- flexible flatfoot: may be divided into congenital and acquired forms:
           - congenital flat foot:
                 - idiopathic
                 - valgus hindfoot deformity in CP
                 - hyper-pronation;
                 - accessory navicular:
                 - Marfan's syndrome;
                 - fragile X syndrome:
                         - this diagnosis should be considered in any male child w/ flat feet and mental retardation;
                         - calcaneovalgus deformity:
                                  - common in infants and often resolves without treatment;
                                  - infants allow dorsiflexion to the tibia and allows full plantar flexion and inversion;
                 - acquired flat foot:
                         - rheumatoid arthritis
                         - plantar fascia rupture;
                         - tibialis posterior rupture
                                 - in this case, flat foot may result from the peroneus brevis muscle, which is a natural antagonist to the tibialis posterior;
    - rigid or spastic flatfoot:
           - accessory navicular
           - congenital vertical talus
           - tarsal coaliltion
           - calcaneovalgus foot
           - equino-valgus
           - osteochondral fracture
           - juvenile rheumatoid arthritis
           - reactive peroneal spasm from frx or chronic joint dz