A computer assisted mandible reconstruction planning (CAMRP) program was used to calculate the optimal cutting length and number of fibula pieces and design the fixtures for mandible cutting, registration, and arrangement of the fibula segments. The mandible cutting and registering fixtures were then generated using an additive manufacturing system. The CAMRP calculated the optimal fibula cutting length and number of segments based on the location and length of the defective portion of the mandible. The mandible cutting jig was generated according to the boundary surface of the lesion resection on the mandible STL model. The fibular cutting fixture was based on the length of each segment, and the registered fixture was used to quickly arrange the fibula pieces into the shape of the defect area. In this study, the mandibular lesion was reconstructed using registered fibular sections in one step, and the method is very easy to perform.
jig and fixture design pdf 13
The application of additive manufacturing technology provided customized models and the cutting fixtures and registered fixtures, which can improve the efficiency of clinical application. This study showed that the cutting fixture helped to rapidly complete lesion resection and fibula cutting, and the registered fixture enabled arrangement of the fibula pieces and allowed completion of the mandible reconstruction in a timely manner. Our method can overcome the disadvantages of traditional surgery, which requires a long and different course of treatment and is liable to cause error. With the help of optimal cutting planning by the CAMRP and the 3D printed mandible resection jig and fibula cutting fixture, this all-in-one process of mandible reconstruction furnishes many benefits in this field by enhancing the accuracy of surgery, shortening the operation duration, reducing the surgical risk, and resulting in a better mandible appearance of the patients after surgery.
Among the above-described methods, application of the medical imaging method can reconstruct a 3D digital model and provide a reference model of the mandible before surgery. However, it does not generate a template as a reference for the fibula, and clinicians need to measure manually the amount of bone required and then consider how to cut and arrange the fibula segments. This often prolongs the process of preoperative preparation and might cause errors due to the lower accuracy of manual measurement. A premade cutting fixture is often not able to fit the defect area due to lesion resection being difficult to predict. Many fixtures cannot be manufactured and applied in a timely fashion during surgery. Application of a metal bone plate provides a good reconstruction target for the mandible defect, but it cannot function effectively as a template for fibula cutting and as a positioning tool for reconstruction.
To overcome the above-mentioned deficiencies, this study first established digital models of the mandible and fibula with the corresponding nodes (locations) for cutting planes (CPs) according to the medical images. The simulation design for the lesion resection was created on the basis of the sequential CP point group. The CAMRP [16, 17] generated by our research group was used to calculate the optimal lengths and number of fibula pieces, based on a digital mandible model for defect resection and reconstruction using the fibula bone. Design of the cutting jig and the registering fixture were rapidly generated according to the preoperative digital model, and the designed cutting jig has many guide slots which could be chosen if the resection conditions changed during the procedure. The digital models for all the design models, including cutting jigs and registered fixtures, can then be simultaneously made using additive manufacturing (AM) technology prior to the operation. This provided all the necessary requirements for every step of the mandible defect reconstruction process. This study established a technique for lesion resection that can simultaneously complete fibula cutting and mandible defect reconstruction surgery in one operation. The technique can significantly shorten the duration of surgery, reduce the number of the visits for patients, and enhance the accuracy and success rate of the surgery.
The flow chart of the study was as shown in Figure 1, which includes five main processes: model digitizing and parameterization, pre-surgical planning and design, cutting fixture design, cutting fixture rapid manufacturing, and assembly and verification. Below is an explanation of each process.
In this study, the digital model of lesion mandible was designed and captured from a skull model which was obtained by 3D tomography from a healthy man. The 3D tomography images which came from an adults sponsor in our previous study approved by IRB (EMRP01099N) of E-DA hospital Taiwan. The data of skull were then manipulated using MIMICS software (version 13.0) to generate a stereolithography (STL) digital file (Figure 2A, left). In order to generate a mandible lesion area, 3Matics software was used to design the lesion area by removing the teeth on the model, which created a mandible digital model (Figure 2A, right). In addition, a digital model of the fibula (Figure 2B) was captured from an artificial teaching sample using a high-resolution scanner (Germany, ATOS 3D SCANNER).
Center line design of the mandible and fibula. (A) The center line of the top view; (B) The center line of the front view; (C) Generation of the reference center line for the mandible; (D) The 101 node of the center line.
By using the parameterized mandible model, the lesion area to be removed was planned based on the planes corresponding to each numbered node. An optimal program was used to calculate the cutting length, the number of the fibula pieces required and the best arrangement under different lesion sizes. Figure 5A shows the results calculated by the optimal program, in which 3 pieces of fibula were arranged in the defect area under different defect conditions. Figure 5B shows the designs of the mandible reconstruction digital models that contain 3 pieces of fibula corresponding to the different defect conditions shown in Figure 5A.
Calculation by an optimal program and the design of model for mandible defect area reconstruction: (A) The case of two pieces of fibula; (B) The cut mandible model with two pieces of fibula combined.
Using the design of the optimal program shown in Figure 5, the cutting fixture for the mandible lesion and the registered fixture for the arrangement of fibula pieces were created to improve the surgical accuracy and efficiency. As a perfect match between the mandible cutting fixture and the surface of the mandible is critical, this study retrieved the points cloud data of the mandible defect area and utilized the data to reconstruct the pad of the cutting fixture. Therefore, the fixture can completely fit onto the surface of the mandible. In order to deal with possible variation of the lesion area found during surgery, the mandible cutting fixture was designed with three cutting grooves, which allowed the cutting to be more flexible when a larger or smaller lesion area was found during the operation.
Design of the cutting fixtures and registered fixtures. (A) Fibula cutting fixture; (B) Cutting fixtures for area mandible lesions; (C) Registered fixtures for the arrangement of cut fibula pieces.
After completion of the cutting of the mandible lesion model and fibula, the pieces of the fibula need to be arranged and positioned into the space between the two cutting ends of the mandible defect. In this study, a registered fixture was designed using Boolean algebra to calculate the optimal combination of fibula pieces. The registered fixture can help to rapidly arrange the fibula pieces onto the defect area (Figure 5), satisfying the clinical needs for mandible defect reconstruction. Figure 6C shows the registered fixtures for fibula arrangements adapted for 3 pieces of lesion conditions.
The completed mandible model, fibula model, cutting fixture and registered fixture are digital models with complicated geometric characteristics. AM technology was applied to rapidly output the entities of the cutting fixture and registered fixture to meet the customized requirements for clinical application in a timely manner. The mandible cutting fixture can be used to fit onto the mandible for rapid and accurate cutting in the clinic, and the registered fixture can ensure that the cut fibula pieces are rapidly positioned and arranged, which can allow mandible reconstruction surgery to be completed in a short time.
The error values of the design files for the cutting fixture and registered fixture were verified using reverse engineering software. To ensure the accuracy of the model, the error of the digital model was controlled to within 0.1 mm. and the physical model of fixture was controlled to within 0.5 mm. The fibula entity, after being output by the AM system, was cut using the fibula cutting fixture. The cut fibula pieces were installed onto the registered fixture and then placed onto the defect area of the mandible. The results showed that this technique can achieve the target of mandible reconstruction.
After completing the design, cutting planning and registration process, the cutting jig and registered fixture were prepared by AM systems before surgery. Figure 7 shows the detailed process of cutting, registering, and mandibular reconstruction. First, the defected mandible STL model was input into the CAMRP, and the doctor decided on the location for lesion resection. Then, the CAMRP calculated the optimal length and pieces of fibula for cutting. The custom-made mandible cutting guide-jigs were generated from the neighboring surfaces of the cutting locations. Meanwhile, the number and length of fibular segments were known, and the registering fixture was ready for surgery (Figure 7A). The second step was fibula cutting according to the physical guiding fixtures. The harvested fibula bone was set and cut on the alumina alloy fixture based on the length and number of sections according to the planning of the CAMRP (Figure 7B). Third, mandibular cutting guide-jigs were snap-fitted, neighboring the lesion area, for resection according to the surgical planning (Figure 7C). Finally, the doctor placed the fibula pieces on the registering fixture at the designed position to shape the mandible (Figure 7D). If the initial resection was not long enough, the guide-jigs provided some more slots for cutting, and the new cutting location was input into the CAMRP for re-planning of the cutting of the fibular bone. The process of this study, which removes and reconstructs the mandibular lesion using fibular bone segments in one step, is easy to reproduce in clinical practice. 2ff7e9595c
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