Computer modelling of the development of the trabecular architecture in the human pelvis

Watson, Peter James

October 2011

Thesis or dissertation

© 2011 Peter James Watson. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

The influence of mechanical loading upon bone growth and remodelling has been widely studied. It has been suggested that functional bone growth is evident within the human adult pelvis, where the internal trabecular structure is purported to align to the principal strain trajectories induced during bipedal locomotion. Ontogenetic studies of the juvenile pelvis have observed that trabecular bone growth becomes progressively ordered from  an initial randomised patterning. This has lead to theories linking the gradual structural optimisation of  trabecular bone to the mechanical forces associated with the development of juvenile locomotion. However, recent studies have observed partially optimised trabecular structures within the human fetal and neonatal  pelvis, in contrast to previous observations. The possible genetic and mechanical factors which cause the in utero formation of these trabecular structures, which are usually associated with a weight bearing function,  remains unknown. Therefore, this thesis aimed to investigate the influence of the mechanical strains associated with juvenile movements, upon the growth of pelvic trabecular bone.Biomechanical analyses were performed on digitised models of juvenile pelvic specimens belonging to the  Scheuer collection. Digitised models of a prenatal, 1 year, 8 year and 19 year old pelvis were constructed  through processing mircocomputed tomography scan data. A geometric morphometric reconstruction technique was devised which enabled the creation of hemi-pelvic models from originally disarticulated bone specimens. This reconstruction technique was validated through a close morphological comparison between a  reconstructed hemi-pelvis, and its originally articulated CT data. The muscular and joint forces associated with  in utero movements and bipedal locomotion, were computed through musculoskeletal simulations. A prenatal  musculoskeletal model was constructed to replicate the in utero mechanical environment, and simulated  interactions between the fetal leg and the womb wall. The forces associated with bipedal locomotion were  evaluated through analysis of a pre-defined subject-specific musculoskeletal model. An attempt was made to  validate the modelling technique of altering generic musculoskeletal models to create subject-specific  representations. However, comparisons between computed and experimentally recorded muscle activities  proved inclusive, although this was attributed to uncertainties in the accuracy of the experimental data. A series of finite element analyses computed the strain distributions associated with the predicted musculoskeletal  loading. A range of load regimes were applied to each juvenile pelves, and were based upon the computed  musculoskeletal forces and the maximum isometric force capabilities of the pelvic muscles. However, despite  the differences between the applied load regimes, the predicted von Mises and compressive strain distributions  displayed similarities for all the ages analysed. All the predicted distributions were characterised  by high strains within the inferior ilium, which correlated to a region of high trabecular organisation. The high  strain magnitudes then travelled superiorly in either a gradual or rapid dissipation, both of which did not  produce a distribution which correlated to the pelvic trabecular histomorphometry. Therefore, no strain  distribution was predicted with divergence of the inferior strains to the anterior and posterior regions of the ilium,  as observed with the trabecular trajectories within the pelvis.As the predicted von Mises and compressive strain distributions failed to match the complete iliac trabecular  histomorphometry, it was suggested that the in utero formation of partially optimised trabecular growth is  possibly due to generic factors. This thesis provided initial investigations into the musculoskeletal and  mechanical loading of the juvenile pelvis, although future work is required to develop the applied modelling  techniques to fully determine the influence of the mechanical strains.

Department of Engineering, The University of Hull
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