1,721,116 research outputs found
The geometry of a circular arc does not accurately describe spinal curvature in scoliosis
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Spinal Accelerations on Theme Park Rides
No full textWhile theme park rides are carefully designed, the spinal accelerations experienced by riders are not well known, thus their suitability for paediatric patients who have undergone surgery for Adolescent Idiopathic Scoliosis (AIS) is not clear. Scoliosis surgery involves spinal fusion, a process which takes 3-6 months post-surgery for bridging bone to grow between adjacent vertebrae. Currently, doctors advise their patients on activities which are suitable to participate in, post surgery. This project, initiated by Surgeons and the Paediatric Spine Research Group at the Mater Hospital, Brisbane, aims to determine the suitability of this popular activity for post surgery AIS patients.\ud
The measured spinal accelerations on various local theme park rides were compared to spinal accelerations experienced during acceptable post surgery activities determined by health professionals. Initial findings suggest slightly higher G forces are experienced riding thene park rides, with little attenuation from L1 to C4. In addition, the data measured was used to perform a biomechanical assessment of the scoliotic spine in comparison to the 'normal' spine
Endogenous musculoskeletal tissue engineering : a focussed perspective
No full textTwo major difficulties facing widespread clinical implementation of existing Tissue Engineering (TE) strategies for the treatment of musculoskeletal disorders are (1) the cost, space and time required for ex vivo culture of a patient’s autologous cells prior to re-implantation as part of a TE construct, and (2) the potential risks and availability constraints associated with transplanting exogenous (foreign) cells. These hurdles have led to recent interest in endogenous TE strategies, in which the regenerative potential of a patient’s own cells is harnessed to promote tissue regrowth without ex vivo cell culture. This article provides a focused perspective on key issues in the development of endogenous TE strategies, progress to date, and suggested future research directions toward endogenous repair and regeneration of musculoskeletal tissues and organs
Lateral bone density variations in the scoliotic spine
No full textAdolescent Idiopathic Scoliosis (AIS) is the most common deformity of the spine, affecting 2-4% of the population. Previous studies have shown that the vertebrae in scoliotic spines undergo abnormal shape changes, however there has been little exploration of how scoliosis affects bone density distribution within the vertebrae. In this study, existing CT scans of 53 female idiopathic scoliosis patients with right-sided main thoracic curves were used to measure the lateral (right to left) bone density profile at mid-height through each vertebral body. Five key bone density profile measures were identified from each normalised bone density distribution, and multiple regression analysis was performed to explore the relationship between bone density distribution and patient demographics (age, height, weight, body mass index (BMI), skeletal maturity, time since Menarche, vertebral level, and scoliosis curve severity). Results showed a marked convex/concave asymmetry in bone density for vertebral levels at or near the apex of the scoliotic curve. At the apical vertebra, mean bone density at the left side (concave) cortical shell was 23.5% higher than for the right (convex) cortical shell, and cancellous bone density along the central 60% of the lateral path from convex to concave increased by 13.8%. The centre of mass of the bone density profile at the thoracic curve apex was located 53.8% of the distance along the lateral path, indicating a shift of nearly 4% toward the concavity of the deformity. These lateral bone density gradients tapered off when moving away from the apical vertebra. Multi-linear regressions showed that the right cortical shell peak bone density is significantly correlated with skeletal maturity, with each Risser increment corresponding to an increase in mineral equivalent bone density of 4-5%. There were also statistically significant relationships between patient height, weight and BMI, and the gradient of cancellous bone density along the central 60% of the lateral path. Bone density gradient is positively correlated with weight, and negatively correlated with height and BMI, such that at the apical vertebra, a unit decrease in BMI corresponds to an almost 100% increase in bone density gradient
Computer Simulation of Microdamage and Microfracture in Vertebral Trabecular Bone
No full textABSTRACT ID 79\ud
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COMPUTER SIMULATION OF MICRODAMAGE AND MICROFRACTURE IN VERTEBRAL TRABECULAR BONE\ud
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INTRODUCTION The existence of both diffuse microdamage and discrete microfractures in trabecular bone has been reported on numerous occasions (eg. 1), and healing cracks appear to be a normal feature of trabecular bone response to physiological loads (2). However, while partial cracks lead to callus formation and repair, through-cracks may cause resorption of entire trabeculae due to the loss of strain in the disconnected strut, contributing to long term bone loss and increased risk of gross fracture (3). For these reasons, the biomechanics of trabecular bone microdamage and microfracture are of significant clinical interest. The aim of this study was to investigate trabecular bone microdamage mechanics using combined finite/discrete element numerical modelling techniques.\ud
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METHOD Two-dimensional models of rectangular samples of trabecular bone subjected to uniaxial compressive loading were created using Voronoi diagrams and solved using a combined finite/discrete element simulation software package. The chosen mesh parameters resulted in a porosity of ~87%, or bone volume to total volume ratio (BV/TV) of 13.4%. Trabecular bone was represented using an elastic-plastic material model which allowed the bone to fracture when a certain tensile strain was reached. Models were held at the lower edge and loaded in compression at the upper edge. Levels of microdamage and microfracture were assessed by counting the number of struts with either plastic strains or distinct cracks at a given strain level.\ud
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RESULTS At an apparent compressive strain of 3%, brittle models showed cracking in up to 8% of the trabecular struts. At lower compressive strain levels, microfractures were randomly distributed throughout the trabecular model. As the compressive strain was increased, cracks rapidly coalesced to form a complete fracture plane through the bone. A much higher proportion of struts experienced 'diffuse' damage (plastic bending) than discrete crack formation. The degree of lateral constraint provided by the surrounding cortical bone was predicted to make a large difference to the apparent elastic modulus (260% higher for a confined than an unconfined cas) and to the maximum compressive stress (90% higher for confined than unconfined case).\ud
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DISCUSSION The computer simulations presented in this study represent an initial application of numerical modelling tools to trabecular microfracture mechanics. The geometry used in the models was highly simplified from actual trabecular bone, but the models correctly predicted (i) the onset of microdamage and microfracture in trabecular bone well before apparent yield, (ii) the prevalence of microdamage (plastic bending) over microfracture (cracking) of trabecular struts, (iii) the low proportion of struts fractured even at high compressive strains. There is a need for better material properties to describe the mechanics of trabecular bone, as well as more realistic geometric representation, however we conclude that computer simulation techniques are a potentially valuable predictive tool for better understanding the mechanics of microdamage and microfracture in vertebral trabecular bone
Distribution of forces during fulcrum bending radiographs on adolescent idiopathic scoliosis patients
No full textAt the Mater Children’s Hospital, approximately 80% of patients presenting with Adolescent Idiopathic Scoliosis requiring corrective surgery receive a fulcrum bending radiograph. The fulcrum bending radiograph provides a measurement of spine flexibility and a better indication of achievable surgical correction than lateral-bending radiographs (Cheung and Luk, 1997; Hay et al 2008). The magnitude and distribution of the corrective force exerted by the bolster on the patient’s body is unknown. The objective of this pilot study was to measure, for the first time, the forces transmitted to the patient’s ribs through the bolster during the fulcrum bending radiograph
Finite element prediction of the performance of sugarcane rolling mills
No full textExtraction of juice from shredded sugarcane is commonly performed using sets of counter-rotating rolls. The design and operation of sugarcane rolling mills has been largely empirical to date, with limited consideration of the underlying physical processes governing mill performance. In particular, maximum roll surface speeds have changed little in the past five decades, requiring large increases in blanket thickness to achieve higher crushing rates. Recent advances in computer simulation using the finite element method have provided new tools to simulate and optimise mill performance however. This study uses finite element (FE) methods to solve the governing mathematical equations for flow of juice through the fibrous blanket during rolling of prepared sugarcane, and to predict roll load and torque, extraction energy, frictional sliding at the roll/blanket interface, and the behaviour of roll grooves. The FE results suggest that higher roll speeds and thinner blankets (than those currently used in industry practice) would maintain crushing rates and juice extraction levels while reducing roll load, torque, and power consumption, and decreasing frictional sliding between rolls and cane blanket
The Neutral Zone In Lumbar Joint Movements And How It Is Affected By Preload
No full textIntroduction \ud
It is important to understand the mechanics of the lumbar spine, as it has been shown that much low back pain is attributable to mechanical factors. One important aspect of spinal mechanics is the neutral zone, defined as a region of little or no resistance to motion on either side of the neutral position for a motion segment. If the neutral zone is a significant feature of intervertebral joint mechanics then the spinal joints will have little intrinsic stability and rely on muscles to control their movement around the neutral position. This has significant implications for our understanding of how degenerative changes to the spinal joints might destabilise the spine. This study was performed to characterise the size of the neutral zone and the effect of axial preload for different spinal motions.\ud
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Methods \ud
Using a 6 degree-of-freedom (DOF) ABB industrial robot incorporating a 6-DOF JR3 force sensor, six isolated ovine lumbar joint segments were subjected to 5 repetitive movements in 3 directions (6° extension / 15° flexion, +/- 7° lateral bend, +/- 3° axial twist) with 4 different preloads (0, 150, 300, 450N) under 2 conditions (facet joints intact and facets removed). For each direction, the fixed axis about which the joint would rotate with a minimal motion-opposing moment was determined in advance. In accordance with a previous study by this group, the neutral zone was defined as the region where absolute rotational stiffness is less than 0.05 Nm/°.\ud
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Results\ud
When moving from 6° of extension to -15° (flexion) a neutral zone was usually observed starting around 0° and continuing as far as -8 or -9°. The neutral zone was in the same region when moving in the opposite direction, except when the specimen showed a considerable amount of hysteresis, in which case the neutral zone could start as early as -11° or -12° and usually continued to -2°or -3°. Increasing preload usually made the joint stiffer in the regions outside the neutral zone, but did not affect the neutral zone itself. If present without preload, hysteresis usually increased with increasing preload. In lateral bend and axial twist no neutral zone was generally observed. In lateral bend the stiffness gradually increased with rotation, whereas in axial twist the stiffness was usually constant over the range of movement. For all movements, the only effect of facet removal was a constant reduction in stiffness over the whole movement. For lateral bend this meant that the stiffness around 0° usually would drop below the threshold of 0.05Nm/°, hence creating a neutral zone extending over a couple of degrees.\ud
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Discussion\ud
Ovine spinal joints have a region where there is little to no resistance to flexion/extension. This region can be in excess of 10°. This means in their neutral position, the individual spinal joints have virtually no stability and the spine depends on other measures such as muscle activation to maintain stability in the sagittal plane. For lateral bend there is a region of little resistance as well, but it is not nearly as profound as in flexion/extension
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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