Thesis (M. Med. Sc.)--University of Hong Kong, 2004. / Also available in print.

Thesis (M. Med. Sc.)--University of Hong Kong, 2004. / Also available in print.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

[Truncated abstract] The cost of managing osteoporotic fractures places a significant financial burden on the health-care system. To reduce the fracture burden, early identification of fracture risk is essential to allow early intervention. The limitations associated with dual-energy X-ray absorptiometry (DXA), such as limited sensitivity and specificity, cost, ionising radiation and accessibility, have resulted in the emergence of other technologies for assessing bone fragility. An example is the portable and non-ionising quantitative ultrasound (QUS) technology. The discriminatory power of quantitative ultrasonometry in fracture risk identification, either independently or in combination with other established risk factors, currently remains contentious. It is recommended that fracture risk assessment should not only focus on bone status, but also on the risk of falls. Additionally, it has been noted that disability arising from osteoporotic fractures, even when these fractures are not identified clinically, can translate into psychosocial symptoms and a poorer perception of health-related quality of life (HRQoL). The primary aim of the present study was to investigate if a composite model comprising: calcaneal QUS, falls risk and HRQoL assessments, can identify a group of elderly women at high risk of osteoporotic fracture from those at lower risk. One hundred and four community-dwelling women (mean age 71.3 ±5.8 years) were recruited for this study. These women underwent a series of tests that included: DXA bone mineral density (BMD) evaluation of the proximal femur and lumbar spine (L1 L4); calcaneal QUS measurement; spinal radiography; rasterstereographic back surface curvature (BSC) examination; and performance-based assessment of strength, mobility and balance. The women were classified into a `High Risk’group or a `Low Risk’ group using three separate classification criteria: i) low BMD, based on the World Health Organisation (WHO) recommended T-score of < -2.5, and⁄or a history of fragility fracture (Osteoporotic [OP] group versus Non-Osteoporotic [NOP] group); ii) presence of at least one radiographically identified prevalent vertebral fracture (Vertebral Fracture [VF] group versus Non-Vertebral Fracture [NVF] group); or iii) a history of either forearm or wrist fracture (Forearm/Wrist Fracture [WF] group versus Non-Forearm/Wrist Fracture [NWF] group)

One indication of increasing fragility of bone is the accumulation of microscopic cracks, or microdamage, within the bone matrix. Microdamage accumulates in bone of the elderly, when changes in bone material properties and matrix architecture coupled with a decrease in bone repair mechanisms compromise bone integrity. To preserve bone mass and reduce fracture risk, therapeutics such as alendronate are prescribed which increase bone volume fraction by decreasing the rate of bone turnover. However, concerns over adverse effects of prolonged turnover suppression have been reinforced by findings of increased microdamage density with alendronate use. Microdamage formation is not always pathologic, but extensive accumulation of damage can be an indicator of reduced bone quality. The work in this thesis explores the hypothesis that microdamage in bone of lower quality will form more easily and progress more extensively than in bone of higher quality. Microdamage initiation stresses and strains were obtained for trabecular bone from older females, older males, and younger females to determine whether thresholds for damage initiation were lower in older females. Results suggest that the stress threshold for damage initiation in older females may indeed be lower compared with younger females, and that normalized strain thresholds for severe damage formation in older males may be decreased compared with older females. Damage propagation was evaluated as a function of age and sex to determine whether damage in older women progressed more extensively than in younger women or men. Results suggest that bone from older individuals had decreased resistance to crack propagation evidenced by an increased number of severely damaged trabeculae which expanded in area under cyclic loading; however no sex differences were uncovered. Finally, the stress/strain thresholds for damage initiation were investigated in alendronate-treated bone, and results indicate that a decreased stress threshold was needed to initiate damage formation of a linear and severe morphology after one year of treatment. After three years of treatment, however, micromechanical properties recovered, perhaps due to increased matrix mineralization which increased tissue level stiffness.