Three‐dimensional geometric morphometric analysis of the distal radius insertion sites of the palmar radiocarpal ligaments in hominoid primates

Abstract

Objectives: To identify anatomic differences in the insertion sites of the palmar radiocarpal ligaments in different species of hominoid primates that may be related to their different types of locomotion. Materials and methods:We have used three-dimensional geometric morphometrics (3D GM) to analyze the distal radius ligament insertion sites in 31 Homo sapiens, 25 Pan troglodytes, 31 Gorilla gorilla, and 15 Pongo pygmaeus. We have also dissected the radioscaphocapitate (RSC), long radiolunate (LRL) and short radiolunate (SRL) ligaments in six H. sapiens and five P. troglodytes to obtain quantitative values that were then compared with the results of the 3D GM analysis.Results: H. sapiens had a relatively larger insertion site of the RSC + LRL ligament than the other hominoid primates. P. pygmaeus and P. troglodytes had a relatively large SRL ligament insertion site with a palmar orientation. In G. gorilla, the two ligament insertion sites were relatively smaller and the SRL insertion site had an ulnopalmar orientation.Discussion: The morphological differences observed can be related to the types of locomotion used by the different species and to quantitative data obtained from the dissection of ligaments in H. sapiens and P. troglodytes. 3D GM analysis of ligament insertion sites can help in interpreting the types of locomotion used by extinct hominoid primates through the analysis of preserved fossilized fragments of the distal radius. K E Y W O R D Sdistal radius, hominoid primates, radiocarpal ligaments

Insertion sites in manual proximal phalanges of African apes and modern humans

“…This indicates that when comparing either gorillas and humans or chimpanzees and humans, FR in PP2–4 may act as functional markers by separating African apes from humans. This is in keeping with Drapeau (2008) and Casado et al (2019) who found that entheses in limbs do indicate functional differences between African apes and humans. Interestingly, although previous research shows that body size is a significant predictor of insertion site variability (e.g., Nolte & Wilczak, 2013; Zumwalt, 2006) and our results suggested that body size exerts an influence on FR (Figure 3 and Table 4), this cannot explain differences in FR when comparing humans to chimpanzees.…”

“…If entheses signal behavior, the higher forces African apes apply on their hands should leave larger insertion sites than in humans. This may help to elucidate the suitability of entheses to inform on the use of the hands in taxa with unknown activity patterns (e.g., human past populations), yet this kind of study is relatively scarce (Casado et al, 2019; Drapeau, 2008; Milella, 2014; Rabey et al, 2015; Zumwalt, 2006).…”

Effects of Captivity on the Morphology of the Insertion Sites of the Palmar Radiocarpal Ligaments in Hominoid Primates

“…The landmarks previously proposed by Casado et al [38] were used to represent the morphology of the two insertion sites of the palmar radiocarpal ligaments in the distal radial epiphysis. Nine Type II and one Type III landmarks were used: the L1-L4 landmarks for the SRL insertion site and the L5-L10 landmarks for the common insertion site of the RSC and LRL (Figure 1).…”

“…We found that the morphology of these two insertion sites was related to the type of locomotion used by each of the species. The insertion sites in the more arboreal species, like Pongo pygmaeus, are larger, with a palmar orientation of the SRL ligament insertion site, while those of the knuckle-walkers (Gorilla gorilla) are smaller, with an ulnopalmar orientation of the SRL ligament insertion site, presenting Pan troglodytes an intermediate position [38]. This relationship between the morphology of a ligament insertion site and type of locomotion has also been observed in other anatomical regions of hominoid primates, such as the insertion sites of the ligaments holding the flexor digitorum profundus and superficialis muscles in proximal phalanges [39].…”

“…This may be due to differences between captive and wild environments, as captive environments generally have less three-dimensional complexity, less variation in heights and slopes, and more hard elements like artificial rocks and cement floors [2]. The palmar radiocarpal ligaments are the main stabilizing elements of the radiocarpal joint [37], and their insertion sites are located in the distal radial epiphysis [38] (Figure 1). The common insertion site of the radioscaphocapitate ligament (RSC) and the long radiolunate ligament (LRL), as well as that of the short radiolunate ligament (SRL), have previously been studied by our group in three species of hominoid primates (Gorilla gorilla, Pan troglodytes and Pongo pygmaeus).…”