted of plaster materials, which amounted to United States dollar (USD) 20 per unit (USD 10 for the plaster bandages used for molding and USD 10 for the positive model creation). In contrast, implementing the 3D scanning method required high initial investments for the equipment, including scanners and editing software. Despite these expenses, we found a marked reduction in working time and improvement in fabrication efficiency. Therefore, long-term operation of digital workflows can become cost-effective, particularly in facilities with high orthosis production volumes.
This study has several limitations. First, mannequins were used instead of actual human subjects. Therefore, factors such as body temperature, skin compliance, and respiratory motion were not reproduced, which could affect TLSO fitting accuracy in the clinical setting. Second, although only a single TLSO was fabricated for each method, potential accidental human errors during molding, carving, and plastic forming cannot be fully excluded. Due to the limited budget, the sample size of fabricated orthoses remains a methodological limitation. Third, although 3D digital scanning showed an acceptable accuracy overall, the method tended to slightly undersize the orthosis in the plus-sized adult woman model with a large and less-curved body surface, indicating the need for further optimization of object scanning and data processing. Technical issues in optical 3D scanning include shallow incident angles on broad, low-curvature surfaces, reduced infrared signal return due to surface reflectivity, and increased shadowing or occlusion along large circumferential contours [
29]. Fourth, investigation of only 4 representative body types in a single center warrants larger-scale, multicenter studies with more heterogeneous cohorts, e.g., those with spinal deformities or postoperative conditions. Finally, gap area and shape reproducibility were evaluated under static, unloaded conditions. Future studies for dynamic, inuse assessments should be conducted to confirm clinical applicability of 3D scanning.
On the basis of the presented preclinical, hypothesis-generating data, we will plan to fabricate TLSOs for healthy volunteers and evaluate their comfort and usability for practical benefits of 3D digital scanning. It remains undetermined whether a very “well-fit” TLSO truly provides comfortable, long-time wearing. This research should further advance noncontact 3D digital technologies to establish seamless workflows integrating scanning, design, and manufacturing for its widespread clinical implementation.
CONCLUSION
More modern noncontact 3D digital scanning technique shows clear advantages in TLSO fabrication compared with the conventional contact plaster-bandage technique. Without any contact molding, 3D digital scanning provides a superior TLSO reproducibility, accuracy, and efficiency for diverse body types. This 3D workflow does not only minimize the patient’s discomfort and physical contact-related risks but also enhances safety, efficiency, and data management throughout the fabrication process. Although initial costs of digital equipment remain a potential barrier, substantial reduction in labor time and improved workflow efficiency are supposed to be beneficial in the long run. 3D digital scanning method has the potential to expand beyond managing scoliosis to wider clinical applications, such as conservative, postoperative, and fracture-related orthoses. Further clinical studies are necessary to validate and optimize this noncontact technology for broader implementation.
NOTES
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Conflict of Interest
NK, TY, MR, YK, KKuroshima, YH, MF, DN, YI, and RK declare no conflicts of interest. YT and KKakutani are the faculty members of the endowed course by Surgical Spine, Inc. (Tokyo, Japan) and SMI, Inc. (Nagoya, Japan).
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Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
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Acknowledgments
The authors thank Kazuki Fujimoto, P.O., Katsuhiro Konishi, P.O., and all prosthetists and orthotists in Sawamura Prosthetics and Orthotics Service Co. (Kobe, Japan) for their technical assistance. We thank Ellen Knapp, Ph.D., from Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript.
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Author Contribution
Conceptualization: TY; Data curation: NK, TY, MR; Formal analysis: NK, TY, MR, YT, YK, KKuroshima, YH, MF, DN, YI, RK, KKakutani; Methodology: NK, TY, MR; Project administration: TY, MR; Visualization: NK, TY, MR; Writing – original draft: NK, TY, MR; Writing – review & editing: YT, YK, KKuroshima, YH, MF, DN, YI, RK, KKakutani.
Fig. 1.Mannequins as well as thoraco-lumbo-sacral orthosis (TLSO) molding and fabrication methods used in the study. (A) Mannequins representing 4 different body types: adult man, adult woman, plus-sized adult woman, and kid with the morphometric data. (B) Conventional contact-based molding technique with plaster bandages. (C) Handheld 3-dimensional (3D) scanner (Structure Sensor Mark II) connected to an iPad Air for 3D digital scanning. (D) More modern noncontact 3D digital scanning technique. (E) Flowchart for the assessment of TLSO shape reproducibility. (F) Mannequins fitted with TLSO during computed tomography scanning.
Fig. 2.Three-dimensional (3D) digital scanning shows a higher thoraco-lumbo-sacral orthosis (TLSO) shape reproducibility measured by a high-precision scanner than plaster-bandage casting across all 4 body types. Color maps of adult man (A), adult woman (B), plus-sized adult woman (C), and kid models (D), illustrating the geometric deviation between TLSO and the mannequin. More intense warm or cool colors indicate greater differences. (E) Graphs of the deviation distributions for each body type with TLSO developed by plaster-bandage casting or 3D scanning. Color scale corresponds to deviation levels from 1 to 13. Categorical distributions were compared between the 2 methods using the chi-square test with residual analysis.
Fig. 3.Three-dimensional (3D) digital scanning demonstrates a higher thoraco-lumbo-sacral orthosis (TLSO) fitting accuracy in computed tomography (CT) measurement than plaster-bandage casting across all 4 body types. (A) Representative CT analysis of the adult woman model. Gap areas between TLSO and the mannequin were quantified on 4 consecutive axial slices at each of bust, underbust, torso, and waist segments (orange lines) and compared between the plaster-bandage casting technique (red area) and the 3D scanning technique (blue area). (B) Graph of the gap areas from the average values at each body segment for the comparison in each body type between TLSOs developed by plaster-bandage casting and 3D scanning. (C) Graph of the gap areas from the average values at each body segment for the comparison between body types with TLSO developed by the plasterbandage casting method. (D) Graph of the gap areas from the average values at each body segment for the comparison between body types with TLSO developed by the 3D scanning method. Two-way analysis of variance followed by Tukey post hoc test was used.
Fig. 4.Three-dimensional (3D) digital scanning demonstrates a higher segment-specific thoraco-lumbo-sacral orthosis (TLSO) fitting accuracy in computed tomography measurement than plaster-bandage casting across all 4 body types. (A) Graph of the gap areas from individual values of 4 consecutive axial slices at each body segment for the comparison in each body type between TLSOs developed by plaster-bandage casting and 3D scanning. Two-way analysis of variance followed by Tukey post hoc test was used. (B) Graph of the gap areas from individual values of 4 consecutive axial slices at each body segment for the comparison between regional differences in each body type with TLSO developed by plaster-bandage casting or 3D scanning. Oneway analysis of variance followed by Tukey post hoc test was used.
Fig. 5.Three-dimensional (3D) digital scanning reduces the total time for thoraco-lumbo-sacral orthosis (TLSO) fabrication compared with plaster-bandage casting across all 4 body types. Actual fabrication time required for each TLSO to compare between the conventional contact plaster-bandage technique and the more modern noncontact 3D digital scanning technique. Unpaired Welch t-test was used. CAD, computer-aided design; CAM, computer-aided manufacturing.
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, Takashi Yurube*
