Pes Planus Affects the Medial Longitudinal Arch
Pes planus (flat foot) is characterized by a reduction or absence of the medial longitudinal arch (MLA) of the foot. 1, 2, 3
Anatomical Specificity
The medial longitudinal arch is the primary arch affected in pes planus and is the arch mainly responsible for related structural problems throughout the lower limb. 2 This arch:
- Extends from the calcaneus (heel bone) through the talus, navicular, cuneiforms, and first three metatarsals 2
- Serves as an adaptable, supportive base for the entire body during weight-bearing activities 2
- When deficient or collapsed, produces unbalanced and functionally unstable conditions of the foot 2
Clinical Presentation Patterns
Flexible pes planus demonstrates a normal arch during non-weight-bearing activity or tiptoeing, with flattening occurring only on standing. 3 This is the most common presentation, particularly in children where it affects up to 14% of the pediatric population. 1
Rigid pes planus shows persistent arch collapse regardless of weight-bearing status and requires subspecialist referral. 3
Biomechanical Impact
The collapsed medial longitudinal arch in pes planus leads to:
- Compensatory pronation, which is one of the most common lower extremity disorders in sports medicine 2
- Altered force dissipation patterns during gait 2
- Abnormal weight-bearing mechanics affecting the entire lower limb kinetic chain 2
- Increased plantar pressures in the midfoot region 4
Diagnostic Confirmation
The medial longitudinal arch height can be objectively assessed through:
- Radiographic measurements: talo-first metatarsal angle and calcaneal pitch angle 5
- Plantar pressure mapping: arch index contact force ratio (AICFR) correlates reliably with radiographic findings 5
- Clinical observation: presence or absence of arch during weight-bearing versus non-weight-bearing positions 3
Up to 25% of the general population has a deficient medial longitudinal arch in at least one foot, making this a common clinical finding. 1