Search results

Due to intrinsic limitations, fused deposition modelling (FDM) products suffer from the bad surface finish and inaccurate dimensional accuracies restricting its usage in many applications. Hence, there is a need for processing polymer patterns before, during and after their productions. This paper aims to highlight the importance of pre- and post-processing treatments on the FDM-based acrylonitrile butadiene styrene patterns improving its surface quality so, that it can be used in rapid investment casting process for making medical implants and other high precision components.

As a part of pre-processing treatment, the machine parameters affecting the surface quality were identified and optimised using design of experiments. The patterns developed after the first stage of optimisation were given different post-processing treatments, which included vapour smoothening, chemical treatment and sand paper polishing. The results were compared and the best ones were used for making patterns for making medical implants via rapid investment casting technique. The surface quality was checked while the dimensional changes happening during the stages of this hybrid technique were recorded using a three-dimensional optical scanner.

The surface roughness of the FDM based ABS patterns reduced from 21.63 to 14.40 µm with pre-processing treatments. Chemical treatment (post-processing treatment) turned to be the most suitable technique for reducing the surface roughness further down to 0.30 µm. Medical implants that used these pre- and post-processing treatments gave an average surface roughness of 0.68 µm. Cost and lead time comparisons showed that rapid investment casting technique can be a better method for low volume, customised and with specific requirements.

FDM parts/medical implants produced by rapid investment casting technique suffer from the inferior surface finish and inaccurate dimensional accuracies limiting its applications. A systematic approach to overcome this issue is presented in this research paper. This will directly help the end users and the manufacturers of medical implants, wherein, better surface finish and dimensionally accurate components are expected.

This bibliography is offered as a practical guide to published papers, conference proceedings papers and theses/dissertations on the finite element (FE) and boundary element (BE) applications in different fields of biomechanics between 1976 and 1991. The aim of this paper is to help the users of FE and BE techniques to get better value from a large collection of papers on the subjects. Categories in biomechanics included in this survey are: orthopaedic mechanics, dental mechanics, cardiovascular mechanics, soft tissue mechanics, biological flow, impact injury, and other fields of applications. More than 900 references are listed.

The purpose of this paper is to present an improved methodology for design of custom‐made hip prostheses, through integration of advanced image processing, computer aided design (CAD) and additive manufacturing (AM) technologies.

The proposed methodology for design of custom‐made hip prostheses is based on an independent design criterion for each of the intra‐medullary and extra‐medullary portions of the prosthesis. The intra‐medullar part of the prosthesis is designed using a more accurate and detailed description of the 3D geometry of the femoral intra‐medullary cavity, including the septum calcar ridge, so that an improved fill and fit performance is achieved. The extra‐medullary portion of the prosthesis is designed based on the anatomical features of the femoral neck, in order to restore the original biomechanical characteristics of the hip joint. The whole design procedure is implemented in a systematic framework to provide a fast, repeatable and non‐subjective response which can be further evaluated and modified in a preplanning simulation environment.

The efficacy of the proposed methodology for design of custom‐made hip prostheses was evaluated in a case study on a hip dysplasia patient. The cortical bone was distinguished from cancellous in CT images using a thresholding procedure. In particular the septum calcar ridge could be recognized and was incorporated in the design to improve the primary stability of the prosthesis. The lateral and frontal views of the prosthesis, with the patient's images at the background, indicated a close geometrical match with the cortical bone of femoral shaft, and a good compatibility with the anatomy of the proximal femur. Also examination of the cross sections of the prosthesis and the patient's intra‐medullary canal at five critical levels revealed close geometrical match in distal stem but less conformity in proximal areas due to preserving the septum calcar ridge. The detailed analysis of the fitting deviation between the prosthesis and point cloud data of the patient's femoral intra‐medullary canal, indicated a rest fitting deviation of 0.04 to 0.11 mm in stem. However, relatively large areas of interference fit of −0.04 mm were also found which are considered to be safe and not contributing to the formation of bone cracks. The geometrical analysis of the extra‐medullary portion of the prosthesis indicated an anteversion angle of 12.5 degrees and a neck‐shaft angle of 131, which are both in the acceptable range. Finally, a time and cost effective investment casting technique, based on AM technology, was used for fabrication of the prosthesis.

The proposed design methodology helps to improve the fixation stability of the custom made total hip prostheses and restore the original biomechanical characteristics of the joint. The fabrication procedure, based on AM technology, enables the production of the customized hip prosthesis more accurately, quickly and economically.

The study aims to analyze the fretting phenomenon, manifested at the taper junctions of modular total hip prostheses (THP). Modularity of prostheses implies the micro-movement occurrence. Fractures can arise as a result of the fretting cracking of the prostheses components, affecting durability of modular THPs. Fretting corrosion is associated with the decrease in the clinical acceptance of hip modular implants.

Starting from the fretting phenomenon influence on modularity, monoblock THPs and prostheses with modular femoral head recovered from some review surgeries were investigated. Modular prostheses have a taper junction femoral head – femoral stem neck. Investigation consisted in the analysis of fretting wear and fretting corrosion, of the femoral heads’ taper and of the femoral stems’ trunnions.

The main result was that the micro-movement that provokes the fretting of the femoral head-femoral stem taper junction analyzed does not have the same direction. It is manifesting in the direction of the axis of the femoral head taper, around this axis or as a composed movement. The authors suspect that this is due to the different design of the taper. In this way, the inclination of the stem’s trunnion into the head hole has a different angular misalignment and may cause greater damages of the taper.

This result can be a starting point from the improvement of the future taper junctions design that will improve the quality, durability and modularity of THPs.

The purpose of this paper is to systematically study the dynamic contact stress, frictional heat and temperature field of femoral head-on-acetabular cup contact pairs in a gait cycle.

In this paper, four common femoral head-on-acetabular cup contact pairs are used as the research objects, mathematical calculations and finite element simulations are adopted. The contact model of hip joint head and acetabular cup was established by finite element simulation to analyze the stress and temperature distribution of the contact interface.

The results show that the contact stress of the head-on-cup interface is inversely proportional to the contact area; high contact stress directly leads to greater frictional heat. However, hip joints with metal-on-polyethylene or ceramic-on-polyethylene paired interfaces have lower frictional heat and show a significant temperature rise in one gait cycle, which may be related to the material properties of the acetabular cup.

Previous studies about calculating the interface frictional heat always ignore the dynamic change process in the contact load and the contact area. This study considered the dynamic changes of the contact stress and area of the femoral head-on-acetabular cup interface, and four common contact pairs were systematically analyzed.

The Actuation Division of Lucas Aerospace, based at Wolverhampton, UK has won three major orders for work on the new Airbus Industrie A320, 150 seat passenger aircraft.

Fracture experiments on real human bodies to examine the protected positions and protective devices for the development of protective clothing to manage fractures is exceedingly difficult. Thus, the experimental design will have limitations, more of which are imposed if subjects are elderly people. To circumvent these limitations, this study proposes a finite element model of the hip joint in elderly women with virtual impact simulations that can replace actual fall and impact tests, and examine the positions and characteristics of fractures resulting from taking a fall.

The hip joints were modeled after the average horizontal surface size and cross-sectional shapes of the lower extremities (waist to knee) in 439 elderly Korean women in that age group. The model was composed of bones, cartilages, and soft tissue.

The fracture was examined by comparing the maximum stress on the hip joint by applying a point force to its adjacent surface. The vulnerable part in the hip joint neck with a high risk of fracture risk on an impact could be determined and used to set the protective device attachment position.

It is significant that this study has developed a partial model of the human body that can be used for a relatively simple simulation by minimizing the highly complex human body as much as possible. Furthermore, the model is easily applicable to the designing of protected positions and protective devices for the development of special clothing, for hip joint fracture prevention.

The purpose of this paper is to compare fracture‐fixation and bone‐healing promotion efficacies of an intramedullary (IM) nail‐type and an external osteosynthesis plate‐type femoral trochanteric‐fracture implants using the results of a combined multi‐body dynamics and finite element analyses. For both implants, fracture fixation was obtained using a dynamic hip blade which is anchored to the femur head on one end and is connected to the IM rod/plate on the other. The analysis was carried out for two pre‐fracture conditions of the femur: healthy and osteoporotic.

The musculoskeletal dynamics portion of the analysis was used to obtain realistic physiological loading conditions (i.e. muscle forces and joint reaction forces and moments) associated with four typical everyday activities of a patient, namely, walking, lunging, cycling and egress (i.e. exiting a passenger vehicle). The subsequent structural finite element analysis of the fractured femur/implant assembly was employed to quantify fracture‐fixation efficacy (as measured by the extents of lateral (found to be minor), flexural and torsional displacements of the two femur fragments) and the bone‐healing promotion efficacy (as quantified by the fraction of the fractured surface area which experienced desirable contact pressures).

The results obtained show that, in general, the IM‐rod type of implant out‐performs the osteosynthesis plate type of implant over a large range of scenarios involving relative importance of the bone‐healing promotion and fracture‐fixation efficacies, health condition of the femur and the activity level of the patient. More specifically, the more active the patient and the larger extent of osteoporosis in the femur, the more justifiable is the use of the IM‐rod type of implant.

The present approach enables assessment of the fracture‐fixation performance of orthopedic implants under physiologically realistic loading conditions.

The purpose of this study was to realize finite element simulation in order to dynamically determine the area of the contact, the contact pressure and the strain energy density (identified as a damage function) for three different activities – normal walking, ascending stairs and descending stairs – that could be considered to define the level of the activity of the patient.

The finite element model uses a modern contact mechanism that includes friction between the metallic femoral condyles or femoral head (considered rigid) and the tibial polyethylene insert or acetabular cup (considering a non-linear behaviour).

For all three activities, the finite element analyses were performed, and a damage score was computed. Finally, a cumulative damage score (that accounts for all three activities) was determined, and the areas where the fatigue wear is likely to occur were identified.

A closer look at the distribution of the damage score reveals that the maximum damage is likely to occur not at the contact surface, but in the subsurface.

The purpose of this paper was development of patient-specific femoral prosthesis using rapid prototyping (RP), a part of additive manufacturing (AM) technology, and comparison of its merits or demerits over CNC machining route.

The customized femoral prosthesis was developed through computed tomography (CT)-3D CAD-RP-rapid tooling (RT)-investment casting (IC) route using a stereolithography apparatus (SLA-250) RP machine. A similar prosthesis was also developed through conventional CT-CAD-CAM-CNC, using RP models to check the fit before machining. The dimensional accuracy, surface finish, cost and time involvement were compared between these two routes.

In both the routes, RP had an important role in checking the fit. Through the conventional machining route, higher-dimensional accuracies and surface finish were achieved. On the contrary, RP route involved lesser time and cost, with rougher surface finish on the prosthesis surface and less internal shrinkage porosity. The rougher surface finish of the prosthesis is favourable for bone ingrowths after implantation and porosity reduce the effective stiffness of the prosthesis, leading to reduced stress shielding effect after implantation.

As there is no AM machine for direct fabrication of metallic component like laser engineered net shaping and electron beam melting in our Institute, the metallic prosthesis was developed through RP-RT-IC route using the SLA-250 machine.

The patient-specific prosthesis always provides better fit and favourable stress distribution, leading to longer life of the prosthesis. The described RP route can be followed to develop the customized prosthesis at lower price within the shortest time.

The described methodology of customized prosthesis development through the AM route and its advantages are applicable for development of any metallic prostheses.