Rapid Prototyping (RP) is used mainly for product design and manufacturing. However, the evolution of RP application has gone beyond product design and manufacturing. In this project, we delved deeper into other RP application; surgical assist. We explored into all types of applications related to surgical assist. At the same time, we have done three case studies on different applications using RP advancement. In the case studies, the implementations, results and observation are discussed thoroughly.
By drawing upon the observations from the various case studies, we have attempted to identify its advantages and limitations pertaining RP technology application in surgical assist.
Rapid Prototyping (RP) is a process which 3-dimensional computerized surface models are converted to physical models. It is originally and widely used in manufacturing designs for consumer products and automobiles. However, the use of Rapid Prototyping has expanded vastly to many areas, including the field of surgical assists technology. With the advanced capabilities afforded by modern imaging devices such as Computer Aided Tomography (CT), Magnetic Resonance Imaging (MRI) and Echocardiography, the use of rapid prototyping has begun expansion into surgical assist applications. The precise stereolithographical model of anatomic structures based on 2-dimensional images produced by CT or MRI enable surgeons to visualize internal and external anatomy previous to surgery. These physical models produced are useful in surgery diagnosis and assist in preoperative planning.
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Figure 1: Example of the RP technology application in the design of a total knee replacement
2.0. APPLICATIONS OF RP IN SURGICAL ASSIST
Figure 2: Applications of RP in Surgical Assist
There are many applications of RP in surgical assist. The applications are the development of surgical assist instruments, planning and explanation of complex surgery and the manufacturing of custom implants.
Firstly, RP is used in the design and development of surgical devices and instruments. Overall development time for the surgical tools and devices can be reduced significantly with the use of RP. With the availability of CAD/CAM software, coupled with RP technology, customized devices for specific surgery or application such as scalpels, retractors and many other useful tools can be produced without much hassle.
Another major application used by surgeons is in planning and explanation to complex surgery. Complex operation depends very much on the surgeon's knowledge, skills and experience. In traditional pre-surgical planning, surgeons depend on the processed 2D images obtained from photography and radiography. The images remain limited in realism and are not easily visualized . Surgeons make judgment and decision mainly based on the 2D images available to them. With such limitation, some important details cannot be determined. However, with the advancement of RP technology, the images obtained from CT can be converted into a 3D physical model. With such model, surgeons can effectively understand the complex problem in details by physical visualization. Surgeons can also plan ahead before the surgery and thus, making the right decision. The model can also enhance visualization and can be useful in communication among the surgical team. Rehearsal can be also done on the physical model to improve skills, optimize and increase confidence before proceeding with the actual surgery. It is always imperative to practice on an exact model to educate the hand. These models are always present in the operation theater where they are used as guidelines. Some examples of this application are treatment for structural heart disease.
Finally, manufacturing of custom implants and prosthetics become an important aspect of RP in surgical assist. With RP, customization of anatomy parts for implantation becomes possible. It offers a simpler way to develop custom implants and produce them within a short period of time. The conventional ways of doing this is by using the standard sized replacement parts produced by the manufacturers. This however does not fit every patient due to limitation of available sizes. Thus, RP solve this limitation by producing customized accurate part that fits the patients. The CT scans the parts and the data scanned is transferred to the RP system where the actual replica of the parts is produced. The part produced is a direct replacement to the actual anatomy parts missing due to injury. Examples of implantation used with RP are chin, knee, hip and cranial reconstructive surgery.
3.0. IMPLEMENTATION OF RP IN SURGICAL ASSIST
Figure 3: Methodology - role of RP in surgical assist
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Figure 3 above shows the typical methodology adopted in the surgical assist applications. The methodology used is almost similar for most of the cases in the medical application using RP. The first step in building physical model for surgical application is to extract information from the respective anatomy parts to diagnose or analyze. Using the CT or MRI scan, 2D planar images are generated and acquired. The 2D images contain complete information in a slice format, revealing the cross-section of the scanned part. The data are then imported into the medical modeling software. Examples of medical modeling software commonly used are Mimics and 3D Doctor. This software is able to reconstruct the CT data into a virtual model showing the lateral and frontal views of the parts scanned. The contours from each of the cross-section images are interpolated and merged together to form a complete 3D object representation. At the same time, 3D CAD software can be used to modify the virtual model through dynamic and interactive simulation by incorporating other objects such as implants if required .
Once the modification is done, the virtual model data can now be translated into .STL (stereolithography) file format that can be understood by all RP machines for fabrication. In rapid prototyping building stage, the virtual model is converted into a physical model through layer-by-layer construction via deposition of material. This process enables the production of geometrically complex shaped models to be constructed. Prior to the production of the physical models, the types of materials suitable for the specific application are evaluated. With introspect to the types of materials, the availability and capabilities of the machines are considered. Once the physical model is created, the final task is the post-processing task where cleaning, post-curing and finishing process are done to enhance surface finish and aesthetic appearance. The model is now ready for application.
For some application such as cranial reconstructive surgery, the physical model developed are used as a positive to produce the mold for pouring biocompatible material such as poly(methyl-methacrylate) . The prosthesis produced is then implanted into the patient. After the surgery, the fibrous tissue will grow through and form an encapsulation of the implant. After the tissue has fully grown and reproduce a new layer on the cranium, the biocompatible material will degrade and dissolve.
4.0. CASE STUDY 1:
DESIGN AND MANUFACTURING OF IMPLANTS BASED ON RP
One of the major applications of RP in surgical assist is the design and manufacturing of implants. With the advancement of RP, a patient with mandible defect underwent reconstruction can use custom made implants. An operation that can transform a person's profile by bringing out the chin which is needed to restore facial balance and aesthetic improvement is a chin augmentation. Chin augmentation is an example of a computer-assisted prefabricated implants design and manufacturing system to improve the aesthetic outcome in chin surgery. A balance profile can be obtained by inserting an implant and the aesthetic result in chin augmentation can be comprised with many factors such as preoperative analysis, the implant design, implant size and shape, and the implant material.
The traditional method uses chin implants in few shapes and sizes and the use of commercially available chin implants can get some difficulty matching with the patient bone. The implant has to be sculpted by the surgeon to fit the patient bone and this procedure spends more time to surgery. Therefore, a new technique is developed to make a suitable implant which is designed from three dimensional (3D) computed tomography (CT) scans of the facial skeleton to get a long term stable, completely fitting with an exact 3D geometry. The purpose of this new technique is to improve the aesthetic outcomes by the combination of the advance manufacturing technology. For chin augmentation implants, the designing methods are based on CT scanning images for medical rapid prototyping (RP) applications.
Our case study for chin implant will be discussed on the patient who is 28 years old lady with small mandible need chin augmentation. To determine the amount of implant projection, the patient was radio-graphed and the orthodontist made a cephalometric analysis.
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Figure 4: Lateral skull radiograph of the patient
Data acquisition for 3D modeling was developed by the using helical tomography (CT) imaging which was performed with the following parameters: 120kV, 150 mA and 1.3mm slice thickness. After the generation of computer based 3D model of bony structure, data were carried to reverse engineering software for the designing. The geometry of the prosthesis is composed of inner surface and outer surface. The inner surface (bone adherent surface) is the one that contacts with the bone surface and it is derived directly from the individual bony structure of the patient. The outer surface is the one which allows the chin projection and it is designed on the basic of another mandible data.
To create a solid model, the inner and outer surface were connected and the complete implant geometry was transferred into STL format file that indicates the boundary surfaces of the solid model and transformed into the data processing software to check the closeness at all surfaces and edges. The optimal orientation for implant building was chosen and the CAD model was sliced into 0.1 mm layer thickness and the support was created. The implant geometry was loaded into RP machine to produce RP implant model and the SLA model was sent to the hospital. The silicon rubber mold was made by the using of the RP implant model as the positive part. The silicon mold was invested to produce wax pattern which was used to fabricate the titanium implant.
Figure 5: Silicon mold and Titanium parts produced
4.0.2 RESULTS AND DISCUSSIONS
The new method gave better result of the prosthesis geometry design because the implant contour gives closeness to the natural chin curvature. The physical implant model was made from CAD data, so the design time was shortened and it was fitted perfectly with the patient's skull anatomy and adequate symmetry and projection of the jaw were obtained. By using this new method, the surgical planning was accurate and it was easier by the RP model. The custom made implant was completely fitted with all the patient bone during the surgery and the adaptation of the implant surfaces to the bony structure can give excellent or good aesthetic and functional results in all the patients. In all cases of surgical operations using implants, they were inserted and fixed by screws, so that the time of surgery was shortened. The aesthetic outcome of the patient was excellent and the patient rehabilitation time was reduced. The use of rapid prototyping (RP) technique in chin surgery gave precisely in fitting, an excellent aesthetic form and surpassed the result obtained through other modeling processes. According to the demonstration of this result, the proposed methodology is capable of applied to chin surgery.
In our case study, chin augmentation with titanium implants gave sufficient aesthetic results. Titanium and its alloys are very useful for manufacturing orthopedic and dental implants because of their mechanical and biological properties such as high strength and excellent fatigue behavior, corrosion resistance to body fluids, bioactivity and biocompatibility. Today, the use of the prefabricated implant is most popular in chin surgery. These implants have different sizes and projections and they are not custom made to the exact size and shape that the patient requires. These implants are difficult to fit on the defect site and their shapes and sizes can have a negative effect on facial appearance.
The use of custom made implant manufactured by RP technique has several benefits. The SLA implant fitted on the skull model to determine the amount of chin projection can be used for pre-operative planning. The RP physical model can determine if the chin implant can match the patient's face. The RP implant is accurate and can give an easy insertion of the prosthesis into the defective site as compared to the commercial available chin implants. Screw fixation of the implant protects both any displacement of the implant and the gap between the implant and mandible.
Figure 6: X-ray revealing the titanium implant in place
The use of RP to make customized chin implant has many advantages such as the physical model can be used for many applications, fitting evaluations, chin augmentation evaluations and so on. The fabrication of implant is accurate and can give the aesthetic satisfaction for the patient. The surgery time was decreased by the integration of this technique in chin augmentation surgery. The use of RP in chin surgery operation gives accurate fitting and also provides an aesthetic form and surpasses the results obtained by other modeling processes.
4.1. CASE STUDY 2:
RECONSTRUCTION OF KNEE USING RP TECHNIQUE
This case study will be discussing on the patient who is 60 years old lady and she has rheumatoid arthritis (RA: chronic disease that damages the joints of the body) medical history such as deformity of fingers at the age of 15, Benjamin's double osteotomy of left knee at the age of 27 (due to potential subluxation, partial dislocation of a joint) and a synovectomy (Surgical removal of the joint lining and it may be done to remove the inflamed lining of a joint in rheumatoid arthritis). It was worsening when she turned to 59 years old like deforming left knee progressively varus (abnormally positioned towards midline).
Figure 7: Rheumatoid Arthritis
Knee cap replacement had been carried out for the patient. CT scan has been performed in a flat plane with along her shin bone axis which has aligned at the right angles to the scanning plane on the machine's couch with soft firm padding. It has an interval of 1.5mm for every slice starting from 30mm below the joint line; about 20 sections have been sliced. The data was stored as DICOM format and converted it accordingly as shown in figure-2-. The stereolithography apparatus (SLA) is used for the model creation. The total time taken for data conversion is less than one half hour and around four hours for building of the model by PR method. By doing so, the three benefits are surgeon are able to pre-examine through the CT scan result, model can be made precisely and less intensive for the computer memory by introducing SLC (2½ Dimension: triangular faceted STL file) format.
Figure 8: Steps for RP assist implementation
After examination on CT scan result, the decision has made to cut 15mm below the lateral joint line. The cortical bone geometry showed where the cut to be and the access area for the surgery. The operation was performed based on the pre-examined data and pre-determination on the reconstructed-model.
Figure 9: Comparison between SLA Model and Resected (Removed Surgically) Bone
4.1.2. RESULTS AND DISCUSSIONS
Although the overall results were positive, the tiny crack fracture of the tibia shaft was spotted out after X-ray scan. It might be due to the marked RA and disuse as no traumatic event. The patient was discharged within 10 days after surgery with the aid of wheel-chair or walking frame but the patient walked with pain free (without support/ walking aids) in 12 weeks time after the fracture had united.
The above mentioned techniques could be used for bone morophology and facilitated the varus as well. The model could be used for either pre-examination purpose or practical purpose for surgeons. This technique also proved that CT scan provides more precise information compared to the traditional radiographs technique.
With RP technology, precise and customized knee cap replacement can be done without much hassle. With such advancement, physical knee cap fabricated can now fit ideally into different patients.
4.2. CASE STUDY 3:
MAXILLOFACIAL SURGERY USING RP TECHNIQUE
This case study will be discussing on the patient who is a 54 years old man and he sustained a 'blowout' fracture of the left orbital floor (the bottom of the eye socket) and presented with diplopia (double vision) and restriction of upward gaze.
It is very crucial that what material and what technique can give the best for this operation . The custom-made titanium material was used because it was inert and widely used. The construction of the model was taken about two hours and the material cost is cheap. After performing CT scan, the data was reconstructed as 1mm slice with the increment of 0.5mm and smooth kernel which was usually for bony anatomy (edge artificial enhancement). Sharp multi-plane reformats are used for the detail of bones and 3D imaging which surgeon could be used as reviewing. In case of any missing data (due to 1mm interval of scanning), 0.5mm overlapping could be overcame and the resolution could be improved. SLA was used for model creation and the epoxy resin (almost no shrinkage during photo-polymerization process) was chosen for better accuracy.
Figure 10: CT-Scan for Blowout
After building the model, the orbital defect is filled with wax in order to reconstruct the contour similar to the right side. An exact replica of orbital floor and rim contour was produced with a layer of 0.5mm medical grade titanium. The titanium sheet was trimmed and fixed with screws followed by polishing the complete model.
Figure 11: Replacement of the Titanium Implant on the Master Model
Herniation and entrapment of the periglobar fat was released during the surgery. The screw was used to fix the prosthesis with the normal force which was to ensure the eye could move freely.
4.2.2. RESULTS AND DISCUSSIONS
Post-operational result was revealed that the positioning of the prosthesis was precisely seated. The vision much clearer the range of ocular (an organ of vision that detects light) movement was normal. The simplicity and the usage of proposed material brought the successful surgery up. The method was simple and useful for most of the maxillofacial operation.
The conventional method for designing and fabrication of facial related surgery is done using handmade model, making use of 2D method for modeling. The efficiency and accuracy of this method is not satisfactory compared to the fabrication of actual 3D physical model from RP which is more precise. The physical model could be used for some applications such as pre-determination and examination on the model before the operation begins. The case-study result has been proven the precise and accurate technique for the surgery with the aids of RP.
5.0. ADVANTAGES OF RP IN SURGICAL ASSIST
With the implementation of RP in surgical field, surgeon can now practice on precise and exact models . Rehearsing on actual models will hence increase greater understanding and knowledge on the complex problems. These will eventually leads to greater success in surgery.
Complex surgery can now be performed without much hassle with the help of RP technology. In the past, only 2-dimensional and 3-dimensional images are used to interpret and understand the complication in the surgery. It has been a painstaking task for surgeons to interpret images. Some essential points might be missed out. Surgeons are also required to be able to imagine and visualize the models from the 2D images provided. Nevertheless, this difficulty can be solved with the aid RP technology. The real physical models produced enables surgeon to visualized and understand the complexity of surgery better.
Besides that, precise planning can be done using real model produced by RP. With the physical model, the accuracy and efficiency of the team is enhanced. Team can now communicate better. For complicated surgery, a team of surgeons can now sit down together to discuss in details with the assist of RP models. Difficult problems can be discussed and solved before surgery. As a result, the quality of the operation is improved and the overall surgery time is reduced significantly. With the well-planned surgical procedure, the chances of success are much higher . This will results in reduce risk and pain of the patient.
Customized implant is made possible with RP. Before RP is used, customization could only be done manually. Manual work means cost is much higher and inefficient. Thus, with RP technology, manual work is removed and customization becomes much easier and streamlined.
The conventional method of implantation requires manual construction of parts. With RP technology in place of the conventional method, the overall time required from scanning of body parts to surgery is reduced significantly.
Overall cost required in term of optimization of surgeon's planning time, improve in overall effectiveness, quality and efficiency is reduced greatly.
Although there is no doubt that physical medical model produced from RP technology are useful aid in solving complex surgical issues, several constraint has been identified.
The main limitation of the use of these technologies is the requirement of highly-skilled manpower. A big team of expertise is required in operating the CT machines, medical modeler software, CAD software and RP systems. This implies a significant investment is largely required for any medical establishment wishing to use this technology. Huge investment is required for training of personnel, purchase of RP machines, materials and a sufficient area space requirement.
Another stumbling block is on the cost . A simple implant for instance will require the usage of expensive RP machines and expertise service charges. Due to this, the patient will have to be prepared to pay a hefty price for such implants. The cost will only be justified in complex surgery cases such as heart surgery.
Only specific RP materials are labeled safe for use in the operating theater and none are able to be used or placed in the body so far. Thus, only certain machines that support the material can be used. This will eventually limit the range of application for physical medical models. The current implementation by using biocompatible material requires extra steps by using produced RP parts as a positive to produce parts suitable for the human body.
Generally RP equipments are developed to solve problems in the area of high-volume manufactured product development rather than to solve problems related to medical issues. As a result, the development of the technology has been focused on improvement to cater for manufacturers rather than surgeons.
Conventionally, Rapid prototyping are used by companies to help them in product designs and manufacturing. It is widely used in manufacturing designs for consumer products and automobiles. Over the last few years, the use of RP has developed further in the area of surgical assist technology. With RP, the precise anatomic structures can be produced by taking inputs from CT and MRI machines 2D images. The actual anatomic structures can then be used in many medical applications such as development of surgical assist tools, manufacturing of custom implants, reconstruction surgery and assisting surgeons in the planning of complex surgery.
There are many benefits gained from implementation of RP in surgical field. In traditional pre-surgical planning, the two Dimensional data is obtained by the radiography and photography. The full appreciation of various bony structure movements is somehow limited to only two dimensions. However, with the implementation of RP, the creation of a 3D physical model is possible. With such, surgeons can use it for comprehensive planning and simulating surgical procedures. This will eventually reduce surgery time, increase efficiency, produce quality surgery and ultimately, reduce surgery risk tremendously.
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