Trabecular architecture of the great ape and human femoral head

Abstract

Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole-epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n = 20), Gorilla gorilla (n = 14), Pongo sp. (n = 5) and Homo sapiens (n = 12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle-walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.

Keywords: Gorilla; Pan; Pongo; African apes; cancellous bone; functional morphology; hominid.

Figure 1

Comparison of hip posture during different habitual locomotor activities in great apes (A,B) and humans (C,D). (A) Great ape hip posture in maximum hip flexion (~ 55°–60°) during climbing (Isler, 2005). (B) Great ape hip posture at toe‐off (~ 110°) during terrestrial knuckle‐walking (Finestone et al. 2018). (C) Human hip posture at toe‐off (~175°). (D) Human hip posture at heel‐strike (~160°).

Figure 2

Pan BV/TV distribution in the femoral head. Five Pan specimens showing variation in the BV/TV distribution across the sample in (A) anterior, (B) posterior and (C) superior views. BV/TV is scaled to 0–0.55. All specimens are from the right side. Specimens from left to right (F, female; M, male): MPITC 14996 (F), USNM 220063 (F), USNM 176228 (M), MPITC 11781 (M), MPITC 11786 (F).

Figure 3

Gorilla BV/TV distribution in the femoral head. Five Gorilla specimens showing variation in the BV/TV distribution across the sample in (A) anterior, (B) posterior and (C) superior views. BV/TV is scaled to 0–0.55. All specimens are from the right side. Specimens from left to right (F, female; M, male): M96 (F), M264 (M), M372 (M), M856 (F), FC123 (M).

Figure 4

Pongo BVTV distribution in the femoral head. Five Pongo specimens showing variation in the BV/TV distribution across the sample in (A) anterior, (B) posterior and (C) superior views. BV/TV is scaled to 0–0.55. All specimens are from the right side. Specimens from left to right (All female): ZSM 1909 0801, 1907 0660, 1973 0270, 1907 0483, 1907 0633b.

Figure 5

Homo BV/TV distribution in the femoral head. Five Homo specimens showing variation in the BV/TV distribution across the sample in (A) anterior, (B) posterior and (C) superior views. BV/TV is scaled to 0–0.55. All specimens are from the right side. Specimens from left to right (F, female; M, male): CAMPUS 36 (F), CAMPUS 93 (M), CAMPUS 74 (F), CAMPUS 417 (sex unknown), CAMPUS 81 (M).

Figure 6

Bivariate plot of mean bone volume fraction (BV/TV) and mean degree of anisotropy (DA) for each individual and species in the sample.

Figure 7

A histogram of mean BV/TV and DA value distributions in the studied taxa.