Impact of Hip Arthroplasty Stiffness on the Biocompatibility

Background. Maintaining bone health after arthroplasty placement is of paramount importance. Different materials used in artificial joint manufacturing are available in the market. Some had remarkable success rates. Ceramics are a group of biomaterials that have to gain special attention as bearing surfaces. Many surgeons and biomechanics researchers attribute their successes to their tribologic features. These are indirect effects. Methods. We had used state of art tool, FEA and linear analysis, to explore another direct impact of these materials on bone remodelling. Strain energy density was used as an objective criterion to evaluate the better model. The Hip model was provided by the local hospital CT-scan database. The comparison was based on the distribution of the strain energy within the model. Results. Due to their high stiffness (high Young modulus) and their resistance to deformation (low poison ratio), they have a more important direct effect on the bone. Nevertheless, their implantation should be considered as part of the total stiffness. The pattern of the strain energy density is better when a judicious choice of ceramic is done. Conclusions. Biocompatibility is a design-dependent subject. Injodious material combination could result in poor performance of the arthroplasty which is reflected upon patient health and welfare. We concluded that in the careful application of ceramics survivability of the arthroplasty could be enhanced. Keyword: Arthroplasty, Biocompatibility, Ceramics, FEA, Stiffness Introduction The hip joint plays a significant rule in the patient daily activity(1). This joint could need replacement in certain situations (2). Loading is an integral part of tissue maintenance(3). The International Journal of Medical Science and Health Research Vol. 5, No. 02; 2021 ISSN: 2581-3366 www.ijmshr. com Page 57 loading had complex considerations that should be clear to understand the complication that results from any conditions that are deviated from that normal loading conditions (4) Sound knowledge provides a sound basis to treat the diseased part and to explain morbidities associated with the current treatment to avoid them in the future What is well known in orthopaedic surgery are Mechanical loads provide physiologic stimulation to the bone. Without such load, disuse atrophy will ensue (5) Stress shielding is resulting in more rigid hardware and stiffer assemblies (6) These two rules could be a keystone in expanding our understanding of hard tissue replacements. We aim to build a model that if give a result close to the reality it could be used to synthesize information regarding other models or anticipating what could happen with a supposed model(7). This could be denoted as a parametric approach(8). We had chosen the hip model as it has had features that demonstrate the concepts we try to reveal as well as it is one of the most replaced joints(9) As biocompatibility is design-dependent, we want to explore the effect of different material combinations on the bone(10) so that we can draw a suggestion about the possible best configuration that could affect the patients` health and to compare numerically different arthroplasties models that are different from each other by the combination of the used materials. Materials and methods We used the COMSOL Multiphysics® software to perform the modelling (11) The model was provided from the local hospital CT-scan database after anonymization of the data. The material properties were provided from MATWEB which is a searchable online database of engineering materials(12), but we had done rounding of the modulus of elasticity of the material to make these values more perceptible Material Ɛ (GPa) Poisson`s ratio PMMA 3 0.3 Ceramic 300 0.22 UHMWPE 1 0.46 6Al4V 100 0.3 Stellite 200 . 03 Cartilage 0.1 1.5 Table 1 Mechanical properties of the used materials International Journal of Medical Science and Health Research Vol. 5, No. 02; 2021 ISSN: 2581-3366 www.ijmshr. com Page 58 The alumina had a higher value than what we had supposed. This was calculated for zirconia-grade ceramic. So alumina even had greater stiffness The ageing of zirconia should be calculated with its thermal conductivity Figure 1 A The model was supposed to be well united and fixed from the base. B, the upper 2 surfaces of the holder had been displaced along the Z-axis by 1mm. C, the femur dimensions. D, dimensions of the arthroplasty. The upper holder is a cube with 0.1m*0.1m*0.1m dimensions. The lower base had the double dimensions of the upper holder The dimensions here were assumed theoretical, as our goal is to reveal the strain energy density pattern, rather than the seeking for the highest and lowest value. The finite models are meshdependent and we suppose them as soli monolithic in a linear fashion. The mesh was generated to be fine with 35849 total elements and 7165 total vertices. The material supposed to be linear with an isotropic constitution and the loading condition was static. The arthroplasty model was composed of the stem head and ace tabular component. Perfect osseointegration was assumed and the tolerances between ball and socket were zero with weld. These conditions had been analyzed: The normal hip model with the presence of highly resilient material that is mimicking the cartilage layer between the femoral head and the acetabular bed Low to high gradient model where: International Journal of Medical Science and Health Research Vol. 5, No. 02; 2021 ISSN: 2581-3366 www.ijmshr. com Page 59 o the acetabular component was assumed to be from UHMWPE o The ball was made from 6Al4V o The stem was made from ceramic High to low gradient model where: o the acetabular component was assumed to be from ceramic o The ball was made from 6Al4V o The stem was made from UHMWPE Intermediate gradient model where: o the acetabular component was assumed to be from ceramic o The ball was made from Stellite o The stem was made from 6Al4V The model where all the arthroplasty was made from UHMWPE The model where all the arthroplasty was made from 6Al4V The model where all the arthroplasty was made from Stellite COC model with 6Al4v stem MOM model with 6Al4v stem MOP model with 6Al4v stem Figure 2 A normal hip model. B model with arthroplasty International Journal of Medical Science and Health Research Vol. 5, No. 02; 2021 ISSN: 2581-3366 www.ijmshr. com Page 60 The strain energy criteria were post-processed to indicate the relevant bone response possible with our loading condition. Strain energy density had gain acceptance in the biomechanics community as a predictive tool for adaptive bone remodelling (13). Our evaluation was done for one aspect, which is the anterior aspect of the femoral bone. In all models, the legend was uniform to facilitate comparison and when we manipulate the colour-related value we had pointed for that. Results and discussion The results are clearly showing the distribution of the strain energy density. And as we are mostly want to reveal these regions the evaluation was qualitative and in the next papers, we could do a more statistical qualitative assessment.