2026 ICD-10-CM Diagnosis Code M65.861Other synovitis and tenosynovitis, right lower leg

ICD-10-CM Codes›M00–M99›M65-M67›M65

ICD-10-CM M65.861
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M65.861 is a billable ICD-10-CM diagnosis code for other synovitis and tenosynovitis, right lower leg. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 557 through 558. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Tendon and synovial disorders.

Code Identity

ICD-10-CM Code
M65.861
Billable Status
Yes — Valid for Submission
Code Describes
Other synovitis and tenosynovitis, right lower leg
Short Description
Other synovitis and tenosynovitis, right lower leg
Same as the full description in the CMS dataset.
Parent Code
M65.86
Other synovitis and tenosynovitis, lower leg

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM65-M67Disorders of synovium and tendon
CategoryM65Synovitis and tenosynovitis
This CodeM65.861Other synovitis and tenosynovitis, right lower leg

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral synovitis of joint of knees
  • Chronic synovitis of bilateral knee joints due to hemarthrosis
  • Chronic synovitis of knee due to hemarthrosis
  • Chronic synovitis of left knee due to hemarthrosis
  • Chronic synovitis of right knee due to hemarthrosis
  • Synovitis of joint of left knee
  • Synovitis of joint of right knee

Clinical ClassificationClinical

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

CCSR MUS009
Tendon and synovial disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Joint Disorders

Your joints are places where two or more bones come together. Your shoulders, elbows, hips, knees, and knuckles are all joints. Your spine has joints, too.

The full article covers:

  • What are joints?
  • What are joint disorders?
  • What diseases can affect the joints?
  • What types of joint disorders happen from sudden injuries?
  • What types of joint disorders happen from overuse?
  • How can I keep my joints healthy?

Read the full article at MedlinePlus

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

Convert M65.861 to ICD-9-CMHistory

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

ICD-9-CM
727.09 Synovitis NEC
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 M65.861Overview

Is M65.861 (Other synovitis and tenosynovitis, lower leg) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other synovitis and tenosynovitis, right lower leg on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M65.861 group to?

When other synovitis and tenosynovitis, right lower leg is the principal diagnosis on an inpatient stay, it groups to MS-DRG 557, 558, with relative weights from 0.8932 to 1.4869 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M65.861?

Under the General Equivalence Mappings, other synovitis and tenosynovitis, right lower leg converts to ICD-9-CM 727.09 (synovitis NEC). 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.