2026 ICD-10-CM Diagnosis Code M85.021Fibrous dysplasia (monostotic), right upper arm

ICD-10-CM Codes›M00–M99›M80-M85›M85

ICD-10-CM M85.021
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M85.021 is a billable ICD-10-CM diagnosis code for fibrous dysplasia (monostotic), right upper arm. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 553 through 554. Coders also document this condition as benign neoplasm of humerus. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified bone disease and musculoskeletal deformities.

Code Identity

ICD-10-CM Code
M85.021
Billable Status
Yes — Valid for Submission
Code Describes
Fibrous dysplasia (monostotic), right upper arm
Short Description
Fibrous dysplasia (monostotic), right upper arm
Same as the full description in the CMS dataset.
Parent Code
M85.02
Fibrous dysplasia (monostotic), upper arm

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM80-M85Disorders of bone density and structure
CategoryM85Other disorders of bone density and structure
This CodeM85.021Fibrous dysplasia (monostotic), right upper arm

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Benign neoplasm of humerus
  • Benign neoplasm of long bone of right upper limb
  • Monostotic fibrous dysplasia of humerus
  • Monostotic fibrous dysplasia of right humerus
  • Neoplasm of right humerus

Clinical ClassificationClinical

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

CCSR MUS028
Other specified bone disease and musculoskeletal deformities
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Arm Injuries and Disorders

Of the 206 bones in your body, three of them are in your arm: the humerus, radius, and ulna. Your arms are also made up of muscles, joints, tendons, and other connective tissue. Injuries to any of these parts of the arm can occur during sports, a fall, or an accident.

Read the full article at MedlinePlus

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

Convert M85.021 to ICD-9-CMHistory

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

ICD-9-CM
733.29 Bone cyst 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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M85.021Overview

Is M85.021 (Fibrous dysplasia (monostotic), upper arm) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report fibrous dysplasia (monostotic), right upper arm on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M85.021 group to?

When fibrous dysplasia (monostotic), right upper arm is the principal diagnosis on an inpatient stay, it groups to MS-DRG 553, 554, with relative weights from 0.8301 to 1.2963 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M85.021?

Under the General Equivalence Mappings, fibrous dysplasia (monostotic), right upper arm converts to ICD-9-CM 733.29 (bone cyst NEC). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.