Biomechanical modelling of the whole human spine for dynamic analysis

Developing computational models of the human spine has been a hot topic in biornechanical research for a couple of decades in order to have an understanding of the behaviour of the whole spine and the individual spinal parts under various loading conditions. The objectives of this thesis are to develop a biofidefic multi-body model of the whole human spine especially for dynamic analysis of impact situations, such as frontal impact in a car crash, and to generate finite element (FE) models of the specific spinal parts to investigate causes of injury of the spinal components. As a proposed approach, the predictions of the multi-body model under dynamic impact loading conditions, such as reaction forces at lumbar motion segments, were utilised not only to have a better understanding of the gross kinetics and kinematics of the human spine, but also to constitute the boundary conditions for the finite element models of the selected spinal components. This novel approach provides a versatile, cost effective and powerful tool to analyse the behaviour of the spine under various loading conditions which in turn helps to develop a better understanding of injury mechanisms

A PATIENT-SPECIFIC MULTIBODY MODEL OF SCOLIOTIC SPINE FOR SURGICAL CORRECTION PREDICTION IN THE CORONAL PLANE

Ph.DDOCTOR OF PHILOSOPH

Dynamic impact testing and computer simulation of wheelchair tiedown and occupant restraint systems (WTORS).

Occupant Restraint Systems (ORS) have been widely used in Public Service Vehicles (PSVs). A Wheelchair Tiedown and Occupant Restraint System (WTORS) has been developed to provide effective occupant protection for disabled people who are seated in wheelchairs. An international laboratory study had been conducted to produce a compliance test protocol that included specification of the sled deceleration versus time history and the crash pulse corridor. Currently effort at the international level is being focused through the International Standards Organisation (ISO) to produce standards for WTORS and transportable wheelchairs. Dynamic sled testing of WTORS was conducted in Middlesex University Road Safety Engineering Laboratory (MURSEL) to develop a test protocol in a WTORS System. This research has been concerned with the effects to which the occupant of a wheelchair secured by a WTORS is subjected in a frontal impact. Both occupant Forward Facing Frontal (FFF) and Rearward Facing Frontal (RFF) impact configurations have been considered. A Surrogate wheelchair with a tiedown restraint System, a Surrogate occupant restraint System, and an Anthropomorphic Test Dummy (ATD) were used to facilitate highly controlled tests. Production wheelchairs were also crash tested to validate the response of the Surrogate System. A 48 km/h-20g crash pulse falling within the ISO standard crash pulse corridor was specified. The Crash Victim Simulation (CVS), one of the computer modelling methods, and Finite Element Analysis (FEA) models were designed to study the dynamic response of a restrained wheelchair and its occupant in a crash environment. Two CVS computer packages: MADYMO®, DYNAMAN® and one of FEA programs: PAFEC were used in WTORS models to predict the occupant response during impacts and hence provide data to optimise future system design. A modelling protocol for WTORS was developed based on the results of ninety (90) sled tests of WTORS Surrogate system and forty (40) dynamic tests of production wheelchairs. To illustrate the potential of these models the results of simulations were validated by sled tests. A random effects Statistical method was used to quantify the results. The load-time histories were also traced to qualify the test and model results. A literature review highlighted twenty years of wheelchair crash research. The correlation between computer model and experimental results was made more accurately. The modelling technique of interconnection of FEA models into CVS program was also introduced. The velocity profile and the natural frequency of WTORS analysis were used to explain why the wheelchair and dummy experienced acceleration amplifications relative to the sled. The shoulder belt load at floor-mounted configuration was found to be higher than that at B pillar configuration. Energy principles were also applied to show why more compliant wheelchair tiedown Systems subjected restraints to a less severe crash environment. A decomposition of forces using the computer model showed why quasi-static analysis is insufficient in WTORS design. It is concluded that the B pillar anchorage of the occupant diagonal strap is superior to the floor-mounted configuration

Understanding sit-to-stand through experimentation and constraint-based modelling

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A quantitative fluoroscopic study of the relationship between lumbar inter-vertebral and residual limb/socket kinematics in the coronal plane in adult male unilateral amputees. (Exploring the spine and lower limb kinematics of trans-tibial amputees).

Introduction Much of lower back pain (LBP) is thought to be mechanical in origin and lower limb amputees have an increased prevalence. There is also evidence that a large proportion of them also have altered spinal posture and it is commonly thought that the movement between the vertebrae (kinematics) may be affected. The current study was designed to explore the kinematics of the lumbar spine segments in trans-tibial amputees and compare it to a similar population with intact lower limbs using quantitative fluoroscopy (QF). The study also investigated possible relationships between lumbar spine stability and the motion between the prosthetic socket and residual limb. It is hoped that these investigations will improve understanding of the importance of limb-socket fit to the functional integrity of the lumbar spine in lower limb amputees Methods A literature review and three preliminary QF studies were carried out; one to the determine the best plane of motion and orientation of participants during QF imaging of the spine, a second to inform the optimal imaging protocol for the limb-socket interface and the third to validate a QF measurement of inter-vertebral stability. This phase determined the measurement parameters and investigative protocols. Given the complexity of the technique, 12 male below knee amputees and 12 healthy male controls of similar age and body mass index were recruited and received passive recumbent coronal QF imaging of their lumbar spines. This was followed immediately by anterior-posterior QF imaging of their limb-socket interfaces during three different forms of simulated gait. Differences between amputee and control spine kinematics and relationships between limb-socket motion and inter-vertebral kinematics in amputees were investigated. Results Passive recumbent coronal plane QF appears to be a valid method for measuring inter-vertebral stability. Although there were no systematic differences between the magnitude of inter-vertebral kinematics variables of amputees and controls, there was a trend towards greater variability in both inter-vertebral range and symmetry of motion in amputees and a significantly higher proportion of correlations in attainment rate between levels among amputees than controls (2-sided p <0.04). There was also a substantial, statistically significant inverse linear relationship between passive inter-vertebral motion symmetry and limb-socket telescoping in amputees. Conclusions This thesis provides evidence that the kinematics of the lumbar spine may be affected by lower limb amputation – particularly in respect of socket fit. The importance of consistency and symmetry of restraint by the intrinsic spinal holding elements in trans-tibial amputees has been highlighted. An indication of a relationship between limb socket telescoping and spine kinematics was identified, suggesting the need for replication of this part of the study in a larger amputee population. The variables of interest and the basis for this have been identified. Finally, inter-vertebral motion pattern variation has been associated with chronic low back pain in the literature. It was discovered that there was more interdependence in passive inter-vertebral motion between and across levels in below knee amputees than controls in terms of laxity, but not range of motion. The apparent relationship between this and socket fit in amputees suggests a possible mechanism and diagnostic subgroup in this population

Hand X-ray absorptiometry for measurement of bone mineral density on a slot-scanning X-ray imaging system

Includes bibliographical references.Bone mineral density (BMD) is an indicator of bone strength. While femoral and spinal BMDs are traditionally used in the management of osteoporosis, BMD at peripheral sites such as the hand has been shown to be useful in evaluating fracture risk for axial sites. These peripheral locations have been suggested as alternatives to the traditional sites for BMD measurement. Dual-energy X-ray absorptiometry (DXA) is the gold standard for measuring BMD due to low radiation dose, high accuracy and proven ability to evaluate fracture risk. Computed digital absorptiometry (CDA) has also been shown to be very effective at measuring the bone mass in hand bones using an aluminium step wedge as a calibration reference. In this project, the aim was to develop algorithm s for accurate measurement of BMD in hand bones on a slot - scanning digital radiography system. The project assess e d the feasibility of measuring bone mineral mass in hand bones using CDA on the current system. Images for CDA - based measurement were acquired using the default settings on the system for a medium sized patient. A method for automatic processing of the hand images to detect the aluminium step wedge, included in the scan for calibration, was developed and the calibration accuracy of the step wedge was evaluated. The CDA method was used for computation of bone mass with units of equivalent aluminium thickness (mmA1). The precision of the method was determined by taking three measurements in each of 1 6 volunteering subjects and computing the root - mean - square coefficient of variation (CV) of the measurements. The utility of the method was assessed by taking measurements of excised bones and assessing the correlation between the measured bone mass and ash weight obtained by incinerating the bones. The project also assessed the feasibility of implementing a DXA technique using two detectors in a slot-scanning digital radiography system to acquire dual-energy X-ray images for measuring areal and volumetric BMD of the middle phalanx of the middle finger. The dual-energy images were captured in two consecutive scans. The first scan captured the low- energy image using the detector in its normal set-up. The second scan captured the high- energy image with the detector modified to include an additional scintillator to simulate the presence of a second detector that would capture the low-energy image in a two-detector system. Scan parameters for acquisition of the dual-energy images were chosen to optimise spectral separation, entrance dose and image quality. Simulations were carried out to evaluate the spectral separation of the low- and high-energy spectra

Determining upper limb kinematics and dynamics during everyday tasks

PhD ThesisIn planning orthopaedic procedures or designing joint replacements for the upper limb, detailed knowledge on the kinematic and dynamic behaviour of the shoulder, elbow and wrist joints during the performance of everyday tasks is essential. Previous studies have included kinematic analyses of everyday activities involved in feeding and personal hygiene though none have included both the kinematic and dynamic analyses of these tasks. This study has involved the development, validation and application of experimental methods and analysis techniques, enabling the measurement and modelling of upper limb kinematics and dynamics. A four camera video-based motion analysis system was used to track reflective spheres attached at specific locations on the upper limb and trunk. Novel methods for the definition of the embedded trunk frame and glenohumeral rotation centre were incorporated. Joint attitudes, cadences, angular velocities and angular accelerations were calculated prior to the determination of external forces and moments through the dynamic modelling of the upper limb. The procedures developed have been validated against known measurements and the results of previous studies. These have been applied to obtain kinematic and dynamic data from unimpaired subjects and subjects with shoulder impairment during performance of ten everyday tasks involved in feeding, personal hygiene and the use of everyday objects. Elbow and shoulder flexion were found to be the primary components for the successful completion of the selected tasks. Reaching to the opposite side of the neck was identified as being the most complex of the activities tested in terms of rotation at the shoulder and elbow. Characteristic patterns of motion at the joints of the upper limb were identified during anterior targeted lifting. Differences in performance between the unimpaired and impaired subjects were identified, particularly in the results for cadence and the individual joint velocities and accelerations.Engineering and Physical Sciences Research Council, DePuy Internationa

The biomechanics of human locomotion

Includes bibliographical references. The thesis on CD-ROM includes Animate, GaitBib, GaitBook and GaitLab, four quick time movies which focus on the functional understanding of human gait. The CD-ROM is available at the Health Sciences Library

Digital x-ray analysis for monitoring fracture healing

X-ray based evaluation of different stages of fracture healing is a well established clinical standard. However, several studies have shown plain radiography alone to be an unreliable method to assess healing. The advent of digital X-ray systems provides the potential to perform quantitative analysis on X-ray images without disrupting normal clinical practice. Two aspects were explored in this study. The first was the measurement of mechanical fracture stiffness under four point bending and axial loading. The second was the inclusion of an Aluminium step wedge to provide Aluminium-equivalent thickness calibration information. Mechanical sti ness studies involved the development of equipment to perform four point bending on intra-medullary (IM) nailed tibial fractures, equipment to perform axial loading on conservatively treated humeral fractures, and fracture models to ex- amine the developed systems. Computational procedures to automatically measure the angle and offset occurring at the fracture site by comparing loaded and unloaded X-ray images were developed utilising cross-correlation. The apparatus and procedures were tested using the fracture models both in X-ray and using the Zwick materials testing machine. The four point bending system was applied clinically to a series of IM nailed tibial fracture patients and the axial loading system to two conservatively treated humeral fracture patients. Mechanical stiffness results showed that the apparatus worked well in the clinical radiography environment and was unobtrusive to normal practice. The developed X-ray analysis procedure provided reliable measurements. However, in the case of IM nailed tibial fractures, both angular and displacement movements were too small to be accurately assessed or to provide reliable stiffness measurements. This indicated that this patient group was possibly unsuitable for mechanical stiffness measurements or that higher loads needed to be applied to the fracture site. The case studies of conservatively treated humeral fractures showed potential in detecting movement between loaded and unloaded X-rays and using this to provide sti ness information. Further investigation is required to show that this technique has the potential to aid fracture healing monitoring. Investigation into Aluminium step wedge calibration began with the design of different step wedges and X-ray phantoms. Initial image analysis involved studying the automatic processing applied by a digital Computed Radiography (CR) Fuji sys- tem and modelling of the inhomogeneities in X-ray images as well as investigation into the effect of and correction for scatter, overlying soft tissue and bone thickness. Computational procedures were developed to semi-automatically detect the steps of the step wedge, form an exponential Aluminium step thickness to grey level calibration graph, measure soft tissue and bone thickness, and correct for the heel effect and scatter contributions. Tests were carried out on pre-clinical models and results compared to ash weight and peripheral quantitative computed tomography (pQCT). A clinical study of radial fractures was used to investigate the effectiveness of the step wedge calibration system in monitoring fracture healing changes. Results using the step wedge indicated that the calibration technique was e ective in detecting and correcting for aspects in uencing Aluminium-equivalent thickness measures. With careful processing, useful information was obtained from digital X- rays that included the Aluminium step wedge and these correlated well with existing density measures. The use of the wedge in patient images showed that small increases in Aluminium-equivalent thickness of the fracture site could be detected. This was most useful for intra-patient comparisons throughout the course of healing rather than providing quantitative measurements which were comparable to other density measures. In conclusion, this thesis shows the potential for accurate analysis of digital X- rays to aid the monitoring of healing changes in fracture patients, particularly with application of axial loading and the use of step wedge calibration