In this study, trabecular architecture is considered as a cellular solid structure, including both intact and damaged bone models. ??Intact?? bone models were constructed based on ideal versions of 25, 60 and 80-year-old specimens with varying trabecular lengths and orientations to 5%, and 10% covariance of variation (COV). The models were also flipped between longer transverse and longer longitudinal trabeculae. With increasing COV of lengths and orientations of trabecular bone, the apparent modulus is linearly decreased, especially in the longer transverse trabeculae lengths. ??Damaged?? bone models were built from the 25 year old model at 5% COV of longer transverse trabeculae, and with removing trabeculae of 5% and 10% of trabecular volume in transverse and longitudinal directions, respectively, as well as in combination to total 10% and 15%. With increasing percent of trabeculae missing, the apparent modulus decreased, especially dramatically when removal was only in the transverse direction. The trabecular bone models were also connected to a cortical shell and it was found that the apparent modulus of an entire slice was increased in comparison to the modulus of trabecular bone alone. We concluded that the architecture of trabecular bone, especially both lengths and percent of trabecular missing in the longitudinal direction, significantly influences mechanical properties.

In this study, trabecular architecture is considered as a cellular solid structure, including both intact and damaged bone models. ??Intact?? bone models were constructed based on ideal versions of 25, 60 and 80-year-old specimens with varying trabecular lengths and orientations to 5%, and 10% covariance of variation (COV). The models were also flipped between longer transverse and longer longitudinal trabeculae. With increasing COV of lengths and orientations of trabecular bone, the apparent modulus is linearly decreased, especially in the longer transverse trabeculae lengths. ??Damaged?? bone models were built from the 25 year old model at 5% COV of longer transverse trabeculae, and with removing trabeculae of 5% and 10% of trabecular volume in transverse and longitudinal directions, respectively, as well as in combination to total 10% and 15%. With increasing percent of trabeculae missing, the apparent modulus decreased, especially dramatically when removal was only in the transverse direction. The trabecular bone models were also connected to a cortical shell and it was found that the apparent modulus of an entire slice was increased in comparison to the modulus of trabecular bone alone. We concluded that the architecture of trabecular bone, especially both lengths and percent of trabecular missing in the longitudinal direction, significantly influences mechanical properties.

Bone quality influences bone strength with important consequences for osteoporosis, fracture risk and dental implant success. Whilst imaging that is capable of capturing bone structure in 3D is becoming more common, quantitative clinical measures of bone quality rely on bone quantity, not structure. If bone quality could be more accurately measured, and the influence of bone architecture better understood, strength may be better predicted. This thesis presents methods for making structural comparisons between successive micro-CT images of loaded bone and explores the limitations of these. I present a novel method to detect where damage occurs in loaded rat vertebrae based on multiscale rigid registration and difference measures. Together these methods represent a quantitative approach to image guided failure analysis. Time-lapsed micro-CT images of 14 successively loaded rat vertebrae were acquired and damaged regions found using these. Using a random forest classifier I tested whether the damaged regions could be predicted by several commonly used structural measures (bone area and volume), three-dimensional texture measures (co-occurrence matrices and fractal dimension) and a more novel type of architectural measure (based on the structure tensor). A combination of parameters was able to predict damage regions with specificities in the range 70-90% and sensitivities of 60-70%.Using ovariectomised rats as a model of osteoporosis I have performed a pilot experiment to investigate how changes in bone quality might effect our results. The wider applicability of my methods are demonstrated by applying them to dental cone beam images of healthy and osteoporotic patients.

[Truncated abstract] In this work a computer simulation program, similar to a finite element program, is used to study the relationship between skeletal tissue structure and function. Though other factors affect the shape of bone (e.g., genetics, hormones, blood supply), the skeleton adapts its shape mainly in response to the mechanical environment to which it is exposed throughout life. The specific relationship between the mechanical environment and the mechanical adaptation response of the skeleton is reviewed. Theories of mechanical adaptation are applied to the sites of tendon attachment to bone (entheses), the adaptation of generalised trabecular bone (i.e., Wolff’s Law of trabecular architecture), sesamoid bones that are often found where a tendon wraps around a bony pulley, and the internal trabecular structure of a whole bony sesamoid such as the patella. The relative importance of compression rather than tension in bone adaptation theories is still not fully understood. Some mechanical adaptation theories suggest that an overwhelming tensile stress at a skeletal location does not stimulate bone deposition, but would instead lead to bone resorption. The skeletal locations studied in this work were chosen because they have been proposed to be in tension. Computer simulations involving models are an ideal method to analyse the mechanical environment of a skeletal location. They are able to determine the mechanical stresses at, and the stress patterns around, complex biological situations. This study uses a two dimensional computer simulation program, Fast Lagrangian Analysis of Continua (Flac), to analyse the stress at the skeletal locations, and to test theories of mechanical adaptation over time by simulating physiological adaptation. The initial purpose of this study is to examine the stress in the skeletal tissue in generalised trabeculae, anatomical sites where a tendon wraps around a bony pulley, in the trabecular networks that fill the patella, and at tendon attachments. A secondary purpose, that follows directly from the first, is to relate the results of these initial stress analyses to existing and hypothetical skeletal tissue remodelling theories, to suggest how the complex skeletal structures might be generated solely in response to their mechanical environment. The term “remodelling” is used throughout this work to refer to mechanical adaptation of bone, usually at a surface of bone, rather than the internal regeneration of osteons (Haversion systems)