2027 ICD-10-CM Diagnosis Code M65.979Unspecified synovitis and tenosynovitis, unspecified ankle and foot

ICD-10-CM Codes›M00–M99›M65-M67›M65

ICD-10-CM M65.979
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M65.979 is a billable ICD-10-CM diagnosis code for unspecified synovitis and tenosynovitis, unspecified ankle and foot. 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. Coders also document this condition as extensor hallucis longus tenosynovitis. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Tendon and synovial disorders.

Code Identity

ICD-10-CM Code
M65.979
Billable Status
Yes — Valid for Submission
Code Describes
Unspecified synovitis and tenosynovitis, unspecified ankle and foot
Short Description
Unspecified synovitis and tenosynovitis, unspecified ank/ft
Parent Code
M65.97
Unspecified synovitis and tenosynovitis, ankle and foot

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM65-M67Disorders of synovium and tendon
CategoryM65Synovitis and tenosynovitis
This CodeM65.979Unspecified synovitis and tenosynovitis, unspecified ankle and foot

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Extensor hallucis longus tenosynovitis
  • Peroneal tenosynovitis
  • Synovitis of ankle joint
  • Synovitis of joint of foot
  • Tenosynovitis of flexor tendon of foot
  • Tenosynovitis of foot

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M65.979: 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.

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

Ankle Injuries and Disorders

Your ankle bone and the ends of your two lower leg bones make up the ankle joint. Your ligaments, which connect bones to one another, stabilize and support it. Your muscles and tendons move it.

Read the full article at MedlinePlus

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

Code History & ChangesHistory

Replacement M65.979 replaces the following previously assigned code(s):

  • M65.9 - Synovitis and tenosynovitis, unspecified
FY 2025AddedAdded to the ICD-10-CM code setEffective October 1, 2024.
FY 2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About M65.979Overview

What is the ICD-10 code for unspecified synovitis and tenosynovitis, unspecified ankle and foot?

The ICD-10-CM code for unspecified synovitis and tenosynovitis, unspecified ankle and foot is M65.979 (sometimes written as M65979). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M65.979 (Unspecified synovitis and tenosynovitis, ankle and foot) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report unspecified synovitis and tenosynovitis, unspecified ankle and foot on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M65.979 group to?

When unspecified synovitis and tenosynovitis, unspecified ankle and foot 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 M65.979 be reported with a code from M70.0?

Not as a rule. The Excludes1 note at M65, which applies to M65.979, 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).