Browsing by Subject "Peripheral quantitative computed tomography"

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    The effects of physical activity, body composition, muscle cross-sectional area and sex steroids on bone volumetric density, strength and geometry in older men.
    (2011-08) Cousins, Julie Marie
    Osteoporosis and related fractures are significant public health and economic burdens. Studies show that factors such as mechanical loading and sex steroids influence the bones of older women. In order to reduce the risk of osteoporosis in older men, it is important to understand what factors affect the strength of the bones of older men. The primary aim of this study was to identify modifiable factors that influence bone volumetric density, bone geometry and estimates of bone strength in old men. This cross-sectional study used data from the MrOS (n=1171) and Tobago Bone Health (n=500) studies. Dual Energy x-ray absorptiometry was used to assess areal bone mineral density, lean mass and fat mass. Peripheral quantitative computed tomography assessed volumetric bone mineral density, bone geometry, estimates of bone strength and muscle cross-sectional area. After adjusting for age, clinic site, body weight, race and limb length, estimates of bone strength at the 4% and 66% site of the tibia were greater in the quartile of men with the greatest leg power compared to the least leg power and in the quartile of men that were the most physically active compared to the least active. Similar results were found at both the distal and midshaft of the radius when looking at physical activity and grip strength. After adjusting for age, clinic site, limb length, and race, estimates of bone strength at the proximal and distal tibia and radius were positively associated with total body weight, BMI, lean mass and fat mass. After adjusting for age, site, and tibia length, bone strength was positively associated with muscle cross-sectional area. Bioavailable testosterone and estradiol were positively associated with cortical vBMD while bioavailable estradiol was also positively associated with total and trabecular vBMD, bone compressive strength, cortical area and section modulus. These finding suggest that greater physical activity, muscle strength, muscle power, lean mass, and muscle cross-sectional area (all surrogates of mechanical load) are important for bone strength. It may be important to utilize the role of muscle to prevent the natural loss of bone that occurs with aging. These findings are congruent with finding from previous studies conducted on older females.
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    Obesity, bariatric surgery, and bone strength: a review and studies in adult cohorts.
    (2011-05) Scibora, Lesley Morgan
    Bone mass and strength changes proceeding weight loss in obese individuals are important for determining risk for skeletal fragility. Understanding the relationship between obesity and bone strength is significant for describing bone's response to changes in body composition. The three manuscripts presented in this dissertation focus on obese adult populations (aged 18 - 64 years). Peripheral quantitative computed tomography (pQCT) was used to assess volumetric bone mineral density, bone geometry, indices of bone strength, and muscle cross-sectional area. Manuscript I reviews the association between bariatric surgery, changes in bone mineral density, and osteoporosis. The review demonstrated significant loss of bone density at hip and spine sites in the first year following bariatric procedures. However, existing research fails to support the concern over risk of osteoporosis in these individuals. Manuscript II of this dissertation, a cross-sectional study, demonstrated that despite greater absolute bone strength observed in obese women compared to their healthy-weight counterparts, bone strength was low relative to their high body weight. Manuscript III was a prospective observational pilot study to examine changes in bone strength and body composition in morbidly obese adults submitted for bariatric surgery. The results showed that bariatric surgery produced significant weight loss that was predominately due to reduction in fat mass, rather that fat-free mass. Despite significant weight loss bone strength indices were not compromised, suggesting that maintenance of lean mass may preserve bone strength. This dissertation contributes to the knowledge base in several ways. First, it provides a comprehensive summary of bariatric surgery and bone density research, while providing an alternative perspective for interpreting dual x-ray absorptiometry-based bone outcomes. Second, bone strength was assessed using pQCT, which provides an understanding of bone from a mechanical perspective that has not been used when interpreting bone outcomes in severely obese populations. Finally, this dissertation includes the first known study to examine changes in bone strength following bariatric surgery in morbidly obese individuals.