2026 ICD-10-CM Diagnosis Code M25.661Stiffness of right knee, not elsewhere classified

ICD-10-CM Codes›M00–M99›M20-M25›M25

ICD-10-CM M25.661
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M25.661 is a billable ICD-10-CM diagnosis code for stiffness of right knee, not elsewhere classified. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 555 through 556. Coders also document this condition as bilateral stiffness of knee joints. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Musculoskeletal pain, not low back pain.

Code Identity

ICD-10-CM Code
M25.661
Billable Status
Yes — Valid for Submission
Code Describes
Stiffness of right knee, not elsewhere classified
Short Description
Stiffness of right knee, not elsewhere classified
Same as the full description in the CMS dataset.
Parent Code
M25.66
Stiffness of knee, not elsewhere classified

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM25Other joint disorder, not elsewhere classified
This CodeM25.661Stiffness of right knee, not elsewhere classified

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral stiffness of knee joints
  • Knee stiff
  • Stiffness of left knee
  • Stiffness of right knee

Clinical ClassificationClinical

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

CCSR MUS010
Musculoskeletal pain, not low back pain
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Knee Injuries and Disorders

Your knee joint is made up of bone, cartilage, ligaments and fluid. Muscles and tendons help the knee joint move. When any of these structures is hurt or diseased, you have knee problems. Knee problems can cause pain and difficulty walking.

Read the full article at MedlinePlus

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

Convert M25.661 to ICD-9-CMHistory

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

ICD-9-CM
719.56 Jt stiffness NEC-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 M25.661Overview

Is M25.661 (Stiffness of knee, not elsewhere classified) a billable code?

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

What MS-DRG does M25.661 group to?

When stiffness of right knee, not elsewhere classified is the principal diagnosis on an inpatient stay, it groups to MS-DRG 555, 556, with relative weights from 0.8306 to 1.3218 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M25.661?

Under the General Equivalence Mappings, stiffness of right knee, not elsewhere classified converts to ICD-9-CM 719.56 (jt stiffness NEC-l/leg). 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.