COMPUTERISED TOMOGRAPHY TO 3D PRINTED MODELS: AN AFFORDABLE, OFFICE-BASED METHOD

Introduction Three-dimensional (3D) printing is a precise method of reproducing complex structures. Orthopaedic surgeons may utilize 3D imaging to better plan procedures, design implants, and communicate with other providers and patients. However, one of the limitations of 3D printed models has been the high cost associated with third-party creation of such tools. With the recent increases in the use of 3D printing many publically available software programs have been developed, which allow for inexpensive office-based production of models. We present a simple, inexpensive technique which can be used by surgeons for the rapid fabrication of 3D models in-office. Technique CT scan and MRI9s are stored in DICOM type format which must be transformed into a 3D image. This can be achieved using publically available programs (for example, 3D slicer (http://www.slicer.org/)). These images can be manipulated with this software, allowing for separation of individual bones. The files can then be exported from this program in an STL format. These models are then further enhanced and smoothed utilizing another open source software (Blender (https://www.blender.org)). The STL file can then be opened in a third open source program (for example, Meshlab http://meshlab.sourceforge.net/) which can analyze the mesh for extra vertices, voids, and discontinuities. At this point the STL file is ready for 3D printing. The file can be loaded onto the slicer software for calculation of a tool path and printing. Case example 1 A 50 year old woman sustained a displaced acetabular fracture during primary total hip arthroplasty. She underwent fracture fixation, but her acetabular component failed to ingrow with bone. Multiple revision procedures were undertaken, but all were unsuccessful. She was finally referred for treatment. Preoperative CT scan showed massive bone loss and distortion of normal pelvic architecture (Figure 1) requiring a custom acetabular implant. A 3D model of the pelvis was produced with the custom implant to assist in preoperative planning (Figure 2a), but this was a costly and time consuming process. Therefore, a smaller scale pelvic model was also rapidly generated using the above technique in order to demonstrate the severity of the patient9s pathology (Figure 2b). Case example 2 A 14 year old male presented with a history of knee pain, weakness and buckling over a decade. A CT scan was obtained which demonstrated a dislocated patella, loss of normal trochlea contour, and a concave patella. For demonstration purposes and patient education, the knee joint was 3D printed using the technique discussed above (Figure 3). Conclusion This technique represents a simple, rapid, and inexpensive method for creation of 3D models. We believe this is a valuable tool in orthopaedic surgery in general and arthroplasty in particular as it can be used for preoperative planning as well as for facilitating communication between surgeons and patients. This technology can greatly increase the surgeon9s ability to visualize anatomy, resulting in improved outcomes in difficult cases such as described here.