2026 ICD-10-CM Diagnosis Code M13.162Monoarthritis, not elsewhere classified, left knee

ICD-10-CM Codes›M00–M99›M05-M14›M13

ICD-10-CM M13.162
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M13.162 is a billable ICD-10-CM diagnosis code for monoarthritis, not elsewhere classified, left knee. 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 knee. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified joint disorders.

Code Identity

ICD-10-CM Code
M13.162
Billable Status
Yes — Valid for Submission
Code Describes
Monoarthritis, not elsewhere classified, left knee
Short Description
Monoarthritis, not elsewhere classified, left knee
Same as the full description in the CMS dataset.
Parent Code
M13.16
Monoarthritis, not elsewhere classified, knee

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM05-M14Inflammatory polyarthropathies
CategoryM13Other arthritis
This CodeM13.162Monoarthritis, not elsewhere classified, left knee

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Monoarthritis of knee
  • Monoarthritis of left knee

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

Arthritis

If you feel pain and stiffness in your body or have trouble moving around, you might have arthritis. Any disorder that affects the joints is often called arthritis. Joints are places where two bones meet, such as your elbow or knee.

The full article covers:

  • What is arthritis?
  • What are the types of arthritis?
  • What are the symptoms of arthritis?
  • Who is more likely to get arthritis?
  • How is arthritis diagnosed?
  • What are the treatments for arthritis?

Read the full article at MedlinePlus

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

Convert M13.162 to ICD-9-CMHistory

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

ICD-9-CM
716.66 Monoarthritis NOS-l/leg
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 M13.162Overview

Is M13.162 (Monoarthritis, not elsewhere classified, knee) a billable code?

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

What MS-DRG does M13.162 group to?

When monoarthritis, not elsewhere classified, left knee 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 M13.162?

Under the General Equivalence Mappings, monoarthritis, not elsewhere classified, left knee converts to ICD-9-CM 716.66 (monoarthritis NOS-l/leg). 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.