Doctoral Dissertation Improvement Grant: The Functional Morphology of Subchondral and Trabecular Bone in the Hominoid Hindfoot

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The external morphology of the hindfoot bones (distal tibia, talus, and calcaneus) have long been held as key indicators of habitual posture and locomotion in hominids. However, previous morphometric studies of some important fossil hindfoot bones reveal unique mosaics of ape-like and human-like features that complicate locomotor reconstruction of these extinct hominins. This study will investigate whether the internal morphology of these bones (subchondral and trabecular bone) hold a diagnostic locomotor signal that may help to further characterize the nature of this mosaicism. From micro-computed tomography (µCT) images of associated hominid hindfoot bones, this study will quantify and concurrently examine strength-related properties of subchondral and trabecular bone, which have both been hypothesized to reflect the habitual compressive joint loads incurred during locomotion. The broader significance of this study is to test the accuracy and consistency of these environmentally-plastic properties in indicating a functional signal of joint load, thus validating the use of subchondral and trabecular bone structural properties as tools to infer locomotor behavior from isolated skeletal elements. The accuracy of these properties in indicating habitual load will first be assessed by comparing the pattern of bone properties in the human talocrural (ankle) and subtalar joints to the contact area and articular pressure patterns that have been quantified in these joints from human biomechanics studies of simulated bipedal gait. Secondly, this study will assess whether these bone properties are consistent with current hypotheses of habitual hindfoot load in hominids and can distinguish among species with different habitual locomotor behaviors. This study will critically evaluate the strengths and limitations of quantitative µCT methods in comparative morphology that will be highly valuable to future researchers who propose to use these methods to address morphological questions in extant or fossil specimens. The quantification and analysis of bone microstructure in the understudied hominid hindfoot region will provide valuable comparative data for both clinical and theoretical biomedical studies of bone biomechanics. This study will address current hypotheses of habitual pedal posture in hominids, as well as reveal new hypotheses that may further our understanding of the morphological evolution of the hominid foot and ankle. Finally, once µCT images of the numerous fossil hominin hindfoot bones are available, this study will provide a comparative sample with which to interpret the subchondral and trabecular bone morphology.