2027 ICD-10-CM Diagnosis Code M66.121Rupture of synovium, right elbow

ICD-10-CM Codes›M00–M99›M65-M67›M66

ICD-10-CM M66.121
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M66.121 is a billable ICD-10-CM diagnosis code for rupture of synovium, right elbow. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) 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
M66.121
Billable Status
Yes — Valid for Submission
Code Describes
Rupture of synovium, right elbow
Short Description
Rupture of synovium, right 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 CodeM66.121Rupture of synovium, right elbow

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M66.121: its own notes plus those printed at M66.1, M66, and Chapter 13. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From M66 Spontaneous rupture of synovium and tendon applies to 103 codes
  • rupture that occurs when a normal force is applied to tissues that are inferred to have less than normal strength

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From M66.1 Rupture of synovium applies to 29 codes
  • rupture of popliteal cyst (M66.0)
From M66 Spontaneous rupture of synovium and tendon applies to 103 codes
  • rotator cuff syndrome (M75.1-)
  • rupture where an abnormal force is applied to normal tissue - see injury of tendon by body region
From Chapter 13 (M00-M99) Diseases of the musculoskeletal system and connective tissue applies to 6,687 codes
  • arthropathic psoriasis (L40.5-)
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • compartment syndrome (traumatic) (T79.A-)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Notes

General instructions on how these codes are used.

From Chapter 13 (M00-M99) Diseases of the musculoskeletal system and connective tissue applies to 6,687 codes
  • Use an external cause code following the code for the musculoskeletal condition, if applicable, to identify the cause of the musculoskeletal condition

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name M66.121, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming M66.121: they are not reported together with it, unless the two conditions are unrelated.

  • M71.3 Other bursal cyst
    synovial cyst with rupture (M66.1-) names M66.1-, which includes this code

Excludes2 1

These codes carry an Excludes2 note naming M66.121: its condition is not part of those codes, and both may be reported when the patient has both.

  • M62.1 Other rupture of muscle (nontraumatic)
    rupture of tendon (M66.-) names M66.-, which includes this code

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 M66.121 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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About M66.121Overview

What is the ICD-10 code for rupture of synovium, right elbow?

The ICD-10-CM code for rupture of synovium, right elbow is M66.121 (sometimes written as M66121). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M66.121 (Rupture of synovium, elbow) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report rupture of synovium, right elbow on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M66.121 group to?

When rupture of synovium, right elbow is the principal diagnosis on an inpatient stay, it groups to MS-DRG 557, 558, with relative weights from 0.8873 to 1.4883 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M66.121?

Under the General Equivalence Mappings, rupture of synovium, right elbow converts to ICD-9-CM 727.59 (rupture of synovium NEC). The mapping is approximate, so confirm the match fits the documentation.