2027 ICD-10-CM Diagnosis Code M21.079Valgus deformity, not elsewhere classified, unspecified ankle

ICD-10-CM Codes›M00–M99›M20-M25›M21

ICD-10-CM M21.079
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M21.079 is a billable ICD-10-CM diagnosis code for valgus deformity, not elsewhere classified, unspecified ankle. 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 valgus heel. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Acquired foot deformities.

Code Identity

ICD-10-CM Code
M21.079
Billable Status
Yes — Valid for Submission
Code Describes
Valgus deformity, not elsewhere classified, unspecified ankle
Short Description
Valgus deformity, not elsewhere classified, unsp ankle
Parent Code
M21.07
Valgus deformity, not elsewhere classified, ankle

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM21Other acquired deformities of limbs
This CodeM21.079Valgus deformity, not elsewhere classified, unspecified ankle

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired valgus heel
  • Bilateral valgus deformities of feet

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M21.079: its own notes plus those printed at M21.0, 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.

From Block M00-M25 applies to 2,249 codes
  • 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.

From M21.0 Valgus deformity, not elsewhere classified applies to 13 codes
  • metatarsus valgus (Q66.6)
  • talipes calcaneovalgus (Q66.4-)
From M21 Other acquired deformities of limbs applies to 124 codes
  • 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: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From M21 Other acquired deformities of limbs applies to 124 codes
  • acquired deformities of fingers or toes (M20.-)
  • coxa plana (M91.2)
From Block M20-M25 Other joint disorders applies to 719 codes
From Chapter 13 (M00-M99) Diseases of the musculoskeletal system and connective tissue applies to 6,687 codes
  • 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.

From Chapter 13 (M00-M99) Diseases of the musculoskeletal system and connective tissue applies to 6,687 codes
  • 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 M21.079, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming M21.079: they are not reported together with it, unless the two conditions are unrelated.

  • M23 Internal derangement of knee
    deformity of knee (M21.-) names M21.-, which includes this code
  • Q66 Congenital deformities of feet
    valgus deformities (acquired) (M21.0-) names M21.0-, which includes this code

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MUS021
Acquired foot deformities
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Ankle Injuries and Disorders

Your ankle bone and the ends of your two lower leg bones make up the ankle joint. Your ligaments, which connect bones to one another, stabilize and support it. Your muscles and tendons move it.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert M21.079 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
736.79 Acq ankle-foot def NEC
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About M21.079Overview

What is the ICD-10 code for valgus deformity, not elsewhere classified, unspecified ankle?

The ICD-10-CM code for valgus deformity, not elsewhere classified, unspecified ankle is M21.079 (sometimes written as M21079). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M21.079 (Valgus deformity, not elsewhere classified, ankle) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report valgus deformity, not elsewhere classified, unspecified ankle on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M21.079 group to?

When valgus deformity, not elsewhere classified, unspecified ankle 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 M21.079 be reported with Q66.6?

Not as a rule. The Excludes1 note at M21.0, which applies to M21.079, lists "metatarsus valgus (Q66.6)". 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 M21.079?

Under the General Equivalence Mappings, valgus deformity, not elsewhere classified, unspecified ankle converts to ICD-9-CM 736.79 (acq ankle-foot def NEC). The mapping is approximate, so confirm the match fits the documentation.