2027 ICD-10-CM Diagnosis Code M79.A21Nontraumatic compartment syndrome of right lower extremity

ICD-10-CM Codes›M00–M99›M70-M79›M79

ICD-10-CM M79.A21
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M79.A21 is a billable ICD-10-CM diagnosis code for nontraumatic compartment syndrome of right lower extremity. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 557 through 558. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 107 closely related codes. Coders also document this condition as bilateral nontraumatic compartment syndrome of lower limbs. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified connective tissue disease.

Code Identity

ICD-10-CM Code
M79.A21
Billable Status
Yes — Valid for Submission
Code Describes
Nontraumatic compartment syndrome of right lower extremity
Short Description
Nontraumatic compartment syndrome of right lower extremity
Same as the full description in the CMS dataset.
Parent Code
M79.A2
Nontraumatic compartment syndrome of lower extremity

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM70-M79Other soft tissue disorders
CategoryM79Other and unspecified soft tissue disorders, not elsewhere classified
This CodeM79.A21Nontraumatic compartment syndrome of right lower extremity

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral nontraumatic compartment syndrome of lower limbs
  • Nontraumatic compartment syndrome of left lower limb
  • Nontraumatic compartment syndrome of lower limb
  • Nontraumatic compartment syndrome of right lower limb

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M79.A21: its own notes plus those printed at M79.A, M79, and Chapter 13. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From M79.A Nontraumatic compartment syndrome applies to 8 codes
  • compartment syndrome NOS (T79.A-)
  • fibromyalgia (M79.7)
  • nontraumatic ischemic infarction of muscle (M62.2-)
  • traumatic compartment syndrome (T79.A-)
From M79 Other and unspecified soft tissue disorders, not elsewhere classified applies to 52 codes
  • psychogenic rheumatism (F45.8)
  • soft tissue pain, psychogenic (F45.41)

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 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)

Code First

The underlying condition named in the note is sequenced before this code.

From M79.A Nontraumatic compartment syndrome applies to 8 codes
  • if applicable, associated postprocedural complication

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 M79.A21, its category, or a range that includes it.

Excludes1 2

These codes carry an Excludes1 note naming M79.A21: they are not reported together with it, unless the two conditions are unrelated.

  • M62.2 Nontraumatic ischemic infarction of muscle
    nontraumatic compartment syndrome (M79.A-) names M79.A-, which includes this code
  • T79.A Traumatic compartment syndrome
    nontraumatic compartment syndrome (M79.A-) names M79.A-, which includes this code

Clinical ClassificationClinical

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

CCSR MUS025
Other specified connective tissue disease
Default principal diagnosis: inpatient Yes · outpatient Yes

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 M79.A21 to ICD-9-CMHistory

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

ICD-9-CM
729.72 Nontraum comp syn-low ex
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 M79.A21Overview

What is the ICD-10 code for nontraumatic compartment syndrome of right lower extremity?

The ICD-10-CM code for nontraumatic compartment syndrome of right lower extremity is M79.A21 (sometimes written as M79A21). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M79.A21 (Nontraumatic compartment syndrome of lower extremity) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report nontraumatic compartment syndrome of right lower extremity on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M79.A21 group to?

When nontraumatic compartment syndrome of right lower extremity is the principal diagnosis on an inpatient stay, it groups to MS-DRG 557, 558, with relative weights from 0.8873 to 1.4883 depending on complications. Higher weights mean higher Medicare reimbursement.

Is M79.A21 a CC or MCC?

CMS lists M79.A21 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 107 closely related codes in its exclusion list.

Can M79.A21 be reported with a code from T79.A?

Not as a rule. The Excludes1 note at M79.A, which applies to M79.A21, lists "compartment syndrome NOS (T79.A-)". 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).