2026 ICD-10-CM Diagnosis Code M79.4Hypertrophy of (infrapatellar) fat pad

ICD-10-CM Codes›M00–M99›M70-M79›M79

ICD-10-CM M79.4
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M79.4 is a billable ICD-10-CM diagnosis code for hypertrophy of (infrapatellar) fat pad. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 606 through 607. Coders also document this condition as bilateral hypertrophy of infrapatellar fat pads. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified connective tissue disease.

Code Identity

ICD-10-CM Code
M79.4
Billable Status
Yes — Valid for Submission
Code Describes
Hypertrophy of (infrapatellar) fat pad
Short Description
Hypertrophy of (infrapatellar) fat pad
Same as the full description in the CMS dataset.
Parent Code
M79
Other and unspecified soft tissue disorders, not elsewhere classified

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM70-M79Other soft tissue disorders
CategoryM79Other and unspecified soft tissue disorders, not elsewhere classified
This CodeM79.4Hypertrophy of (infrapatellar) fat pad

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral hypertrophy of infrapatellar fat pads
  • Hypertrophy of fat pad of knee
  • Hypertrophy of fat pad of left knee
  • Hypertrophy of fat pad 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.

    • Degeneration, degenerative
      • infrapatellar fat pad
    • Degeneration, degenerative
      • popliteal fat pad
    • Fat
      • localized (pad)
        • knee
    • Fat
      • localized (pad)
        • retropatellar
    • Fat
      • pad
        • knee
    • Fibrosis, fibrotic
      • infrapatellar fat pad
    • Fibrosis, fibrotic
      • popliteal fat pad
    • Hypertrophy, hypertrophic
      • fat pad
        • knee (infrapatellar) (popliteal) (prepatellar) (retropatellar)

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MUS025
Other specified connective tissue disease
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 M79.4 to ICD-9-CMHistory

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

ICD-9-CM
729.31 Hypertrophy of fat pad
Exact Match The mapping is direct, with no qualifiers.

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 M79.4Overview

Is M79.4 a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report hypertrophy of (infrapatellar) fat pad on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M79.4 group to?

When hypertrophy of (infrapatellar) fat pad is the principal diagnosis on an inpatient stay, it groups to MS-DRG 606, 607, with relative weights from 0.9064 to 1.5132 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M79.4?

Under the General Equivalence Mappings, hypertrophy of (infrapatellar) fat pad converts to ICD-9-CM 729.31 (hypertrophy of fat pad). The mapping is a direct match.

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.