Pes planus

Pes planus (also called flatfoot) is a deformity of the foot where the longitudinal arch of the foot is abnormally flattened.

It results from loss of the medial longitudinal arch and can be either rigid or flexible. These deformities are usually flexible, which means that on non-weightbearing views, the alignment of the plantar arch normalises.

In the paediatric population, the degree of ligamentous laxity of the foot results in relative pes planus that resolves over time 5. Within the first decade, there is spontaneous development of a strong arch.

Pes planus may occur in as many as 20% of the adult population, although the majority of patients are asymptomatic and require no treatment. There is some evidence to suggest that flat feet protect against stress fractures.

There are several conditions associated with pes planus:

The longitudinal arch of the foot must be assessed on a weightbearing lateral foot radiograph. If the patient is unable to stand or weightbear, a simulated weightbearing radiograph should be obtained.

In normal feet, the relationship between the talus and the 1st metatarsal results in a straight line being formed along their axes (Meary's angle = 0 degrees). Pes planus, in contrasdistinction, will show:

  • loss of the normal straight line relationship
  • a sag at the talonavicular joint or naviculocuneiform joint
  • angle of the longitudinal arch increased to greater than 170 degrees

It is important to assess:

Acquired pes planus (i.e., foot collapse), can be distinguished from congenital pes planus by carefully assessing the calcaneus and midtarsal joint: 6

  • in the acquired form, the calcaneal pitch is at least 10 degrees; in congenital pes planus it is less
  • in the acquired form, the calcaneus is downwards-concave; in the congenital form it is downwards-convex or flat
  • in the acquired form, the midtarsal joint is altered by a forward-jutting talus; in the congenital form the talus is medially displaced, but the midtalar line appears normal (i.e., it is pseudonormal)

Treatment depends on whether

  • there are symptoms
  • pes planus is fixed or mobile
  • there are associated findings, e.g. hindfoot valgus
  • any associated pathology

Non-operative management for the fixed flat foot is unlikely to be beneficial since there is a fixed relationship between osseous structures.

Foot alignment abnormalities

Adequate radiographs are required for the accurate assessment of foot alignment. Basic assessment includes weightbearing dorsoplantar and lateral views.

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Article information

rID: 20888
Section: Gamuts
Synonyms or Alternate Spellings:
  • Pes planus deformity
  • Flat foot deformity
  • Flat foot
  • Flat feet
  • Flatfoot

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Cases and figures

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    Weight bearing la...
    Case 1
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    Calcaneonavicular...
    Case 2 : with underlying calcaneonavicular coalition
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    Case 3
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    Case 4: treated with triple arthrodesis
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    Case 5
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