2026 ICD-10-CM Diagnosis Code M85.631Other cyst of bone, right forearm

ICD-10-CM Codes›M00–M99›M80-M85›M85

ICD-10-CM M85.631
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M85.631 is a billable ICD-10-CM diagnosis code for other cyst of bone, right forearm. 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 bone cyst of right radius. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified bone disease and musculoskeletal deformities.

Code Identity

ICD-10-CM Code
M85.631
Billable Status
Yes — Valid for Submission
Code Describes
Other cyst of bone, right forearm
Short Description
Other cyst of bone, right forearm
Same as the full description in the CMS dataset.
Parent Code
M85.63
Other cyst of bone, forearm

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 CodeM85.631Other cyst of bone, right forearm

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bone cyst of right radius
  • Bone cyst of right ulna

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

Bone Diseases

Your bones help you move, give you shape and support your body. They are living tissues that rebuild constantly throughout your life. During childhood and your teens, your body adds new bone faster than it removes old bone. After about age 20, you can lose bone faster than you make bone.

Read the full article at MedlinePlus

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

Convert M85.631 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 M85.631Overview

Is M85.631 (Other cyst of bone, forearm) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report other cyst of bone, right forearm on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M85.631 group to?

When other cyst of bone, right forearm 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 M85.631?

Under the General Equivalence Mappings, other cyst of bone, right forearm converts to ICD-9-CM 733.29 (bone cyst NEC). 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.