2027 ICD-10-CM Diagnosis Code M21.40Flat foot [pes planus] (acquired), unspecified foot
ICD-10-CM Codes›M00–M99›M20-M25›M21
- Billable — Valid for Submission
- Not Chronic
M21.40 is a billable ICD-10-CM diagnosis code for flat foot [pes planus] (acquired), unspecified foot. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 564 through 566. Coders also document this condition as acquired flexible flat foot. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Acquired foot deformities.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Acquired flexible flat foot
- Acquired pes planus
- Acquired spastic flat foot
- Hypermobile flat foot
- Peroneal spastic flat foot
- Rigid flat foot
- Talipes planus
- Talipes transversoplanus
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to M21.40: its own notes plus those printed at M21.4, M21, block M00-M25, block M20-M25, and Chapter 13. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- Disorders affecting predominantly peripheral (limb) joints
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- arthropathic psoriasis (L40.5-)
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- compartment syndrome (traumatic) (T79.A-)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
Notes
General instructions on how these codes are used.
- Use an external cause code following the code for the musculoskeletal condition, if applicable, to identify the cause of the musculoskeletal condition
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name M21.40, its category, or a range that includes it.
Excludes1 2
These codes carry an Excludes1 note naming M21.40: they are not reported together with it, unless the two conditions are unrelated.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Foot Injuries and Disorders
Each of your feet has 26 bones, 33 joints, and more than 100 tendons, muscles, and ligaments. No wonder a lot of things can go wrong. Here are a few common problems:
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert M21.40 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About M21.40Overview
What is the ICD-10 code for flat foot [pes planus] (acquired), unspecified foot?
The ICD-10-CM code for flat foot [pes planus] (acquired), unspecified foot is M21.40 (sometimes written as M2140). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is M21.40 (Flat foot [pes planus] (acquired)) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report flat foot [pes planus] (acquired), unspecified foot on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does M21.40 group to?
When flat foot [pes planus] (acquired), unspecified foot is the principal diagnosis on an inpatient stay, it groups to MS-DRG 564, 566, 565, with relative weights from 0.7374 to 1.4909 depending on complications. Higher weights mean higher Medicare reimbursement.
Can M21.40 be reported with a code from Q66.5?
Not as a rule. The Excludes1 note at M21.4, which applies to M21.40, lists "congenital pes planus (Q66.5-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).
What is the ICD-9 equivalent of M21.40?
Under the General Equivalence Mappings, flat foot [pes planus] (acquired), unspecified foot converts to ICD-9-CM 734 (flat foot). The mapping is approximate, so confirm the match fits the documentation.
