Muhamad Noor Harun

Wear Prediction on Total Ankle Replacement : Effect of Design Parameters

This book develops and analyses computational wear simulations of the total ankle replacement for the stance phase of gait cycle. The emphasis is put on the relevant design parameters. The book presents a model consisting of three components; tibial, bearing and talar representing their physiological functions

A Narrative Review of Morphology of Cancellous Bone at Different Human Anatomy - Methods and Parameters

Morphology of cancellous bone has been studied for years, with researchers always seeking accurate methods to assess the parameters. They also study the importance of cancellous morphology in itself. Despite the amount of previous research, there are currently no reviews on the morphology at different anatomy. This paper evaluate the methods and parameters of cancellous bone morphology at different human anatomy. From 1997 to February 2014 we found the articles published on cancellous bone morphology vary in parameters at different anatomy of human bone. Further, researchers are also interested in finding the precision methods for identifying the parameters of cancellous bone. Both in vitro and in vivo were used in finding the accurate result of cancellous bone parameters whilst also searching the importance of the morphology parameters. The morphology studies are vital due to the direct relation with the mechanical properties of cancellous bone. Based on the morphology data, it is found that the morphology parameters are dissimilar at different human anatomy sites. A variety of methods were used by researchers in identifying the morphology parameters, with each method having its own advantages and disadvantages. This review paper summarises the pros and cons of all methods available, in order to help researchers select the best methods for their future studies.

Finite Element Simulation: The Effects of Loading Modes at Different Anatomical Sites of Trabecular Bone on Morphological Indices

The relationship between morphological parameter and different type of loading orientation on elastic behavior and yielding of trabecular may provide insight towards osteoporotic bone losses during normal activities. This paper attempts to predict the elastic and failure behavior of different loading modes (tensile and compression) on anatomic sites and morphological indices through finite element (FE) simulation. Specimens extracted from bovine femoral trabecular bone were imaged using micro computed tomography (μCT). Morphological studies were done followed by FE analysis. Results demonstrated differences between yield behaviors on anatomic sites were reflected onto the morphological indices and the type of loading modes. The yield initiated earlier in rod-like than plate-like trabecular in both loading condition but showed different failure behavior in rod-like trabecular with small differences in maximum stress between tensile and compressive. However, in many cases, trabecular models tend to have oblique fracture pattern in all anatomic sites. Through these findings, improved prediction of elastic properties and yield behavior by computational means provide insight in the development of bone substitute material depending on the anatomic site as well as in osteoporotic bone pathological treatment to monitor losses in trabecular struts.

Effects of Different Angulation Placement of Mini-Implant in Orthodontic

Orthodontic is one of the treatments in dentistry field which concerned on malocclusion treatments such as improper bites, tooth irregularity and disproportionate jaw relationships. The mini-implant (OMI) is one of the components used in the orthodontic treatment, besides braces and spring. The application of OMI has been well accepted in orthodontic treatment. However, one of the main factors of OMI failures is the implant insertion procedure in which the clinician find it difficult to obtain the best angle to insert the OMI. Therefore, this study aims to evaluate stress in an OMI and bones using the finite element analysis (FEA) with variations of insertion angles and to identify their optimal angle for the implant placement. The three dimensional (3D) model of a left maxillary posterior bone section was constructed based on CT image dataset. That 3D model consists of cortical bone, cancellous bone, second premolar, first molar and second molar teeth. The 3D model of OMI was placed between root of second premolar and first molar teeth. The OMI was simulated with seven different angles of insertions: 30˚, 40˚, 50˚, 60˚, 70˚, 80˚ and 90˚. Within the seven different insertion angles, the results showed that the increase of insertion angle reduced the maximum equivalent von Mises stress in cortical bone, cancellous bone and OMI. Based on this FEA study, the optimal angle placement of OMI is when the implant positioned at vertical angle (90˚) to the bone surface.

Long-Term Contact-Coupled Wear Prediction for Total Metal-on-Metal Hip Joint Replacement

Wear debris has been recognised as constraining factor for man-made hip joints to stay long enough in the body. The major long-term failure identified for metal-on-UHMWPE is aseptic loosening. Metal-on-metal hip joint implant has been found to have minimal wear compared to metal-on-UHMWPE. The purpose of this study was to apply the computational simulation in predicting wear of metal-on-metal total hip joint replacement. Finite element model of half ball and the 45° inclined cup was developed to represent the femoral head and acetabular cup, respectively. A simple Archard’s equation was used to simulate the wear process combining with the finite element model. Two constant wear factors taken from experimental hip simulator were used, representing the running-in and steady state phases. All motions, flexion-extension, abduction-adduction and internal-external rotation of hip joint, and a vertical load at the centre of the femoral head with a maximum value of 2200N during gait were considered. The wear simulation of 28mm femoral head with 60μm diametral clearance was carried out for up to 50 million cycles, and subsequently analysed. The contact pressure decreased dramatically from the initial cycle to the first million cycles accompanied by an increase of contact area; however the decrease of contact pressure was very small between 30th to 50th year. Biphasic linear and volumetric wear were observed due to the use of two different wear factors for running-in and steady state periods. There was relatively good agreement in volumetric wear between the present and hip simulator study. The total predicted volumetric wear for 50 yeas was 4.2 mm3. It was found that the post-wear bearing surface would be advantageous to the hip implant by increasing the lubricating film and thus decreasing wear.

3D Modeling of Cancellous Bone

Three-dimensional models of cancellous bone samples were constructed for FE simulations. The response of the models toward simulated mechanical loading was investigated. Preparation of the models begins with 3D reconstruction of micro-CT stacked images, follows by segmentation, meshing, and refurbishing process.

Time- and cycle-dependent mechanical behavior of cancellous bone

The secant’s slope of the first loop represents the initial elastic modulus, E, while the decrease of the slope gives value of damage parameter. The point of intersection between the strain axis and the extended secant line at zero defines the residual strain, e res .

Monotonic Behavior of Cancellous Bone

Study of cancellous bone structure involves the evaluation of its mechanical properties, either through experimental testing or computational simulation. The prediction of the mechanical properties of cancellous bone ware made previously using small size samples. As the experimental analysis is tedious and time-consuming, many authors suggested prediction of the mechanical properties of cancellous bone to be made using finite element analysis (FEA). However, the prediction is limited to the size of model used, not the bone as a whole.

Analysis on stress and micromotion on various peg fixation at glenoid implant

Six commercially available implant designs were simulated via finite element analysis. The objectives of this study are (1) to determine the effect of peg numbers and orientations to the stress distribution at the implant and cement (2) to compare the micromotion between fully cemented and partially cemented implant. An applied load of 750 N was subjected to the implant at inferior location in which pegs were distributed. The result showed, by increasing the peg numbers, implant stress decreased and increased maximum stress at cement. While, fully cemented implant had higher micromotion compared to partially cemented implant. There are no significant differences between four-fins and six-fins implants under both load conditions. In conclusion, increase in peg numbers results in decreased stress at implant and partially cemented implant can provide better stability in terms of micromotion than fully cemented as it allows bone in-growth between fins. While, adding more fins in partially cemented implant does not influence the micromotion of the implant at all.

Effect of Design Parameter Towards Wear Generation

Wear performance was affected by several factors to contribute towards wear generation. Prospect of minimize wear is needed further study by using optimize design parameter. Inevitability to optimize the design is to improve the understanding of reducing wear in human ankle joint. Change in implant dimension has been suggested, may result in better implant lifespan. The effect of design parameter towards wear generation were analysed the thickness and radial contact of meniscal bearing.