2027 ICD-10-CM Diagnosis Code M65.161Other infective (teno)synovitis, right knee

ICD-10-CM Codes›M00–M99›M65-M67›M65

ICD-10-CM M65.161
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M65.161 is a billable ICD-10-CM diagnosis code for other infective (teno)synovitis, right knee. 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
M65.161
Billable Status
Yes — Valid for Submission
Code Describes
Other infective (teno)synovitis, right knee
Short Description
Other infective (teno)synovitis, right knee
Same as the full description in the CMS dataset.
Parent Code
M65.16
Other infective (teno)synovitis, knee

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM65-M67Disorders of synovium and tendon
CategoryM65Synovitis and tenosynovitis
This CodeM65.161Other infective (teno)synovitis, right knee

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M65.161: its own notes plus those printed at M65 and Chapter 13. A note printed at a category, block or chapter applies to every code under it.

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From M65 Synovitis and tenosynovitis applies to 133 codes
  • chronic crepitant synovitis of hand and wrist (M70.0-)
  • current injury - see injury of ligament or tendon by body region
  • soft tissue disorders related to use, overuse and pressure (M70.-)

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 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 M65.161, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming M65.161: they are not reported together with it, unless the two conditions are unrelated.

  • M25.4 Effusion of joint
    other infective (teno)synovitis (M65.1-) names M65.1-, 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

Joint Disorders

Your joints are places where two or more bones come together. Your shoulders, elbows, hips, knees, and knuckles are all joints. Your spine has joints, too.

The full article covers:

  • What are joints?
  • What are joint disorders?
  • What diseases can affect the joints?
  • What types of joint disorders happen from sudden injuries?
  • What types of joint disorders happen from overuse?
  • How can I keep my joints healthy?

Read the full article at MedlinePlus

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

Convert M65.161 to ICD-9-CMHistory

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

ICD-9-CM
727.09 Synovitis 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 M65.161Overview

What is the ICD-10 code for other infective (teno)synovitis, right knee?

The ICD-10-CM code for other infective (teno)synovitis, right knee is M65.161 (sometimes written as M65161). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M65.161 (Other infective (teno)synovitis, knee) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other infective (teno)synovitis, right knee on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M65.161 group to?

When other infective (teno)synovitis, right knee 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.

Can M65.161 be reported with a code from M70.0?

Not as a rule. The Excludes1 note at M65, which applies to M65.161, lists "chronic crepitant synovitis of hand and wrist (M70.0-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

What is the ICD-9 equivalent of M65.161?

Under the General Equivalence Mappings, other infective (teno)synovitis, right knee converts to ICD-9-CM 727.09 (synovitis NEC). The mapping is approximate, so confirm the match fits the documentation.