INVESTIGATING GEOMETRIC RELATIONSHIPS OF CORTICAL BONE DISTRIBUTION IN THE ADULT LOWER LIMB
The purpose of this study was to test the relationships between cortical bone geometry and expected patterns of bone loss with age in both males and females. It was hypothesized that an increase in age would result in a decrease in mechanical strength as a function of bone loss. Computed tomography (CT) scans of 189 modern individuals (n = 90 females, n = 99 males) aged 40-99 were collected. The long bones of the lower limb were individually segmented and a model was created to align each stack of images to the principle axis of the bone. Image slices at 20, 35, 50, 65, and 80 percent of bone length were then analyzed for cross-sectional geometric (CSG) properties. CSG properties were compared with age using non-parametric methods, including ANOVAs. Results suggest that across the entire lower limb, the diameter of the diaphysis increases significantly with age, more so in females. Concurrently, the size of the medullary cavity increases, but at a faster rate. As such, total cortical area decreases with age, resulting in a weaker structure. Deposition on the periosteal surface may function as a means of increasing bone strength by increasing the amount of bone furthest from the central axis. This phenomenon is likely in reaction to reduced strength as a result of increased endosteal resorption, a part of the normal aging process. Establishing an age range at which bone geometry changes to mechanically adjust for normal processes of aging is vital to documenting bone loss with age. These findings allow the influence of other environmental factors (e.g. diet, subsistence strategies, social status) to be empirically tested against patterns of bone loss in past populations.