The deep trabecular structure of first metacarpals in extant hominids

Abstract

ObjectivesRecent studies have associated subarticular trabecular bone distribution in the extant hominid first metacarpal (Mc1) with observed thumb use, to infer fossil hominin thumb use. Here, we analyze the entire Mc1 to test for interspecific differences in: (1) the absolute volume of trabecular volume fraction, (2) the distribution of the deeper trabecular network, and (3) the distribution of trabeculae in the medullary cavity, especially beneath the Mc1 disto‐radial flange.Materials and MethodsTrabecular bone was imaged using micro‐computed tomography in a sample of Homo sapiens (n = 11), Pan paniscus (n = 10), Pan troglodytes (n = 11), Gorilla gorilla (n = 10) and Pongo sp., (n = 7). Using Canonical Holistic Morphometric Analysis (cHMA), we tested for interspecific differences in the trabecular bone volume fraction (BV/TV) and its relative distribution (rBV/TV) throughout the Mc1, including within the head, medullary cavity, and base.ResultsP. paniscus had the highest, and H. sapiens the lowest, BV/TV relative to other species. rBV/TV distribution statistically distinguished the radial concentrations and lack of medullary trabecular bone in the H. sapiens Mc1 from all other hominids. H. sapiens and, to a lesser extent, G. gorilla also had a significantly higher trabecular volume beneath the disto‐radial flange relative to other hominids.DiscussionThese results are consistent with differences in observed thumb use in these species and may also reflect systemic differences in bone volume fraction. The trabecular bone extension into the medullary cavity and concentrations beneath the disto‐radial flange may represent crucial biomechanical signals that will aid in the inference of fossil hominin thumb use.

Mary Marzke, PhD: A pioneer and innovator in the study of the evolution of the human hand

“…Mary's vast body of work also inspired research deriving functional information from internal bone structure. Patel (2024) explores rigidity of the catarrhine metatarsals via cross‐sectional geometry, while two articles apply holistic, comparative analyses of trabecular bone structure: (1) Bird et al (2024) look for evidence of the dart‐throwers motion of the wrist in the proximal capitate in extant hominids and fossil hominins while (2) Dunmore et al (2024) explore the first metacarpal of the extant hominids.…”

Trabecular architecture of the distal femur in extant hominids

“…BV/TV and DA can together explain up to 97% of the variation in elastic properties of trabecular bone (Homminga et al, 2003;Maquer et al, 2015;Van Rietbergen et al, 1998;Zysset, 2003). BV/TV and DA have been shown to reflect the presumed predominant direction and relative magnitude that joints are loaded in, during different locomotor and manipulative behaviours; in previous landmark studies (Dunmore et al, 2019(Dunmore et al, , 2020Sylvester & Terhune, 2017), throughout an entire bone or epiphysis (Kuo et al, 2022;Ryan et al, 2019;Saers et al, 2022;Skinner et al, 2013;Stephens et al, 2016;Tsegai et al, 2018) or by using holistic morphometric approaches (Bachmann et al, 2022;DeMars et al, 2022;Dunmore et al, 2023). Recent methodological advancements allow comprehensive statistical analysis of trabecular bone structure within and between species, particularly those that vary in external bone shape (Bachmann et al, 2022;Gross et al, 2014).…”