Measuring muscle and fat with peripheral quantitative computed tomography : precision, annual changes, monitoring intervals, and associations with fall status in older adults
Objectives: The overall aim of this thesis was to investigate the precision error, annual changes, and monitoring time intervals of muscle and fat outcomes measured by peripheral quantitative computed tomography (pQCT), as well as explore the strength of their associations with fall status in older adults. Methods: Participants aged >60 years old (N=190) were recruited from the Saskatoon Cohort of the Canadian Multicentre Osteoporosis Study (CaMOs). The precision error (Root Mean Squared Co-efficient of Variation, CV%RMS) of soft-tissue outcomes from previously reported pQCT image analysis protocols (n=6) were calculated and compared using repeat forearm and lower leg scans collected from a random sub-sample of women (n=35). Prospective scans were collected with 1 and/or 2 years of follow-up (n=97) to estimate annual changes and monitoring time intervals for pQCT-derived muscle and fat outcomes in women. Imaging data and responses from a retrospective fall status questionnaire were analyzed to investigate the associations of muscle density, functional mobility, and health- related factors to fall status for both men and women (n=183). Results: Precision errors of muscle and fat outcomes ranged from 0.7 to 6.4% in older women, however not all protocols were equally precise. Muscle cross-sectional area decreased by 0.8 to 1.2% per year, with greater losses in the lower limb. Biological changes in muscle area and density may be detected with 80 and 95% certainty within monitoring time intervals of 4 to 9 years. The odds of having reported a fall increased by 17% for every unit decrease in muscle density (mean 70.2, SD 2.6mg/cm3) after adjusting for age, sex, body mass index, general health status, diabetes, the number of comorbidities, and functional mobility. Discussion: This dissertation demonstrated the potential for pQCT to study changes in muscle and fat outcomes in older adults. Both muscle area and density can be precisely measured. Observed annual changes in soft-tissue outcomes were small in older adults; highlighting the importance of precise measurements to detect changes beyond measurement error. Together with the estimated monitoring time intervals, these findings can assist the planning of prospective investigations of musculoskeletal health in aging. Furthermore, based on the observed independent association between muscle density and fall status, monitoring muscle density may further complement the study of musculoskeletal health and fall risk in community-dwelling older adults.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorKontulainen, Saija A.
CommitteeChilibeck, Philip D.; Farthing, Jonathan P.; Kim, Soo
Copyright DateSeptember 2015
Aging, Adipose, Image Analysis, Sarcopenia, Myosteatosis, Fall Risk, Musculoskeletal