Biomedical subjects

K E Tanner

Publications and source records attributed to K E Tanner.

At least 37 records · Page 2Linked to original sources

PubMed2002

Effects of acetabular resurfacing component material and fixation on the strain distribution in the pelvis.

A 3D finite element (FE) model of an implanted pelvis was developed as part of a project investigating an all-polymer hip resurfacing design. The model was used to compare this novel design with a metal-on-metal design in current use and a metal-on-polymer design typical of early resurfacing implants. The model included forces representing the actions of 22 muscles as well as variable cancellous bone stiffness and variable cortical shell thickness. The hip joint reaction force was applied via contact modelled between the femoral and acetabular components of the resurfacing prosthesis. Five load cases representing time points through the gait cycle were analysed. The effect of varying fixation conditions was also investigated. The highest cancellous bone strain levels were found at mid-stance, not heel-strike. Remote from the acetabulum there was little effect of prosthesis material and fixation upon the von Mises stresses and maximum principal strains. Implant material appeared to have little effect upon cancellous bone strain failure with both bended and unbonded bone-implant interfaces. The unbonded implants increased stresses in the subchondral bone at the centre of the acetabulum and increased cancellous bone loading, resembling behaviour obtained previously for the intact acetabulum.

Acetabulum↗

PubMed2002

Roentgen single-plane photogrammetric analysis (RSPA.) A new approach to the study of musculoskeletal movement.

We present a new approach for the accurate reconstruction of three-dimensional skeletal positions using roentgen single-plane photogrammetric analysis (RSPA). This technique uses a minimum of three markers embedded in each segment which allow continuous, real-time, internal skeletal movement to be measured from single-plane images, provided that the precise distance between the markers is known. A simulation study indicated that the error propagation in this approach is influenced by focus position, object position, the number of control points, the accuracy of the previous measurement of the distance between markers and the accuracy of image measurement. For reconstruction of normal movement of the knee with an input measurement error of SD = 0.02 mm, the rotational and translational differences between reconstructed and original movement were less than 0.27 degrees and 0.9 mm, respectively. Our results showed that the accuracy of RSPA is sufficient for the analysis of most movement of joints. This approach can be applied in combination with force measurements for dynamic studies of the musculoskeletal system.

Computer Simulation↗

PubMed2002

The effect of intra-articular methylprednisolone acetate and exercise on equine carpal subchondral and cancellous bone microhardness.

Dorsal carpal osteochondral injury is a major cause of lameness in horses undergoing high intensity training. Intra-articular corticosteroid treatment is used commonly to manage exercise-associated articular pain, but its use remains highly controversial in the equine athlete. This project, therefore, aimed to compare the mechanical properties of intra-articular MPA and diluent-treated middle carpal subchondral and cancellous bone in horses undergoing a short-term treadmill exercise programme. It was hypothesised that subchondral and cancellous bone mechanical properties are influenced by intra-articular administration of methylprednisolone acetate (MPA). Eight 2-year-old female horses had MPA or diluent administered into contralateral middle carpal joints at 14 day intervals, for a total of 4 treatments per horse. Horses underwent a standard treadmill exercise protocol until euthanasia (Day 70). Standard sites were located on the dorsal aspect of third, radial and intermediate carpal bones. Osteochondral samples from each test site were divided into subchondral bone and cancellous bone portions. These were dried, resin-embedded and gold-coated. Microhardness measurements were obtained at each test site. No significant effect of intra-articular treatment was detected. At each site, cancellous bone trabecular struts had an 18-19% higher microhardness value than the overlying subchondral bone. These findings indicate that intra-articular administration of MPA at this dose has no effect on subchondral or cancellous bone adaptation to short-term exercise and, therefore, on the propensity of carpal bones to injury. Further investigation into the calcified cartilage layer, effect of different corticosteroid preparations and diffusion of medication are required.

Animals↗

PubMed2001

Dynamic mechanical characterization of biodegradable composites of hydroxyapatite and polylactides.

The thermo-mechanical analysis of some novel, totally bioactive, three-component composite systems intended for the repair and augmentation of bone has been performed. The composites are composed of hydroxyapatite (HA), particulate reinforced biodegradable polylactic acid (PDLLA), with a second reinforcing phase of semi-crystalline, unidirectional fibers of polylactic acid (PLLA) homopolymer. Dynamic mechanical analysis (DMA) applied small-strain cyclic deformations to simulate physiological loading. The effect of the two fillers on the glass transition temperature of the matrix (Tg-PDLLA) and on the viscoelastic parameters, storage modulus (EI), and tan delta were analyzed. Thermal characterization with differential scanning calorimetry (DSC) was compared to the DMA data. It was established that the addition of HA and/or PLLA fibers increased EI, both below and above Tg-PDLLA. The combination of both reinforcing agents was the most effective. The damping was reduced with the addition of HA alone and in combination with PLLA fibers. Tg-PDLLA was increased by the addition of HA, PLLA fibers, and the combination of the two reinforcing agents. The magnitude of the increase in Tg-PDLLA was similar for both types of reinforcement.

Biocompatible Materials↗

PubMed2001

Fatigue of cortical bone under combined axial-torsional loading.

The influence of torsional loading on the fatigue life of cortical bone was investigated by conducting in vitro testing. Fatigue tests were conducted on cylindrical dumbbell bovine cortical bone specimens in an environmental chamber under axial loading, torsional loading and various combinations of axial-torsional loading where the phase relationship and relative magnitudes of axial and torsional loadings were systematically varied. It was found that the superposition of torque on axial loading reduced the fatigue life of cortical bone. The reduction in fatigue life was significant when the maximum shear stress was greater than 59% of the maximum normal stress. The magnitude of reduction in the fatigue life of bone at low as well as high levels of axial loading depended on the magnitude of torsional loading, but was independent of the phase angle by which the torsional loading lagged the axial loading. Furthermore, oblique fracture profiles, characteristic of torsion-induced failure, were observed for combined axial-torsional load cases. Based on these results, it is suggested that torsional loading plays a significant role in determining the fatigue life of cortical bone.

Animals↗

PubMed2000

Fatigue characterization of a hydroxyapatite-reinforced polyethylene composite. I. Uniaxial fatigue.

The fatigue behavior of 40 volume % hydroxyapatite-reinforced polyethylene composite (HAPEXtrade mark) at 37 degrees C in saline was determined. S-N curves for this material, both in fully reversed axial tension-compression and fully reversed torsion, have been established. In tension, the cycles to failure ranged from 1000 cycles at 13 MPa to more than 1 million cycles at 4.4 MPa while in torsion they ranged from 100 cycles at 14.4 MPa to more than 1 million cycles at 4.8 MPa. Changes in strain range, tangent modulus, and cyclic energy dissipated during fatigue loading also were examined. Torsional fatigue was found to be considerably more damaging than axial fatigue. The fatigue damage accumulation process occurring in the composite was monitored by observing the reduction in modulus and the increase in energy dissipated.

Biocompatible Materials↗

PubMed2000

Fatigue characterization of a hydroxyapatite-reinforced polyethylene composite. II. Biaxial fatigue.

Previously, the uniaxial fatigue behavior of 40 volume % hydroxyapatite-reinforced polyethylene composite (HAPEXtrade mark) at 37 degrees C in saline was studied. Fatigue limits between 37 and 25% of the ultimate strengths of the material were established. This study investigates the biaxial fatigue behavior of the same material using various combinations of axial and torsional stresses. The addition of torsional to axial loading significantly reduced the fatigue life. When torsion at 25% of the ultimate strength was applied in addition to axial loading at 25% of the ultimate tensile strength, the fatigue life remained more than 1 million cycles. Out-of-phase loading was less detrimental to the fatigue life of the composite than in-phase. Fatigue damage was monitored by hysteresis loops, the increase in dissipated energy, the reduction in tangent modulus, and the increase in strain values.

Biocompatible Materials↗

PubMed2000

Contribution, development and morphology of microcracking in cortical bone during crack propagation.

A fracture mechanics study of cortical bone is presented to investigate the contribution, development morphology of microcracking in cortical bone during crack propagation. Post-hoc analyses of microcrack orientation, crack propagation velocity and fracture surface roughness were conducted on previously tested human and bovine bone compact tension specimens. It was found that, consistent with its higher toughness, bovine bone formed significantly more longitudinal, transverse and inclined microcracks than human bone. However, in human bone more of the microcracks that formed were longitudinal than transverse or inclined, a feature that would optimise bone's toughness. Crack propagation velocity in human and bovine bone displayed the same characteristic pattern with crack extension, where an increase in velocity is followed by a consequent decrease and vice versa. On the basis of this pattern, a model or crack propagation has been proposed. It provides a detailed account of mocrocrack formation and contribution towards the propagation of a fracture crack. Analyses of fracture surfaces indicated that, consistent with its higher toughness, bovine bone displays a rougher surface than human bone but they both have the same basic fractured element, i.e. a mineralised collagen fibril.

Animals↗

PubMed2000

Acetabular morphology and resurfacing design.

The bony surfaces of 18 archaeological hemipelves were scanned using a 3D laser surface scanner and CyDir software on a Silicon Graphics workstation. The acetabular area was selected and point data from the approximately spherical bone surface saved. These data were input to a MATLAB routine that calculated the radius and centre of the best-fit sphere. The goodness of fit was estimated using the mean and standard deviation of the distance of the bone surface points from the sphere surface. Eight points, at approximately equal distances around the acetabular rim, were selected with reference to bony landmarks. A plane containing three of these points served as an orientation reference plane. The vectors joining the eight rim points to the centre of the best-fit sphere were found. The angles between these vectors and the normal to the reference plane were calculated. Paired angles were summed to give the angle subtended by the acetabular rim in four directions. The overall mean angle was 158 degrees (range of mean angles 145 degrees -173 degrees ). The largest individual angles, some exceeding 180 degrees, were in the superior-inferior direction, while the mean angle in the anterior-posterior direction, i.e. that controlling flexion-extension, was 152 degrees. Males had larger subtended angles than females, although the difference was not statistically significant. Simulated reaming increased all angles by approximately 10 degrees. The subtended angles are important parameters in the design of the acetabular component of a hip replacement and particularly important in resurfacing hip replacement when the volume available is tightly constrained.

Acetabulum↗

PubMed2000

Bone fracture analysis on the short rod chevron-notch specimens using the X-ray computer micro-tomography.

Mechanical fatigue of bone leads to micro-cracking which is associated with remodeling, establishing a balance in the microcrack population of the living tissue, thus, in the steady-state, the microstructure of bone provides sites of discontinuity acting as stress raisers. Hence fracture toughness plays a decisive role in bone functionality by determining the level to which the material can be stressed in the presence of cracks, or, equivalently, the magnitude of cracking which can be tolerated at a given stress level. Cortical bone, which behaves as a quasi-brittle solid when fractured, was tested as short-rod chevron-notched tension specimens (CNT). The main features of the CNT specimen are its geometry and the V shaped notch. The notch leads to steady-state crack propagation whilst the requested geometry allows a diameter 40% smaller than the thickness of a standard compact tension specimens (CT). These features are essential to distinguish the inhomogeneties in the fracture properties of materials like bone. Bone structure and crack propagation of the CNT specimens were analyzed using X-ray computed micro-tomography (XMT), which is a non-invasive imaging technique. The unique feature of the micro-CT is the high resolution three-dimensional image which consists of multi-sliced tomographs taken in a fine pitch along the rotational axis. Fracture toughness (K(IC)) computed according to the peak load was 4.8 MNm(-3/2) while that derived from experimental calibration tests using XMT was 4.9 MNm(-3/2).

Journal Article↗

PubMed2000

Dynamic mechanical characterization of hydroxyapatite reinforced polyethylene: effect of particle size.

Dynamic mechanical analysis (DMA) was used to characterize biomedical composites consisting of synthetic hydroxyapatite (HA) particulate reinforced polyethylene (PE). The effects of the HA volume fraction, temperature and HA particle on the storage modulus (E(I)) and damping (tan delta) were investigated. Increasing HA volume fractions increased E(I) and decreased tan delta. E(I) was found to be linearly related to the Young's modulus values obtained from quasi-static tensile tests. Relative modulus and damping studies showed that the viscoelastic behavior of unfilled PE was different to that of the filled matrix due to the presence of thermally induced tensile stresses in the matrix at the filler-matrix interface.

Journal Article↗

PubMed1999

In vivo measurement of acetabular cement pressurization using a simple new design of cement pressurizer.

Aseptic loosening of the acetabular component remains a limiting factor in the long-term success of total hip replacement. An instrumented pressurizer has been designed to allow the intraoperative measurement of acetabular cement pressurization, which is known to contribute to implant fixation. Average intraoperative cement pressures in 16 operations performed by 2 surgeons were 49 +/- 17 kPa (6.4 +/- 2.3 psi) and 47 +/- 17 kPa (6.2 +/- 2.2 psi), and peak pressures were 76 +/- 5 kPa (10.0 +/- 0.6 psi) and 93 +/- 15.kPa (12.2 +/- 1.9 psi), comparable to previous work in vitro. The pressurization required for optimal cement penetration into cleaned low-density cancellous bone is reported to be of the order of 35 to 50 kPa (4.6-6.6 psi) for 30 to 60 seconds, and the present data show that this is attainable in vivo using a simple device.

Acetabulum↗

PubMed1999

Torsional stability of primary total knee replacement tibial prostheses: a biomechanical study in cadaveric bone.

The significance of torsional loads on the tibial component of total knee replacement prostheses is not clearly established. This study investigated the micromotion induced by torsion, under physiologic loads. Three forms of fixation were sequentially tested in cadaveric tibiae: press-fit, press-fit plus 4 peripheral corticocancellous screws, and horizontally cemented. The implanted tibia was loaded with an axial force between 0.5 and 2.2 kN and a cyclic torque of +/- 5 Nm. The relative motion between the prosthesis and the bone was measured. Our results show little difference between the 3 methods of fixation at high axial loads. At low axial loads, however, the press-fit prosthesis may permit micromotions high enough to interfere (theoretically) with bone ingrowth. Motion is reduced when the same prosthesis is augmented with screws. The cemented prosthesis produces the lowest average micromotion. Our study indicates that rotational micromotion is unlikely to contribute to the failure of ingrowth into the uncemented tibial prosthesis under normal physiologic loads. At low axial loads, which may be encountered in the immediate postoperative period, ingrowth may be compromised. Thus, initial rotational stability is an important consideration in uncemented total knee replacement design and postoperative management. In poor-quality tibiae, cementation may be the only method of fixation to provide sufficient torsional stability.

Adult↗

PubMed1998

Influence of sterilization by gamma irradiation and of thermal annealing on creep of hydroxyapatite-reinforced polyethylene composites.

Sterilization of medical devices by gamma (gamma)-irradiation is common. The effect of irradiation on a bone replacement material, HAPEX (hydroxyapatite-reinforced polyethylene composite), was investigated. Unfilled and hydroxyapatite-filled polyethylene at 0.20 and 0.40 filler volume fractions were gamma-irradiated at 2.5 Mrad, and the modified properties were studied by differential scanning calorimetery, isochronous experiments, and creep tests. The effect of thermal annealing of the samples from 140 degrees C also was examined. The results suggest that both irradiation and annealing increase creep resistance of the materials. These are associated with the formation of crosslinks and an increase in crystallinity, respectively.

Biocompatible Materials↗

PubMed1998

Finite element analysis of the implanted proximal tibia: a relationship between the initial cancellous bone stresses and implant migration.

The cancellous bone stresses within the implanted proximal tibia were examined using a three-dimensional anatomical finite element model. Three versions of a proximal tibial prosthesis were examined: an all polyethylene press-fit design; a metal backed, stemmed press-fit design and a (horizontally) cemented metal backed, stemmed design. All three designs had published migration and survivorship data. The objectives of the study were (i) to compare the stresses generated by each of the tibial components, (ii) examine the influence of the resected surface morphology and (iii) compare the initial cancellous bone stresses with the published migration and survivorship data. The all polyethylene prosthesis generated the highest cancellous bone stresses. Addition of a metal backing and a stem reduced the stresses, but the cemented device produced the lowest cancellous bone stresses. The surface morphology had a significant effect on the cancellous bone stresses generated by press-fit prostheses. As the bone-prosthesis contact area decreased, the peak cancellous bone stresses increased by as much as 243%. The surface morphology had no effect on the cancellous bone stresses generated by the cemented implant. Good correlation was found between the predicted cancellous bone stresses and the migration and survivorship data, with the implant generating the highest cancellous bone stresses migrating the most and having the poorest survival rates at 5 year. The results support the hypothesis that the progressive failure of cancellous bone is a mechanism of implant migration regardless of the method of fixation and the implantation site.

Biomechanical Phenomena↗

PubMed1998

Isothermal and non-isothermal polymerization of a new bone cement.

A new bone cement based on poly(ethylmethacrylate) (PEMA), hydroxyapatite powder (HA) and n-butylmethacrylate monomer (n-BMA) has been studied using isothermal and non-isothermal polymerization. Methacrylate monomers are highly reactive and release a considerable amount of heat during polymerization. A quantitative understanding of the methacrylate polymerization is necessary because the thermal history of the polymerization has considerable influence on the final properties of a bone cement. In the first part, polymerization kinetics are analysed by means of differential scanning calorimetry (DSC). DSC data are used to evaluate a phenomenological model describing the cure kinetics of this new bone cement. In the second part, a kinetic model coupled with the energy balance is used to obtain temperature and degree of conversion profiles in the bone-cement-prosthesis system, under non-isothermal conditions, as function of initial temperature and thickness of the cement. Material properties, boundary and initial conditions and the kinetic behaviour are the input data for the numerically solved heat-transfer model. The temperature at the bone/cement interface, can be considered as a weak point, often responsible for total joint replacement failure. For this particular bone cement exhibiting a low exotherm and low glass transition temperature, the interfacial temperature is lower than the threshold level for thermal tissue damage (50 degrees C). The conversion occurs almost completely, avoiding problems with unreacted monomers that can be released by the cement, giving rise to tissue damage.

Journal Article↗

PubMed1998

Comparison between the polymerization behavior of a new bone cement and a commercial one: modeling and in vitro analysis.

The polymerization behavior of a new bone cement based on poly(ethylmethacrylate), hydroxyapatite powder and n-butylmethacrylate monomer and a commercial cement have been studied. Polymerization kinetics were analyzed by means of differential scanning calorimetry (DSC). DSC data have been used to evaluate a phenomenological model describing the cure kinetics of this new bone cement. The kinetic model coupled with the energy balance was then used to obtain temperature and degree of conversion profiles in the bone-cement-prosthesis system, under non-isothermal conditions, as function of initial temperature and thickness of the cement. Material properties, boundary and initial conditions and the kinetic behavior were the input data for the numerically solved heat-transfer model. The modeling results have been compared with in vitro results.

Journal Article↗

PubMed1998

Histomorphological and biomechanical characterization of calcium phosphates in the osseous environment.

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.

Animals↗