Pes planus

Pes planus (also called flat foot) 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 protects against stress fracture.

There are several conditions that are associated with pes planus:

Plain film

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.

Weightbearing lateral

In normal feet, the relationship between talus and 1st metatarsal results in a straight line being formed along their axis (Meary's angle = 0 degrees). This is not the case in flat feet where there will be:

  • loss of the normal straight line relationship
  • sag at the talonavicular joint or naviculocuneiform joint
  • angle of the longitudinal arch increases to be greater than 170 degrees
Weightbearing DP (dorso-plantar)

It is important to assess:

Treatment depends on whether there a symptoms and whether pes planus is fixed or mobile, whether there are associated findings such as hindfoot valgus and whether there is any associated pathology.

Non-operative management for the fixed flat foot is unlikely to be useful 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

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Cases and Figures

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    Case 4: treated with triple arthrodesis
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