No description available.

No description available.

No description available.

No description available.

No description available.

Osteoporosis is a major metabolic bone disease that causes reduced bone mass, deteriorated bone microstructural and increased fracture risk. In clinical practice, the gold standard to examine bone quality and evaluate fracture risk is using dual energy X-ray absorptiometry through measurements of areal bone mineral density (aBMD). However, it has been well accepted that in addition to aBMD, bone geometry, microstructure and material properties also play important roles in determining overall bone mechanical competence, which is directly related to fracture risk. High-resolution peripheral quantitative computed tomography (HR-pQCT) has the capability to image three-dimensional (3D) bone microstructures in vivo and provide quantitative measurements of bone mineral density as well as cortical and trabecular microstructure. Based on the HR-pQCT images, micro finite element (µFE) models can be constructed to directly estimate bone strength. HR-pQCT has become a widely used imaging tool in clinical research to evaluate the effect of aging, drug treatment, and metabolic bone disease on bone quality. The work in this thesis focuses on evaluating the accuracy and capability of HR-pQCT in quantifying microstructural properties of human radius and tibia bone, exploring its prediction power of whole bone strength and discussing potential applications in clinical studies. In this thesis, we quantified the accuracy of the standard HR-pQCT microstructural measurements of human distal radius and tibia through comparisons with gold standard µCT-based morphological measures. The results showed that the BV/TVd, Tb.N*, Tb.Th and Tb.Sp from HR-pQCT were significantly and highly correlated with those from gold-standard µCT measurements. Strong correlations between the HR-pQCT µFE predictions and direct mechanical testing measures suggest that HR-pQCT µFE is a robust method to determine bone mechanical properties. In a clinical setting, standard HR-pQCT scans are performed on the non-dominant wrist (usually the left) and the corresponding tibia. However, the contralateral side is selected for scanned when there is a fracture the non-dominant wrist. It remains unclear whether the dominant side is representative of the non-dominant side and how much error it will bring into a study where subjects include mixed scans of both sides. In this thesis, we applied HR-pQCT and µCT based morphological and mechanical measurements to characterize the symmetric nature of distal radius and tibia. We found that the right radius tend to be larger than the left radius. However, at the tibia, the bone size was found to be similar between left and right. By micro computed tomography (µCT), microstructural parameters such as BV/TV were also found to be larger at the right radius, while no difference was found at the tibia. Trabecular number, trabecular thickness, trabecular separation and cortical thickness were not different between left and right radius. µFE analyses demonstrated that stiffness and strength of right radius were significantly higher than left radius, while there was no difference at the tibia. The standard clinical region of interest HR-pQCT is recommended by the manufacturer; however, it is not clear whether a segment HR-pQCT scan is representative of whole bone mechanical properties. Therefore we quantified the associations of microstructural and mechanical measurements of the radius and tibia segments with whole bone stiffness and examined if we can improve the correlation when we select a different region. The microstructural and mechanical measurements at the two regions next to the standard HR-pQCT segment (proximal and distal) were also examined. The results showed that the bone microstructure from proximal and distal sections is highly correlated to standard region at both distal radius and tibia. The mechanical properties of the three segments were strongly correlated with overall bone mechanical properties. The microstructural measurements at the most distal section were correlated with whole bone stiffness better compared to those from standard and proximal regions. DXA is incapable of discriminating patients with wrist fracture from those without. In this study, we examined the microstructural and mechanical properties in patients with and without wrist fracture through HR-pQCT based analyses. We demonstrated that wrist fracture patients had lower plate and rod bone volume fraction, less plate and rod trabecular number, thinner cortex and lower whole bone stiffness and strength, compared to healthy controls. Failure analyses also depicted significantly lower trabecular plate compression and tension failure fraction in wrist fracture patients.

The highly optimized hierarchical structure of trabecular bone is a major contributor to its remarkable mechanical properties. At the micro-scale level, individual plate-like and rod-like trabeculae are interconnected, forming a complex trabecular architecture. It is widely believed that bone strength, an important mechanical characteristic that describes the capability of bone to resist fracture, is largely determined by the tissue-level material properties of these microscopic trabecular elements. However, due to the complicated microstructure and irregular morphology of trabecular bone, a link between the tissue-level and the apparent level mechanics in trabecular bone has never been established. Thus, the goal of this thesis is to examine the tissue-level material properties of trabecular bone and their contribution to apparent-level bone mechanics, and ultimately to improve our fundamental understanding and assessment of bone strength in diseased and healthy patients. At the micro-scale level, plate-like and rod-like trabeculae are distinctly aligned along different orientations on the anatomical axis of the skeleton. Also, the highly organized underlying ultrastructure of bone tissue suggests trabecular bone might possess an anisotropic tissue modulus, i.e. different modulus in the axial and lateral cross-section of a trabecula. In this thesis, we studied this tissue-level anisotropy by examining mechanical properties of individual trabecular plates and rods aligned longitudinally, obliquely, and transversely on the anatomical axis using micro-indentation. We discovered that, despite the different orientations of trabeculae, tissue moduli are higher in the axial direction than in the lateral direction for both plates and rods. We also discovered that plates have a higher tissue modulus than rods, suggesting different degrees of mineralization. Furthermore, the tissue mineral density correlated strongly but distinctly with tissue modulus in the axial and lateral directions, providing descriptions on how spatially heterogeneous mineralization at the tissue level affects the tissue modulus. After characterization of the anisotropic and heterogeneous modulus of trabecular bone at the tissue level, we then sought to investigate its contribution to apparent-level mechanical properties, including apparent Young’s modulus and yield strength. Non-linear FE voxel models incorporating experimentally determined anisotropy and heterogeneity were created from micro-computed tomography (µCT) images of healthy trabecular bone samples. Apparent Young's modulus and yield strength predicted by the models were compared to and correlated with gold standard mechanical testing measurements, as well as to the same FE models without incorporation of anisotropy and/or heterogeneity. We discovered that the anisotropic model prediction was highly correlated and indistinguishable from mechanical testing measurements. However, the prediction power of the model was not enhanced by incorporating anisotropy and heterogeneity (compared to a homogeneous and isotropic model), suggesting that variances in tissue-level material properties contribute minimally to the apparent level bone behaviors in healthy bone. However, the possibility remained that a more substantial contribution could arise in diseased bone, particularly diseases in which tissue-level properties are compromised. Therefore, we studied trabecular bone in two diseased conditions – subchondral bone in human knees affected by osteoarthritis and pelvic bone affected by adolescent idiopathic sclerosis – to see how disease can alter the tissue-level and, consequently, apparent-level bone mechanics. In OA bone, we found a significant decrease in tissue modulus in the subchondral bone under severely damaged cartilage compared to control, which provides an explanation for a minimal increase in apparent stiffness with an almost doubled bone volume fraction. In AIS bone, no differences were found in tissue-level or apparent level Young’s modulus compared to control. However, the mineral density was found to play a distinct role in the modulus of growing bone tissue compared to mature bone.

No description available.

No description available.

Doctorat en kinésithérapie et réadaptation / info:eu-repo/semantics/nonPublished