Trapeziometacarpal joint mobility in gibbons (fam. Hylobatidae) and rhesus macaques (Macaca mulatta)

Abstract

Objectives: The purpose of this study is to investigate the differences in 3D kinematics of the trapeziometacarpal (TMC) joint between gibbons (fam. Hylobatidae) and macaques (Macaca mulatta), two non-human primate groups with a distinct locomotor behavior. Gibbons are highly arboreal species, while macaques are quadrupeds.Here, we investigate the mobility and structural constraints of the TMC joint in both these primates and evaluate the hypothesis that differences in locomotor mode are reflected in joint structure and function. Materials and methods:We have developed an innovative software suite allowing for the quantification of in situ 3D kinematics based on medical imaging of the primate TMC joint using a unique sample of eight gibbons and seven macaques. These analyses are further supported by detailed dissection of the surrounding ligaments. Results:The data demonstrate distinct differences in TMC joint mobility between gibbons and macaques, with wide ranges of motion in the gibbon TMC joint and restricted movement in macaques. Furthermore, the dissections show little dissimilarity in ligament anatomy that could be associated with the differences in TMC joint capabilities. Conclusion:We conclude that gibbons possess a highly mobile TMC joint and the ball-and-socket morphology allows for large ranges of motion. This type of morphology, however, does not offer much inherent stabilization. Lack of structural joint reinforcement suggests that gibbons may have difficulty in performing any type of power grasp with high loads. Macaques, on the other hand, are shown to have a considerably reinforced TMC joint, which is likely related to the habitual loading of the thumb during locomotion.

Form, function and evolution of the human hand

“…This distinct FPL muscle inserts at the distal pollical phalanx, facilitating the flexion of the interphalangeal joint that is critical to forceful opposition in modern humans (Hamrick et al, 1998;Marzke, 1997;Marzke et al, 1998). Bonobos have a well-developed tendon that splits off from the flexor digitorum profundus muscle belly, while in chimpanzees the long tendon to the pollical distal phalanx is vestigial or even absent (Tuttle, 1969;Van Leeuwen et al, 2018). In Pan, the shared muscle belly between the pollex and second ray limits the amount of independent movement of these digits compared with modern humans.…”

“…The other main difference in intrinsic musculature between modern humans and the other African apes involves the muscles that lie between the metacarpal bones, most notably the distinct intermetacarpales and flexor brevis profundi muscles in Pan and Gorilla that in modern humans combine to form the dorsal interossei muscles (Diogo et al, 2012;van Leeuwen et al, 2018). The differences between the hand muscles of modern humans and other great apes translate into relative differences in the mass of muscles in the regions of the hand (Table 1).…”

“…In contrast, non-human great apes have greater relative extrinsic flexor mass to the fingers (Tuttle, 1969). However, it is important to note the substantial inter-individual variation in forearm and hand musculature in apes, including modern humans (Diogo et al, 2012;Linburg & Comstock, 1979;van Leeuwen et al, 2018).…”

“…For example, in African apes and modern humans, the flexor digitorum profundus muscle belly (and consequently, the tendon) associated with the second digit is largely independent from the muscle belly of the third, fourth, and fifth digits. As a result, the second digit has a greater degree of independence, particularly at the proximal interphalangeal joint, compared with the more medial digits (Schieber, 1995;van Leeuwen et al, 2018). Other primates without separate muscle bellies to the digits produce movement of an individual digit by activating multiple muscles as antagonists or synergists to restrict the movements of other digits (Schieber, 1995).…”

“…Figure 6).Kinematic studies of ape trapeziometacarpal joints are limited(van Leeuwen et al, 2019;van Leeuwen et al, 2021;van Leeuwen et al, 2022). Bonobos have a similar range of motion at the trapeziometacarpal joint as modern humans, with the latter having a notably larger range of Mc1 extension(van Leeuwen et al, 2019).…”