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Title: Structural failure and fracture of immature bone
Author: Cheong, Vee San
ISNI:       0000 0004 6061 4397
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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Radiological features alone do not allow the discrimination between accidental paediatric long bone fractures or those caused by child abuse. Therefore, for those cases where the child is unable to communicate coherently, there is a clinical need to elucidate the mechanisms behind each fracture to provide a forensic biomechanical tool for clinical implementation. 5 months old ovine femurs and tibiae were used as surrogates for paediatric specimens and were subjected to micro-CT scans to obtain their geometrical and material properties. A novel methodology to align long bones so that they would be loaded in a state of pure bending and torsion was developed and compared against the use of a standard anatomical coordinate system. The second moment of area and its coefficient of variation (COV) for each alignment method were calculated to ascertain the reference axes that minimised the effect of eccentric loading. Wilcoxon-signed rank test showed a significant reduction in COV of the second moment of area using this new method, indicating that the bone has a more regular cross-section when this methodology is implemented. The algorithm generated the locations of subject-specific landmarks that can be used as a reference to align the bones in experimental testing. A low-cost platform that synchronized the data acquisition from the tensile testing machine and the strain gauges was built and used with a high speed camera to capture the fracture pattern in four-point bending at three strain rates and in torsion at two different strain rates, following commonly reported case histories. Finite element (FE) models of ovine tibiae in their optimised alignment were generated to replicate the fracture patterns that were obtained. Fracture initiation and propagation was simulated through the use of element deletion with a maximum principal strain criterion. The experiments produced transverse, oblique, and spiral fractures consistently, which were correlated with the finite element analysis, demonstrating the ability of this pipeline to now be adapted for use in forensic analysis.
Supervisor: Bull, Anthony M. J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral