an activity that is natural to or the purpose of a person or thing.
(Oxford English Dictionary)

Attempts to define human foot function have a long history. This article provides a brief overview of these attempts and their strengths and weaknesses, ending with a new definition of a functional human foot.

The Foot as a Tripod

The ‘tripod’ theory of foot function which describes the architecture of the foot as being formed by three anatomical arches (medial, lateral and transverse) was first proposed in a German medical textbook by Henle in 1871 and began to appear as an anatomical ‘fact’ in medical textbooks in the english speaking world throughout the 1900s Scholl (1915), Dickson & Dively (1953) and Kapandji (1970).

Despite various researchers providing evidence that the ‘anterior transverse metatarsal arch’ does not exist in functional, asymptomatic feet Morton (1930), Cavanagh et al (1987), Hennig & Milani (1993), Luger et al (1999) and therefore proving the foot ‘tripod’ to be an anatomical myth it still regularly appears in the medical literature even to this day.

The Foot as a Half Dome

Ellis (1889), supported later by Wood Jones (1944), McKenzie (1955) and McKeon et al (2015) describe a longitudinal arch with the weight bearing area forming a half dome between the heel, medial border of the midfoot and metatarsals.

Most studies of asymptomatic-functional feet provide evidence to support the half-dome concept during weight bearing.

The Flexible-Flat Foot

Bankart (1935) believed a natural foot had a flexible and compliant arch that only appeared as an arch when unloaded, but which completely flattened in weight bearing, providing a large contact area with the ground. He believed an arch that did not flatten was dysfunctional and subject to injury due to the strain imposed by its resistance to flattening.

Such footprints are rare and generally observed only in some habitually-barefoot populations.

The Foot as a 'hexapod'

Morton (1935) believed the foot resembled a ‘hexapod’ with five longitudinal ‘arcs’ formed by the calcaneus and the five metatarsal bones . These five arcs formed one functional longitudinal arch that never fully flattened to become part of the weight-bearing area.

Morton’s observations appear to represent a ‘normal’ foot structure in modern shod populations but is rarely observed in populations that are habitually barefoot.

The 'Functional' Foot Defined

One problem characteristic of all four definitions is the single focus on arch function, and the failure to include toe function. Only Lambrinudi (1938) recognised the essential role of the toes in stabilising the arch function described first by Ellis then Wood Jones. Only the toes, in combination with the half-dome arch, can bring stability to the entire foot.

Acknowledging the attempts of our predecessors and the unique contribution of Lambrinudi (1938), we have synthesised a definition of a functional foot that is summarised below:

The functional foot provides a half-dome weight-bearing surface that is supported by the stabilising action of the toes.

Saxby & Wilkinson 2018


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