What is Pes Planus
Pes planus, commonly known as flatfoot, is a foot deformity characterized by the reduction or complete absence of the medial longitudinal arch of the foot, which may occur with or without additional deformities of the foot and ankle. 1, 2
Anatomical Definition
- Pes planus represents a structural deviation where the medial longitudinal arch—the primary arch responsible for weight distribution and shock absorption—collapses or fails to develop properly 2, 3
- The condition results in the midfoot making increased or complete contact with the ground during weight-bearing activities 4
- The arch of the foot normally serves as an adaptable, supportive base for the entire body, and its collapse creates biomechanical consequences throughout the lower extremity 3
Clinical Classification
Flexible vs. Rigid Pes Planus
- Flexible pes planus is defined by a normal arch present during non-weight-bearing activity or when standing on tiptoes, with flattening occurring only upon full weight-bearing 5
- Rigid pes planus maintains a stiff, collapsed arch regardless of weight-bearing status and requires subspecialist referral 5
- In children, flexible flatfoot is often part of normal developmental variation and typically resolves with age as foot musculature strengthens 5, 6
Congenital vs. Acquired
- Congenital pes planus in children is common, affecting up to 14% of children, and usually resolves spontaneously during development 2
- Acquired pes planus in adults most commonly results from posterior tibial tendon dysfunction, which can develop from repetitive loading stress during high-impact activities like running, rucking, and marching 7, 5
- Up to 25% of the total adult population has a deficient medial longitudinal arch in at least one foot 2
Clinical Significance as a Risk Factor
- Pes planus is recognized as a significant foot deformity that increases risk for foot ulcer development in patients with peripheral artery disease (PAD) and diabetes 1
- The deformity can lead to ulcers through mechanisms of joint immobility, friction, and abnormal pressure distribution 1
- Patients with pes planus and PAD or diabetes should be referred to a podiatrist for evaluation and consideration of therapeutic footwear 1
- The collapsed arch increases plantar pressures in the midfoot during walking and standing, which can perpetuate tissue damage in a vicious cycle 7
Associated Complications
- Persons with flatfoot experience increased risk of injuries including hallux valgus (bunion), tendinitis, plantar fasciitis, metatarsal pain, knee pain, and lower-back pain, particularly with prolonged walking 4
- The condition creates unbalanced, functionally unstable weight-bearing that affects force dissipation and normal gait mechanics 3
- In severe cases, particularly when acquired in adults, delayed recognition can lead to progression to rigid, irreversible deformity and potential midfoot ulceration 7
Context-Specific Presentations
- In cardio-facio-cutaneous syndrome, pes planus or planovalgus occurs in two-thirds of affected individuals and tends to be more severe than in the general population, with significant forefoot valgus 1
- Treatment in syndromic cases is generally nonsurgical unless there is severe deformity with significant functional impairment 1