Eko Saputra

Numerical Study of Salat Movements for Total Hip Replacement Patient

Salat as a daily Muslim activitiy in praying contains several movements which are not suggested by orthopaedic doctor to be conducted by patient with total hip replacement (THR). Sujud and sitting are two movements in Salat which is recommended to be done above the chair for THR patients. There are lacks of scientific discussions about the consequences of the normal salat movement for Muslim THR patients. This paper observes the effect of these movements to the artificial hip joint in THR patient body. A three-dimensional finite element simulation is used to investigate the resisting moment, the contact pressure and the von Mises stress. An artificial hip joint model proposed by previous researcher is used in the simulations. The results show that sujud induces the impingement and plastic deformation whereas sitting is relatively safe to be conducted by THR patients. Some suggestions are also discussed with respect to the design of new artificial hip joint model which allows THR patients to conduct Salat in a normal way. The reduction of inset at the liner, the new profile at circumferential edge inner liner and the increase in the femoral head diameter can be considered as a guideline for new design of the artificial hip joint for Muslim.

The Effect of Repeated Impingement on UHMWPE Material in Artificial Hip Joint during Salat Activities

In Indonesia, a country with largest Muslim population in the world, the necessity to study the artificial hip joint which allows Muslim patients with total hip replacement to have normal Salat becomes important issues. This paper discusses the effect of impingement which occurs during one of the Salat movements. i.e. last tashahhud sitting motion. An artificial hip joint model, proposed by previous researcher from developed country, is simulated using finite element analysis to perform last tashahhud sitting motion. The result shows that impingement occurs and causes the plastic deformations and plastic strains in the acetabular liner component which is manufactured from UHMWPE material. The repetition of Salat movement induces repeated impingements and higher plastic deformation. It experiences dimensional change in the liner lip and has a potency to cause clinical failure of total hip replacement. A new design of the artificial hip joint is required to be proposed to avoid the repeated impingement and deformations.

Modeling of Repeated Rolling Contact on Rough Surface: Surface Topographical Change

An finite element analysis (FEA) of a repeated rolling contact over an elastic-plastic deforming rough surface is performed. The surface topographical change is calculated to determine the running-in phase to the steady-state rolling contact situation. A rigid hemisphere is repeatedly rolled over a rough flat aluminum surface and the effect of the contact load and the number of overrollings is studied. It is found that the change in surface topography due to the repeated rolling contact results in smoothening of the rough surface due to the flattening of the highest asperities. The result shows that the running-in of the repeated rolling contact takes place within the first few overrollings.

Finite element study of contact pressure distribution on inner and outer liner in the bipolar hip prosthesis

Wear in the hip prosthesis due to sliding contact as a product of human activity is a phenomenon which cannot be avoided. In general, there are two modelof hip prostheses which are widely used in total hip replacement, i.e. unipolar and bipolar models. Wear in the bipolar model is more complex than the unipolar model due to its contact motion. The bipolar model has two contact mechanisms while the unipolar model has only one contact mechanism. It means that the bipolar model has two wear positions, i.e. wear on inner and outer liner surface. Fortunately, wear phenomena in the hip prosthesis can be predicted by analytical or numerical method. Wear on the inner and outer liner surface in the bipolar model itself can be early predicted by contact pressure distribution that is obtained from contact mechanic analysis.The contact pressure distribution itself is an essential variable in wear equations. This paper is aimed to studythe difference of the contact pressure distribution on the inner and outer liner surface in the bipolar model. To obtain the contact pressure distribution at each surface, contact mechanic analysis on the inner and outer liner surface by analytical and numerical method were performed. Results showedthat there was significant difference of the contact pressure distribution on the inner and outer liner surface in the bipolar model. Therefore, it is expected that there is significant wear difference on the inner and outer liner in the bipolar model.

Study of unipolar and bipolar hip prostheses using finite element simulation: Contact stress analysis

One of phenomena which cannot be avoided in the hip prosthesis due to sliding contact as a product of human activity is wear on the surface of contact interaction Wear in the bipolar model is more complicated than the unipolar model. There are two contact interaction in the bipolar model, while the unipolar model has only one contact interaction. Wear on the liner and cup surfaces of the bipolar model itself can be early estimated by investigation the contact stresses due to their contact interactions. The contact stress on the liner surface of unipolar model can be estimated using analytical method. However, the estimation of contact stress on the liner and cup surface of the bipolar model using analytical method still need to consider. The aiming of this paper is to study the contact stresses on the liner and cup surfaces in the bipolar model of hip prosthesis using the finite element simulation. There are three model of hip prostheses which are simulated in this research, i.e. the unipolar, bipolar and big head unipolar models. The result showed that the maximum contact stress on the liner surface of bipolar model is higher than the unipolar model. The maximum contact stress on the cup surface of the bipolar model is lower than the big head unipolar model. Based on this results, it can be concluded that the contact stress on the liner and cup surfaces of the bipolar model cannot be estimated using analytical method.

Study the effect of wear rate on impingement failure of an acetabular liner surface based on finite element analysis

In this study, correlation of wear inside of an acetabular liner surface (ALS) and damage on an acetabular liner rim (ALR) due to impingement effect are investigated. The analysis included evaluation of the macrostructure of the damage based on visual investigation and computer simulation analysis. A commercial finite element method ABAQUS software package is used to simulate local impingement on the ALR due to wear depth variations (wear rates) inside the ALS. Here, the wear depth is based on the data of wear experiment from literature. The von Mises stress and contact deformation on the ALR at impingement is presented. In addition, the initial impingement angle is also presented to show the correlation between the wear inside of the ALS and the angle of impingement occurrence. The results show that the existence of wear inside of the ALS can increase the damage of the ALR due to impingement effect.

Finite Element Study of the Effect of UHMWPE Liner Thickness on the Contact Area and Stress Distribution in a Bipolar Hip Joint

Contact area and stress distribution of the polyethylene liner (PE liner) have a major influence on the wear process. The main factor that affects the contact area and stress on the PE liner is thickness. The International Standards Organization (ISO) recommends a minimum PE liner thickness of 6 mm. However, the thickness of PE liner in a bipolar hip prosthesis has a limited range of motion compared to the unipolar one due to the addition of the outer liner component. Therefore, the study of the effect of PE liner thickness on the contact area and stress distribution in the bipolar model is interesting. Theaim of this research is to investigate the effect of the PE liner thickness to the contact area and stress distribution on the surface of contact between head and PE liner and the contact between outer liner and cup in the bipolar model. This research was carried out by finite element analysis. The results showed that the highest contact stress on the liner occurred at the lowest liner thickness. The maximum contact radius on the liner surface took place at the highest liner thickness. The bipolar model with the liner thickness of 4.5 mm in this research provided the lowest contact stress.

Human bone marrow-derived mesenchymal cell reactions to 316L stainless steel : An in vitro study on cell viability and interleukin-6 expression

Purpose: Human bone marrow-derived mesenchymal cell (hBMC) reactions to 316L stainless steel (316L-SS) have never been evaluated. The objective of this study was to assess cell viability and interleukin-6 expression of hBMC cultures upon treatment with a 316L-SS implant. Methods: A cytotoxicity analysis was conducted with a 3-(4,5-dimethylthiazol 2-yl)-2,5-diphenyltetrazolium (MTT) assay after a period of 24, 48 and 72 hours of incubation. Expression of interleukin-6 was measured using enzyme-linked immunosorbent assay (ELISA). Results: Cell viability measurement was performed via IC50 formula. All treatment group showed a > 50 % cell viability with a range of 56,5 - 96,9 % at 24 hours, 51,8-77,3% at 48 hours and 70,1- 120 % at 72 hours. Interleukin-6 expression was downregulated subsequent to treatment with 316L-SS compared to the control group. Conclusion: We found that 316L-SS did not exhibit toxicity towards hBMC culture.

Finite element analysis of the impingement on the acetabular liner rim due to wear of the acetabular liner surface

This workstudies the impingement on the rim of acetabular liner due to wear on the surface of acetabular liner using finite element simulation. A three dimensional contact model between a femoral head and an acetabular liner was developed. There are three steps in this simulation, i.e. creating the virtualwear on the surface of acetabular liner, applying the load at the femoral head, and rotating the femoral head from neutral position till the impingement occurrence. The virtualwear is created based on the data of wear depth which was obtained from literature. Results showed that the wear on the acetabular liner surface wouldaffected the impingement occurrence, in which the impingement angle becomes narrow. In addition, the failure possibility of the acetabular liner rimwould become higher.

Fixation strength analysis of cup to bone material using finite element simulation

Fixation of acetabular cup to bone material is an important initial stability for artificial hip joint. In general, the fixation in cement less-type acetabular cup uses press-fit and screw methods. These methods can be applied alone or together. Based on literature survey, the additional screw inside of cup is effective; however, it has little effect in whole fixation. Therefore, an acetabular cup with good fixation, easy manufacture and easy installation is required. This paper is aiming at evaluating and proposing a new cup fixation design. To prove the strength of the present cup fixation design, the finite element simulation of three dimensional cup with new fixation design was performed. The present cup design was examined with twist axial and radial rotation. Results showed that the proposed cup design was better than the general version.