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

NewsBot · Aug 15, 2015

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Functional aspects of metatarsal head shape in humans, apes, and Old World monkeys
Peter J. Fern?ndez et al
Journal of Human Evolution; 12 August 2015

Modern human metatarsal heads are typically described as ?dorsally domed,? mediolaterally wide, and dorsally flat. Despite the apparent functional importance of these features in forefoot stability during bipedalism, the distinctiveness of this morphology has not been quantitatively evaluated within a broad comparative framework. In order to use these features to reconstruct fossil hominin locomotor behaviors with any confidence, their connection to human bipedalism should be validated through a comparative analysis of other primates with different locomotor behaviors and foot postures, including species with biomechanical demands potentially similar to those of bipedalism (e.g., terrestrial digitigrady). This study explores shape variation in the distal metatarsus among humans and other extant catarrhines using three-dimensional geometric morphometrics (3DGM). Shape differences among species in metatarsal head morphology are well captured by the first two principal components of Procrustes shape coordinates, and these two components summarize most of the variance related to ?dorsal doming? and ?dorsal expansion.? Multivariate statistical tests reveal significant differences among clades in overall shape, and humans are reliably distinguishable from other species by aspects of shape related to a greater degree of dorsal doming. Within quadrupeds, terrestrial species also trend toward more domed metatarsal heads, but not to the extent seen in humans. Certain aspects of distal metatarsus shape are likely related to habitual dorsiflexion of the metatarsophalangeal joints, but the total morphological pattern seen in humans is distinct. These comparative results indicate that this geometric morphometric approach is useful to characterize the complexity of metatarsal head morphology and will help clarify its relationship with function in fossil primates, including early hominins.
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NewsBot · Nov 2, 2016

Metatarsal shape and foot type: a geometric morphometric analysis.
Telfer S et al
J Biomech Eng. 2016 Nov 1. doi: 10.1115/1.4035077

Planus and cavus foot types have been associated with an increased risk of pain and disability. Improving our understanding of the geometric differences between bones in different foot types may provide insights into injury risk profiles and have implications for the design of musculoskeletal and finite element models. In this study we performed a geometric morphometric analysis on the geometry of metatarsal bones from 65 feet, segmented from computed tomography scans. These were categorized into four foot types: pes cavus, neutrally aligned, asymptomatic pes planus, and symptomatic pes planus. Generalized Procrustes analysis followed by permutation tests were used to determine significant shape differences associated with foot type and sex, and principal component analysis used to find the modes of variation for each metatarsal. Significant shape differences were found between foot types for all metatarsals (p<0.01), most notably in the case of the second metatarsal which showed significant pairwise differences across all foot types. Analysis of the principal components of variation showed pes cavus bones to have reduced cross-sectional areas in the sagittal and frontal planes. The first and fourth metatarsals were found to have significant sex-based differences, with first metatarsals from females shown to have reduced width, and fourth metatarsals from females shown to have reduced frontal and sagittal plane cross sectional areas. Overall, these findings suggest that metatarsal bones have distinct morphological characteristics that are associated with foot type and sex, with implications for our understanding of anatomy and numerical modelling of the foot.
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NewsBot · Jun 22, 2017

Age- and sex-associated morphological variations of metatarsal torsional patterns in humans.
Kitashiro M et al
Clin Anat. 2017 Jun 20. doi: 10.1002/ca.22944.

It has been demonstrated that the torsional patterns of the metatarsal heads are associated with the presence or absence of the medial longitudinal arch in hominoid feet. The relatively untwisted second metatarsal is unique in humans, but that of the African apes is much more inverted, suggesting that the torsion of the second metatarsal might represent the overall shape and flatness of the foot. Some clinical studies have recently argued that the onset of foot pathologies such as hallux valgus might be related to the torsional pattern of the metatarsals. However, to date, no studies have systematically investigated the morphological variations of the torsional patterns of human metatarsals. In the present study, therefore, the aim was to clarify the age- and sex-associated variations in the torsional patterns of human metatarsals using three-dimensional computed tomography. The torsion angles of the five metatarsals were calculated by defining the dorsopalmar vector of the metatarsal base and the vector corresponding to the rotational axis of the metatarsal head. The present result demonstrated that the second metatarsals of females were significantly more inverted with increasing age. Flat foot is known to be most common in elderly women. Whether there is a cause-effect relationship between second metatarsal torsion and flattening of the medial longitudinal arch has yet to be answered, but the present study suggested that torsion of the second metatarsal might possibly be used as an indicator for the early diagnosis of flat foot and associated foot pathologies.
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