Abstract
BackgroundIn addition to external bone shape and cortical bone thickness and distribution, the distribution and orientation of internal trabecular bone across individuals and species has yielded important functional information on how bone adapts in response to load. In particular, trabecular bone analysis has played a key role in studies of human and nonhuman primate locomotion and has shown that species with different locomotor repertoires display distinct trabecular architecture in various regions of the skeleton. In this study, we analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime.MethodsMicro-computed tomography scans of Homo sapiens (n = 11), Pan troglodytes (n = 18), Gorilla gorilla (n = 14) and Pongo sp. (n = 7) were used to investigate trabecular structure throughout the distal epiphysis of the femur. We predicted that bone volume fraction (BV/TV) in the medial and lateral condyles in Homo would be distally concentrated and more anisotropic due to a habitual extended knee posture at the point of peak ground reaction force during bipedal locomotion, whereas great apes would show more posteriorly concentrated BV/TV and greater isotropy due to a flexed knee posture and more variable hindlimb use during locomotion.ResultsResults indicate some significant differences between taxa, with the most prominent being higher BV/TV in the posterosuperior region of the condyles in Pan and higher BV/TV and anisotropy in the posteroinferior region in Homo. Furthermore, trabecular number, spacing and thickness differ significantly, mainly separating Gorilla from the other apes.DiscussionThe trabecular architecture of the distal femur holds a functional signal linked to habitual behaviour; however, there was more similarity across taxa and greater intraspecific variability than expected. Specifically, there was a large degree of overlap in trabecular structure across the sample, and Homo was not as distinct as predicted. Nonetheless, this study offers a comparative sample of trabecular structure in the hominoid distal femur and can contribute to future studies of locomotion in extinct taxa.
Highlights
Extant great apes are often used as models to help reconstruct the origin and evolution of bipedality, and to help interpret the variable hindlimb morphology that is preserved in the hominin fossil record
Qualitative analysis shows that in Pongo, there is a consistent distribution of high BV/TV values over the posterosuperior margin of both condyles, where the gastrocnemius heads originate (Diogo et al, 2013a); this concentration is occasionally found in African apes
This study provided the first holistic study of trabecular bone within the hominoid distal femur
Summary
Extant great apes are often used as models to help reconstruct the origin and evolution of bipedality, and to help interpret the variable hindlimb morphology that is preserved in the hominin fossil record. Studying the morphology of the knee joint and its links to locomotion in extant apes can help reconstruct how early hominins (e.g. australopiths, early Homo) walked bipedally, as well as other potential locomotor behaviours in which they may have engaged (e.g. arboreal climbing). We analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime. We predicted that bone volume fraction (BV/TV) in the medial and lateral condyles in Homo would be distally concentrated and more anisotropic due to a habitual extended knee posture at the point of peak ground reaction force during bipedal locomotion, whereas great apes would show more posteriorly concentrated BV/TV and greater isotropy due to a flexed knee posture and more variable hindlimb use during locomotion. This study offers a comparative sample of trabecular structure in the hominoid distal femur and can contribute to future studies of locomotion in extinct taxa
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