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Vaibhav Bagaria. A short summary of this paper. Download Download PDF. Translate PDF. Dept of Orthopaedic Surgery. Introduction Rapid Prototyping is a promising powerful technology that has the potential to revolutionise certain spheres in the ever changing and challenging field of medical science.
The process involves building of prototypes or working models in relatively short time to help create and test various design features, ideas, concepts, functionality and in certain instances outcome and performance. The technology is also known by several other names like digital fabrication, 3D printing, solid imaging, solid free form fabrication, layer based manufacturing, laser prototyping, free form fabrication, and additive manufacturing.
The history of use of this technique can be traced back to sixties and its foundation credited to engineering Prof Herbert Voelcker who devised basic tools of mathematics that described the three dimensional aspects of the objects and resulted in the mathematical and algorithmic theories for solid modelling and fabrication.
However the true impetus came in through the work of Carl Deckard, a university of Texas researcher who developed layered manufacturing and printed 3 D model by utilizing laser light for fusing the metal powder in solid prototypes, single layer at a time. The first patent of an apparatus for production of 3D objects by stereolithography was awarded to Charles Hull whom many believe to be father of Rapid prototyping industry. Since its first use in industrial design process, Rapid prototyping has covered vast territories right form aviation sector to the more artful sculpture designing.
The use of Rapid prototyping for medical applications although still in early days has made impressive strides. Its use in orthopaedic surgery, maxillo-facial and dental reconstruction, preparation of scaffold for tissue engineering and as educational tool in fields as diverse as obstetrics and gynecology and forensic medicine to plastic surgery has now gained wide acceptance and is likely to have far reaching impact on how complicated cases are treated and various conditions taught in medical schools.
Steps in production of rapid prototyping models The various steps in production of an RP model include- 1. STL files. Evaluation of the design 5. Surgical planning and superimposition if desired 6.
Additive Manufacturing and creation of model 7. Validation of the model. It is preferable that the CT scan is of high slice calibre and that slice thickness is of 1- 2mm. STL file format: After the data is exported in DIACOM file format, it needs to be converted into a file format which can be processed for computing and manufacturing process.
In most cases the desired file format for Rapid manufacturing is. STL or sterolithographic file format. These softwares process the data by segmentation using threshold technique which takes into the account the tissue density. This ensures that at the end of the segmentation process, there are pixels with value equal to or higher than the threshold value. A good model production requires a good segmentation with good resolution and small pixels.
Segmentation using the software Fig. It is important that unnecessary data is discarded and the data that is useful is retained.
This decreases the time required for creating the model and also the material required and hence cost of production. Sometimes this data can be sent directly to machine for the production of model especially when the purpose of model is to teach students. The real use however is in surgical planning in which it is critical that the surgeon and designer brain storm to create the final prototype.
There may be a need to incorporate other objects such as fixation devices, prosthesis and implants. The step may involve a surgical simulation carried out by the surgeon and creation of templates or jigs. The choice of the technology depends on the need for accuracy, finish, surface appearance, number of desired colours, strength and property of the materials. It also takes a bit of innovation and planning to orient the part during production so as to ensure that minimum machine running time is taken.
The model can also be made on different scale to original size like 1: 0. Rapid prototyping applications 1. Orthopaedic and Spinal Surgery 2. Maxillofacial and Dental Surgeries 3. Oncology and Reconstruction surgeries 4. Customised joint replacement Prosthesis 5. Patient Specific Instrumentation 6. Patient Specific Orthoses 7.
Implant design Testing and Validation 8. Table 1. Key Medical speciality areas in which Rapid Prototyping is currently used: 4. Surgical simulation and virtual planning The importance of preoperative templating is well known to surgeons.
Especially in difficult cases it gives the surgeon an opportunity to plan complex surgery accurately before actual performance. Advanced technologies like digital templating, computer aided surgical simulation; patient matched instrumentation and use of customized patient specific jigs are increasingly gaining ground.
Once the entire process of model generated is accomplished, the surgeon can study the fracture configuration or the deformity that he wants to manage Different surgical options and modalities can be thought of and even be simulated upon the model.
In the next stage, the surgeon can contour the desired implant according to bony anatomy. Often as in the complex cases involving acetabulum, calcaneum and other peri- articular area contouring the implant in three planes is usually necessary.
The fixation hardware can thus be pre-planned, pre-contoured and prepositioned. Once the implant is contoured, computer generated inter-positioning templates or jigs can be used for easy, accurate, preplanning of the screw trajectories and osteotomies.
Finally the surgeon can also accurately measure the screw sizes that he desires to use in the surgery thus saving valuable intraoperative time. The model could also be referred to intra operatively should a help is required in understanding the orientation during the surgery. Better understanding of the fracture configuration or disease pathology. Helped to achieve near anatomical reduction 3. Reduced the surgical time 4. Decreased intra-operative blood loss 5. Decreased the requirement of anaesthetic dosage Table 2.
Advantages of Rapid Prototyping 4. B, C: CT scan showing a vertical displaced a fracture involving iliac blade starting 3 cm below the iliac crest and extending forward reaching up to the acetabular roof and triradiate cartilage, involving both anterior and posterior column. There is also a mild protrusion of the femoral head and the fracture line extension was present till the superior pubic rami. Other fractures included grade IIIb open fractures of the lower third of the right humerus, left volar Barton fracture, and a bicolumnar fracture of the acetabulum on the left side.
His vitals were stable and after appropriate stabilization, a CT scan of the pelvis was taken. The CT scan showed a vertical displaced fracture involving the iliac blade starting 3 cm below the iliac crest and extending forward, reaching up to the acetabular roof and triradiate cartilage, involving both anterior and posterior columns.
There was a mild protrusion of the femoral head and the fracture line extension was present till the superior pubic rami [Figure 5A, B, C]. The preoperative planning before surgery of the acetabulum comprised sequential steps: 3- D reconstruction and segmentation of CT scan data], surgical simulation, template design, sizing and alignment of the implant and production of the templates using the RP technology [Figure 6]. CT scanning of all sections was done with 1-mm-thick slices.
For the preoperative planning process, template was used to contour a 4. The screw sizes were determined preoperatively and the position of the plate and holes was also decided and marked with indelible ink on the 3D model. An ilioinguinal approach was used for anteriorly exposing the fracture site.
The total surgical time required was 3 h 10 min. Of this, the instrumentation took only 20 min. Next morning, a haemoglobin check was done which was in the normal range and no postoperative transfusion was given. Post operative period was uneventful and normal postoperative rehabilitation protocol was followed.
The postoperative evaluation was carried out using radiographs and CT scans. Computer- assisted analyses were carried out for judging the accuracy of the reduction and sizing of the implants [Figures 7, 8]. Postoperative Judets view obturator view of Acetabulum. Axial sections CT images along the plate showing the well contoured plate and fracture reduction. Spine screening and other examinations were normal. After the swelling decreased as proven by the appearance of wrinkles on day 8, surgery was planned.
The 3D model showed the fracture lines clearly and helped plan the surgery [Figures 10]. Fracture Calcaneum CT scan image reconstruction. Fracture Calcaneum Rapid prototype Model. An open reduction and internal fixation was done using a lateral approach. The subtalar joint was anatomically reduced and a stable fixation was done. Postoperative radiographs [Figure 11] revealed an acceptable fracture reduction and the patient was mobilized at 6 weeks. At 2-year follow-up he is ambulating well without any pain and disability.
ORIF done for fracture calcaneum showing good reduction. His right knee CT scan was done and the data was used to make a 3D model depicting the fracture pattern. The model was used to study the fracture pattern, for the possible reduction manoeuvre, and to decide the screw trajectory and length. Other important applications of the prototyping technology are in the development of medical devices and instrumentations. Medical instruments that have been upgraded using the 3D technology include surgical fasteners, scalpels, retractors, display systems, among many others.
Besides the designing of the medical devices, the prototyping technology is also used in the manufacturing of these devices. Devices that need to be specifically individualized for a particular patient are the candidates of the additive technologies.
Most hearing aid devices are designed using the stereolithography or the selective laser sintering. Other areas that are adapting the rapid prototyping technology is the replacement of teeth. Some drug dosage forms are also designed by the use of these technology.
Especially the dosage forms that are difficult to design using any other method. Tablets having a sustained drug release are also being manufacture using the rapid prototyping technology. The new technology has improved the safety of drugs to patients by minimizing the adverse drug reactions that may arise. Rapid prototyping plays a crucial role when it comes to implantations and use of prostheses.
Through the technology, prostheses that have been specifically designed for a particular patient are now available. Patients whose requirement is outside the standard size or those who require special treatments can now get some customized prostheses that fits them at an affordable cost. Rapid prototyping and computed tomography technologies utilize techniques, such as X-rays and NMRI , and enable the transfer of data generated to be used as the input data for the rapid prototyping process.
A lot of development have been done to enhance the accuracy, interpretation, and the translation of the CT scan results. The accuracy of the models generated from the rapid prototyping systems have also been improved over time.
Various types of rapid prototyping technology have been applied in the various medical uses with some of them being selected as the standard method. An example of standard method used for medical purposes is the CT scan used in the hip replacement surgical procedure.
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