2026 ICD-10-CM Diagnosis Code M13.171Monoarthritis, not elsewhere classified, right ankle and foot

ICD-10-CM Codes›M00–M99›M05-M14›M13

ICD-10-CM M13.171
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M13.171 is a billable ICD-10-CM diagnosis code for monoarthritis, not elsewhere classified, right ankle and foot. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 553 through 554. Coders also document this condition as monoarthritis of ankle and/or foot. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified joint disorders.

Code Identity

ICD-10-CM Code
M13.171
Billable Status
Yes — Valid for Submission
Code Describes
Monoarthritis, not elsewhere classified, right ankle and foot
Short Description
Monoarthritis, NEC, right ankle and foot
Parent Code
M13.17
Monoarthritis, not elsewhere classified, ankle and foot

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM05-M14Inflammatory polyarthropathies
CategoryM13Other arthritis
This CodeM13.171Monoarthritis, not elsewhere classified, right ankle and foot

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Monoarthritis of ankle and/or foot
  • Monoarthritis of joint of ankle
  • Monoarthritis of joint of right ankle
  • Monoarthritis of right foot

Clinical ClassificationClinical

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

CCSR MUS007
Other specified joint disorders
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 M13.171 to ICD-9-CMHistory

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

ICD-9-CM
716.67 Monoarthritis NOS-ankle
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 M13.171Overview

Is M13.171 (Monoarthritis, not elsewhere classified, ankle and foot) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report monoarthritis, not elsewhere classified, right ankle and foot on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M13.171 group to?

When monoarthritis, not elsewhere classified, right ankle and foot is the principal diagnosis on an inpatient stay, it groups to MS-DRG 553, 554, with relative weights from 0.8301 to 1.2963 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M13.171?

Under the General Equivalence Mappings, monoarthritis, not elsewhere classified, right ankle and foot converts to ICD-9-CM 716.67 (monoarthritis NOS-ankle). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.