function

ˈfʌŋ(k)ʃ(ə)n/
noun
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

References

Bankart, A.S.B. (1935). The treatment of minor maladies of the foot. The Lancet, Feb 2, 249.

Cavanagh PR et al (1987) Pressure Distribution under Symptom-Free Feet during Barefoot Standing Foot Ankle Int 7: 262

Dickson, F.D and Diveley, R.L. (1953). Functional Disorders of the Foot 3rd Ed. Philidephia: Lippincott.

Ellis, T.S. (1889). The Human Foot: Its form and structure. London: J.A. Churchill.

Hennig EM, Milani L (1993) Die Driepuntunterstützung des Fusses. Z Orthop 279-131.

Henle, J. (1871) Handbuch der Knochenlehre des Menschen. Vieweg, Braunschweig

Kanatli U et al (2003): Evaluation of the transverse metatarsal arch of the foot with gait analysis. Arch Orthop Trauma Surg 123(4)

Kapandji, L.A. (1970) The Physiology of the Joints. E & S Livingstone, Edinburgh

Lambrinudi, C. (1938). The feet of the industrial worker. The Lancet, Dec 24, 1450.

Luger EJ, et al (1999) Patterns of weight distribution under the metatarsal heads. J Bone Joint Surg, 81(2)

McKenzie, J. (1955). The foot as a half dome. British Medical Journal, April 30, 1068.

McKeon PO et al (2015). The foot core system: a new paradigm for understanding Intrinsic foot muscle function. Br J Sports Med 49:290

Morton, D.J. (1935). The Human Foot: Its evolution, physiology and functional disorders. London: Oxford University Press.

Scholl, WM. (1915). The Human Foot: Anatomy, Deformities and Treatment. A textbook for the student and practitioner. Foot Specialist Publishing Co. Chicago USA

Schwartz RP, Heath AL, Misiek W (1934). The making and interpretation of electrobarographic records of gait: The influence of rate of walking and the height of shoe heel on duration of weightbearing on the osseous tripod of the respective feet. J Bone Joint Surg 16:343-350

Wilkinson M, Stoneham R, Saxby L (2018) Feet and Footwear: Applying Biological Design and Mismatch Theory to Running Injuries. Int J Sports Exerc Med 4:090. doi.org/10.23937/2469-5718/1510090

Wood Jones, F. (1944). Structure and Function as seen in the Foot. London: Bailliere, Tindall & Cox.