2026 ICD-10-CM Diagnosis Code M71.20Synovial cyst of popliteal space [Baker], unspecified knee

ICD-10-CM Codes›M00–M99›M70-M79›M71

ICD-10-CM M71.20
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M71.20 is a billable ICD-10-CM diagnosis code for synovial cyst of popliteal space [Baker], unspecified knee. 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 synovial cyst of knee. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Tendon and synovial disorders.

Code Identity

ICD-10-CM Code
M71.20
Billable Status
Yes — Valid for Submission
Code Describes
Synovial cyst of popliteal space [Baker], unspecified knee
Short Description
Synovial cyst of popliteal space [Baker], unspecified knee
Same as the full description in the CMS dataset.
Parent Code
M71.2
Synovial cyst of popliteal space [Baker]

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM70-M79Other soft tissue disorders
CategoryM71Other bursopathies
This CodeM71.20Synovial cyst of popliteal space [Baker], unspecified knee

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Synovial cyst of knee
  • Synovial popliteal cyst

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 M71.20 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.

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 M71.20Overview

Is M71.20 (Synovial cyst of popliteal space [Baker]) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report synovial cyst of popliteal space [Baker], unspecified knee on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M71.20 group to?

When synovial cyst of popliteal space [Baker], unspecified knee 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 M71.20?

Under the General Equivalence Mappings, synovial cyst of popliteal space [Baker], unspecified knee converts to ICD-9-CM 727.51 (popliteal synovial cyst). 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.