2026 ICD-10-CM Diagnosis Code M66.0Rupture of popliteal cyst

ICD-10-CM Codes›M00–M99›M65-M67›M66

ICD-10-CM M66.0
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M66.0 is a billable ICD-10-CM diagnosis code for rupture of popliteal cyst. 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
M66.0
Billable Status
Yes — Valid for Submission
Code Describes
Rupture of popliteal cyst
Short Description
Rupture of popliteal cyst
Same as the full description in the CMS dataset.
Parent Code
M66
Spontaneous rupture of synovium and tendon

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM65-M67Disorders of synovium and tendon
CategoryM66Spontaneous rupture of synovium and tendon
This CodeM66.0Rupture of popliteal cyst

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Injury of bursa of knee
  • Rupture of bursa
  • Rupture of popliteal bursa
  • Rupture of synovial cyst of knee
  • Rupture of synovial cyst of left knee
  • Rupture of synovial cyst of right knee
  • Rupture of synovial popliteal cyst
  • Rupture of synovial popliteal cyst of left knee
  • Rupture of synovial popliteal cyst of right knee
  • Rupture of synovium - knee
  • Synovial cyst of left knee
  • Synovial cyst of right knee
  • Synovial popliteal cyst
  • Synovial popliteal cyst of left knee
  • Synovial popliteal cyst of right knee

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

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

    • Cyst(colloid) (mucous) (simple) (retention)
      • Baker's
        • ruptured

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

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 M66.0 to ICD-9-CMHistory

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

ICD-9-CM
727.51 Popliteal synovial cyst
Approximate The match is approximate rather than exact.
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 M66.0Overview

Is M66.0 (Spontaneous rupture of synovium and tendon) a billable code?

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

What MS-DRG does M66.0 group to?

When rupture of popliteal cyst 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 M66.0?

Under the General Equivalence Mappings, rupture of popliteal cyst converts to ICD-9-CM 727.51 (popliteal synovial cyst) and 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.