2026 ICD-10-CM Diagnosis Code T79.A21ATraumatic compartment syndrome of right lower extremity, initial encounter

ICD-10-CM Codes›S00–T88›T79›T79

ICD-10-CM T79.A21A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T79.A21A is a billable ICD-10-CM diagnosis code for traumatic compartment syndrome of right lower extremity, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 922 through 923, 963 through 965. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified injury.

Code Identity

ICD-10-CM Code
T79.A21A
Billable Status
Yes — Valid for Submission
Code Describes
Traumatic compartment syndrome of right lower extremity, initial encounter
Short Description
Traumatic compartment syndrome of r low extrem, init
Parent Code
T79.A21
Traumatic compartment syndrome of right lower extremity

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT79Certain early complications of trauma
CategoryT79Certain early complications of trauma, not elsewhere classified
This CodeT79.A21ATraumatic compartment syndrome of right lower extremity, initial encounter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Anterior tibial compartment syndrome
  • Anterior tibial compartment syndrome due to traumatic injury
  • Anterior tibial compartment syndrome of left lower leg
  • Anterior tibial compartment syndrome of left lower leg due to traumatic injury
  • Anterior tibial compartment syndrome of right lower leg
  • Anterior tibial compartment syndrome of right lower leg due to traumatic injury
  • Bilateral anterior tibial compartment syndrome of lower legs due to traumatic injury
  • Compartment syndrome of left lower limb due to traumatic injury
  • Compartment syndrome of lower leg due to traumatic injury
  • Compartment syndrome of right lower limb due to traumatic injury

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Certain early complications of trauma, not elsewhere classified (T79). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

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

CCSR INJ026
Other specified injury
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Muscle Disorders

Your muscles help you move and help your body work. Different types of muscles have different jobs. There are many problems that can affect muscles. Muscle disorders can cause weakness, pain or even paralysis.

Read the full article at MedlinePlus

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

Convert T79.A21A to ICD-9-CMHistory

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

ICD-9-CM
958.92 Trauma comp synd low ext
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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T79.A21AOverview

Is T79.A21A (Traumatic compartment syndrome of right lower extremity) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report traumatic compartment syndrome of right lower extremity, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T79.A21A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for traumatic compartment syndrome of right lower extremity, such as an emergency visit or first evaluation.

What MS-DRG does T79.A21A group to?

When traumatic compartment syndrome of right lower extremity, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 922, 923, 963, 964, 965, with relative weights from 0.9405 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of T79.A21A?

Under the General Equivalence Mappings, traumatic compartment syndrome of right lower extremity, initial encounter converts to ICD-9-CM 958.92 (trauma comp synd low ext). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.