Research Article: Feasibility study applying a parametric model as the design generator for 3D–printed orthosis for fracture immobilization

Date Published: January 11, 2018

Publisher: Springer International Publishing

Author(s): Jianyou Li, Hiroya Tanaka.


Applying 3D printing technology for the fabrication of custom-made orthoses provides significant advantages, including increased ventilation and lighter weights. Currently, the design of such orthoses is most often performed in the CAD environment, but creating the orthosis model is a time-consuming process that requires significant CAD experience. This skill gap limits clinicians from applying this technology in fracture treatment. The purpose of this study is to develop a parametric model as the design generator for 3D–printed orthoses for an inexperienced CAD user and to evaluate its feasibility and ease of use via a training and design exercise.

A set of automatic steps for orthosis modeling was developed as a parametric model using the Visual Programming Language in the CAD environment, and its interface and workflow were simplified to reduce the training period. A quick training program was formulated, and 5 participants from a nursing school completed the training within 15 mins. They verified its feasibility in an orthosis design exercise and designed 5 orthoses without assistance within 8 to 20 mins. The few faults and program errors that were observed in video analysis of the exercise showed improvable weaknesses caused by the scanning quality and modeling process.

Compared to manual modeling instruction, this study highlighted the feasibility of using a parametric model for the design of 3D–printed orthoses and its greater ease of use for medical personnel compared to the CAD technique. The parametric model reduced the complex process of orthosis design to a few minutes, and a customized interface and training program accelerated the learning period. The results from the design exercise accurately reflect real-world situations in which an inexperienced user utilizes a generator as well as demonstrate the utility of the parametric model approach and strategy for training and interfacing.

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Integration of 3D printing and medical image capturing technologies has been widely applied in medicine. CT or MRI anatomic imaging techniques can capture volumetric images of bones and soft tissues, and these images can be materialized by 3D printing devices as physical models to aid surgical planning or training [1–3]. Moreover, non-contact scanners based on a laser source and depth camera have become an option to replace the use of a conventional physical casting to acquire the anatomic surfaces necessary for the fabrication of orthoses or prosthetics. The 3D scanning technique prevents patient discomfort and induces less distortion of the target region [4, 5]. In addition to representing the anatomic form, the 3D printing technology also provides various physical properties to support the specific requirements of implants, orthotics, braces and prostheses via materials or structures that are built by manual or computational design [6, 7].

In this section, we describe the 5 stages of transferring the results of a Direct Modeling approach to develop a practical parametric model (Fig. 2), as well as the volunteers who participated in the subsequent training and evaluation. The points of each stage are listed as follows:Direct Modeling process of orthosis design: A compact process developed based on the clinician, the inexperienced CAD user’s thinking and limited geometric knowledge.Parametric model: Reconstruction based on the results of previous stages; the main parameters in every step were collected and optimized in iterative tests.Interface customization: All unnecessary menu, toolbars and panels in the main CAD environment were removed, until only a basic interface remained.Quick training: Fundamental knowledge for utilizing the parametric model was provided in a one-on-one tutorial, including viewport navigation, poly-line drawing in Rhino and object setting in Grasshopper. Five nursing students who were familiar with manipulating fracture immobilizations were invited to participate in the training.Orthosis design exercise: After the training, the participants performed a computer-based exercise to design orthoses for 5 different arm models by themselves, and their design processes on the screens were recorded for further analyses.Fig. 2Development process for transferring the explored modeling process into the parametric model

A parametric CAD model for 3D–printed orthosis design was developed for clinicians who were inexperienced with CAD tools. The model utilized Rhino 3D V5, and its parametric program was constructed using Grasshopper 3D. We input 10 different limb models into this parametric model representing the patients’ affected limb and used different immobilization areas to generate a printable model. Overall, the parametric model was stable if no hole or edge was present in the immobilization area.

In this study, to address the relative advantages and disadvantages of Direct Modeling and Parametric Modeling, a design generator of 3D–printed orthosis and its detailed modeling process were created and developed by the Visual Programming Language in an engineering CAD environment. The interface and workflow of the parametric model were successful for use by clinicians who were inexperienced to CAD software.




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