Apparent density of the primate calcaneo‐cuboid joint and its association with locomotor mode, foot posture, and the “midtarsal break”

Abstract

Primates use a range of locomotor modes during which they incorporate various foot postures. Humans are unique compared with other primates in that humans lack a mobile fore- and midfoot. Rigidity in the human foot is often attributed to increased propulsive and stability requirements during bipedalism. Conversely, fore- and midfoot mobility in nonhuman primates facilitates locomotion in arboreal settings. Here, we evaluated apparent density (AD) in the subchondral bone of human, ape, and monkey calcanei exhibiting different types of foot loading. We used computed tomography osteoabsorptiometry and maximum intensity projection (MIP) maps to visualize AD in subchondral bone at the cuboid articular surface of calcanei. MIPs represent 3D volumes (of subchondral bone) condensed into 2D images by extracting AD maxima from columns of voxels comprising the volumes. False-color maps are assigned to MIPs by binning pixels in the 2D images according to brightness values. We compared quantities and distributions of AD pixels in the highest bin to test predictions relating AD patterns to habitual locomotor modes and foot posture categories of humans and several nonhuman primates. Nonhuman primates exhibit dorsally positioned high AD concentrations, where maximum compressive loading between the calcaneus and cuboid likely occurs during "midtarsal break" of support. Humans exhibit less widespread areas of high AD, which could reflect reduced fore- and midfoot mobility. Analysis of the internal morphology of the tarsus, such as subchondral bone AD, potentially offers new insights for evaluating primate foot function during locomotion.

Kinematics of primate midfoot flexibility

“…Clinical literature has shown this difference in humans (Elftman & Manter, 1935b; Manter, 1941; Elftman, 1960; Ouzounian & Shereff, 1989; Astion, et al 1997; Sammarco & Hockenbury, 2001; Nowak, et al 2010), although we infer that some of these researchers may have been examining dorsiflexion at the lateral cubometatarsal joint and not the calcaneocuboid joint as is commonly reported. The difference in the medial and lateral foot joint axes has been associated with a “locking” mechanism that converts the human foot into a rigid lever for effective propulsion at toe-off.…”

“…Nevertheless, our non-human primate sample sizes are comparable to those associated with human cadaver based studies (e.g., Bojsen-Møller, 1979; Gomberg, 1985; Ouzounian & Shereff, 1989; Blackwood, et al 2005; Nester, et. Al 2007; DeSilva, 2010; Nowak, et al 2010). …”

Functional aspects of metatarsal head shape in humans, apes, and Old World monkeys

“…However, we hypothesize that some of these characters might reflect signals of terrestriality more generally for other taxa that stereotypically dorsiflex their forefoot joints during quadrupedal locomotion. For example, different foot postures (e.g., plantigrade versus digitigrade), substrate use (e.g., terrestrial versus arboreal), and even speed of travel can also influence habitual MTPJ ROM during locomotion (Meldrum, 1991;Hayama et al, 1994;Schmitt and Larson, 1995;Vereecke et al, 2003;Nowak et al, 2010; see also Patel, 2009 andPolk, 2010 for analogous data in the MCPJs). If dorsal orientation of the MT head facilitates greater potential for dorsiflexion at the MTPJs (Susman, 1983;Stern and Susman, 1983;Susman and de Ruiter, 2004;Ward et al, 2011Ward et al, , 2012DeSilva et al, 2012), we expect to see at least some evidence of dorsal MT head orientation in digitigrade, more habitually terrestrial genera such as Papio (Meldrum, 1991;Schmitt and Larson, 1995;but see Patel, 2010).…”

Joint Loads in Marsupial Ankles Reflect Habitual Bipedalism versus Quadrupedalism

“…Nowak et al [22] observed the predicted correspondence between presumed joint loading patterns and locations of maximum radiodensity areas in primates that experience a “mid-tarsal break” versus humans that typically do not, but that may in small frequencies [56]. Observation of the predicted distinctiveness of bipedal marsupials in the extent of maximum radiodensity area in their distal tibiae also accords well with predicted patterns of radiodensity distribution observed in the forelimb joints of primates and xenarthrans.…”

“…Quadrupedal primates exhibit the most extensive distribution of high radiodensity in their distal radii, even differing in predictable ways according to hand postures habitually adopted during quadrupedalism [19]. Similarly, the distribution of high radiodensity areas in the primate foot (e.g., calcaneocuboid joint) corroborates theoretical differences in loading arising from overall foot mobility and habitual foot postures adopted during quadrupedalism [22].…”