Development of a biaxial compression device for biological samples : preliminary experimental results for a closed cell foam

Biological tissues are subjected to complex loading states in vivo and in order to define constitutive equations that effectively simulate their mechanical behaviour under these loads, it is necessary to obtain data on the tissue's response to multiaxial loading. Single axis and shear testing of biological tissues is often carried out, but biaxial testing is less common. We sought to design and commission a biaxial compression testing device, capable of obtaining repeatable data for biological samples. The apparatus comprised a sealed stainless steel pressure vessel specifically designed such that a state of hydrostatic compression could be created on the test specimen while simultaneously unloading the sample along one axis with an equilibrating tensile pressure. Thus a state of equibiaxial compression was created perpendicular to the long axis of a rectangular sample. For the purpose of calibration and commissioning of the vessel, rectangular samples of closed cell ethylene vinyl acetate (EVA) foam were tested. Each sample was subjected to repeated loading, and nine separate biaxial experiments were carried out to a maximum pressure of 204 kPa (30 psi), with a relaxation time of two hours between them. Calibration testing demonstrated the force applied to the samples had a maximum error of 0.026 N (0.423% of maximum applied force). Under repeated loading, the foam sample demonstrated lower stiffness during the first load cycle. Following this cycle, an increased stiffness, repeatable response was observed with successive loading. While the experimental protocol was developed for EVA foam, preliminary results on this material suggest that this device may be capable of providing test data for biological tissue samples. The load response of the foam was characteristic of closed cell foams, with consolidation during the early loading cycles, then a repeatable load-displacement response upon repeated loading. The repeatability of the test results demonstrated the ability of the test device to provide reproducible test data and the low experimental error in the force demonstrated the reliability of the test data.

Lateral bone density variations in the scoliotic spine

Adolescent 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.

I-cobb - An innovative technique in spinal radiographic measurement

The measurement of Cobb angles on radiographs of patients with spinal deformities is routine practice in spinal clinics. The technique relies on the use and availability of specialist equipment such as a goniometer, cobbometer or protractor. The aim of this study was to validate the use of i-Phone (Apple Inc) combined with Tilt Meter Pro software as compared to a protractor in the measurement of Cobb angles. The i-Phone combined with Tilt Meter Pro software offers a faster alternative to the traditional method of Cobb angle measurement. The use of i-Phone offers a more convenient way of measuring Cobb angles in the outpatient setting. The intra-observer repeatability of the iPhone is equivalent to the protractor in the measurement of Cobb angles.

The relationship between deformity correction and clinical outcomes after thoracoscopic scoliosis surgery

Surgical treatment of scoliosis is quantitatively assessed in the clinic using radiographic measures of deformity correction, as well as the rib hump, but it is important to understand the extent to which these quantitative measures correlate with self-reported improvements in patients’ quality of life following surgery. The purpose of this prospective study was to evaluate the relationship between clinical outcomes of thoracoscopic anterior scoliosis surgery and deformity correction using the Scoliosis Research Society questionnaire (SRS-24). Patients undergoing thoracoscopic anterior scoliosis correction report good SRS scores which are comparable to those reported in previous studies for both open and thoracoscopic scoliosis correction procedures. Major Cobb correction is a significant predictor of patient satisfaction when comparing subgroups of patients with the highest and lowest major curve corrections.

The effect of insertion time on the axial pullout strength of anterior vertebral body screws

Top screw pullout occurs when the screw is under too much axial force to remain secure in the vertebral body. In vitro biomechanical pullout tests are commonly done to find the maximum fixation strength of anterior vertebral body screws. Typically, pullout tests are done instantaneously where the screw is inserted and then pulled out immediately after insertion. However, bone is a viscoelastic material so it shows a time dependent stress and strain response. Because of this property, it was hypothesised that creep occurs in the vertebral trabecular bone due to the stress caused by the screw. The objective of this study was therefore to determine whether the axial pullout strength of anterior vertebral body screws used for scoliosis correction surgery changes with time after insertion. This study found that there is a possible relationship between pullout strength and time; however more testing is required as the sample numbers were quite small. The design of the screw is made with the knowledge of the strength it must obtain. This is important to prevent such occurrences as top screw pullout. If the pullout strength is indeed decreased due to creep, the design of the screw may need to be changed to withstand greater forces.

Web-based public participatory GIS

Decision support systems (DSS) have evolved rapidly during the last decade from stand alone or limited networked solutions to online participatory solutions. One of the major enablers of this change is the fastest growing areas of geographical information system (GIS) technology development that relates to the use of the Internet as a means to access, display, and analyze geospatial data remotely. World-wide many federal, state, and particularly local governments are designing to facilitate data sharing using interactive Internet map servers. This new generation DSS or planning support systems (PSS), interactive Internet map server, is the solution for delivering dynamic maps and GIS data and services via the world-wide Web, and providing public participatory GIS (PPGIS) opportunities to a wider community (Carver, 2001; Jankowski & Nyerges, 2001). It provides a highly scalable framework for GIS Web publishing, Web-based public participatory GIS (WPPGIS), which meets the needs of corporate intranets and demands of worldwide Internet access (Craig, 2002). The establishment of WPPGIS provides spatial data access through a support centre or a GIS portal to facilitate efficient access to and sharing of related geospatial data (Yigitcanlar, Baum, & Stimson, 2003). As more and more public and private entities adopt WPPGIS technology, the importance and complexity of facilitating geospatial data sharing is growing rapidly (Carver, 2003). Therefore, this article focuses on the online public participation dimension of the GIS technology. The article provides an overview of recent literature on GIS and WPPGIS, and includes a discussion on the potential use of these technologies in providing a democratic platform for the public in decision-making.

Computer simulation in spine biomechanics : An application in adolescent idiopathic scoliosis

Scoliosis is a spinal deformity, involving a side-to-side curvature of the spine in the coronal plane as well as a rotation of the spinal column in the transverse plane. The coronal curvature is measured using a Cobb angle. If the deformity is severe, treatment for scoliosis may require surgical intervention whereby a rod is attached to the spinal column to correct the abnormal curvature. In order to provide surgeons with an improved ability to predict the likely outcomes following surgery, techniques to create patient-specific finite element models (FEM) of scoliosis patients treated at the Mater Children’s Hospital (MCH) in Brisbane are being developed and validated. This paper presents a comparison of the simulated and clinical data for a scoliosis patient treated at MCH.

The measurement of applied forces during anterior single rod correction of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is the most common form of spinal deformity in paediatrics, prevalent in approximately 2-4% of the general population. While it is a complex three-dimensional deformity, it is clinically characterised by an abnormal lateral curvature of the spine. The treatment for severe deformity is surgical correction with the use of structural implants. Anterior single rod correction employs a solid rod connected to the anterior spine via vertebral body screws. Correction is achieved by applying compression between adjacent vertebral body screws, before locking each screw onto the rod. Biomechanical complication rates have been reported as high as 20.8%, and include rod breakage, screw pull-out and loss of correction. Currently, the corrective forces applied to the spine are unknown. These forces are important variables to consider in understanding the biomechanics of scoliosis correction. The purpose of this study was to measure these forces intra-operatively during anterior single rod AIS correction.

The effect of bone graft type on fusion rates following anterior thoracoscopic scoliosis correction

Bone graft is generally considered fundamental in achieving solid fusion in scoliosis correction and pseudarthrosis following instrumentation may predispose to implant failure. In thoracoscopic anterior-instrumented scoliosis surgery, autologous rib or iliac crest graft has been utilised traditionally but both techniques increase operative duration and cause donor site morbidity. Allograft bone and bone morphogenetic protein (BMP) alternatives may improve fusion rates but this remains controversial. This study's objective was to compare two-year postoperative fusion rates in a series of patients who underwent thoracoscopic anterior instrumentation for thoracic scoliosis utilising various bone graft types.

A study of Australian company responses to email complaints

As businesses and organisations move online, many question how to use Internet communication tools effectively, such as Web sites and electronic mail (Porter, 2001). Where and how should they invest their time and money in technology? This research explores a small part of this broad question, online complaining and electronic customer service. This paper extends prior US-based research of consumer complaints by email (Strauss and Hill, 2001) in several ways. First, it replicates their research in an Australian setting. Second, this research addresses several future research issues that Strauss and Hill (2001) raised. And third, this paper uses diffusion of innovation (Rogers, 1995) to explain some of the results. The results partially support the findings of Strauss and Hill (2001), take a small step towards further investigation of effective email responses and provide practical suggestions for better email customer service.

Location constraints in digital rights management

Digital rights management allows information owners to control the use and dissemination of electronic documents via a machine-readable licence. This paper describes the design and implementation of a system for creating and enforcing licences containing location constraints that can be used to restrict access to sensitive documents to a defined area. Documents can be loaded onto a portable device and used in the approved areas, but cannot be used if the device moves to another area. Our contribution includes a taxonomy for access control in the presence of requests to perform non-instantaneous controlled actions.

The Clubcultures Reader: Readings in Popular Cultural Studies

This reader in popular cultural studies meets the need for an up-to-date collection of readings on contemporary youth cultures and youth music. Table of Content: Introduction: Reading Pop(ular) Cult(ural) Stud(ie)s: Steve Redhead. Part I: Theory I:. 1. Pearls and Swine: Intellectuals and the Mass Media: Simon Frith and Jon Savage. 2. Over-the-Counter Culture: Retheorising Resistance in Popular Culture: Beverly Best. Part II: Commentaries. 3. Organised Disorder: The Changing Space of the Record Shop: Will Straw. 4. Spatial Politics: A Gendered Sense of Place: Cressida Miles. 5. Let's All Have a Disco? Football, Popular Music and Democratisation: Adam Brown. 6. Rave Culture: Living Dream or Living Death?: Simon Reynolds. 7. Fear and Lothing in Wisconsin: Sarah Champion. 8. The House Sound of Chicago: Hillegonda Rietveld. 9. Cocaine Girls: Marek Kohn. 10. In the Supermarket of Style: Ted Polhemus. 11. Love Factory: The Sites, Practices and Media Relationships of Northern Soul: Kate Milestone. 12. DJ Culture: Dave Haslam. Plates: Patrick Henry. Part III: Theory II: . 13. The Post-Subculturalist: David Muggleton. 14. Reading Pop: The Press, the Scholar and the Consequences of Popular Cultural Studies: Steve Jones. 15. Re-placing Popular Culture: Lawrence Grossberg. Index.

Development of a computer simulation tool for application in adolescent spinal deformity surgery

Scoliosis is a three-dimensional spinal deformity which requires surgical correction in progressive cases. In order to optimize correction and avoid complications following scoliosis surgery, patient-specific finite element models (FEM) are being developed and validated by our group. In this paper, the modeling methodology is described and two clinically relevant load cases are simulated for a single patient. Firstly, a pre-operative patient flexibility assessment, the fulcrum bending radiograph, is simulated to assess the model's ability to represent spine flexibility. Secondly, intra-operative forces during single rod anterior correction are simulated. Clinically, the patient had an initial Cobb angle of 44 degrees, which reduced to 26 degrees during fulcrum bending. Surgically, the coronal deformity corrected to 14 degrees. The simulated initial Cobb angle was 40 degrees, which reduced to 23 degrees following the fulcrum bending load case. The simulated surgical procedure corrected the coronal deformity to 14 degrees. The computed results for the patient-specific FEM are within the accepted clinical Cobb measuring error of 5 degrees, suggested that this modeling methodology is capable of capturing the biomechanical behaviour of a scoliotic human spine during anterior corrective surgery.