AIP Conference Proceedings 2193, 050020 (2019); https://doi.org/10.1063/1.5139393 2193, 050020
© 2019 Author(s).
Finite element analysis of porous stemmed hip prosthesis for children
Cite as: AIP Conference Proceedings 2193, 050020 (2019); https://doi.org/10.1063/1.5139393 Published Online: 10 December 2019
Daniel Panghihutan Malau, Muhammad Satrio Utomo, Dhyah Annur, et al.
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Finite Element Analysis of Porous Stemmed Hip Prosthesis for Children
Daniel Panghihutan Malau
1, Muhammad Satrio Utomo
1, Dhyah Annur
1, Talitha Asmaria
1, Yogi Prabowo
2, Ahmad Jabir Rahyussalim
3, Sugeng Supriadi
4,a),
Muhamad Ikhlasul Amal
1,b)1Research Center for Metallurgy and Materials, Indonesian Institute of Sciences, Kawasan PUSPIPTEK, Gedung 470, Setu, South Tangerang, Banten, 15314, Indonesia
2Dr. Cipto Mangunkusumo Hospital, Jl. Pangeran Diponegoro No. 71, Kenari, Senen, RW. 5, Kenari, RW.5, Kenari, Senen, Central Jakarta, 10430, Indonesia
3Faculty of Medicine Universitas Indonesia, Jl. Salemba Raya No. 6, Central Jakarta 10430, Indonesia
4Faculty of Engineering Universitas Indonesia, Gedung Dekanat Lt. 2, Kampus UI Depok, West Java, Indonesia Corresponding author: a)[email protected]
Abstract. Femur bone stress shielding is known to be a significant factor in aseptic loosening or failure of hip replacements.
This paper considers the development of a porous stemmed hip implant for children patient in order to reduce the effects of stress shielding and also maintaining acceptably low levels of stress in other areas of prosthesis. By using finite element modeling, the stresses in the proximal femur using porous stem were calculated and analyzed. The developed model is considered safe in terms of mechanical strength. The porous region does not bring significant effect on stress distribution but produces a considerable amount of compressive strain.
Keywords: finite element analysis, hip prosthesis, porous biomaterial
INTRODUCTION
Total hip replacement has been in clinical use for over three decades. One of the most common causes of total hip replacement is femoral fracture. Femoral neck fracture in young kids and adolescents is an uncommon injury, and it happens with approximately 1% of the occurrence of femur neck fractures in elderly adults [1-3]. Femoral neck fractures in children generally occur due to high-energy events such as falls from height or motorcycle accident, whereas in older humans it is typically due to osteoporosis [2]. Besides, fractures can also occur due to low-energy trauma and routine activities such as jumping and running, even though it rarely happens [1]. The anatomy of the hip of children is different compared to adults. It is what causes the complications that occur are also various; thus, research on fractures in a child’s hip is considered a relatively crucial clinical entity [4]. The number of total hip replacement operations increases every year, especially those that occur in young patients, who are relatively more active resulting in more loading than the elderly, this also causes the prosthesis to be more easily damaged [5, 6].
Other common causes of total hip replacement are bone diseases. In older patients, the indication for total hip replacement is mostly based on the diagnosis of a primary coxarthrosis. In young patients, on the other hand, various underlying diseases lead to the indication. Another critical factor is the increased physical activity (sports, occupation, sexuality) with high postoperative expectancy, the often-incomplete body growth, the lower body weight, the increased range of motion, the lower preoperative comorbidity, the different bone quality especially in bone density and the altered bone structure under a drug therapy or inactivity in systemic diseases [7]. The most common medical
conditions that lead to the artificial replacement of the hip joint in children and young adults are juvenile polyarthritis and other rheumatic diseases, septic arthritis, acetabular dysplasia of the hip, primary or secondary femoral head necrosis, tumor diseases, and various systemic diseases [7].
To achieve success in arthroplasty, the main things to consider are the implant design, material properties, and appropriate surgical techniques [8]. The previous study showed that accurate prosthesis size was essential to allow joint stability while supporting a human's body weight and motion [9]. More studies have attempted to create stems made of various materials and designs including composite materials [10, 11]. To minimize clinical failures of a prosthesis and numerically analyze the design, finite element analysis (FEA) will be used as it is the most widely used tool to get performance data of new prosthesis designs [12-16].
This study aimed to develop a patient-specific model of porous proximal femur prosthesis for a young child by investigating numerically the performance of the stem using a finite element method, in accordance to Indonesian children anthropometry. The advanced custom femoral component design will have some advantages compared with a conventional hip stem. (i) Optimal strength-to-weight ratio based on patient's condition will bring less postoperative care and reduce the risk of implant failure. (ii) Optimal stress distribution of prosthesis can potentially minimize wear on the opposing contacting surface and the risk of early loosening. With this new prosthesis design, the patients are expected to have an excellent long-term outcome, not only that but they can back to their healthy day-to-day activities, and they can have a good quality of life.
MATERIALS AND METHODS
The basic form of a hip joint implant model is taken from the form of commercial implants on the market. The dimensions used are implant dimensions that correspond to 10-year-old children. Dimensional data were obtained from several studies that discussed the development of femur and hip joints at the age of 5 to 15 years [17, 18]. The femoral bone morphometry data used are femoral neck length (FNL), femoral neck-shaft angle (FNSA) and medial offset (MO). The porous portion is made in the middle area of the hip stem, with a transverse pore direction as shown in Figure 1 and pore size of 800 µm with a pore distance of 1600 µm [19].
The first step is 3D modeling according to the morphometry of the femur obtained from the literature. Bone morphometry factors used are FNL, FNSA, and MO because of these three factors that have a significant role in the strength of the femur [20]. The 3D model is then stored in the STP or IGS file and then processed at a later stage. The next step is to import 3D model files into the finite element analysis software. The meshing process will be carried out automatically in the finite element analysis software. The selection of mesh dimensions in finite element analysis is done by mesh convergence process.
In this initial study, the assumption of the weight of the patients used was 30 kg. The load amount used in modeling is physical load on walking conditions such as walking slowly on a flat surface, climbing stairs, going downstairs, and extreme conditions such as falling. Calculation of the load that occurs in the hip joint was obtained from a study conducted by Bergmann et al in 2001 with patients who weighed 88 kg or 860 N [21]. Assuming that the load received by the hip joint is proportional to body weight, the maximum static load that will be used for finite element analysis in this study can be seen in Table 1. An analytical method on linear elastic material will be used to find out the maximum Von Mises stress that occurs in the implant model.
TABLE 1. Maximum load on hip joint in specific walking conditions.
Activity Maximum load
(% of body weight) Maximum force in hip joint (N)
Slow walking on flat surface 282 830
Climbing upstairs 356 1048
Climbing downstairs 387 1139
Tripping 720 2119
Several specific boundary conditions were used for numerical analysis in this study, including making the lower surface of the stem to be a fixed constraint, and loading is carried out on the surface of the femoral head with the direction of earth's gravitational force. The hip stem and femoral head are modeled as one unit. The material used in this modeling is Ti-6Al-4V metal alloy with specific mechanical properties, as shown in Table 2.
TABLE 2. Mechanical Properties of Ti-6Al-4V.
Parameters Minimum Value Maximum Value
Density (kg/m3) 4429 4512
Tensile strength (MPa) 900 950
Yield strength (MPa) 880 920
Elastic modulus (GPa) 104 113
Shear modulus (GPa) 40 45
Poisson's ratio 0.31 0.37
RESULTS AND DISCUSSION
Figure 1 shows the porous hip implant design. The design was based on a commercial product and modified to achieve a suitable dimension to young kids patient. Previous study shows that hip stem neck would be the most critical part, but since this study involves a porous region, then it will be the most crucial area. Stress analysis was performed using static loads for four different walking conditions.
FIGURE 1. 3D model of hip stem and femoral head as an assembly.
Meshing was performed automatically using a specific mesh size range and built by linear geometry shape. Figure 2a shows the meshing result that will be used in this study. Figure 2b shows the boundary conditions used in this study. Fixed constraints are located in the bottom part of hip stem. The distributed boundary load will be placed on top of the femoral head surface.
(a) (b)
FIGURE 2. (a) Finite element discretization of hip stem and femoral head; (b) Boundary load conditions on the outer surface of the femoral head and the bottom surfaces of hip stem as fixed constraints.
Figure 3a shows the von Mises stress distribution as the result of the computation process. Red to green colors represents stress values from low to high, respectively. Stresses were calculated to estimate the probability of failure of an implant under the effect of the maximum load that can happen during walking; in this case, it is tripping or
falling. Figure 3b shows the strain results from finite element analysis. The highest tensile strain area is located at the farthest point from the center of the load force distribution, while the most top compressive strain is situated in one of the pore holes which has the closest distance to the center of the load force.
(a) (b)
FIGURE 3. Finite element analysis result; (a) Stress distribution; (b) Strain distribution.
Results of the numerical analysis of the developed model for four different walking conditions are shown in Table 3. As expected before, the stress distribution on the prosthesis did not occur evenly. The highest stress occurred at the back side of the hip stem. This region experienced tensile stress until it reaches a maximum value of 433 MPa. It represents the location of critical tensile stress concentration. This stress occurred in maximum static loads for tripping conditions. Meanwhile, the pore section does not experience high tension, including both tensile and compressive.
Calculated von Mises stress, as shown in Table 3, are significantly lower than the yield stress value of Ti-6Al-4V metal alloy, which is 880 MPa. Therefore, this design can be considered safe in terms of mechanical strength.
TABLE 3. Numerical analysis results of developed model.
Activity Maximum von Mises stress (MPa)
Slow walking on flat surface 165
Climbing upstairs 198
Climbing downstairs 233
Tripping 433
CONCLUSION
Design and numerical analysis of porous hip prosthesis for children have been conducted. The basic shape was based on a commercial product to achieve the best-fitted implant for the patient’s body. By using static load to the model, finite element analysis results showed uneven von Mises stress and strain distribution. The critical concentration of stresses was located at the back of the hip stem even though the stress value were a lot lower than the yield stress of Ti-6Al-4V alloy. The porous area does not have a significant effect on the stress distribution but produces a considerable compressive strain.
ACKNOWLEDGMENTS
Authors would like to thank the Indonesian National Development Planning Agency for funding the research activity.
REFERENCES
1. T. Palocaren, Indian Journal of Orthopaedics 52 (5), 501-506 (2018).
2. S. T. Canale, Current Orthopaedics 14 (2), 108–113 (2000).
3. W. Pförringer, B. Rosemeyer, Acta Orthopaedica Scandinavica 51 (1), 91-108 (1980).
4. K. Bali, P. Sudesh, S. Patel, V. Kumar, U. Saini, M. S. Dhillon, Clinics in Orthopedic Surgery 3 (4), 302-308 (2011).
5. S. Gross, E. W. Abel, Journal of Biomechanics 34 (8), 995-1003 (2001).
6. C. Caouette, L. H. Yahia, M. N. Bureau, Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine 225 (9), 907-919 (2011).
7. M. Jäger, S. Endres, A. Wilke, Zeitschrift fur Orthopadie und ihre Grenzgebiete 142 (2), 194-212 (2004).
8. D. P. Malau, Y. Whulanza, D. Annur, Y. Prabowo, M. S. Utomo, M. I. Amal, AIP Conference Proceedings 2088 (1), 040004 (2019).
9. R. Magetsari, Suyitno, R. Dharmastiti, U. A. Salim, L. Hidayat, T. Yudiman, Z. A. Lanodiyu, P. Dewo, International Journal of Morphology 33 (4), 1255-1260 (2015).
10. R. De Santis, L. Ambrosio, L. Nicolais, Journal of Inorganic Biochemistry 79 (1-4), 97-102 (2000).
11. S. Srinivasan, J. R. de Andrade, S. B. Biggers Jr, R. A. Latour Jr, Biomaterials 21 (19), 1929-1940 (2000).
12. H. Yildiz, S. K. Ha, F. K. Chang, Journal of Biomedical Materials Research 39 (1), 92-101 (1998).
13. M. Taylor, K. E. Tanner, M. A. R. Freeman, A. L. Yettram, Medical Engineering & Physics 17 (7), 544-550 (1995).
14. C. L. Tai, C. H. Shih, W. P. Chen, S. S. Lee, Y. L. Liu, P. H. Hsieh, W. J. Chen, Clinical Biomechanics 18 (6), S53–S58 (2003).
15. J. Stolk, N. Verdonschot, L. Cristofolini, A. Toni, R. Huiskes, Journal of Biomechanics 35 (4), 499-510 (2002).
16. R. Sakai, M. Itoman, K. Mabuchi, Clinical Biomechanics 21 (8), 826-833 (2006).
17. L. Billing, Acta Radiologica 51 (sup174), 7-26 (1959).
18. T. Mészáros, L. Kéry, Acta Orthopaedica Scandinavica, 51:1-6, 275-283 51 (1-6), 275-283 (1980).
19. S. Arabnejad, R. B. Johnston, J. A. Pura, B. Singh, M. Tanzer, D. Pasini, Acta Biomaterialia 30 (1), 345-356 (2016).
20. P. Dewo, M. Nasrulloh, Z. Lanodiyu, R. Magetsari, Jacobs Journal of Orthopedics and Rheumatology 1 (2), 009 (2015).
21. G. Bergmann, G. Deuretzbacher, M. Heller, F. Graichen, A. Rohlmann, J. Strauss, G. N. Duda, Journal of Biomechanics 34 (7), 859-871 (2001).
