2027 ICD-10-CM Diagnosis Code M21.279Flexion deformity, unspecified ankle and toes

ICD-10-CM Codes›M00–M99›M20-M25›M21

ICD-10-CM M21.279
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M21.279 is a billable ICD-10-CM diagnosis code for flexion deformity, unspecified ankle and toes. 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 ankle joint deformity. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Acquired deformities (excluding foot).

Code Identity

ICD-10-CM Code
M21.279
Billable Status
Yes — Valid for Submission
Code Describes
Flexion deformity, unspecified ankle and toes
Short Description
Flexion deformity, unspecified ankle and toes
Same as the full description in the CMS dataset.
Parent Code
M21.27
Flexion deformity, ankle and toes

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM21Other acquired deformities of limbs
This CodeM21.279Flexion deformity, unspecified ankle and toes

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Ankle joint deformity
  • Ankle joint fixed flexion deformity
  • Flexion contracture of metatarsophalangeal joint
  • Flexion contracture of toe interphalangeal joint
  • Flexion contracture of toe joint
  • Flexion deformity of toe
  • Hallux flexus

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M21.279: its own notes plus those printed at 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 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 M21.279, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming M21.279: 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

Clinical ClassificationClinical

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

CCSR MUS023
Acquired deformities (excluding foot)
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 M21.279 to ICD-9-CMHistory

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

ICD-9-CM
736.89 Oth acq limb deformity
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 M21.279Overview

What is the ICD-10 code for flexion deformity, unspecified ankle and toes?

The ICD-10-CM code for flexion deformity, unspecified ankle and toes is M21.279 (sometimes written as M21279). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M21.279 (Flexion deformity, ankle and toes) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report flexion deformity, unspecified ankle and toes on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M21.279 group to?

When flexion deformity, unspecified ankle and toes 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 M21.279 be reported with a code from Z89?

Not as a rule. The Excludes1 note at M21, which applies to M21.279, lists "acquired absence of limb (Z89.-)". 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 M21.279?

Under the General Equivalence Mappings, flexion deformity, unspecified ankle and toes converts to ICD-9-CM 736.89 (oth acq limb deformity). The mapping is approximate, so confirm the match fits the documentation.