2026 ICD-10-CM Diagnosis Code M66.129Rupture of synovium, unspecified elbow

ICD-10-CM Codes›M00–M99›M65-M67›M66

ICD-10-CM M66.129
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M66.129 is a billable ICD-10-CM diagnosis code for rupture of synovium, unspecified elbow. 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. Coders also document this condition as leaking synovial cyst of elbow. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Tendon and synovial disorders.

Code Identity

ICD-10-CM Code
M66.129
Billable Status
Yes — Valid for Submission
Code Describes
Rupture of synovium, unspecified elbow
Short Description
Rupture of synovium, unspecified elbow
Same as the full description in the CMS dataset.
Parent Code
M66.12
Rupture of synovium, elbow

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM65-M67Disorders of synovium and tendon
CategoryM66Spontaneous rupture of synovium and tendon
This CodeM66.129Rupture of synovium, unspecified elbow

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Leaking synovial cyst of elbow
  • Mass of joint of elbow
  • Rupture of synovium of elbow
  • Synovial cyst of elbow

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

Elbow Injuries and Disorders

Your elbow joint is made up of bone, cartilage, ligaments and fluid. Muscles and tendons help the elbow joint move. When any of these structures is hurt or diseased, you have elbow problems.

Read the full article at MedlinePlus

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

Convert M66.129 to ICD-9-CMHistory

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

ICD-9-CM
727.59 Rupture of synovium 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 M66.129Overview

Is M66.129 (Rupture of synovium, elbow) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report rupture of synovium, unspecified elbow on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M66.129 group to?

When rupture of synovium, unspecified elbow 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 M66.129?

Under the General Equivalence Mappings, rupture of synovium, unspecified elbow converts to ICD-9-CM 727.59 (rupture of synovium 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.