Design for a Reusable High‐Fidelity Pediatric Epidural and Caudal Phantom for Haptic Learning

High-fidelity phantoms present learners with repeated opportunities to develop procedural skills and teachers to provide feedback in a stress-free practice environment [1]. In this publication, the authors describe the development of a high-fidelity pediatric epidural block trainer that can be used to practice both landmark-based or ultrasound-aided neuraxial blocks. Institutional review board exemption was obtained to procure deidentified spine imaging. The processes include integrating medical images, three-dimensional (3D) modeling software, a 3D printer, silicone casting, and gelatin molding that allows for high-quality insonation and tactile feedback to ‘loss of resistance’ (Figure 1). A high-fidelity aspect of this phantom is integration of the tactile feedback to ligamentum flavum penetration and penetration of the sacrococcygeal ligament upon entering the caudal space using a loss of resistance (LOR) syringe. The gelatin molding allows the trainee to familiarize themselves with typical sonoanatomic views of the thoracic, lumbar, and sacral spines; practice real-time advancement and confirmation of the needle tip location in the epidural space (Figure 2). The image segmentation step starts with importing a spine computer tomography (CT) scan into the Mimics 3D software (version 26, Materialize, Leuven, Belgium). Mimics' segmentation tools are used to isolate the spine. The isolated spine is then imported into 3-Matic (version 18, Materialize, Leuven, Belgium). 3-Matic software features facilitate the creation of the 3D printed spine model and the molds for creating ligamentum flavum. The characteristic feel of ligamentum flavum in the pediatric age group is obtained using soft and stretchy high-performance silicone (Smooth-On Dragon Skin 10). The 3D components within 3-Matic are imported into GrabCAD 3D printing software (GrabCAD, Waltham, Massachusetts) where their print settings, orientation, and alignment are finalized prior to sending the tray to a 3D printer (F370 Printer, Stratasys, Rehovot, Israel) and printed with acrylonitrile styrene acrylate filaments. The fabrication step includes creating a gelatin-filled ligamentum flavum and assembling it within the 3D printed spine structure where a tissue mimicking gelatin is then molded over. The Supporting Information provide examples of this workflow implementation on infant and adolescent spine models (Figures S1–S3). Our phantom has a high degree of tactile feedback. The Humimic gelatin used to fabricate the back allows palpation of spinous processes and the silicone mold filled with soft medical gelatin offers the characteristic “loss of resistance” feedback of needle passing through the ligamentum flavum to enter the epidural space. Humimic gelatin is a better alternative than ballistic gel (used in previously described “do it yourself” phantoms) for a neuraxial injection phantom design as it allows high-quality insonation and can better mimic back tissues and muscles [2-4] (Figure 2). Additionally, it can be repeatedly melted and reused, reducing waste and production costs. Pricing for disposables is appended in the Table S1. The ligamentum flavum material is the only component in this design that cannot be reused (Table S2). The phantom is customizable in its complexity by manipulating the opacity of the gelatin layer representing the back muscle. When this back muscle layer is transparent, instructors can demonstrate the implications of different angles of epidural needle trajectory for paramedian and midline approach and help the trainee visualize and practice the concept of ‘walking off the lamina’ in landmark-based epidural block placement (Figure S3E). As the novice advances in training, phantoms with opaque back tissue can serve to practice both landmark and ultrasound-guided epidural blocks. The 3D parts created within the 3-Matic software application are exported as a stereolithography file format. These files can be easily shared with other training centers or open-source platforms to print off institutional 3D printers or outsourced to 3D printing businesses. Anesthesiologists with a diverse range of experiences at the authors' institution (pediatric anesthesia fellows, new faculty < 5 years. experience, experienced faculty > 5 years experience) and at national workshops (fellows and consultant anesthesiologists) evaluated the epidural block trainer for its needle-tracking capabilities with an ultrasound system (Sonosite, Bothell, Washington, USA), and the tactile feedback for loss of resistance while traversing the ligamentum flavum using an epidural needle and saline-filled LOR syringe from a standard epidural kit (Perifix, Braun Medical Inc., Bethlehem, PA). The feedback from these participants' experiences was essential to the development of the final design. The trainees validated that the model improved understanding of anatomy and sonoanatomy of the spine; midline and paramedian needle projection angles for entering into the caudal, lumbar, and thoracic epidural spaces. The faculty reported the phantom to be a valuable tool in their teaching armamentarium. Practitioners reported that acquiring needle tip tracking skills is a useful tool to validate correct block placement. One limitation of this task trainer is that the CT scan image acquisition process has the patient laying supine in the scanner with their back flat to the scanning table whereas a typical epidural block procedure has the patient positioned in the lateral decubitus position with a significant flexion of the spine. Therefore, the epidural phantom is restricted to conceptual training because the spine curvature of the 3D printed model does not exactly mimic what an epiduralist might experience in the field. The success of the design concept and scalability of the haptic phantom described in this article opens the possibilities for advanced innovation as can be applied to varied skeletal anatomy. The data that support the findings of this study are available from the corresponding author upon reasonable request. Figure S1: 3D modeling with Mimics and 3-Matic software. (A) Sagittal, coronal and axial cross-sectional views of the image segmentation performed on the spine CT scan with the Mimics software. (B) The anatomical parts created were imported and visualized in 3-Matic's software platform. Figure S2: An overview of the ligamentum flavum mold and spine assembly of infant spine model. (A) The individual components of the 3D printed parts. (B) Front view of the ligamentum flavum mold secured to the back side of the anterior spine section. Figure S3: A step-by-step progression of the assembly and molding of the thoracic spine phantom (65 kg, adolescent). (A) The individual components of the 3D printed spine and lungs. (B) Assembly of the printed parts on a 3D printed base. (C) The ‘detachable skin’ layer is attached and the epidural space has the gelatin-filled ligamentum flavum positioned within the spine. (D) Fully assembled 3D printed epidural injection phantom with the semi-transparent gelatin mold representing the back muscle. (E) View of “transparent back” model. Table S1: Cost of the 3D printed and disposable materials associated with the thoracic and infant epidural phantoms. Table S2: Anatomical parts and their corresponding synthetic material. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.