bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of elastohydrodynamic lubrication in a novel metal-on-metal hip joint replacement
Authors: Jagatia M , Jin Z M
Published: October 2002

Elastohydrodynamic lubrication (EHL) analysis was carried out in this study for a novel metal-on-metal hip prosthesis, which consists of a cobalt-chrome alloy femoral head articulating against a cobalt-chrome alloy acetabular insert connected to a titanium fixation shell through a taper. Finite element models were developed to investigate the effect of the pelvic bone and the load on the predicted contact pressure distribution between the two bearing surfaces under dry conditions. The finite element method was used to develop elasticity models for both the femoral and the acetabular components; it was found that the elastic deformation of the acetabular insert was mainly dependent on the load, rather than the detailed pressure distribution. A modified solution methodology was accordingly developed to couple the elasticity models for both the femoral and the acetabular surfaces with the Reynolds equation and to solve these numerically by the finite difference method. It was found that a load increase from 500 to 2500 N had a negligible effect on the predicted maximum contact pressure and the minimum film thickness, due to the relatively flexible and accommodating structure of the acetabular insert. Furthermore, the predicted minimum film thickness was shown to be significantly greater than the simple estimation based on the assumption of semi-infinite solids (mono-block design) using the Hamrock and Dowson formula. The effects of the viscosity of the lubricant and the radial clearance between the femoral and the acetabular components on the predicted lubricating film thickness were investigated under both in vitro simulator testing and in vivo walking conditions.
An in vitro study of the reduction in wear of metal-on-metal hip prostheses using surface-engineered femoral heads
Authors: Fisher J , Hu X Q , Tipper J L , Stewart T D , Williams S , Stone M H , Davies C , Hatto P , Bolton J , Riley M , Hardaker C , Isaac G H , Berry G , Ingham E
Published: October 2002

Although the wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/106 cycles) is much lower than the more widely used polyethylene-on-metal bearings, there are concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically, in the human body. The aim of this study was to investigate the possibility of reducing the volume of wear, the concentration of metal debris and the level of metal ion release through using surfaceengineered femoral heads. Three thick (8-12 μm) coatings (TiN, CrN and CrCN) and one thin (2 μm) coating (diamond-like carbon, DLC), were evaluated on the femoral heads when articulating against high carbon content cobalt-chromium alloy acetabular inserts (HC CoCrMo) and compared with a clinically used MOM cobalt-chromium alloy bearing couple using a physiological anatomical hip joint simulator (Leeds Mark II). This study showed that CrN, CrCN and DLC coatings produced substantially lower wear volumes for both the coated femoral heads and the HC CoCrMo inserts. The TiN coating itself had little wear, but it caused relatively high wear of the HC CoCrMo inserts compared with the other coatings. The majority of the wear debris for all half-coated couples comprised small, 30 nm or less, CoCrMo metal particles. The Co, Cr and Mo ion concentrations released from the bearing couples of CrN-, CrCN- and DLC-coated heads articulating against HC CoCrMo inserts were at least 7 times lower than those released from the clinical MOM prostheses. These surface-engineered femoral heads articulating on HC CoCrMo acetabular inserts produced significantly lower wear volumes and rates, and hence lower volumetric concentrations of wear particles, compared with the clinical MOM prosthesis. The substantially lower ion concentration released by these surface-engineered components provides important evidence to support the clinical application of this technology.
Analysis of contact mechanics in ceramic-on-ceramic hip joint replacements
Authors: Mak M M , Jin Z M
Published: October 2002

The contact mechanics in ceramic-on-ceramic hip implants has been analysed in this study using the finite element method. Only the ideal conditions where the contact occurs within the acetabular cup were considered. It has been shown that the contact pressure distribution and the contact area at the main articulating bearing surfaces depend largely on design parameters such as the radial clearance between the femoral head and the acetabular cup, as well as the thickness of the ceramic insert. For the ceramic-on-ceramic hip implants used in clinics today, with a minimum 5-mm-thick ceramic insert, it has been shown that the radius of the contact area between the femoral head and the acetabular cup is relatively small compared with that of the femoral head and the ceramic insert thickness. Consequently, Hertz contact theory can be used to estimate the contact parameters such as the maximum contact pressure and the contact area.
The validity of using a video-based motion analysis system for measuring maximal area of fingertip motion and angular variation
Authors: Su F-C , Kuo L-C , Chiu H-Y , Hsu H-Y
Published: October 2002

The aim of the study was to verify the application of a three-dimensional video motion analysis system to evaluate maximal fingertip motion area and angular variation of the hand by comparison and correlation with videofluoroscopic analysis. Eight normal subjects were recruited in this study. The maximal motion area of the fingertip and the angles of the metacarpal phalangeal (MP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints in performing five sequential postures for functional evaluation of the hand were measured using a video motion analysis system and a fluoroscopy system respectively. The results indicated that the intraclass correlation coefficient (ICC) of the calculated maximal fingertip motion area between the two methods was 0.9597. The ICC for total active motion (TAM) measurements of three finger joints was 0.940 between the surface and bony landmarks by fluoroscopy, 0.952 between the surface landmarks from fluoroscopy and motion analysis, and 0.927 between the bony landmark from fluoroscopy and surface markers from motion analysis. The ICC for angular measurements between three different paired assessments was 0.9650, 0.8896 and 0.8799 for the MP, PIP and DIP joints respectively. The results indicate that motion analysis is a practical method for assessing impairment of the hand.
An automated method for assessing routine radiographs of patients with total hip replacements
Authors: Redhead A L , Kotcheff A C W , Taylor C J , Porter M L , Hukins D W L
Published: October 2002

This paper describes a new, fully automated method of locating objects on radiographs of patients with total joint replacements (TJRs). A statistical computer model, known as an active shape model, was trained to identify the position of the femur, pelvis, stem and cup marker wire on radiographs of patients with Charnley total hip prostheses. Once trained, the model was able to locate these objects through a process of automatic image searching, despite their appearance depending on the orientation and anatomy of the patient. Experiments were carried out to test the accuracy with which the model was able to fit to previously unseen data and with which reference points could be calculated from the model points. The model was able to locate the femur and stem with a mean error of approximately 0.8 mm and a 95 per cent confidence limit of 1.7 mm. Once the model had successfully located these objects, the midpoint of the stem head could be calculated with a mean error of approximately 0.2 mm. Although the model has been trained on Charnley total hip replacements, the method is generic and so can be applied to radiographs of patients with any TJR. This paper shows that computer models can form the basis of a quick, automatic method of taking measurements from standard clinical radiographs.
Stump-socket interface pressure as an aid to socket design in prostheses for trans-femoral amputees—a preliminary study
Authors: Lee V S P , Solomonidis S E , Spence W D
Published: October 2002

A system for measuring the stump-socket interface pressure was designed and built using a strain gauged type load cell. The system was utilized to study the pressure distribution in the quadrilateral and ischial containment type sockets. Two volunteer trans-femoral amputees fitted with both types of socket participated in the experiments. Pressures were measured while the subjects were standing and during walking. The maximum pressure recorded for standing was 34 kPa and for walking 95 kPa. Comparison made between the two sockets indicated that higher pressures were recorded at the proximal brim of the quadrilateral socket whereas the ischial containment socket produces a more evenly distributed pressure profile. The pressure distribution on the medial and lateral walls of both types of sockets were similar but in the anterior and posterior walls, significant differences were noted. The results obtained from this study were compared with those found in published literature and the biomechanics of the two types of socket is discussed.
The influence of the stem-cement interface in total hip replacement—a comparison of experimental and finite element approaches
Authors: Wheeler J P G , Miles A W , Clift S E
Published: October 2002

Experimental and finite element investigations were carried out on axisymmetric models of the femoral component of a total hip replacement. In one instance, the interface between the stem and the surrounding bone cement was assumed to be rigidly bonded; in a second, it was allowed to slip. For the latter case, a friction coefficient of 0.2 was determined experimentally. The predictions of the finite element models demonstrated excellent agreement with the results from the experimental tests at all sites where comparisons were made, thus validating these models. The effect of stemcement slip was shown to reduce the maximum shear stress in the cement mantle by approximately 30 per cent.
Biological reaction to debris in relation to joint prostheses
Authors: Revell P A , AL-Saffar N , Kobayashi A
Published: October 2002

Bone loss induced by the inflammatory response to wear particles is a major cause of long-term failure of total joint replacement. This review describes the cellular reaction occurring in response to these particles and what is currently known about the inflammatory mechanisms contributing to bone resorption.
Analysis of fluid film lubrication in artificial hip joint replacements with surfaces of high elastic modulus
Authors: Jin Z M , Dowson D , Fisher J
Published: October 2002

Lubrication mechanisms and contact mechanics have been analysed for total hip joint replacements made from hard bearing surfaces such as metal-on-metal and ceramic-on-ceramic. A similar analysis for ultra-high molecular weight polyethylene (UHMWPE) against a hard bearing surface has also been carried out and used as a reference. The most important factor influencing the predicted lubricating film thickness has been found to be the radial clearance between the ball and the socket. Full fluid film lubrication may be achieved in these hard/hard bearings provided that the surface finish of the bearing surface and the radial clearance are chosen correctly and maintained. Furthermore, there is a close relation between the predicted contact half width and the predicted lubricating film thickness. Therefore, it is important to analyse the contact mechanics in artificial hip joint replacements. Practical considerations of manufacturing these bearing surfaces have also been discussed.
A computer assisted orthopaedic surgical system for distal locking of intramedullary nails
Authors: Viant W J , Phillips R , Griffiths J G , Ozanian T O , Mohsen A M M A , Cain T J , Karpinske M R K , Sherman K P
Published: October 2002

This paper presents a prototype system for computer assisted surgery, the purpose of which is to assist orthopaedic surgeons when performing distal locking of intramedullary nails. This system comprises three components, namely: an Intelligent Image Intensifier, a Trajectory Tactician and an Intelligent Trajectory Guide. The Intelligent Image Intensifier is an X-ray vision system that provides accurate X-ray images. Such images enable the Trajectory Tactician software to analyse the operation site and calculate the trajectory required for a screw to lock an intramedullary nail. This involves the capture of two X-ray images from which are extracted the projections of the nail's edge boundaries and its distal locking holes. Using an analytical mathematical model of the nail, the position and orientation of the nail is determined. The trajectory is then implemented by the surgeon using the Intelligent Trajectory Guide. Evaluation in the laboratory suggests that the system is capable of reliably inserting a locking screw into an intramedullary nail. The rapidity with which this computer assisted method achieves locking should benefit both patient and surgeon by reducing radiation dosage and the length of time required to lock a nail.
A model for fatigue crack propagation and remodelling in compact bone
Authors: Taylor D , Prendergast P J
Published: October 2002

The process of fatigue in bone is of interest for a number of reasons. Fatigue damage in vivo can eventually lead to stress fracture, and may also act as a stimulus for bone remodelling and adaptation. The aim of this paper is to develop a theoretical model which describes the growth of fatigue cracks, especially of microcracks. The growth behaviour of microcracks is complicated by their interactions with the surrounding microstructure. This problem has been identified by researchers working on fatigue in engineering materials. Their work can be adapted to develop an equation in which the growth rate of cracks is related to applied stress conditions and also to a microstructural parameter, d, which is defined as the spacing of barriers to crack growth. The model can be used to generate stress/life data for comparison with in vitro fatigue experiments. It can also be used to investigate two hypotheses: that microcracking stimulates repair and that the level of fatigue damage can act as a signal to initiate adaptation processes of deposition or resorption.
Rolling resistance of articular cartilage due to interstitial fluid flow
Authors: Ateshian G A , Wang H
Published: October 2002

A mechanism which may contribute to the frictional coefficient of diarthrodial joints is the rolling resistance due to hysteretic energy loss of viscoelastic cartilage resulting from interstitial fluid flow. The hypothesis of this study is that rolling resistance contributes significantly to the measured friction coefficient of articular cartilage. Due to the difficulty of testing this hypothesis experimentally, theoretical predictions of the rolling resistance are obtained using the solution for rolling contact of biphasic cylindrical cartilage layers [Ateshian and Wang (1)]. Over a range of rolling velocities, tissue properties and dimensions, it is found that the coefficient of rolling resistance μR varies in magnitude from 10−6 to 10−2; thus, it is generally negligible in comparison with experimental measurements of the cartilage friction coefficient (10−3-10−1) except, possibly, when the tissue is arthritic. Hence, the hypothesis of this study is rejected on the basis of these results.
Charnley wear model for validation of hip simulators' ball diameter versus polytetrafluoroethylene and polyethylene wear
Authors: Clarke I C , Good V , Anissian L , Gustafson A
Published: October 2002

Wear rates of polytetrafluoroethylene (PTFE) and polyethylene cups were compared in 9-channel and 12-channel simulators, using serum lubrication and gravimetric techniques for wear assessment. Cobalt-chromium (CoCr) and alumina ceramic femoral heads in 22-42 mm diameter range were used to validate simulator wear rates against clinical data. This was also the first study of three femoral head sizes evaluated concurrently in a simulator (with three replicate specimens) and also the first report in which any wear experiments were repeated. Fluid absorption artefacts were within ± 1 per cent of wear magnitude for PTFE and ± 8 per cent for polyethylene and were corrected for. Wear rates were linear as a function of test duration. Precision within each set of three cups was within ±6 per cent. The wear rates from experiments repeated over 15 months were reproducible to within ± 24 per cent. However, the magnitudes of the simulator wear rates were not clinically accurate, the PTFE wear rates (2843 mm3/106 cycles; 22 mm diameter) were over three times higher than in vivo, the polyethylene 30 to 50 per cent on the low side (23 mm3/106 cycles; 22 mm diameter). Volumetric wear rate increased with respect to size of femoral head and a linearly increasing relationship of 7-8 per cent/mm was evident with respect to femoral head diameter for both PTFE and polyethylene. These data compared well with the clinical data.
The role of polyethylene wear in joint replacement failure
Authors: McGee M A , Howie D W , Neale S D , Haynes D R , Pearcy M J
Published: October 2002

Aseptic loosening is the major cause of failure of joint replacement prostheses. Polyethylene implants removed at revision surgery regularly show wear. It is proposed that the polyethylene particles released into the tissues as a consequence of this wear induce a tissue response that precedes aseptic loosening. This paper presents the results of recent in vivo and in vitro studies of the biological response to polyethylene wear particles undertaken in the authors' laboratories. A clinical perspective is provided by the inclusion of the authors' recent observations of retrieval analyses of joint replacement implant wear and the tissue response to polyethylene in humans.
Composite hydrogels for implants
Authors: Ambrosio L , De Santis R , Nicolais L
Published: October 2002

Hydrophilic composite structures are designed to mimic the transport and mechanical properties of natural soft tissue such as tendons, ligaments and intervertebral discs. Mechanical and viscoelastic behaviour of a soft composite material based on a hydrogel matrix reinforced with bundles of polyethylene therephthalate (PET) fibres is analysed. The typical J-shaped stress-strain behaviour, displayed by natural tendons and ligaments, is reproduced. The mechanical characteristics, such as the extent of the ‘toe-in region’ and the elastic modulus in the linear region, can be controlled by varying the winding angle of the fibres and the matrix composition. Dynamic mechanical analysis showed the dual behaviour of the composite systems due to the progressive contribution of the PET fibres.

Different poly (2-hydroxyethylmethacrylate)/polycaprolactone (PHEMA/PCL) semi-interpenetrating polymer networks (IPNs) hydrogel composite systems reinforced with PET fibres have been investigated for potential use as intervertebral disc prostheses. Compression properties have been evaluated by static and dynamic tests. Uniaxial compression tests on the swollen samples showed an increase of the modulus and maximum stress with increasing content of PCL and PET fibres. Creep behaviour is also dependent on the hydrogel composition. The composite PHEMA/PCL hydrogels showed compression properties similar to those expressed by canine intervertebral discs in different spinal locations.
Bioabsorbable polymers: Materials technology and surgical applications
Authors: TÖrmälä P , Pohjonen T , Rokkanen P
Published: October 2002

Biostable and bioabsorbable biomaterials are used to manufacture implants for supporting, replacement, augmentation and guiding of growth of tissues. Bioabsorbable implants are a better choice for applications where only the temporary presence of the implant is needed. Because of bioabsorption of such implants, there is no need for a removal operation after healing of the tissue and the risks of implant related, long-term complications are eliminated or strongly reduced. Reinforcing of bioabsorbable materials is necessary in order to develop strong and safe, small implants for fixation of bone fractures and connective tissue damage. Self-reinforced bioabsorbable polymeric implants have been used so far extensively in the treatment of traumas of the musculoskeletal system.
Mechanical properties of bioactive glasses, glass-ceramics and composites
Authors: Thompson I D , Hench L L
Published: October 2002

The application of bioactive glass and glass-ceramics has been widely documented over the past twenty years but the high modulus and low fracture toughness has made them less applicable for clinical, load bearing, applications. The development of non-resorbable polyethylene and poly-sulphone matrices for these materials has improved the mechanical properties. However, the primary concern of whether the bioactivity of the composites is reduced is still unresolved. The more recent development of resorbable carrier systems, dextran and collagen, for bioactive glasses does not introduce such problems, hence making this form of composite suitable for novel soft tissue applications. The development of a simple quality index has enabled some of the materials described within this paper to be ranked by their ability to replace bone, thus enabling possible new research directions to be emphasized.
In vivo distraction forces in extendible endoprosthetic replacement—a study of 34 patients
Authors: Meswania J M , Walker P S , Sneath R S , Grimer R J
Published: October 2002

Using an instrumented distraction tool 34 extendible endoprosthetic replacements were lengthened to measure total resistance to extension. The study consisted of 19 distal femoral, 2 proximal femoral, 1 total femoral, 8 proximal tibial, 1 distal humeral, 2 proximal humeral and 1 total humeral replacements. Among these prostheses a total of 76 measurements were made. The initial load on the prosthesis due to soft tissues and muscles varied between 0 and 578 N with an overall mean of 128 N. There was a linear relationship between extension and load. At 6 mm extension the load varied between 42 and 1513 N with a mean of 476 N. There was very little difference between the means of femoral and tibial measurements. There was very little resistance to extension in the total humeral replacement due to the absence of glenoid and muscle attachment. In the distal humeral replacement all three measurements were comparable with the forces in proximal tibial replacements. Two cases showed very high resistance to extension, which was mainly attributed to the presence of large amounts of scar tissues observed at surgery. During one lengthening operation a 30 s pause at 1 mm increments from 0 to 9 mm showed load recovery of approximately 10 per cent for up to 3 mm, beyond which there appeared to be stiffening of tissues.
Flow characteristics of curing polymethyl methacrylate bone cement
Authors: Dunne N J , Orr J F
Published: October 2002

During polymerization, polymethyl methacrylate bone cements have complex viscoelastic characteristics. Within a short working time they transform from dough-like consistencies to solid cements. Therefore, the time at which a cement is introduced to cancellous bone surfaces and subjected to pressure is important, to achieve optimum flow and mechanical interdigitation. Achieving adequate mechanical interlock increases the area for load transfer and reduces localized bone-cement interface stresses. The aim of this study was to measure the flow characteristics for commercial bone cements as a function of time and calculate the apparent viscosities for the curing bone cements

The capillary extrusion method was used to measure the rate of flow of the curing cement, by means of a melt flow index apparatus, which was manufactured in-house. The tests were conducted using nozzles of different lengths and under two loads. This enabled the power index value, n, and the pressure at the die entry, Po, to be calculated for each material with respect to time. Once the flow characteristics were determined, a series of formulae were used to calculate the shear rates, y, the shear stresses, r, and the apparent viscosities, na, of the curing bone cements.

The results indicated that acrylic bone cements are non-Newtonian, pseudoplastic materials, since the power index values are less than 1.0 during the curing stage. The consistency indices, K, were calculated from the shear stress versus shear rate data. The apparent viscosities of the cements were found to increase with respect to increases in time. Clinically, it was considered desirable to inject and pressurize the cement into the medullary canal while its viscosity is relatively low in order to obtain maximum interdigitation into cancellous bone, provided adequate containment and a means of pressurization can be achieved. The pseudoplastic character of bone cements is responsible for their reduction in viscosity with increased shear rate, a property that may be exploited to enhance penetration with appropriate delivery.
The numerical analysis of fluid-solid interactions for blood flow in arterial structures Part 1: A review of models for arterial wall behaviour
Authors: Zhao S Z , Xu X Y , Collins M W
Published: October 2002

The structural response of a large artery is characteristically complex and includes the highly non-linear, history-dependent response of a nonhomogeneous anisotropic structure undergoing finite deformations. The mechanics of the arterial wall has been studied for nearly two centuries. The goals of such research range from the desire to have a basic knowledge and understanding of the mechanics and physiology of this complex structure to the need for data and methods for the design of arterial prostheses. In this paper, the models for arterial wall behaviour are critically reviewed. Firstly, the structure and general characteristics of the arterial wall are discussed. This is followed by a comprehensive review of the constitutive laws. Finally, structural analyses of the arterial wall by mathematical and numerical methods are discussed. Predictions using the authors' preferred models give focus to important issues, and in Part 2 the review and predictions are extended to the fluid-solid coupled situation.
The post-buckling behaviour of the pressurized abdominal cavity during knees-bent lifts
Authors: Thomson K D
Published: October 2002

When a person bends over to lift an object, the intra-abdominal pressure is insufficient to prevent the abdominal cavity from buckling. This paper is concerned with estimation of the extent of buckling, its effect on the bending moment capability of the abdominal cavity and the stress distributions in the abdominal muscles. Buckling decreases the bending moment capability of the abdominal cavity, increases the stresses in the oblique muscles and transversus, and reduces to zero the stress in the rectus muscles.
Mechanical properties of vertebrate hard tissues
Authors: Currey J D
Published: October 2002

The main mechanical properties of bone and dentine are reviewed.
Histomorphological and biomechanical characterization of calcium phosphates in the osseous environment
Authors: Hing K A , Best S M , Tanner K E , Revell P A , Bonfield W
Published: October 2002

The standardization of characterization techniques is becoming increasingly important for bone replacement materials as it becomes apparent that, for the field to advance, testing must be developed to allow the biocompatibility or bioactivity of a new material to be assessed and directly compared with existing materials. Currently there are many forms of biocompatibility test for materials destined for the osseous environment, ranging from immersion in simulated body fluid to implantation into living bone. However, the variety of ways in which the data from these tests may be acquired and interpreted, as a result of changes in parameters such as surgical technique and mechanical test conditions, means that much of the published data within the field is not comparable. This paper will introduce the concept of biocompatibility by considering calcium phosphate bioceramics, and discusses some aspects of in vivo experimental design, including simple histomorphometry techniques, in addition to considering practical methods for the assessment of the biomechanical characteristics of an osseointegrated implant.
Polymers in dentistry
Authors: Deb S
Published: October 2002

There is a wide choice of materials available for restorative dentistry covering a range of requirements. Fundamental knowledge about the properties of the polymers in use in dentistry is an advantage as it provides information relevant to clinical practice. Dentistry, perhaps, has the unique distinction of using the widest variety of materials, ranging from polymers, metal and metal alloys, ceramics, inorganic salts and composite materials. In the present paper, polymers and polymer composites used directly or indirectly for restorations, prostheses or for production of appliances in dentistry is discussed.
Shape memory alloys for medical applications
Authors: Gil F J , Planell J A
Published: October 2002

The shape memory alloys exhibit a number of remarkable properties, which open new possibilities in engineering and more specifically in biomedical engineering. The most important alloy used in biomedical applications is NiTi. This alloy combines the characeristics of the shape memory effect and superelasticity with excellent corrosion resistance, wear characteristics, mechanical properties and a good biocompatibility. These properties make it an ideal biological engineering material, especially in orthopaedic surgery and orthodontics. In this work the basis of the memory effect lies in the fact that the materials exhibiting such a property undergo a thermoelastic martensitic transformation. In order to understand even the most elementary engineering aspects of the shape memory effect it is necessary to review some basic principles of the formation and the characteristics of the martensitic phase. The different properties of shape memory, superelasticity, two-way shape memory, rubber-like behaviour and a high damping capacity are reviewed. Some applications proposed in recent years are described and classified according to different medical fields.
Stress analysis of glenoid component designs for shoulder arthroplasty
Authors: Lacroix D , Prendergast P J
Published: October 2002

Secure and lasting fixation of the glenoid component in total shoulder arthroplasty is difficult because there is an insufficient volume of strong bone in the scapula. Consequently, radio-lucencies of the glenoid component are common (much more common than radiolucencies of the humeral component). Early glenoid component designs were fabricated wholly from polyethylene, were fixated with PMMA cement, and had various degrees of constraint and conformity between the glenoid surface and the ball of the humeral component. More recent design variations include metal backing and non-cemented anchorage systems. In this study, various designs of cemented glenoid component are analysed using the finite element method. These are examined for (a) two different abduction angles; 60° and 90°; (b) high and low conformity and (c) high and low constraint. Stress distributions are compared with the failure strengths of the components and the influence of the various design factors can be observed.
A modified semi-automated technique for in vitro assessment of encrustation of materials
Authors: Gepi-Attee S , Feneley R C L
Published: October 2002

In vitro study of encrustation is an important part of assessment of materials as potential alloplasts or devices in the urinary tract. This modified semi-automated technique comprises a circular reaction chamber with an encrustation mixture, the level of which is controlled by a float switch which operates the exit peristaltic pump. The composition of the reactants used simulates infected urine with alkaline pH. Results of a preliminary study of the deposits by scanning electron micrography (SEM) and energy dispersive X-ray (EDX) microanalysis are consistent with struvite and hydroxyapatite, similar to the main minerals deposited on urinary catheters. It is a relatively simple, effective and inexpensive set-up for study of encrustation on materials.
Calculation of multi-segment rigid body joint dynamics using MATLAB
Authors: Barker T M , Kirtley C , Ratanapinunchai J
Published: October 2002

A computational model of the human upper limb was developed utilizing a matrix calculation software package (MATLAB) and a public domain suite of subroutines [Robotics Toolbox (1)]. An easily configurable model of a rigid body, serially linked manipulator was established, avoiding the need for complex numerical equations to be formulated. A generalized model of the upper limb was used to study throwing action of individual subjects by incorporating body segment parameters and kinematic data. Estimates of joint moments were calculated for multiple time instances. This technique can be utilized and adapted for modelling any arbitrary serially linked manipulator system. Inverse and forward kinematics and kinetics can be calculated, enabling biomechanical simulations to be undertaken.
The effect of cartilage deformation on the laxity of the knee joint
Authors: Huss R A , Holstein H , O'Connor J J
Published: October 2002

In this paper, deformation of the articular cartilage layers is incorporated into an existing two-dimensional quasi-static model of the knee joint. The new model relates the applied force and the joint displacement, as measured in the Lachmann drawer test, and allows the effect of cartilage deformation on the knee joint laxity to be determined. The new model augments the previous knee model by calculating the tibio-femoral contact force subject to an approximate ‘thin-layer’ constitutive equation, and a method is described for finding the configuration of the knee under a specified load, in terms of a displacement from a zero-load reference configuration. The results show that inclusion of deformable cartilage layers can cause a reduction of between 10 and 35 per cent in the force required to produce a given tibial displacement, over the range of flexion angles considered. The presence of cartilage deformation was found to be an important modifier of the loading response but is secondary to the effect of ligamentous extension. The flexion angle dependence of passive joint laxity is much more strongly influenced by fibre recruitment in the ligaments than by cartilage deformation.
Measurement of tissue motion
Authors: Anderson T , McDicken W N
Published: October 2002

A number of ultrasonic methods are available for the detection of tissue motion as it occurs physiologically in the body. The detection of echoes from within the body in less than 1 ms after the initial transmission of ultrasound and the Doppler effect have enabled a range of instrumentation to be developed. The subject owes a great deal to advances in transducer design, electronics and computer technology. Over many years fast B-mode imaging and M-mode traces of boundary position versus time have been the main clinical tools. Currently new sophisticated detection and imaging techniques are being produced based on the Doppler effect and on tracking motion in tissue images. The measurement of several velocity components is permitting velocity vectors to be determined more completely, adding to accuracy. Not surprisingly, cardiology is the main field of application but there are other areas of interest, e.g. vascular, musculo-skeletal and foetal function studies.
Estimation of blood perfusion using ultrasound
Authors: Jansson T , Peresson H W , Lindström K
Published: October 2002

Ways to measure blood perfusion using ultrasound techniques such as continuous-wave Doppler, pulsed Doppler, colour Doppler and power Doppler will be reviewed. From a certain standpoint, blood perfusion may be defined as the difference between arterial inflow and arterial outflow from a considered volume, i.e. capillary flow. The low velocities and small blood volumes involved make the signal-to-noise ratio, dynamic range and frequency resolution critical factors in the detection system. Another limiting factor is tissue motion which obscures the blood signal. Perfusion may still under certain conditions be estimated with the first moment of the Doppler power spectrum, as obtained with any Doppler ultrasound method. Modern flow mapping techniques also make it possible to estimate perfusion by counting the number of pixels that indicate flow, but low flow velocities cannot be included in the estimate. Future high-frequency systems may, however, provide very detailed images of minute flow distributions in superficial layers. Contrast agents are widely used today to enhance the blood signal, and a technique named harmonic imaging can suppress movement artefacts from surrounding tissue. Transient signals from disrupting contrast agent particles in an ultrasound field can potentially be used for perfusion quantification. Future developments to extract the blood flow signal from its noisy environment, aside from contrast agents, may be multiple sample volumes, frequency compounding and/or improved signal processing. The lack of an adequate perfusion phantom for verification of measurements of microcirculatory flow becomes, however, more apparent with improved detectability of slow flows.
Elastography: Ultrasonic estimation and imaging of the elastic properties of tissues
Authors: Ophir J , Alam S K , Garra B , Kallel F , Konofagou E , Krouskop T , Varghese T
Published: October 2002

The basic principles of using sonographic techniques for imaging the elastic properties of tissues are described, with particular emphasis on elastography. After some preliminaries that describe some basic tissue stiffness measurements and some contrast transfer limitations of strain images are presented, four types of elastograms are described, which include axial strain, lateral strain, modulus and Poisson's ratio elastograms. The strain filter formalism and its utility in understanding the noise performance of the elastographic process is then given, as well as its use for various image improvements. After discussing some main classes of elastographic artefacts, the paper concludes with recent results of tissue elastography in vitro and in vivo.
Measurements of organ volume by ultrasonography
Authors: Gilja O H , Hausken T , Berstad A , Ødegaard S
Published: October 2002

In a clinical context, measurements of organ volume are often performed in the diagnosis and follow-up of patients with a variety of diseases. Ultrasonography is a cheap, widely available and non-hazardous imaging modality to use for estimation of volumes, and a range of two- and three-dimensional methods have emerged to accomplish this task. This paper reviews some of the ultrasound methods available in cardiology, gastroenterology, nephrology/urology and gynaecology/obstetrics. Using two-dimensional (2D) ultrasound, the simplest method of calculating the volume of an organ is based on the multiplication of three diameters perpendicular to each other. These 2D methods are often based on geometrical assumptions which may introduce significant errors in volume estimation. Therefore, volume estimation based on three-dimensional (3D) ultrasound has been developed to increase accuracy and precision. At present, the process of making 3D images based on ultrasonography is divided into five steps: data acquisition, data digitization, data storage, data processing and data display. In conclusion, ultrasonography is a useful and reliable tool to calculate volumes of organs. In particular, 3D ultrasonography seems promising in this respect and appears to be superior to 2D ultrasonography in accuracy and precision in volume measurements.
Acoustic and ultrasonic tissue characterization—assessment of osteoporosis
Authors: Langton C M , Njeh C F
Published: October 2002

Osteoporosis, often termed the ‘silent epidemic’, has been defined as ‘a decrease in bone mass and architectural deterioration of bone tissue, leading to enhanced bone fragility and consequent increase in fracture risk’. In the United Kingdom alone, the annual health costs are in excess of £750 million, with 60 000 patients suffering a hip fracture each year. A quarter of these will die within 12 months of their fracture, half of the remainder will never regain independent living. The established procedure for assessing the risk of osteoporotic fracture is via bone mineral density (BMD) assessment using dual-energy X-ray absorptiometry (DXA). However, DXA is an expensive technique and is not widely available. Within the past 15 years, ultrasound assessment of bone has rapidly advanced in scientific understanding, technical development and clinical utility. Measurements of cancellous bone (particularly at the calcaneus) are generally performed in preference to those of cortical bone (tibial cortex). There are currently 15 commercial systems available and over 3500 systems are in use world-wide. The low cost and portability offered by ultrasound systems should enable an integrated community-based screening programme to be established in the near future.

Ultrasound measurements of bone are generally obtained using transmission rather than pulse-echo techniques owing to its highly attenuating nature. Ultrasound velocity and attenuation measurements are utilized. For velocity, there are well-defined fundamental relationships describing the dependence upon the elasticity and density of bone.
A hip joint simulator study using simplified loading and motion cycles generating physiological wear paths and rates
Authors: Barbour P S M , Stone M H , Fisher J
Published: October 2002

In some designs of hip joint simulator the cost of building a highly complex machine has been offset with the requirement for a large number of test stations. The application of the wear results generated by these machines depends on their ability to reproduce physiological wear rates and processes. In this study a hip joint simulator has been shown to reproduce physiological wear using only one load vector and two degrees of motion with simplified input cycles. The actual path of points on the femoral head relative to the acetabular cup were calculated and compared for physiological and simplified input cycles. The in vitro wear rates were found to be highly dependent on the shape of these paths and similarities could be drawn between the shape of the physiological paths and the simplified elliptical paths.
Estimation of loads in the lumbar spine during slow symmetrical lifts and a method for their reduction
Authors: Thomson K D
Published: October 2002

During slow, symmetrical lifts the anterior abdominal wall buckles at about the level of L3 vertebra, causing a local reduction in the cross-sectional area of the abdominal cavity. Calculations are made on the effect this buckling has on both lumbar vertebral compression and erector muscle tension. A simple exercise in statics shows that the size of the diaphragm is not relevant in determining the load relief due to intra-abdominal pressure, nor are the tensile loads in the abdominal muscles arising from this pressure.

Finally a description is given of a simple harness worn on the torso, which is predicted to reduce substantially the loads in both the erector muscles and the lumbar vertebrae.
Feasibility study on a composite material construction technique for highly stressed components in reciprocal walking orthoses for paraplegic patients
Authors: Woollam P J , Dominy J , McCleod N , Stallard J , Major R E
Published: October 2002

Reciprocal walking for thoracic level paraplegic patients using reciprocal walking orthoses has become a routine treatment option. Two general design options are currently deployed within an overall treatment regime. Research has shown that one has better walking efficiency but is cosmetically less acceptable to the patient. Design analysis and experimental data have shown that a major factor in improved walking efficiency is the lateral stiffness of the body brace section of the orthosis. This is the area where problems of cosmesis in the more efficient orthosis are perceived because of the employment of metallic structures.

The use of composite material structures to achieve shapes which are more closely conforming to the patient is an attractive option. However the brittle nature of these materials makes it unlikely that the requirement for the ductile failure mode will be achieved from a straightforward moulding. A new construction technique has been devised which has the potential to provide a safe failure mode with greater stiffness and lighter weight. This feasibility study has been undertaken to demonstrate its potential so that further work can be justified which will provide sufficient evidence to support a patent application.

The successful outcome of the study, in which stiffness was increased by 60 per cent with a weight reduction of 50 per cent and a failure mode comparable with the original metal structure, suggests that further work will enable the dilemma in the choice of orthosis to be resolved.
Three-dimensional unsteady Navier—Stokes analysis of stator—rotor interaction in axial-flow turbines
Authors: He L
Published: October 2002

A three-dimensional full Navier-Stokes method is developed and applied to calculations of unsteady flows through multiple blade rows in axial-flow turbomachinery. The solver adopts the cellcentred finite volume discretization and the four-stage Runge-Kutta time-marching scheme. Unsteady calculations are effectively accelerated by using a time-consistent multi-grid technique, resulting in a speed-up by a factor of 10–20 with adequate temporal accuracy. The computational efficiency and validity of the present multi-grid technique are illustrated by comparisons with the results of the conventional dual time-stepping scheme. Calculated unsteady pressures on blade surfaces for a turbine stage performances at different stator-rotor axial gaps reveals a marked three-dimensional behaviour of the interaction between incoming wakes and rotor passage-vortex structures. The time-averaged losses from unsteady calculations show a noticeable spanwise redistribution compared with the steady results. Two dimensional and three-dimensional calculations indicate opposite trends in stage efficiency variation when the stator—rotor gap is reduced.
Feasibility of energy recovery from a wastewater treatment scheme
Authors: Griffin F M
Published: October 2002

This paper describes a study that was undertaken to determine the potential of energy recovery from a new wastewater treatment scheme being built for the Kent towns of Dover and Folkestone. The paper reviews the potential sites and describes how their energy-generating potential was evaluated using spreadsheet-based software models. Two schemes demonstrated sufficient potential for further study. The paper describes the potential operating problems and explains how the generating and control equipment was selected to achieve the optimum performance at minimum cost. Designs for the schemes were developed such that the costs and generating potential could be determined with sufficient accuracy to allow their financial rate of return to be estimated.