Catherine Dobson | Hull - Academia.edu (original) (raw)

Papers by Catherine Dobson

Medical Engineering & Physics, May 1, 2017

The use of finite element analysis (FEA) to investigate the biomechanics of anatomical systems cr... more The use of finite element analysis (FEA) to investigate the biomechanics of anatomical systems critically relies on the specification of physiologically representative boundary conditions. The biomechanics of the pelvis has been the specific focus of a number of FEA studies previously, but it is also a key aspect in other investigations of, for example, the hip joint or new design of hip prostheses. In those studies, the pelvis has been modelled in a number of ways with a variety of boundary conditions, ranging from a model of the whole pelvic girdle including soft tissue attachments to a model of an isolated hemi-pelvis. The current study constructed a series of FEA models of the same human pelvis to investigate the sensitivity of the predicted stress distributions to the type of boundary conditions applied, in particular to represent the sacro-iliac joint and pubic symphysis. Varying the method of modelling the sacro-iliac joint did not produce significant variations in the stress distribution, however changes to the modelling of the pubic symphysis were observed to have a greater effect on the results. Over-constraint of the symphysis prevented the bending of the pelvis about the greater sciatic notch, and underestimated high stresses within the ilium. However, permitting medio-lateral translation to mimic widening of the pelvis addressed this problem. These findings underline the importance of applying the appropriate boundary conditions to FEA models, and provide guidance on suitable methods of constraining the pelvis when, for example, scan data has not captured the full pelvic girdle. The results also suggest a valid method for performing hemi-pelvic modelling of cadaveric or archaeological remains which are either damaged or incomplete.

Bone, Apr 1, 1998

A stochastic simulation of cancellous bone resorption was developed and applied to a simple two-d... more A stochastic simulation of cancellous bone resorption was developed and applied to a simple two-dimensional lattice structure representing the vertebral body. The simulation is based upon the concept of a basic multicellular unit (BMU) where net resorption (-deltaB.BMU) is considered at bone/marrow surfaces. The cancellous bone structure is defined as a binary matrix with the size of the pixels corresponding to a square element of approximately 20 microm dimension. The simulation considers both the probability that any surface pixel will be activated into a BMU and, if activated, the length of the resorption cavity. The relationship between relative stiffness and density for the simulation was predicted by finite element analysis. The stochastic simulation was iterated eight times with the mechanical properties assessed after each stage. Perforation of a single trabeculae was first observed at step 2, the structure completely lacking connectivity and mechanical integrity by step 8. The slope of the stiffness-porosity graph was greater than unity for the first five steps, but thereafter approached zero because the structure had lost connectivity and effectively collapsed. The eight-step simulation was repeated five times and demonstrated that, although the stiffness/density relationships were similar at the extremes of density, the dependence of stiffness upon density varied. This clearly demonstrates the stochastic nature of the simulation upon cancellous bone structure, and is probably indicative of a significant dependence of mechanical integrity upon perforation effects.

Computer Methods in Biomechanics and Biomedical Engineering, Jun 13, 2020

Remodelling and adaptation of bone within the pelvis is believed to be influenced by the mechanic... more Remodelling and adaptation of bone within the pelvis is believed to be influenced by the mechanical strains generated during locomotion. Variation in the cortical bone thickness observed in the prenatal ilium has been linked to the musculoskeletal loading associated with in utero movements; for example the development of a thicker gluteal cortex is a possible response to contractions of the gluteal muscles. This study examines if the strains generated in the prenatal iliac cortex due to musculoskeletal loading in utero are capable of initiating bone remodelling to either maintain homeostasis or form new bone. Computational modelling techniques were used firstly to predict the muscle forces and resultant joint reaction force acting on the pelvis during a range of in utero movements. Finite element analyses were subsequently performed to calculate the von Mises strains induced in the prenatal ilium. The results demonstrated that strains generated in the iliac cortex were above the thresholds suggested to regulate bone remodelling to either maintain homeostasis or form new bone. Further simulations are required to investigate the extent to which the heterogeneous cortex forms in response to these strains (i.e. remodelling) or if developmental bone modelling plays a more pivotal role.

Proceedings Of The Institution Of Mechanical Engineers, Part H: Journal Of Engineering In Medicine, Dec 26, 2014

Biomechanical analysis of juvenile pelvic growth can be used in the evaluation of medical devices... more Biomechanical analysis of juvenile pelvic growth can be used in the evaluation of medical devices and investigation of hip joint disorders. This requires access to scan data of healthy juveniles, which are not always freely available. This article analyses the application of a geometric morphometric technique, which facilitates the reconstruction of the articulated juvenile pelvis from cadaveric remains, in biomechanical modelling. The sensitivity of variation in reconstructed morphologies upon predicted stress/strain distributions is of particular interest. A series of finite element analyses of a 9-year-old hemi-pelvis were performed to examine differences in predicted strain distributions between a reconstructed model and the originally fully articulated specimen. Only minor differences in the minimum principal strain distributions were observed between two varying hemi-pelvic morphologies and that of the original articulation. A Wilcoxon rank-sum test determined there was no statistical significance between the nodal strains recorded at 60 locations throughout the hemi-pelvic structures. This example suggests that finite element models created by this geometric morphometric reconstruction technique can be used with confidence, and as observed with this hemi-pelvis model, even a visual morphological difference does not significantly affect the predicted results. The validated use of this geometric morphometric reconstruction technique in biomechanical modelling reduces the dependency on clinical scan data.

Computer Methods in Biomechanics and Biomedical Engineering, Jan 25, 2018

Legg-Calvé-Perthes disease (LCP) is one of the most poorly understood diseases in paediatric orth... more Legg-Calvé-Perthes disease (LCP) is one of the most poorly understood diseases in paediatric orthopaedics. One common trait of LCP is the marked morphological difference between healthy and pathological hips, early deviations of which (i.e. prior to disease onset) have been suggested to lead to the overload and collapse of the epiphysis. Here, the impact of common variations in geometry is investigated with a finite element model of a juvenile femur under single leg standing and landing. Here, the impact of typical variations in geometry is investigated with a finite element model of a juvenile femur under single leg standing and landing. The variations appear to have only a limited effect on the stress distribution in the femoral epiphysis even during high impact activities. This suggests that, for this individual at least, they would be unlikely to cause epiphyseal overload and collapse, even in the presence of a skeletally immature epiphysis.

Gait & Posture, Jul 1, 2018

Title: Relationships between walking speed, T-score and age with gait parameters in older post-me... more Title: Relationships between walking speed, T-score and age with gait parameters in older post-menopausal women with low bone mineral density Background: The gait patterns of women with low bone mineral density (BMD) or osteoporosis have not been thoroughly explored, and when examined, often studied in relation to falls and kyphosis. Research question: The aim of this study was to investigate the relationships between gait parameters and comfortable, self-selected walking speed and BMD in older post-menopausal women with a range of T-scores (healthy to osteoporotic). Methods: 3D kinematic and kinetic data were collected from forty-five women mean (SD) age 67.3 (1.4) years during level walking at their preferred speed. Multiple regression analysis explored the explained variance attributable to speed, femoral neck T-score, and age. Results: The mean (SD) walking speed 1.40 (0.19) m•s-1 explained the variance in most temporalspatial, kinematic and joint powers (R 2 =12-68%, P≤0.001). T-score accounted for (R 2 =23%, P≤0.001) of the shared explained variance in stride width. It also increased the explanatory power for knee flexion (R 2 =7%, P≤0.05) and knee range of motion (R 2 =12%, P≤0.01). Power absorption by the knee flexors in terminal swing (K4) was the only power burst resulting in significant slope coefficients for all predictor variables (R 2 =52 and 54%) (P≤0.001) and (R 2 =68%, P≤0.05). Significance: Speed alone explained much of the variance of gait parameters, while speed and Tscore combined increased the explained variance in some knee variables. Our findings demonstrate that older post-menopausal women with a broad range of T-scores can walk at comfortably fast speeds. The results also suggest that strengthening the hip abductor, knee extensor and flexor muscle groups may benefit the gait patterns of older postmenopausal women with low BMD.

Proceedings Of The Institution Of Mechanical Engineers, Part H: Journal Of Engineering In Medicine, Jul 29, 2010

Three-dimensional reconstructions of bone geometry from microCT (computed tomography) data are fr... more Three-dimensional reconstructions of bone geometry from microCT (computed tomography) data are frequently used in biomechanical and finite element analyses. Digitization of bone models is usually a simple process for specimens with a complete geometry, but in instances of damage or disarticulation it can be very challenging. Subsequent to digitization, further imaging techniques are often required to estimate the geometry of missing bone or connecting cartilage. This paper presents an innovative approach to the reconstruction of incomplete scan data, to reproduce proper anatomical arrangements of bones, including absent connecting cartilaginous elements. Utilizing geometric morphometric tools, the reconstruction technique is validated through comparison of a reconstructed 9 year old pelvis, to the original CT data. A principal component analysis and an overlay of the two pelves provide a measure of the accuracy of the reconstructed model. Future work aims to investigate the biomechanical effects of any minor positional error on the bone's predicted structural properties through the use of finite element analysis.

Gait & Posture, Sep 1, 2016

 Non-motorised treadmill locomotion creates large reductions in tibial acceleration.  Non-motor... more  Non-motorised treadmill locomotion creates large reductions in tibial acceleration.  Non-motorised treadmill locomotion increases lower limb muscular activation.  Non-motorised treadmill locomotion decreases cycle time/increases step frequency.

Proceedings Sixth International Conference on Information Visualisation

ABSTRACT A set of algorithms has been developed and applied, in order to quantify the morphology ... more ABSTRACT A set of algorithms has been developed and applied, in order to quantify the morphology of structures produced by our work on computer simulation of cancellous bone remodelling. The set of algorithms is organised in three themes, based on the set of metrics they compute. The first one deals with the direct derivation of basic metrics such as the trabecular thickness, separation and number. The second deals with the area/volume distribution of bone and marrow, while the third one considers surface roughness and perimeter/area. The algorithms were tested on sample sections of cancellous bone and applied to a simulation of strain adaptation incorporating complex multi-axial loading. The metrics have shown to be independent of structural anisotropy, in contrast to some established methods that assume certain morphologies.

Journal of Biomechanics, 2022

To study essential anterior-posterior and medial-lateral sways of the stance caused by rotational... more To study essential anterior-posterior and medial-lateral sways of the stance caused by rotational movements about the ankle and hip joints, a mathematical model is developed for the 3D postural kinematics and dynamics. The model is in the form of nonlinear differential-algebraic equations corresponding to a biomechanical system with holonomic constraints. A nonlinear feedback control law is further derived for stabilizing the upright stance, whilst eliminating internal torques induced by the constraints on postural movements. Numerical simulations of the model parametrized with experimental data of human body segments illustrate the performance of postural balancing with the proposed control. This work is an essential step towards a much improved understanding of constrained geometry and balancing control of 3D human standing dynamics.

Bone & Joint Research, 2018

Objectives Legg–Calvé–Perthes’ disease (LCP) is an idiopathic osteonecrosis of the femoral head t... more Objectives Legg–Calvé–Perthes’ disease (LCP) is an idiopathic osteonecrosis of the femoral head that is most common in children between four and eight years old. The factors that lead to the onset of LCP are still unclear; however, it is believed that interruption of the blood supply to the developing epiphysis is an important factor in the development of the condition. Methods Finite element analysis modelling of the blood supply to the juvenile epiphysis was investigated to understand under which circumstances the blood vessels supplying the femoral epiphysis could become obstructed. The identification of these conditions is likely to be important in understanding the biomechanics of LCP. Results The results support the hypothesis that vascular obstruction to the epiphysis may arise when there is delayed ossification and when articular cartilage has reduced stiffness under compression. Conclusion The findings support the theory of vascular occlusion as being important in the patho...

Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2002

Many areas of biomedical engineering involve the modelling of biological systems, often using dat... more Many areas of biomedical engineering involve the modelling of biological systems, often using data from medical scanning techniques such as computed microtomography (μCT), and the prediction of the mechanical properties of these systems via finite element models. These models, and also those produced from remodelling simulations on idealized bone structures, are inherently highly pixelated and therefore have a high degree of surface roughness. The purpose of this paper is to demonstrate that this surface roughness need not necessarily have an influence on the predicted properties of the object under examination. To demonstrate this, two-dimensional idealized models of cancellous bone structures were used that were initially depleted and then rebuilt stochastically. A hysteresis effect was observed such that a significant amount of rebuilding beyond the original density was required to regain the initial intact stiffness. To ensure that this effect was not an artefact of the high deg...

Proceedings Fifth International Conference on Information Visualisation, 2001

ABSTRACT A set of algorithms has been developed and evaluated for 3D and 2&frac12;D rapid... more ABSTRACT A set of algorithms has been developed and evaluated for 3D and 2&frac12;D rapid prototyping replication of 3D reconstructions of cancellous bone samples. The algorithms replicate a voxel map without any loss of fidelity, so as to increase the validity of the comparison of mechanical tests on the 3D reconstructed models with those predicted by finite element analyses. The evaluation is both in terms of algorithmic complexity and the resultant data set size. The former determines the feasibility of the conversion process, whereas the latter the potential success of the manufacturing process

Rapid Prototyping Journal, 2002

... Hull and East Yorkshire Hospitals NHS Trust. The authors would also like to thank Bert van Ri... more ... Hull and East Yorkshire Hospitals NHS Trust. The authors would also like to thank Bert van Rietbergen (Eindhoven, The Netherlands) for providing the data for the human bone samples, along with Chris Manners (3D Systems Inc, USA), Colin Blain (3D Systems, UK), and Kris ...

Computer Methods in Biomechanics and Biomedical Engineering, 1999

A stochastic simulation of the resorption of cancellous bone has been developed and integrated wi... more A stochastic simulation of the resorption of cancellous bone has been developed and integrated with a finite element model to predict the resultant change in structural properties of bone as bone density decreases. The resorption represents the net imbalance of osteoclast and osteoblast activity that occurs in osteoporosis. A simple lattice structure of trabecular bone is considered, with an examination of the lattice geometry and discretization indicating that just five trabeculae need to be modelled. The results from the analysis show how the mechanical properties of the cancellous bone degrade with osteoporosis and demonstrate how the method can be used to predict the relationships between stiffness and density or porosity.

Bone, 2000

The aim of this study was to investigate the recovery in cancellous bone stiffness resulting from... more The aim of this study was to investigate the recovery in cancellous bone stiffness resulting from anabolic treatment following varying degrees of resorption, using a stochastic simulation applied to a simplistic structure consisting of five vertical and five horizontal trabeculae. The structure was initially resorbed, and "bone" elements were stochastically removed until nominal resorptions of 10%, 15%, 20%, 25%, and 30% were achieved. A stochastic simulation of anabolic treatment was then applied where bone elements were added, continuing until the original stiffness had been regained, for example, simulating treatment of a patient with an anabolic agent after a period of postmenopausal resorption. The resorption and anabolic simulations were repeated three times for each of the nominal resorptions. The stiffness of the bone structure decreased linearly with resorption, with a slope of approximately -2 and an R(2) of 97.0%; hence, the stiffness fell at approximately twice the rate of the reduction in density. When the various structures regained their original density, the resultant stiffness also had a linear relationship with the original resorption, with a slope of -1 and a lower R(2) of 86.1%. This implies that the reduction in stiffness, when original density was regained, fell proportionately with the degree of initial resorption and, therefore, after a resorption of 30%, when original density was regained, the stiffness of the resultant structure was approximately 30% less than that of the original structure. The density required for the original stiffness to be regained increased linearly with the degree of initial resorption, with a slope of approximately 0.5 and an R(2) of 65.2%, lower than that observed for the previous relationships. This indicates a greater spread of data and suggests greater variability in the formation phase beyond the point of regained original density. Because irreversible connectivity reduction is widely considered to be one of the earliest manifestations of estrogen loss, these findings, although obtained on a simulation of a simplistic cancellous bone structure, support the concept of early intervention to prevent potentially irreversible deterioration of trabecular architecture after menopause.

Journal of Anatomy, Jun 1, 2007

The mammalian aortic tunica media is, in its entire length, conventionally believed to comprise m... more The mammalian aortic tunica media is, in its entire length, conventionally believed to comprise medial lamellar units (MLU). Each of these units consists of an elastic lamella and the subjacent smooth muscle and collagen. Studies suggested that these units may be resolved into musculoelastic fascicles (MEF). Studies have reported regional and interspecies variation in the structure of the aortic tunica media. Less attention, however, has been paid to that of the goat aorta. The goat may be a suitable model for vascular studies because of its size and ease of handling. The objective of the present study is to elucidate the regional differences in the structure of the tunica media of the goat aorta. Samples were obtained from 20 domestic adult male goats ( Capra ibex ). Before sacrificing, the animals were anaesthetized with ketamine. After opening the thorax and abdomen, 1–2 mm transverse segments of the aorta from different vertebral levels were fixed by immersion in 10% formal saline, processed for paraffin embedding. 7 μ m thick sections were stained with Masson’s trichrome and Weigert resorsin and counterstained with Van Gieson stains to demonstrate the components of the aortic media., Observations reveal that the tunica media of the ascending, arch and proximal thoracic aorta comprise 2 zones, namely a luminal zone with regular concentric elastic lamellae and an adventitial zone in which the elastic lamellae are interrupted by islands of smooth muscle. There appears to be a transitional zone at about T10–T12 in which the muscle islands gradually diminish until by T13 the aorta assumes a typical elastic structure. The tunica media of the abdominal aorta appears to be composed mostly of elastic lamellae between which are regularly disposed concentric smooth muscle fibres, and collagen. Based on these observations, the tunica media of the goat aorta may be divided into 3 regions namely, a proximal musculoelastic segment extending down to T9; a transitional segment spanning T10–T12 and an elastic segment from T13 to the bifurcation., It is proposed that the muscle islands in the tunica media of the proximal parts of the goat aorta augment the windkessel mechanism in aortic function, which was previously attributed only to elastic fibres, and may also be part of the systolic thrust absorbing mechanism. The uniform predominantly elastic structure of the abdominal aorta may be involved in the conventional stretch-recoil mechanism.

Journal of Electromyography and Kinesiology, 2018

High impact exercise can reduce postmenopausal bone loss, however stimulus frequency (loading cyc... more High impact exercise can reduce postmenopausal bone loss, however stimulus frequency (loading cycles per second) can affect osteogenesis. We aimed to examine the effect of stimulus frequency on the mechanical loading of four common osteoporosis prevention exercises, measuring body acceleration and muscle activation with accelerometry and electromyography (EMG), respectively. Fourteen early postmenopausal women completed randomised countermovement jumps (CMJ), boxdrops (BD), heel-drops (HD) and stamp (STP) exercises for continuous and intermittent stimulus frequencies. Sacrum accelerometry and surface electromyography (EMG) of four muscles were recorded. CMJ (mean ±

Journal of Anatomy, 2007