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

Abstract

This contribution is a short review of the functional significance of the patella in extant catarrhines and extinct hominins and of current functional, adaptive and evolutionary-related questions concerning the fossil hominin record. The patella plays a key functional role in the knee joint and thus reflects habitual postural and locomotion modes. However, patellar remains are rare in the hominin fossil record and it is still unclear whether and how their differences in shape and proportions compared to extant humans affect knee kinesiology. Here, we illustrate with a first example from a sample of human, Pan, Papio and Neanderthal patellae that the development of a "whole-bone" endostructural analysis has the potential to provide relevant functional information for reconstructing the knee loading environment in fossil taxa, combined, whenever necessary, with a subsampling approach. This method relies on the plastic nature of the cortical and trabecular bony tissues and the modelling and remodelling dynamics during life to adjust structurally to the site-specific loading environment. This kind of information would bring new contributions not only to ongoing discussions on the evolutionary forces that shaped the knee joint in association with postural and locomotor adaptations, but also to the tentative taxonomic identification of isolated fossil specimens. Keywords -patella, cortical bone, trabecular bone, fossil hominins, "whole-bone" analysis Mots clés -patella, os cortical, os trabéculaire, hominines fossiles, analyse intégrale de l'os

The trabecular architecture of the popliteal sesamoid bone (cyamella) from a New Zealand white rabbit (Oryctolagus cuniculus)

“…Similar to other short bones and sesamoid bones, the cyamella has a relatively thin cortical shell and high trabecular BV/TV (Cazenave, 2022; Currey, 2002). This study results show that cortical bone contributes only about 25% of the cyamella volume, half the value of trabecular bone (about 52%), which also demonstrates a high trabecular BV/TV (67.2 ± 3.4%), (Table 1).…”

“…Comparing the results of this study to other studies that looked at the trabecular structure in another sesamoid bone, the patella, supports this conclusion (Table 3). Several studies investigated the internal trabecular structure in humans (Cazenave, 2022; Cazenave et al, 2019; Hoechel et al, 2015; Toumi et al, 2006, 2012), some nonhuman primates (i.e., chimpanzees and baboons), (Cazenave et al, 2019; Cazenave, 2022), and odd‐toed ungulates (Houssaye et al, 2022). These studies reported trabecular BV/TV values ranging between 24% and 77%, Tb.Th values between 90 and 270 µm, and Tb.N values between 0.9 and 2 mm −1 .…”

The Neanderthal patellae from Krapina (Croatia): A comparative investigation of their endostructural conformation and distinctive features compared to the extant human condition

“…Given the ability of the mechanosensitive cortical and trabecular bony tissues to adjust structurally during life to the site-specific loading environment (e.g., Hoechel et al, 2015;Katoh et al, 1996;Mazurier, 2006;Mazurier et al, 2010;Raux et al, 1975;Toumi et al, 2006Toumi et al, , 2012Townsend et al, 1975;Van Kampen & Huiskes, 1990), the assessment of patellar endostructural features such as cortical bone thickness variation and trabecular network arrangement have the potential to provide subtle functionally related information about the knee joint mechanical environment (Cazenave et al, 2019;Cazenave et al, 2022). A preliminary comparative study noninvasively investigating the inner organizational pattern of the adult patella in two Neanderthals (from Krapina, Croatia, and Regourdou, France), one anatomically modern fossil human (the Magdalenian from Chancelade, France), and in a sample of African-and Europeanderived Holocene individuals revealed marked differences not only between the Neanderthal and the fossil and Holocene humans, but also between the two Neanderthal specimens (Cazenave et al, 2020).…”