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

长期以来，后足骨(胫骨远端、距骨和跟骨)的外部形态一直被认为是原始人习惯性姿势和运动的关键指标。然而，之前对一些重要的后足骨化石的形态计量学研究揭示了类人猿和类人特征的独特马赛克，这使得这些灭绝的原始人的运动重建变得复杂。这项研究将调查这些骨(软骨下骨和小梁骨)的内部形态是否具有诊断运动信号，这可能有助于进一步描述这种嵌合体的性质。根据相关的人类后足骨的微型计算机断层扫描(µCT)图像，这项研究将量化并同时检查软骨下骨和小梁骨的与强度相关的特性，这两个特性都被假设为反映在移动过程中产生的习惯性关节压缩负荷。这项研究的更广泛的意义是测试这些环境塑料特性在指示关节负荷的功能信号方面的准确性和一致性，从而验证使用软骨下和松质骨结构特性作为工具来从分离的骨骼元素推断运动行为。首先，通过将人类距小腿(踝关节)和距下关节的骨骼特性模式与这些关节中的接触面积和关节压力模式进行比较，来评估这些特性在指示习惯性负荷方面的准确性。这些接触面积和关节压力模式是通过模拟两足步态的人体生物力学研究得出的。其次，这项研究将评估这些骨骼特性是否与目前关于原始人习惯性后足负荷的假设一致，并能够区分具有不同习惯性运动行为的物种。这项研究将严格评估定量µCT方法在比较形态学方面的优势和局限性，这将对未来建议使用这些方法解决现存或化石标本的形态问题的研究人员具有很高的价值。对未被研究的人类后足区的骨微结构进行量化和分析，将为骨生物力学的临床和理论生物医学研究提供有价值的比较数据。这项研究将解决目前关于原始人习惯性踏板姿势的假说，并揭示新的假说，可能会进一步加深我们对原始人脚和脚踝形态进化的理解。最后，一旦有了大量人类后足骨化石的微CT图像，这项研究将提供一个对比样本，用来解释软骨下骨和小梁骨的形态。

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.