Author investigates the potential of implementing digital
design and Electron Beam Melting(EBM) for manufacturing of fixation plates within trauma orthopedics.
A contribution to the development of a routine for the customization of trauma
plates for complex fractures was made. The routine has to be
streamlined, especially as regards the modeling, the post processing and the
Sharing of digital information to be implementable within the orthopedics Design procedure for patient-specific implants using AM.
The design procedure from computed tomography (CT) scan to final implant is described, with an example of a fracture in the distal tibia, Fig. 6.
The purpose of acquiring a 3D CT scan is to produce a volumetric data set of the fractured bone or part of the skeleton that needs an implant. Two different medical imaging techniques are magnetic resonance imaging (MRI) and CT. A CT is built up of a large series of 2D slices of data to represent the 3D geometry and each CT image is written as an individual file within a directory structure. The format of the images follows the medical industry standard, called DICOM (digital imaging and communications in medicine). The design procedure starts with removing the unwanted structures (skin, fat, muscles) from the CT data, using a threshold segmentation technique, where pixels are distinguished within an image by their grey-scale value. In CT the pixel values, also known as Hounsfield units, range from -1024 to +3072. Bone, is represented by the CT number range from approximately +100 to +2000, where the highest number indicates the densest bone. After bone segmentation, the part of the skeleton is mathematically modeled into a 3D model, where the surface contours of the geometry are described by small, triangular surface elements. The full data set is known as a stereolitography (STL) file. This format is commonly used in AM, as it is easily transferrable between many software packages 24.
Based on the type of implant to be manufactured, the STL file of the bone model can be used as it is, or should be modified in proper way. In this case, the fracture needed to be reduced (moving the fractions to their correct positions) to form the base for modeling the final implant. Different software packages can be used for this purpose. The reduced bone model is later used as a base for orientation of the screws and modeling of the implant. When the final design of the plate is obtained, the STL-file of the plate is prepared for manufacturing and sent to the Additive Manufacturing Machine. Preferably, several different implants, or other parts are made in the same build (Fig. 6) since the build time is primarily affected by the height of the build. Finally the parts are post processed to meet the demands of the specific implant.