High Precision Orthopaedic Implant Design and 3D Printing Based on Patient-Specific 3D Modelling of Complex Pelvis Fractures
Creators: name: Chai, Yuan
Publisher: name: The Australian National University
Year: 2019

description: Unstable and displaced pelvic ring disruptions of trauma patients are high energy injuries, associated with increased levels of morbidity. Time is life. Can pelvic fracture be better managed? One answer lies within an integrated process of patient's images specific modelling, surgical planning and rapidly producing case specific 3D printed fixation implants. 3D printing is an advanced manufacturing technique that builds items in a layering manner by reshaping the source material. While it is becoming more widely adopted for clinical applications, the precision is yet to be thoroughly investigated or optimised across the production line. This study explored the ways of improving the accuracy of the three-dimensional (3D) model and object in three different aspects. Firstly, this project devised a novel, yet simple and rapid modelling process, using Drishti software, to convert the CT image directory acquired from patients to a 3D bone model. Secondly, the project used human pelvis bones investigating the geometrical difference between hemipelves, and developed a deviation colour map (DCM) highlighted the regions that had high potential to be geometrically different between bilateral bones. The project designed and 3D-printed customised fixation plates using fracture registration technique, and compared their geometrical fitness to the bone models. Thirdly, this study developed the laser surface modification method making the 3D-printed object cater the requirement of the surgical guide. The project used the low cost and accessible CO2 laser scanning machine and fused deposition modelling 3D printer to achieve the surface modification, which can shorten manufacturing time for urgent medical needs. The study further investigated the mechanical behaviour and biocompatibility of laser polished 3D printed object. As a result, this project created the entire process of case-specific medical 3D printing from 3D modelling, fabrication to post treatment. At the first place, patient computed tomography data from complex fracture cases were converted into high quality anatomical replicas suitable for 3D printing. A virtual model was reconstructed using third-party Drishti software following which implant design was trialled. The pelvic models converted by Drishti were further compared geometrically for symmetrical analysis. The results were summarised in a DCM, which offers an effective tool to guide bioengineers selecting a proper design technique to customise an implant. A pair of patient-specific fixation plates were designed and 3D-printed using selective laser melting technique in Ti6Al4V material. The implants exhibited better geometrical fitness when it compared to the re-stitched fracture side of the pelvic bone. This study found that CO2 laser polishing was more suitable for poly-lactic acid (PLA) material than acrylonitrile butadiene styrene. Mechanical test, including tensile, compression and bending, showed that laser treatment had a less negative influence on mechanical strength than grinding, and better biocompatibility. In conclusion, the 3D modelling and printing techniques provide an innovative approach increasing the accuracy in fabricating surgical implants, improving reconstructive surgery and reducing the risk of a second intervention. This study created and described an integrated process of patient specific modelling, surgical planning and rapid production of 3D printed fixation implants.