2026 ICD-10-CM Diagnosis Code M65.90Unspecified synovitis and tenosynovitis, unspecified site

ICD-10-CM Codes›M00–M99›M65-M67›M65

ICD-10-CM M65.90
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M65.90 is a billable ICD-10-CM diagnosis code for unspecified synovitis and tenosynovitis, unspecified site. 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
M65.90
Billable Status
Yes — Valid for Submission
Code Describes
Unspecified synovitis and tenosynovitis, unspecified site
Short Description
Unspecified synovitis and tenosynovitis, unspecified site
Same as the full description in the CMS dataset.
Parent Code
M65.9
Synovitis and tenosynovitis, unspecified

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM65-M67Disorders of synovium and tendon
CategoryM65Synovitis and tenosynovitis
This CodeM65.90Unspecified synovitis and tenosynovitis, unspecified site

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Capsulitis of left ankle
  • Chronic synovitis
  • Chronic synovitis due to hemarthrosis
  • Enthesitis
  • SAPHO syndrome
  • Synovitis
  • Synovitis and tenosynovitis
  • Synovitis AND/OR tenosynovitis associated with another disease
  • Synovitis of ankle joint
  • Synovitis of left ankle joint
  • Tendon sheath crepitus
  • Tenoperiostitis
  • Tenosynovitis

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

  • - Synovitis - See Also: Tenosynovitis; - M65.90

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Synovitis
    • Tenosynovitis

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

Clinical InformationClinical

  • Acquired Hyperostosis Syndrome

    syndrome consisting of synovitis; acne conglobata; palmoplantar pustulosis; hyperostosis; and osteitis. the most common site of the disease is the upper anterior chest wall, characterized by predominantly osteosclerotic lesions, hyperostosis, and arthritis of the adjacent joints. the association of sterile inflammatory bone lesions and neutrophilic skin eruptions is indicative of this syndrome.

  • Synovitis

    inflammation of the synovial membrane.

  • Synovitis, Pigmented Villonodular

    diffuse outgrowth arising from the synovial membrane; synovial bursa; or tendon sheath around the joint cavity, with extension to surrounding soft tissue. it is characterized by pigmented hemosiderin-containing macrophages; foam cells; and multinucleated giant cells. it usually occurs in the hands and feet, and around large joints, such as in the ankle and knee joints.

  • Giant Cell Tumor of Tendon Sheath

    a tumor arising in the synovial membrane; synovial bursa; or tendon sheath. it is characterized by osteoclast-like giant cells; foam cells; pigmented hemosiderin-laden macrophages and inflammatory infiltrate. it is classified either as diffuse or localized tenosynovitis.

  • Tendon Entrapment

    narrowing or stenosis of a tendon's retinacular sheath. it occurs most often in the hand or wrist but can also be found in the foot or ankle. the most common types are de quervain disease and trigger finger disorder.

  • Tenosynovitis

    inflammation of the synovial lining of a tendon sheath. causes include trauma, tendon stress, bacterial disease (gonorrhea, tuberculosis), rheumatic disease, and gout. common sites are the hand, wrist, shoulder capsule, hip capsule, hamstring muscles, and achilles tendon. the tendon sheaths become inflamed and painful, and accumulate fluid. joint mobility is usually reduced.

  • Synovial Membrane

    the inner membrane of a joint capsule surrounding a freely movable joint. it is loosely attached to the external fibrous capsule and secretes synovial fluid.

  • Enthesitis

    inflammation at the site of insertion of ligaments, tendons, and other fibrous structures into bone.

  • Enthesitis-Related Arthritis|ERA|ERA|Enthesitis-Related JIA|Enthesitis-Related JIA|Enthesitis-Related Juvenile Idiopathic Arthritis|Enthesitis-Related Juvenile Idiopathic Arthritis

    a category of juvenile idiopathic arthritis associated with arthritis and enthesitis, which may involve the axial skeleton. it is a form of juvenile spondyloarthritis.

Code History & ChangesHistory

Replacement M65.90 replaces the following previously assigned code(s):

  • M65.9 - Synovitis and tenosynovitis, unspecified
FY 2025AddedAdded to the ICD-10-CM code setEffective October 1, 2024.
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M65.90Overview

Is M65.90 (Synovitis and tenosynovitis, unspecified) a billable code?

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

What MS-DRG does M65.90 group to?

When unspecified synovitis and tenosynovitis, unspecified site 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.

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.