Pes planus or flat feet are feet with minimal to no arches. A child may have flat feet for a variety of reasons, including developmental changes that may be outgrown with no lasting problems. Treatment becomes necessary if flat feet are associated with foot or leg pain, lead to difficulty walking, or if one foot is flat relative to the other. Certain congenital foot defects that cause severe flattening will also require treatment. A common treatment for flat feet is orthotic or arch supports which control pronation. Pronation is the tendency for the arch to collapse and the foot to splay outward.