Patterns of internal bone structure and functional adaptation in the hominoid scaphoid, lunate, and triquetrum

Abstract

The morphology of the proximal carpals (scaphoid, lunate, triquetrum) are linked to the range of motion (ROM) at the radiocarpal and midcarpal joints. While the relationship between ROM and habitual locomotor mode is well established, it has yet to be investigated whether relative patterns of internal bone architecture reflect the kinematics and kinetics at the proximal row. As internal bone is known to model its structure to habitually incurred forces, internal architecture has the potential to provide insight into how joints have been loaded during the lifetime of an individual.Using a broad sample of extant great apes and humans (n = 177 total bones), this study investigates whether relative differences in the bone volume to total volume (BV/TV) and degree of anisotropy (DA) across the scaphoid, lunate and triquetrum correlate with the presumed force transfer and biomechanics of the hominoid wrist.Results reveal that broad patterns in BV/TV and DA differentiate hominoids by their predominant locomotor mode. The human pattern suggests the lunate may be the most highly strained bone within the proximal row. Both knuckle-walking taxa (Gorilla, Pan) exhibited similar architectural patterns suggesting they are adapted to resist similar forces in this region of the wrist. The relatively high DA across all Pongo carpals suggests it may have more stereotypical wrist loading than commonly assumed. Finally, the distinctly low DA in the triquetrum across all taxa suggests force transfer via the synapomorphic triangular fibrocartilage complex may leave a distinctive signature in the internal bone architecture that requires further investigation.Objectives: Functional adaptation in the trabecular and cortical bone of individual wrist bones has been investigated across hominoid species but functional conclusions remain limited. This study examines whether relative patterns in internal bone architecture across multiple carpal bones can be correlated to the known or assumed kinetics and kinematics of the wrist joint in extant hominoids. Materials and Methods: This study applied a whole-bone methodology to quantify the internal architecture (cortical and trabecular bone) of the scaphoid, lunate, and triquetrum of suspensory (Pongo sp.), knuckle-walking (Pan paniscus, Pan troglodytes, Gorilla sp.) and bipedal (Homo sapiens) hominoids (n = 177 total bones).Results: H. sapiens showed unique patterns in both measured parameters: a decrease in degree of anisotropy (DA) from the scaphoid to the triquetrum with higher bone volume to total volume (BV/TV) in the lunate relative to the other bones. Knuckle-

Cortical bone architecture of hominid intermediate phalanges reveals functional signals of locomotion and manipulation

“…Studies of internal structure of the hand have generally focused on the metacarpus and elements of the carpus, with the phalanges being comparatively understudied (e.g., Bird et al, 2022;Dunmore et al, 2019;Marchi, 2005;Skinner et al, 2015). Here, we investigated…”

“…Studies of internal structure of the hand have generally focused on the metacarpus and elements of the carpus, with the phalanges being comparatively understudied (e.g., Bird et al, 2022; Dunmore et al, 2019; Marchi, 2005; Skinner et al, 2015). Here, we investigated variation in hominoid cortical bone distribution patterns of the intermediate phalanges of digits 2–5 in relation to hand use and postures, building upon our previous study of proximal phalanges in the same taxa (and specimens) (Syeda et al, 2023).…”

“…Extant great apes and modern humans use a range of hand postures during positional (locomotor and postural) and manipulative behaviors (e.g., Kivell et al, 2020; Schmitt et al, 2016), which have been successfully linked to the morphological variation within great ape hands (Bird et al, 2021, 2022; Dunmore et al, 2019; Dunmore, Bardo, et al, 2020; Dunmore, Skinner, et al, 2020; Marchi, 2005; Matarazzo, 2008, 2015; Tsegai et al, 2013). This form‐function link among extant taxa has been used to infer habitual manual activities of fossil taxa, ranging from Miocene apes (Almecija et al, 2009; Almécija et al, 2012; Susman, 2004) to fossil Homo sapiens (Bardo et al, 2020; Kivell et al, 2022; Stephens et al, 2018).…”

Functional insights from an exploration of the inner structure of the patella: new perspectives for the study of the hominin fossil record

“…Following a generation of virtually-based endostructural studies focussing on specific VOIs, some so-called "whole-epiphyses/bone" analytical methods have been developed (e.g., Pahr and Zysset, 2009;DeMars et al, 2021;Veneziano et al, 2021) and applied to characterize the entire endostructural organisation of several regions/elements of the extant primate skeleton and also to tentatively assess some hominin fossil specimens. Such an approach has been applied, for instance, to investigate the upper limb elements (Kivell et al, 2018;Arias-Martorell et al, 2021), the hand bones (Tsegai et al, 2013;Skinner et al, 2015;Stephens et al, 2016;Dunmore et al, 2019;2020a;2020b;Bird et al, 2021a;2021b), the femur (Georgiou et al, 2018;Sukhdeo et al, 2020), the distal tibia and the foot bones (Tsegai et al, 2013;, as well as to directly compare different skeletal parts (Tsegai et al, 2018).…”

Trabecular bone structure of the proximal capitate in extant hominids and fossil hominins with implications for midcarpal joint loading and the dart‐thrower's motion

“…The first study of trabecular functional adaptation in the primate wrist failed to find support for several functional predictions (Schilling et al, 2014); however, the development of new 'whole-bone' techniques have yielded functionally meaningful results in this regard (Bird et al, 2021(Bird et al, , 2022Stephens et al, 2018). Stephens et al (2018) found that the distribution of trabecular bone in the proximal capitate of recent humans coincided with its oblique range of motion across the scapho-lunate articular surface and therefore associated this pattern with the predicted kinematics of the dart-thrower's motion (DTM).…”