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:
- 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.
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:
- hindfoot valgus (where the talocalcaneal angle is greater than 35 degrees)
- talonavicular uncoverage or subluxation
Treatment and prognosis
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
- 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
- 4. Supple KM, Hanft JR, Murphy BJ et-al. Posterior tibial tendon dysfunction. Semin. Arthritis Rheum. 1992;22 (2): 106-13. 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