Custom Made Cranial Implants - Dissertation Example

Custom Made Cranial Implants In orthopedics, customization is the most recent paradigm adapted in the reconstruction of cranial facial defects (Chen et al 30). Over the years, it has been extremely challenging for surgeons to conduct the cranial facial skeleton surgery due to the complexity associated with its structure. The use of auto grafts has been the main mode of reconstructing cranial injuries over the past years (Goyal et al 45). However, this technique has had limitations in that suitable donor sites are so hard to find and if present, the compatibility between the donor and the recipient site is rare. Other disadvantages of using auto grafting include donor site morbidity, tissue harvesting difficulties, and high chances of contagion to both the recipient and donor site. Moreover, such drawbacks include additional surgeries to ensure reabsorption of the graft and the availability of highly skilled surgeons to undertake the extensive procedure. Cranial injuries can be because of traumas, fractures, infections or degenerative diseases (Hallermann et al 10). Often, the bone layer remains expansively damaged to an extent that the tissues cannot regenerate and reintegrate to reinstate the patient’s appearance. This has thus prompted the use of cranial implants. Cranial implants are able to specifically adapt to the region of implantation, reduce the surgical time and reinstate the appearance of the patient. Scientists have developed preoperative techniques to enable the surgeons plan effectively for the surgery and to prepare biomodels for the cranial implants. Visualization techniques have remained greatly embraced to ensure that these preoperative measures are attained (Kozakiewicz et al 32). Computer assisted design and computer assisted manufacturing systems are the recent computational techniques that have made visualization more effective (Kozakiewicz et al 34). Manufacture of the custom made cranial implants can occur in a number of ways for example the use of 3D modelling, radiolucent or electron beam melting technology. They all aims at eliminating the constraints, which have been previously associated with cranial facial surgeries in the past years such as the internal structure, size, shape and mechanical properties of the patient (Schilickewei and Schilickewei et al 15). Cranial implants can be manufactured from a variety of alloplastic materials such as 2 titanium. The material used to make the implant determines its success and longevity of the surgery. This project deals extensively on how custom made cranial implant can be manufacture using the DICOM images technology (Hou et al 45). The DICOM image technology incorporates techniques such as 3D image printing, CAD-CAM technology and incremental sheet forming. This technology is preferred in that it creates low cost custom-made implants and bio models of fractured skulls for effective cranial facial surgical procedures. The low cost enables large number of people to be beneficiaries of the implant whereas biomodels are used to ensure the expected outcome is achieved.This technique involves construction of a CAD model and implant from CT scan images virtually. The biomodel then undergoes physical manufacture by 3D printing and the implant by incremental sheet forming on 2 titanium. The implant undergoes heat treatment before cutting into the desired shape to avoid deformations that may arise due to mechanical stresses (Chen et al 29). Methods of manufacturing cranial implants Manufacturing of custom-made cranial implants requires high level of skill and planning in order to give a precise design that is compatible to the region of injury. Various materials can be used to prepare the implants such as biodegradable polymers, bioceramics, titanium, autologous bone flaps or polymethylmethacrylate (Hallermann et al 32). Surgeons have a wide variety to choose from, however, 2 titanium is the most preferred due to its elasticity, resistance to corrosion and its long term results. Preparation of custom-made cranial implants from DICOM is carried out through seven major steps that as discussed below (Hou et al 46). These steps are discussed in depth to help understand how each stage plays its role in the manufacturing of the implant and biomodel. Step 1: Biomedel computational modelling This step involves the use of DICOM (digital imaging and communications in medicine) images (Chen J et al 36). DICOM images are in electronic format and comply with the set standards for imaging, storage and transmission of data that is of medical origin. This format enables various devices, computers and equipment to communicate easily. Computed tomography (CT) scans finds use in obtaining DICOM images from the longitudinal sections of the injured region on the skull. In Vesaliuscomputer, software is then able to convert these DICOM images into 3D CAD vector file (STL extension) which help in the diagnosis and surgical planning. At the end of this step, virtual models of the injured section can remain visualized in 3D format from the CT images (Hau et al 44). Step 2: Biomodel manufacturing This step involves the use of 3D printing to construct replicas of broken bones, restorative alloplastic implants and to create models from various materials. The alloplastic material majorly used for this purpose id the 2 titanium. However, other materials such as the biodegradable polymers, bioceramics, autologous bone flaps or polymethylmethacrylate can also find use depending on the manufacturer’s choice (Kozakiewicz et al 33). Step3: Implant modelling CAD 3D software remains applicable to design contours of the implant (peripheral contours) depending on the rupture. Based on the axial equilibrium between the right and the left sides of the skull, CAD guidelines are designed in to act as the skeleton of the implant surface (Hau et al 50). Step 4: Implant manufacturing by incremental sheet forming In implant manufacturing, incremental sheet forming are used because they are inexpensive and easy to obtain. In addition, they can be used together with machines that are not specifically designed for them such as CNC machining centers (Schilikewei and Schilickewei et al 14). This non-specificity property of the increment sheet forming enables sheet metal parts for various geometrics to be manufactured using the same tool. The CNC machining enables geometry and tool paths to be generated through CAD/CAM systems. The sheet remains first deformed slowly in coordinated XYZ movements using tools with a generic profile and without cutting edges (Goyal and Goyal et al 64). Plastic deformation within a small region of the sheet is results from movements and changes based on the movement of the tool resulting in progressive deformation hence an increase in conformability of the sheet to other conventional forming processes. Two-point incremental forming is a form of lower support incremental sheet forming that relies on polymer support in addition to the forming tool. This lower support tool is used to ensure the parts are accurately carved and that the geometric range is stretched since its both specific and semi- specific. It is majorly applicable in situations whereby geometries are of organic or asymmetric nature (Kozakiewicz et al 39). Edge CAM software is also used during this step to carry out the machining of the lower support increment forming, to form the 2-titanium sheet and to cut the end-product depending on the intention of the manufacturer (Chen J et al 52). Consequently, an extra forming region remains generated before the implant CAD file is sent to CAM environment. The purpose of creating extra forming region is because increment sheet forming starts on a flat and horizontal plane. However, the implant produced usually has an irregular perimeter and therefore a region to join the perimeter and the surface of the implant is necessary (Chen J et al 28). The manufacturing schedule of the implant therefore takes place in two phases that is lower support machining to form titanium sheet and the cutting of the implant. The schedules’ characteristics include precise speeds,features and dynamic tool strategies. Once the simulations have been completed, the programs created are sent to the CNC machine for the purpose of metal machining. The CNC machine consists of two major parts that is a rod made of 4340 steel and a tip made of pure titanium (Hallermann et al 33). The increment sheet forming process often involves lubrication of the equipment being used and this could be a source of contamination to the custom-made implant. The choice of the lubricant to be used therefore determines the purity of the implant formed. Lubricants of mineral based origins contain chemical components that are detrimental to human health and thus should never be used to lubricate these machines. However, inert lubricants such as glycerin, Vaseline, animal-based lubricants or propylene glycols recommendable for any lubrication in implant manufacture (Hou J et al 55). Step 5: Heat treatment of titanium sheet Heat treatment is carried out before cutting, to relive the stress on the sheet thus preventing any possible deformations. When heat treatment is unavailable, the deformations formed are enormous such that comparison of the CAD model and the implant is unnecessary (Hou J et al 45). Step 6: Dimensional analysis A 3D scanner is used to evaluate the dimensional concordance between the reference CAD model and the implant (Kozakiewicz et al 36). The scanner is passed over the titanium sheet creating a CAD surface, which is then accumulated with the novel CAD sculpt of the implant, and the two are compared. Step 7: Physical assembly implant The CAD biomodel and implant are assembled for aiding a physician or a surgeon to predict movements, make preplanning of the surgery, evaluate how the implant fixation will be carried out and in providing relevant explanation to patient or their family on how the surgical process will take place (Chen et al 53). Results The manufacturing of custom-made cranial implants from DICOM images has remained studied for a number of years by various researchers. A research carried out by Goyal and Goyal 58 aimed at finding out how efficient this technique is. They carefully analyzed the data obtained, compared it to that of other researchers and were able to come up with a number of findings. These findings remain consistent when carrying out the custom-made manufacture of implants and CAD biomodels as discussed below. There appear positive and negative discrepancies during comparison of the reference CAD model and manufactured implant. Positive discrepancies characterize a positive value. This value is an indicator that the titanium implant exceeds the respective CAD model in the negative Z direction. The possible cause of positive discrepancies is the stresses that remain and accumulate when the heat treatment procedure is carried out. These stresses are reducible by adjusting temperature, the ramp or carrying out post treatment procedures (Hou et al 54). Negative discrepancy characterizes the titanium implant having smaller dimensions than the respective CAD model in the negative Z direction. This majorly occurs due to the cutting operation rotation defect. The rotation of the machine distorts the sheet size causing one side to be larger than the other (Kozakiewicz et al 37). This discrepancy can be corrected by using laser based cutting method which produces improved, smaller and more uniform surface finish of the cutting area. In addition, further findings through visual techniques show that by these discrepancies affects the symmetry between the healthy and recovered side. Thus, scientists should carefully scrutinize maintenance of the symmetry to provide an efficient working system. Further chemical analysis of the titanium sheet formation using ED’s analysis is used to confirm the purity of the implant in to ensure it is safe for use and free from any contamination. The purity of the implant is maintainable by working under aseptic conditions and using inert lubricants (Schilickewei and Schilickewei 22). Discussion To reduce discrepancies between the reference CAD model and the manufactured implant, low support polymers which have precise formats of the implant such as TPIF (two point increment forming) is encouraged (Schilickewei and Schilickewei 20). Heat treatment should also remain performed under correct and controlled temperature and duration to maintain a correlation of the model and the implant. However, with the recent advances in technology, better methods for manufacturing of the custom made cranial implant are underway with the aim of providing a more precise output. The use DICOM images has made great strides in the cranial facial surgery due to the reduced cost of implants and the use of existing sources such as the CAD-CAM mechanical software (Hallermann et al 30). Fabrication of custom-made cranial implants is an automation that scientists have recently adopted to reconstruct cranial facial defects. Other researchers have also been able to develop preoperative implant manufacturing systems. For example, a research conducted by (Goyal S et al 56) to develop a mechanized and parametric manufacturing process used fabrication of custom implants using various alloplastic biomaterials to verify their efficiency and the results obtained from their experiments was similar to those of the DICOM images system. However, their models were manually prepared and thus their efficiency was dependent on the manual skills of the biomodeler. Computational softwarehas played key role in enabling the surgeon preplan the surgery by visualizing and assembling various parts virtually. Consequently, the surgery time remains significantly reduced, the possibility of errors during the surgery also reduced and the end result cosmesis proven better and similar to the original patient’s appearance (Goyal and Goyal 67). The manufacture of custom made implants from DICOM images using 3D printing, CAD-CAM technology and incremental sheet forming study has however been faced with a number of limitations such as the aseptic conditions of the environment where the studies are conducted. Sterility of the implants is of great importance in order to avoid complications that can result from contaminated implants (Hou et al 22). Despite the availability of disinfectants and sterilizing tools for the prepared implants, it is necessary to work in an aseptic environment with controlled humidity, temperature and a certified facility for creation and operation of implants. Conclusion 3D printing is an effective technique in the manufacture of implants and CAD biomodels. It has positively influenced the orthopedics surgery as a whole by providing a cost efficient and easier preoperative and operative procedure. The implants and models created are of high purity and reduced dimensional variability. Advances in material science are still underway in order to eliminate the use of alloplastics (Chen J et al 33). Regenerative medicine that would allow tissues and bones to grow naturally and similar to the region of implantation is what the future in orthopedics still holds and is subject to exploration and discovery in the manufacture of custom made implants. Works Cited Chen, J. J., Liu, W., Li, M. Z., & Wang, C. T. "Digital manufacture of titanium prosthesis for cranioplasty." The International Journal of Advanced Manufacturing Technology 27.11-12 (2010): 1148-1152. Goyal, S., & Goyal, M. K.. "Restoration of large cranial defect for cranioplasty with alloplastic cranial implant material: a case report." The Journal of Indian Prosthodontic Society 14.2 (2014): 191-194. Hallermann, W., Olsen, S., Bardyn, T., Taghizadeh, F., Banic, A., & Iizuka, T. "A new method for computer-aided operation planning for extensive mandibular reconstruction." Plastic and reconstructive surgery 117.7 (2006): 2431-2437. Hou, Jin-Song, Mu Chen, Chao-Bin Pan, Miao Wang, Jian-Guang Wang, Bin Zhang, Qian Tao, Cheng Wang, and Hong-Zhang Huang. "Application of CAD/CAM-assisted technique with surgical treatment in reconstruction of the mandible." Journal of Cranio-Maxillofacial Surgery 40.8 (2012): e432-e437. Kozakiewicz, M., Elgalal, M., Loba, P., Komuński, P., Arkuszewski, P., Broniarczyk-Loba, A., & Stefańczyk, L. "Clinical application of 3D pre-bent titanium implants for orbital floor fractures." Journal of Cranio-Maxillofacial Surgery 37.4 (2009): 229-234. Schlickewei, Wolfgang, and Schlickewei, Carsten. "The use of bone substitutes in the treatment of bone defects–The clinical view and history." Macromolecular Symposia. Vol. 253. No. 1. WILEY‐VCH Verlag, 2007. Read More