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Trabecular bone forms the internal scaffolding of most bones, and consists of a microscopic lattice-like structure of interconnected bony struts. Experimental work has demonstrated that trabecular bone adapts its structural rigidity and orientation in response to the strains placed upon the skeleton during life, a concept popularly known as “Wolff’s Law” or “bone functional adaptation”. Anthropological work has focused on correlating variation in primate trabecular bone to locomotor and masticatory function, to provide a context for the interpretation of fossil morphology. However, intraspecies variation and its underlying mechanisms are still poorly understood. In this thesis, variation in trabecular bone structure is examined in the human foot in four archaeological populations. The aim is to tease apart the factors underlying variation in human trabecular microstructure to determine whether it may be a suitable proxy for inferring terrestrial mobility in past populations. μCT scanning is used to image the three-dimensional trabecular structure of the talus, calcaneus, and first metatarsal in samples from four archaeological populations. Trabecular structure is quantified in seventeen volumes of interest placed throughout the foot. Trabecular bone is influenced by a variety of factors including body mass, age, diet, temperature, genetics, sex, and mechanical loading. Before trabecular structure can be used to infer habitual behaviour, the effects of these factors need to be understood and ideally statistically accounted for. Therefore, the effects of variation in bone size and shape, body mass, age, and sex on human trabecular structure are examined in four populations. Significant effects of body mass and age are reported, but little sexual dimorphism was found within populations. Taking these results into account, variation in trabecular structure is compared between archaeological populations that were divided into high and low mobility categories. Results demonstrate that the four populations show similar patterns of trabecular variation throughout the foot, with a signal of terrestrial mobility level superimposed upon it. Terrestrial mobility is associated with greater bone volume fraction and thicker, more widely spaced, and less interconnected trabeculae. Ontogeny of trabecular bone in the human calcaneus is investigated in two archaeological populations in the final chapter of the thesis. Results indicate that calcaneal trabecular bone adapts predictably to changes in loading associated with phases of gait maturation and increases in body mass. This opens the possibility of using trabecular structure to serve as a proxy of neuromuscular development in juvenile hominins. This work demonstrates that trabecular bone may serve as a useful proxy of habitual behaviour in hominin fossils and past populations when all contributing factors are carefully considered and ideally statistically controlled for.

Canine hip dysplasia is a chronic, debilitating developmental condition where incongruity of the coxofemoral joint often results in osteoarthrosis. Multiple radiographic methods for assessment of hip dysplasia are available, however can be limited in their capability to reliably diagnose hip dysplasia within juvenile dogs. As a new approach to the understanding of the pathologic processes and potential for earlier diagnosis of canine hip dysplasia, our objective was to determine if acetabular and femoral subchondral bone density (SBD) changes can be detected within normal and dysplastic coxofemoral joints using CT osteoabsorptiometry at 6 months of age. Thirty-three Labrador Retrievers from the U.S. Department of Defense Military Working Dog Breeding Program were diagnosed with normal or dysplastic coxofemoral joints based on computed radiographic pelvic studies by a consensus of 3 board-certified radiologists using the OFA evaluation grades at 6, 12, 18, and/or 24 months of age. Helical pelvic CT studies at 6 months of age were obtained with the patient in dorsolateral subluxation positioning (3.0 mm slice thickness, bone algorithm). A calcium hydroxyapatite calibration phantom was placed into the field of view of every study to standardize and allow conversion of all Hounsfield Unit values to Calcium Hydroxyapatite Equivalent Density units (CHED, mg/ml). CT data was converted into 3D reconstructions for volumetric assessment of SBD along the load-bearing regions of the femoral heads and acetabula 2 mm beneath their articular margins. Color mineral density distribution patterns were generated by assigning a color scale to the calculated density values. Nine standardized ROI were made within the load-bearing regions of the acetabula (n = 3) and femoral heads (n = 6). Descriptive statistics and a mixed model repeated measures ANOVA with associated partial correlation coefficients were used to evaluate the mean CHED values of ROI between dogs of the same and differing OFA radiographic classifications. Significance was set at P < 0.05. Seventeen, 11, and 5 dogs were diagnosed with bilaterally normal, bilaterally dysplastic, or unilaterally dysplastic coxofemoral joints, respectively. Strong correlations were present between all mean CHED values of the ROI within bilaterally normal and dysplastic dogs except for two (caudodorsal aspect of the acetabulum and craniolateral aspect of the femoral heads), which had moderate to weak correlations (r = 0.47 and 0.56, respectively). Bilaterally dysplastic dogs had a significant decrease (P < 0.01) in mean CHED ROI values along the caudodorsal aspect of the acetabulum (484.16 mg/ml) and craniolateral aspect of the femoral heads (350.03 mg/ml) when compared with bilaterally normal dogs (533.14 mg/ml and 404.74 mg/ml, respectively). The decrease in mean SBD within the dysplastic joints is likely attributed to decreased distribution of load bearing forces through these regions of the incongruent and/or subluxated joints in accordance with Wolff’s Law. A concurrent increase in mean SBD was not seen in the other ROI as expected, which may be attributed to degree of severity of disease, study limitations (sample size and volume averaging), or age at time of imaging.