Trabecular Bone Structure in the Distal Femur of Humans, Apes, and Baboons.

Trabecular bone structure has been used to investigate the relationship between skeletal form and locomotor behavior on the premise that trabecular bone remodels in response to loading during an animal's lifetime. The aim of this study is to characterize human distal femoral trabecular bone structure in comparison to three non-human primate taxa and relate the patterns of trabecular structural variation in the distal femur to knee posture during habitual locomotor behavior. A whole-epiphysis approach was applied using microCT scans of the distal femora of extant Homo sapiens, Pan troglodytes, Pongo pygmaeus, and Papio spp. (N = 48). Bone volume fraction (BV/TV) was quantified in the epiphysis and analyzed with both whole-condyle and a novel sector analysis. The results indicate high trabecular bone structural variation within and between species. The sector analysis reveals the most distinctive patterns in the stereotypically loaded human knee, with a pattern of high BV/TV distally. In general, Pan, Pongo, and Papio show evidence of flexed knee postures, typical of their locomotor behaviors, with regions of high BV/TV posteriorly within the condyles. The pairwise comparisons confirm the unique pattern in Homo and reveal a shared high BV/TV region in the patellar groove of both Homo and Papio. The distinct pattern found in Homo relative to the other primate taxa suggests a plastic response to unique loading patterns during bipedal locomotion. Results may facilitate resolving the antiquity of habitual bipedality in the hominin fossil record. This analysis also presents new approaches for statistical analysis of whole-epiphysis trabecular bone structure. Anat Rec, 2018. © 2018 American Association for Anatomy.