Statistical parametric mapping of the regional distribution and ontogenetic scaling of foot pressures during walking in Asian elephants (Elephas maximus)

Abstract

SUMMARYFoot pressure distributions during locomotion have causal links with the anatomical and structural configurations of the foot tissues and the mechanics of locomotion. Elephant feet have five toes bound in a flexible pad of fibrous tissue (digital cushion). Does this specialized foot design control peak foot pressures in such giant animals? And how does body size, such as during ontogenetic growth, influence foot pressures? We addressed these questions by studying foot pressure distributions in elephant feet and their correlation with body mass and centre of pressure trajectories, using statistical parametric mapping (SPM), a neuroimaging technology. Our results show a positive correlation between body mass and peak pressures, with the highest pressures dominated by the distal ends of the lateral toes (digits 3, 4 and 5). We also demonstrate that pressure reduction in the elephant digital cushion is a complex interaction of its viscoelastic tissue structure and its centre of pressure trajectories, because there is a tendency to avoid rear ʻheelʼ contact as an elephant grows. Using SPM, we present a complete map of pressure distributions in elephant feet during ontogeny by performing statistical analysis at the pixel level across the entire plantar/palmar surface. We hope that our study will build confidence in the potential clinical and scaling applications of mammalian foot pressures, given our findings in support of a link between regional peak pressures and pathogenesis in elephant feet. Supplementary material available online at

Foot pressure distributions during walking in African elephants (Loxodonta africana)

“…The experimental approach was similar to that previously used by Panagiotopoulou et al . [4] and did not cause any discomfort to the animals.…”

“…The template image (isocontour of threshold 5 kPa), with which all other images were aligned, was the first image to meet the inclusion criteria (see Panagiotopoulou et al . [4]: Material and Methods). Source (non-template) images were manually translated and rotated using the keyboard to align them with the template of each foot (fore left (FL), fore right (FR), hind left (HL), hind right (HR)).…”

“…the maximum pressure over time at a particular location) were focused towards the tips of the outermost (lateral) toes (digits III, IV and V) where pathologies are most prevalent in elephants in general, and that the lowest pressures were in the middle and towards the rear of the feet, directly under the fat pad. Pressure reduction underneath the fat pad can be attributed to the compliance of the tissue but also to the observation that elephants minimize heel-only contact while walking, using mainly the front part of their feet to produce vertical forces as they roll over the fat pad during ground contact [4]. …”

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“…Elephants are unusual in that they have a subunguligrade skeletal foot posture, but their digital cushion renders them functionally plantigrade, because the digital cushion (containing an enlarged strut-like "predigit") directly supports body weight Hutchinson et al, 2011).Their substantial digital cushions extend proximally from the sole to the metacarpals, providing almost 40 % of the foot's total volume (Warner, 2014). Elephant digital cushions are formed of chambers of differing geometry filled with adipose tissue, with collagen, reticulin and elastic fibers also present (Weissengruber et al, 2006 PrePrints horse digital cushions, meaning that they are better adapted to distributing and thus minimising high pressures (Panagiotopoulou et al, 2012) and dampening impact forces (Aerts et al, 1996;Warner et al, 2013)? And do supposedly disproportionate external foot pressures present a challenge to large animals with regards to foot health?…”

“…Does the material composition of elephant digital cushions lead to greater compliance and viscosity compared to horse digital cushions, meaning that they are better adapted to distributing and thus minimising high pressures (Panagiotopoulou et al, 2012) and dampening impact forces (Aerts et al, 1996;Warner et al, 2013)? And do supposedly disproportionate external foot pressures present a challenge to large animals with regards to foot health?…”