2026 ICD-10-CM Diagnosis Code M70.40Prepatellar bursitis, unspecified knee

ICD-10-CM Codes›M00–M99›M70-M79›M70

ICD-10-CM M70.40
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M70.40 is a billable ICD-10-CM diagnosis code for prepatellar bursitis, unspecified knee. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 557 through 558. Coders also document this condition as infection of prepatellar bursa. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified connective tissue disease.

Code Identity

ICD-10-CM Code
M70.40
Billable Status
Yes — Valid for Submission
Code Describes
Prepatellar bursitis, unspecified knee
Short Description
Prepatellar bursitis, unspecified knee
Same as the full description in the CMS dataset.
Parent Code
M70.4
Prepatellar bursitis

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM70-M79Other soft tissue disorders
CategoryM70Soft tissue disorders related to use, overuse and pressure
This CodeM70.40Prepatellar bursitis, unspecified knee

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Infection of prepatellar bursa
  • Prepatellar bursitis

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

Bursitis

A bursa is a small, fluid-filled sac that acts as a cushion between a bone and other moving parts, such as muscles, tendons, or skin. Bursitis occurs when a bursa becomes inflamed. People get bursitis by overusing a joint. It can also be caused by an injury. It usually occurs at the knee or elbow.

Read the full article at MedlinePlus

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

Convert M70.40 to ICD-9-CMHistory

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

ICD-9-CM
726.65 Prepatellar bursitis
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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M70.40Overview

Is M70.40 (Prepatellar bursitis) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report prepatellar bursitis, unspecified knee on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M70.40 group to?

When prepatellar bursitis, unspecified knee is the principal diagnosis on an inpatient stay, it groups to MS-DRG 557, 558, with relative weights from 0.8932 to 1.4869 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M70.40?

Under the General Equivalence Mappings, prepatellar bursitis, unspecified knee converts to ICD-9-CM 726.65 (prepatellar bursitis). The mapping is approximate, so confirm the match fits the documentation.

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.