Malleable Resin-Based 3D-Printed Patient-Specific Head, Ear, and Rib Models for Costal Cartilage-Based Microtia Reconstruction

Introduction: Microtia reconstruction using autologous costal cartilage is challenging. 3D digital imaging such as computed tomography scans (CT) has been utilized concurrently with 3D-printing techniques to produce patient-specific models to assist with preoperative planning.

Methods: Proof-of-concept study of a 9-year-old female with left grade III microtia using both a CT-chest and CT-internal auditory canal/temporal bone completed during pre-operative planning. We demonstrate a novel approach for enhanced preoperative planning using rib and ear models 3D printed with malleable resins.

Results: Models were designed using pre-existing CT imaging scans obtained (SOMATOM Force Dual Source CT, Siemens Healthineers, Erlangen Germany) of both the ear (0.6 mm axial cuts; 267 slices) and rib (1.0 mm axial cuts; 608 slices). CT data was converted to a stereolithographic (STL) file. The costal bone/cartilage and normal ear soft tissue were modeled in Mimics/3-Matics (Materialise, Leuven Belgium). A subtraction of 1 mm from the ear model was performed to account for the skin thickness. Models were printed on a Stratasys-J750 printer (Stratasys Ltd., Rehovot Israel) using multi-materials (Agilus 30 for the ear, Structural-Frame 4 for cartilaginous portions of rib). Resin selection was conducted to optimize hardness for surgical realism and the ability to manually cut/segment with tools to use as a template. Final shore-A hardness for the resins was level 35 for the ear, level 100 for bones of the rib, and level 60 for the rib cartilage. This allowed for realistic “just-in-time" simulation including pre-determining location where framework pieces could be carved from the patient’s rib. The institutional cost was $331.55.

Conclusions: We demonstrate a novel approach to the use of custom 3D printed ear and rib models, which will aid in understanding unique anatomical features, assist in preoperative planning, enhance resident/trainee education, and improve patient counseling.