Chasing footprints in time – reframing our understanding of human foot function in the context of current evidence and emerging insights

In this narrative review we evaluate foundational biomechanical theories of human foot function in light of new data acquired with technology that was not available to early researchers. The formulation and perpetuation of early theories about foot function largely involved scientists who were medically trained with an interest in palaeoanthropology, driven by a desire to understand human foot pathologies. Early observations of people with flat feet and foot pain were analogized to those of our primate ancestors, with the concept of flat feet being a primitive trait, which was a driving influence in early foot biomechanics research. We describe the early emergence of the mobile adaptor–rigid lever theory, which was central to most biomechanical theories of human foot function. Many of these theories attempt to explain how a presumed stiffening behaviour of the foot enables forward propulsion. Interestingly, none of the subsequent theories have been able to explain how the foot stiffens for propulsion. Within this review we highlight the key omission that the mobile adaptor–rigid lever paradigm was never experimentally tested. We show based on current evidence that foot (quasi-)stiffness does not actually increase prior to, nor during propulsion. Based on current evidence, it is clear that the mechanical function of the foot is highly versatile. This function is adaptively controlled by the central nervous system to allow the foot to meet the wide variety of demands necessary for human locomotion. Importantly, it seems that substantial joint mobility is essential for this function. We suggest refraining from using simple, mechanical analogies to explain holistic foot function. We urge the scientific community to abandon the long-held mobile adaptor–rigid lever paradigm, and instead to acknowledge the versatile and non-linear mechanical behaviour of a foot that is adapted to meet constantly varying locomotory demands.     

The extensibility of the plantar fascia influences the windlass mechanism during human running

The arch of the human foot is unique among hominins as it is compliant at ground contact but sufficiently stiff to enable push-off. These behaviours are partly facilitated by the ligamentous plantar fascia whose role is central to two mechanisms. The ideal windlass mechanism assumes that the plantar fascia has a nearly constant length to directly couple toe dorsiflexion with a change in arch shape. However, the plantar fascia also stretches and then shortens throughout gait as the arch-spring stores and releases elastic energy. We aimed to understand how the extensible plantar fascia could behave as an ideal windlass when it has been shown to strain throughout gait, potentially compromising the one-to-one coupling between toe arc length and arch length. We measured foot bone motion and plantar fascia elongation using high-speed X-ray during running. We discovered that toe plantarflexion delays plantar fascia stretching at foot strike, which probably modifies the distribution of the load through other arch tissues. Through a pure windlass effect in propulsion, a quasi-isometric plantar fascia''s shortening is delayed to later in stance. The plantar fascia then shortens concurrently to the windlass mechanism, likely enhancing arch recoil at push-off.     

Midtarsal break variation in modern humans: Functional causes,skeletal correlates,and paleontological implications

The midtarsal break was once treated as a dichotomous, non-overlapping trait present in the foot of non-human primates and absent in humans. Recent work indicates that there is considerable variation in human midfoot dorsiflexion, with some overlap with the ape foot. These findings have called into question the uniqueness of the human lateral midfoot, and the use of osteological features in fossil hominins to characterize the midfoot of our extinct ancestors. Here, we present data on plantar pressure and pedal mechanics in a large sample of adults and children (n = 671) to test functional hypotheses concerning variation in midfoot flexibility. Lateral midfoot peak plantar pressure correlates with both sagittal plane flexion at the lateral tarsometatarsal joint, and dorsiflexion at the hallucal metatarsophalangeal joint. The latter finding suggests that midfoot laxity may compromise hallucal propulsion. Multiple regression statistics indicate that a low arch and pronation of the foot explain 40% of variation in midfoot peak plantar pressure, independent of age and BMI. MRI scans on a small subset of study participants (n = 19) reveals that curvature of the base of the 4th metatarsal correlates with lateral midfoot plantar pressure and that specific anatomies of foot bones do indeed reflect relative midfoot flexibility. However, while the shape of the base of the 4th metatarsal may reliably reflect midfoot mobility in individual hominins, given the wide range of overlapping variation in midfoot flexibility in both apes and humans, we caution against generalizing foot function in extinct hominin species until larger fossils samples are available. Am J Phys Anthropol 156:543–552, 2015. © 2015 Wiley Periodicals, Inc.     

Homologies of the branchial arch muscles in Zacco platypus (Teleostei: Cypriniformes: Cyprinidae): Evidence from innervation pattern

Homologies of the branchial arch muscles in the cyprinid Zacco platypus are assessed based on their innervation. Muscles serving the first gill arch are innervated by branches of the glossopharyngeal (IX) nerve and those serving other arches by the vagal (X) nerve. Absence of the levator posterior is confirmed. Five pairs of muscles originating from the cranium and inserted onto the specialized 5th ceratobranchial, all unique to cyprinids, are innervated by the 4th branchial trunks of X, indicating that all pairs are derivatives of the sphincter oesophagi, involving reorganization from intrinsic to extrinsic elements. Homologies of some ventral branchial muscles are also discussed and the criteria for homology improved by clarifying the innervation pattern. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

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

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. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

Dandy�CWalker malformation: An incidental finding

Dandy–Walker malformation (DWM) is a rare intracranial congenital abnormality that affects the cerebellum and some of its components; particularly cerebellar vermis, fourth ventricle and is characterized by an enlarged posterior fossa. Although there is an extensive list of signs attributed to DWM, final diagnosis is solely dependent on imaging techniques as there are no signs that are characteristic of DWM. This article reports a case with DWM who was diagnosed by magnetic resonance imaging.