AIP Conference Proceedings 2344, 050021 (2021); https://doi.org/10.1063/5.0047182 2344, 050021
© 2021 Author(s).
Design, development, and finite
element study on the novel biomimetic lumbosacroiliac prosthesis
Cite as: AIP Conference Proceedings 2344, 050021 (2021); https://doi.org/10.1063/5.0047182 Published Online: 23 March 2021
Sugeng Supriadi, Paskal Rachman, Agung Shamsuddin Saragih, Yudan Whulanza, Ahmad Jabir Rahyussalim, and Arsanto Triwidodo
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Design, Development, and Finite Element Study on the Novel Biomimetic Lumbosacroiliac Prosthesis
Sugeng Supriadi
1,2,a), Paskal Rachman
1,2,b), Agung Shamsuddin Saragih
1,2,c), Yudan Whulanza
1,2,d), Ahmad Jabir Rahyussalim
3,e), Arsanto Triwidodo
3,f)1Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, West Java 16424 Indonesia
2Research Center for Biomedical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, West Java 16424 Indonesia
3Department of Orthopaedics and Traumatology, Faculty of Medicine, Universitas Indonesia, Cipto Mangunkusumo General Hospital, Jakarta 10320, Indonesia
DCorresponding author:[email protected]
b)[email protected], c)[email protected], d)[email protected], e)[email protected], f)[email protected]
Abstract. This study focused on the design of specific prostheses in the case of patients affected by Chordoma of the lumbar 4, lumbar 5, sacrum, and coccyx. A chordoma is a group of malignant and rare cancers, commonly found in the spine or skull bones. As a treatment method, if cancer has not spread beyond the bone, the infected bone's removal procedure is replaced with an artificial bone (prosthesis). The design method is carried out using a CT Scan of patient data, which is processed into a 3D model with Materialise Mimics software, 3D model engineering is done using Solidworks software and finite element analysis with ANSYS. The design process is carried out with several kinds of design variations, including the bone-implant model with a solid and shell model which is divided into several components, the use of iliac screw lateral connector, modification of iliac screw locking head, and modification of iliac screw locking head with cross connector. From the results of the calculation analysis and simulation, the best concept chosen based on the lowest dominant Peak von Mises Stress value in the iliac screw section is designs using the Iliac Screw Locking Head with Shell Model Lattice Structure.
Keywords: prosthesis, lumbar, sacrum, Chordoma, pedicle screw, pull out, 3d bone modeling, simulation
INTRODUCTION
There is a type of cancer that attacks the bone called Chordoma, which is a malignant and rare cancer, commonly found in the spine or skull bone [1]. Surgical treatment methods are needed if cancer has not spread beyond the bone by removing the infected bone [2]. With the latest technology, it is possible to replace removed bone with an artificial bone (prosthesis) [2]. It is necessary to reconstruct the pelvis and spinal column with a special prosthesis design that mimics specific patients' anatomy. This particular design can reduce the risk of infection, the possibility of dislocation, or failure of an implant [3].
The human spinal column is anatomically composed of vertebrae, intervertebral discs, muscles, ligaments and nervous systems. The vertebrae consist of 7 cervical segments (C1-C7), 12 thoracic segments (T1-T12), 5 lumbar segments (L1-L5), 5 sacral joints (S1-S5), and 4 coccygeal.
There is a method to stabilize the spine; the method is called the pedicle screw instrumentation system, which is one of the posterior fixation techniques [4]. Pedicle screw testing has been standardized with ASTM F543 to test the pullout screw, torque insertion, and torsional strength of metallic bone screw. Based on some literature, the size of
titanium pedicle screws for the thoracic spine and lumbar spines ranging from 5.5 to 6 mm in diameter with a length ranging from 35-50 mm [5].
Several techniques in the spinopelvic fixation process, which are commonly used, are the Iliac Screw Technique, S2 Alar Iliac Screw, and the Galveston Technique [6]. The development of iliac screws has provided a markedly easier way for spinopelvic instrumentation than the classical Galveston technique [6]. The method of placing the Iliac Screw is by inserting it from the Posterior Superior Iliac Spine (PSIS), which is directed to the Anterior Inferior Iliac Spine (AIIS) [7]. Iliac screws with a diameter of 6.5 mm are suitable for most patients; 7.5 mm or 8.5 mm is still within tolerance [8]. The screw's length is based on an agreement using the iliac screw technique ranging from 70 mm to 90 mm [7].
The most widely used material for pelvic reconstruction prosthesis is titanium alloy [3]. The material used in the intervertebral prosthesis is UHMWPE. The manufacturing process for special implants with complex geometries that produce accurate products best suited are using 3D printing or can be called additive manufacturing (AM) or conventional methods for complex models such as Casting. This research aims to design and produce a special prosthesis design as a substitute for lumbar 4, lumbar 5, sacrum, and iliac bones affected by Chordoma with the shape and features resembling real bones (biomimetic), which can be called Lumbosacroiliac prosthesis.
METHODS Design Concept
The main components consist of the lumbar implant, sacrum, pelvis, and intervertebral disc. Initial data processing was performed with diagnostic imaging in the form of DICOM from CT Scan. Then the selection of bone for 3d modeling is done with Materialise Mimics software with thresholding HU (Hounsfield unit) feature, and then 3D rendering will appear on the screen. The 3D model processing is performed on the Materialise 3-Matic software. In this study, exporting to IGES file format was done for the next step designing on the Solidworks software. 3D bone models obtained for this study are Lumbar, Sacrum, and Pelvis. Another 3D Modeling for standard components and anchor components is done by the reverse engineering method from the existing product. These components are iliac screws, pedicle screws, rods, set screws, and bolts.
Some design concepts added as special features for this design are concepts to reduce implant mass with a solid design (Figure 1a) or shell design (Figure 1b). A shell design consists of a shell model without a lattice (porous) design and a shell model with lattice design. This design concept is intended so that the prosthesis has a light mass close to bone mass.
D(b)
FIGURE 1. Mass Reduction Design Concepts. (a) the solid lumbar body is cut in half, (b) the lumbar shell body is cut in half
The second concept is modeling implants by designing component segments with 2 or 3 parts per segment. This is intended to facilitate the implantation process by the operator (medical doctor).
(a) (b)
FIGURE 2. (a) Lumbar is cut into 2 components, (b) Lumbar is cut into 3 components
The third concept is the type of fixation for easy implantation, faster and better performance using iliac screw techniques with locking heads, the use of pedicle screws with polyaxial or monoaxial, and the use of rod systems with cross connectors or without cross connectors. Some of these components need to be chosen to get the best prosthesis design among the variations of fixation types mentioned. The selection process is using analysis from obtained result simulation data.
(a) (b)
(c) (d)
FIGURE 3. (a) Modified iliac screw with locking head, (b) Iliac screw with lateral connector, (c) Rod system with cross connector, (d) Rod system without cross connector
Set-Up Finite Element Analysis
The software used in this finite element analysis is ANSYS Workbench and Solidworks Simulation. The material used in this study consists of 3 types of materials, as shown in Table 1.
TABLE 1. Material Properties
Part Material Yield
Strength (MPa)
Young’s Modulus (MPa)
Poisson’s
Ratio Density
(g/mm3) Reference
Bone Cancellous Bone - 150 0.2 0.0008 [10]
Intervertebral Disc
Implant UHMWPE - 227 0.42 0.00095 [11]
Implant Ti-6Al-4V grade 23 795 110000 0.3 0.00443 [12]
The assumptions used in this simulation are:
1. Contact of the Titanium implant model with UHMWPE has a coefficient of friction of 0.2 [13]
2. The contact screw is considered bonded to compensate for the absence of the initial tightening force [10]
3. Contact between the ilium bone and the sacrum implant is assumed to be without friction; as compensation, the iliac screw in contact with the ilium bone and sacrum implant is considered bonded.
In this simulation process, simplification is carried out on the screw and bolt model parts without thread. If the model used uses threads, this could give uncertainty to the analysis results [10].
FIGURE 4. Loading Modes
In this research, the finite element study process is given 5 types of loading modes on Lumbar L3. Compression (A), Flexion (A + B), Extension (A + B), Rotation (A + C) and Lateral (A + D). With A as a compressive force of 450 N [14]. B, C, and D in the form of a moment of 10 Nm [15]. And E as fixed support applied to the acetabulum.
RESULTS Design Result
FIGURE 5. Exploded View Total Assembly
1. Lumbar part 2. Sacrum part
3. Intervertebral Disc Part 4. Pedicle Screw
5. Iliac Screw 6. Rod 7. Set Screw 8. Bolt
This main design has 8 components (Figure 5). It consists Lumbar part (L4 and L5 segment), the Sacrum part, Intervertebral Disc part (L4 and L5 segment). Pedicle screw (4 pieces), Iliac screw (4 pieces), Rod (2 pieces), Set screw, and Bolt. According to the design concept that already mentioned, 3 design variations have been developed.
These variations design is the Model with Iliac Screw Locking Head (LH) (Figure 6a), Model with Iliac screw locking head + cross connector (LHC) (Figure 6b), and Model with iliac screw + lateral connector (LC) (Figure 6c).
(a)
(b) (c)
FIGURE 6. Developed design variations. (a) Models with Iliac Screw Locking Heads (LH), (b) Models with Iliac Screw locking heads + cross connectors (LHC), (c) Models with iliac screws + lateral connectors (LC) Based on literature searches and subjective views of the authors, variations of these 3 designs can be compared for each of the advantages and disadvantages, shown in Table 2.
TABLE 2. Comparison of 3 Variations in Iliac Screw System Design
Advantages Disadvantages
LC Design x More rigid
x Easy to find the position of screw insertion
x The position of screw insertion is in the iliac crest, causing bulge of the screw head
x Need more components to compare to LH design LH Design x No head screw protrusion
x Fewer components used
x The accuracy of its use has not been confirmed x Only as a fastener for implantation systems with
other implants (paired with other implants) LHC Design x Increase rigidity x Need more components to compare to LH Design
x It needs cutting in the spinous process and or transverse process in the lumbar
Convergence and Mesh Size for Finite Element
The type of mesh used is Automatic mesh with the applied mesh size is 5 mm, 4 mm, and 3 mm.
TABLE 3. Results of mesh size and convergence Mesh Size Number of Elements Number of Nodes Max von misses
Screw (MPa) Percent of Change (%)
5 mm 181186 311504 213.4724931 0
4 mm 274981 453930 173.6994219 18.63147361
3 mm 522888 815485 169.8239422 2.231141369
The verification in this simulation process uses a comparison between the results of stress simulation with mathematical calculations taking into account the position of loading and the point of fixed support. The set-up based on the load distribution is reviewed on one half because it is in the middle of the load distribution divided by 2. The calculation results are 165.37 MPa, while the Finite element simulation results are 169.82 MPa. In this case, both have
Assembly Simulation Analysis
First of all, the analysis focuses on the results of peak von mises stress (PVMS) values for each design variation.
This is done with the consideration that PVMS has the most significant role in safety failure. In terms of safety, if the stress does not reach Yield Strength, it means that the implant does not deform and still in a good and safe condition.
TABLE 4. PVMS from several design variations
Design Type PVMS (MPa)
Axial Flexion Rotation Lateral Extension
LC Design 169.82 211.39 167.4 195.84 126.69
LH Design 162.37 259.8 307.03 165.67 360.99
LHC Design 166.34 244.26 331.85 187.09 145.32
The green color mark means the lowest stress among 3 types of design, the yellow mark is middle stress, and the highest stress is in red mark. In this case, iliac with lateral connector (LC) has the advantage that in some loading modes has the lowest 3 PVMS stress, among others. But LC has the highest stress in axial and lateral loading.
TABLE 5. PVMS location
Design Type PVMS Location
Axial Flexion Rotation Lateral Extension
LC Design Iliac Screw Iliac Screw Pedicle Screw L4 Iliac Screw Iliac Screw LH Design Pedicle Screw L5 Rod L Pedicle Screw L5 Pedicle Screw L5 Rod L LHC Design Pedicle Screw L5 Pedicle S1 Pedicle Screw L5 Pedicle S1 Pedicle Screw L3 From the result data, every design type has the highest and lowest PVMS in one or more of loading mode. So, the best design cannot be chosen yet. Further analysis needs to be done, especially on the iliac screw, which is the main component of this fixation system. The iliac screw system that we used is a dual iliac screw. It means that it has 2 iliac screws on the Right side (lower and upper R) and 2 iliac screws in the Left side (lower and upper L).
TABLE 6. Iliac screw PVMS from several design variations
Loading Mode Screw Position LC Design LH Design LHC Design
Axial (MPa)
Lower Screw R 104.58 124.82 126.28
Upper Screw R 169.82 92.74 93.409
Lower Screw L 119.51 126.57 127.91
Upper Screw L 136.18 95.316 97.233
Flexion (MPa)
Lower Screw R 129.83 157.92 159.01
Upper Screw R 211.39 120.45 120.52
Lower Screw L 146.91 161.03 162.59
Upper Screw L 180.11 125.3 127.27
Rotation (MPa)
Lower Screw R 83.719 106.65 107.59
Upper Screw R 150.28 86.74 87.071
Lower Screw L 141.04 145.9 147.89
Upper Screw L 139.96 101.78 104.01
Lateral (MPa)
Lower Screw R 119.31 145.26 146.63
Upper Screw R 195.84 104.45 105.12
Lower Screw L 100.11 107.9 109.56
Upper Screw L 120.4 83.94 85.769
Extension (MPa)
Lower Screw R 77.56 90.578 92.403
Upper Screw R 126.69 64.297 65.32
Lower Screw L 91.08 91.293 93.19
Upper Screw L 91.611 64.03 65.965
It can be seen that the PVMS in the iliac screw locking head (LH) system has the most of the lowest (most green and yellow mark) PVMS value than other types of designs. So, the LH system can be concluded safer than another design concept.
Simulation Analysis per Component
TABLE 7. Comparison of Stress on Shell models and Shell lattice models Part Stress Shell Model Stress
(MPa) Stress Shell Lattice Model Stress (MPa)
L4 172.54 520.32
L5 186.54 220.99
Sacrum 116.2 171.2
Based on the results of finite element analysis, it can be seen that the stress value increases when the lattice model feature is added. But this is still below the yield strength of the material, which is 795 MPa, so it is said that the lattice's design is still safe with a lighter excess mass compared to without the lattice model.
Selection of Design Variations
Based on this result, the best concept is the iliac screw locking head (LH) system that has the lowest PVMS value.
The concept of mass reduction in implants Shell model lattice structure has the lowest mass but the highest stress, among other concepts, but this is still below the yield strength of the material used.
DISCUSSION
It is necessary to further develop the design by considering each component's modularity with several standardized sizes. Manufacturing processes with complex anatomy such as bones, need to be further analyzed. One of the choices is the manufacturing process with conventional manufacturing, such as investment casting or advanced manufacturing such as Metal FDM, Powder Metallurgy, etc. The process of verifying and validating implants' production needs to pay attention to the standard of medical devices so that the implants can be applied to patients.
CONCLUSION
Based on the results from this study, it can be concluded that the best concept is the iliac screw locking head with lattice structure model implant shell. An implant that mimics bone anatomy with a mass close to bone mass can be achieved with this design. Implants that have been designed can meet biomechanical performance. The need for doctors to make a variety of standardized sizes cannot be done because the design of CT scans obtained only one size.
So, the design process in this study can be used as a design basis for further research.
ACKNOWLEDGMENT
The authors would like to thank to Universitas Indonesia for funding this research under Publikasi Terindeks Internasional (PUTI) Saintekes Nomor: NKB-2486/UN2.RST/HKP.05.00/2020
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