Regional plantar pressure distribution during walking in hoofed mammals

Plantar pressures during locomotion have causal links with foot pathologies e.g. osteoarthritis and foot abscesses. The causes of these pathologies are multifactorial but the foot-ground interaction is a major factor, particularly the frequencies and amplitudes of loading at foot impact, which can exacerbate pathology even if not the primary cause. Foot anatomy varies enormously amongst hoofed mammals, yet the functional consequences of foot anatomical variations are still a mystery. Elephants and rhinos respectively have five and three toes bound in a flexible pad of fibrous tissue (digital cushion), which is heavy and costly to swing, but seems to dampen vibrations when the foot hits the ground. Are the digital cushion and multi-toed foot structure thus marvellous solutions that control peak foot pressures in giant animals? How then do intermediate designs such as cows and giraffes work? We here study six species (pigs, horses, cows, rhinos, giraffes and elephants) to determine how foot anatomy and body mass influence the distribution of regional plantar pressures during walking. Our results show that peak pressure levels are maintained at near-constant relative levels across animal sizes by foot specializations, but that pressures on the distal ends of middle toes are significantly beyond those of other parts of the feet. Our study is the first attempt to measure plantar pressure distributions using spatially continuous descriptive statistical images and subsequent topological analysis, a set of techniques recently developed for human plantar pressure studies