ICD-10-CM > M00-M99 > M20-M25 > M21 > M21.4 M21.4 Flat foot [pes planus] (acquired) Non-Billable/Non-Specific Type 1 Excludes congenital pes planus (Q66.5-) Codes M21.40Flat foot [pes planus] (acquired), unspecified footM21.41Flat foot [pes planus] (acquired), right footM21.42Flat foot [pes planus] (acquired), left foot