2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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 2027 (October 1, 2026 through September 30, 2027) 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

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M79.4: its own notes plus those printed at M79 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 M79 Other and unspecified soft tissue disorders, not elsewhere classified applies to 52 codes
  • psychogenic rheumatism (F45.8)
  • soft tissue pain, psychogenic (F45.41)

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.

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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

Questions About M79.4Overview

What is the ICD-10 code for hypertrophy of (infrapatellar) fat pad?

The ICD-10-CM code for hypertrophy of (infrapatellar) fat pad is M79.4 (sometimes written as M794). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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 607, 606, with relative weights from 0.8772 to 1.5721 depending on complications. Higher weights mean higher Medicare reimbursement.

Can M79.4 be reported with F45.8?

Not as a rule. The Excludes1 note at M79, which applies to M79.4, lists "psychogenic rheumatism (F45.8)". 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 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.