The technique for 3D printing patient-specific models for auricular reconstruction
Introduction
Microtia is a congenital malformation of the ear, which occurs approximately 1:6,000 (∼0.03%) births in the general population (Jeon et al., 2016). It has been reported that the right ear is affected twice as often as the left (Berens et al., 2016, Jeon et al., 2016) and that nearly 90 percent of cases are unilateral (Staffenberg, 2003, Quinn and Ryan, 2004, Zeng et al., 2008). Total auricular reconstruction is uniquely challenging to surgeons because of the ear's complex and unique anatomy. Construction of an anatomically accurate framework is key for an esthetic result. Autogenous costal cartilage is the most commonly used donor site for reconstruction (Brent, 1980, Nagata, 1994). However, even with experience, aesthetic outcomes can be compromised due to a lack of fidelity of the constructed auricular framework.
Currently, surgeons approach autogenous microtia repair by creating a two-dimensional (2D) tracing of the unaffected ear (Fig. 1) (Walton and Beahm, 2002, Witek et al., 2016) and using this 2D line drawing as a model to approximate a three-dimensional (3D) construct from the 2D illustration, a process that is difficult, tedious, and imprecise (Lee and Boahene, 2013, Kim et al., 2014). While useful, sketched images do not offer the true shape, detail, and visuospatial aspects of a three-dimensional ear, e.g., relief of the helix, scapha, anti-helix and concha.
In order to address the shortcomings of 2D tracings, constructs of the unaffected ear have been digitally produced and mirrored to create a patient-specific model (Jeon et al., 2016). More recently, the contributions of 3D printing have dramatically improved upon the fabrication of framework for the ear in need of reconstruction. Engineers and surgeons have described an approach utilizing computed tomography (CT) scan data of the patient's contralateral, unaffected ear to generate a 3D printed ear (Zeng et al., 2008, Witek et al., 2016). Although this method was reported to be effective, some of the technology utilized is expensive, time consuming, and not readily accessible to all surgeons.
The aforementioned limitations can be compensated for using a high-resolution 3D photograph that can be easily acquired in the office setting. Irrespective of imaging equipment used, the acquired data is converted and saved in the common DICOM (Digital Imaging and Communications in Medicine) format. This exported data can then be imported into different software platforms to be modified and forwarded to rapid prototyping (RP) software to print the ear framework in a layer-by-layer fashion. We have recently reported in a letter the feasibility of this approach to the fabrication of sterilizable, patient-specific 3D printed auricular models for autogenous auricular reconstruction (Witek et al., 2016). This proof of concept report lacked detailed description of the multiple step workflow utilized to generate adequate 3D models based on the actual shape and size of the opposite unaffected ear.
This report describes the step-by-step methodology utilized by our group which employs available 3D digital photography combined with computer-aided design (CAD) software and 3D printing to fabricate inexpensive patient-specific printouts based on the actual shape and size of the opposite unaffected ear (Zeng et al., 2008, Witek et al., 2016).
Section snippets
Materials & methods
To create the cartilaginous ear-model for a patient with unilateral microtia, a high-resolution 3D digital photograph (3DMD, Atlanta, GA) was first captured of the patient's unaffected ear and surrounding anatomic structures (Fig. 2). The photographs were then exported in their raw data format and uploaded into Amira (FEI Company, Hillsboro, Oregon, USA), for transformation into a digital (.stl) model, which was then imported into Blender™ (version 2.77, Amsterdam, The Netherlands), an open
Results
Prior to surgical procedure, the constructs were placed into autoclave pouches and subjected to sterilization following manufacturer's guidelines (121 °C for 1 h and 30 min dry cycle) (Rankin et al., 2014). These sterilized, patient-specific 3D models were brought to the operating room and placed on a dedicated table along with the essential ear sculpting tools. The sterilized models were placed alongside cartilage grafts where they could be held, turned and studied by the surgeon. The forms
Discussion
One of the more challenging aspects of microtia reconstruction is the creation of a 3D cartilaginous framework by referencing a 2D tracing (Walton and Beahm, 2002, Wilkes et al., 2014). 2D, mirrored drawings lack the detail and 3D contours for proper reconstruction because they do not appropriately reproduce the complex features (i.e., height, depth, width, thickness, etc.) of the contralateral, unaffected ear (Walton and Beahm, 2002, Wilkes et al., 2014).
Analogous to modern day, image-guided
Conclusion
We present a proof of concept in creating patient-specific, cost-effective 3D models for microtia reconstruction. The identification of the ideal software platform, digital preparation protocol, printer ink, and printer device remains a work in progress. The authors emphasize that the only cost-effective way to accomplish the aims described herein is to fabricate constructs “in house”, by leveraging departmentally-available resources and technology for the purposes of optimizing surgical
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