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:
- tarsal coalition 1
- tibialis posterior tendon dysfunction 4
- certain connective tissue disorders:
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 view
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
Weightbearing dorsoplantar view
It is important to assess:
- hindfoot valgus (where the talocalcaneal angle is greater than 35 degrees)
- talonavicular uncoverage or subluxation
- forefoot abduction
Congenital versus acquired pes planus
- 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 and prognosis
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.
- 4. Supple KM, Hanft JR, Murphy BJ et-al. Posterior tibial tendon dysfunction. Semin. Arthritis Rheum. 1992;22 (2): 106-13. Pubmed citation
- 1. Crim JR, Kjeldsberg KM. Radiographic diagnosis of tarsal coalition. AJR Am J Roentgenol. 2004;182 (2): 323-8. AJR Am J Roentgenol (full text) - Pubmed citation
- 2. Chew FS. Skeletal Radiology. Lippincott Williams & Wilkins. (2010) ISBN:1608317064. Read it at Google Books - Find it at Amazon
- 3. Dimmick S, Chhabra A, Grujic L et-al. Acquired flat foot deformity: postoperative imaging. Semin Musculoskelet Radiol. 2012;16 (03): 217-32. doi:10.1055/s-0032-1320122 - Pubmed citation
- 5. Staheli LT, Chew DE, Corbett M. The longitudinal arch. A survey of eight hundred and eighty-two feet in normal children and adults. J Bone Joint Surg Am. 1987;69 (3): 426-8. Pubmed citation
- 6. Francis A. Burgener, Martti Kormano, Tomi Pudas. Bone and Joint Disorders: Differential Diagnosis in Conventional Radiology. 2nd edition (2006) ISBN: 9781588904454