M21.42 Flat foot [pes planus] (acquired), left foot

Billable ICD-10-CM code, FY2026.

Applies from M21 Other acquired deformities of limbs

Excludes1 (never code together)

• acquired absence of limb (Z89.-)
• congenital absence of limbs (Q71-Q73)
• congenital deformities and malformations of limbs (Q65-Q66, Q68-Q74)

Excludes2 (not included here)

• acquired deformities of fingers or toes (M20.-)
• coxa plana (M91.2)

Applies from M21.4 Flat foot [pes planus] (acquired)

Excludes1 (never code together)

• congenital pes planus (Q66.5-)

MS-DRG index

Defines the logic of DRG(s) 564-566 in MDC 08.

Approximate ICD-9-CM (GEMs)

• 734 Flat foot (approximate)

Code annotations containing back-references to M21.42

Back-references to M21.4

• Type 1 Excludes: Q66.5 Congenital pes planus ("pes planus, acquired (M21.4)")

Back-references to M21

• Type 1 Excludes: M23 Internal derangement of knee ("deformity of knee (M21.-)")
• Type 2 Excludes: M24.5 Contracture of joint ("acquired deformities of limbs (M20-M21)")
• Type 2 Excludes: M25 Other joint disorder, not elsewhere classified ("acquired deformities of limb (M20-M21)")
• Type 2 Excludes: M95 Other acquired deformities of musculoskeletal system and connective tissue ("acquired deformities of limbs (M20-M21)")
• Type 1 Excludes: Z89 Acquired absence of limb ("acquired deformities of limbs (M20-M21)")

Nearby codes

• M21.372 Foot drop, left foot
• M21.379 Foot drop, unspecified foot
• M21.4 Flat foot [pes planus] (acquired)
• M21.40 Flat foot [pes planus] (acquired), unspecified foot
• M21.41 Flat foot [pes planus] (acquired), right foot
• M21.42 Flat foot [pes planus] (acquired), left foot (this code)
• M21.5 Acquired clawhand, clubhand, clawfoot and clubfoot
• M21.51 Acquired clawhand
• M21.511 Acquired clawhand, right hand
• M21.512 Acquired clawhand, left hand
• M21.519 Acquired clawhand, unspecified hand