2026 ICD-10-CM Diagnosis Code M21.831Other specified acquired deformities of right forearm

ICD-10-CM Codes›M00–M99›M20-M25›M21

ICD-10-CM M21.831
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M21.831 is a billable ICD-10-CM diagnosis code for other specified acquired deformities of right forearm. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 564 through 566. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Acquired deformities (excluding foot).

Code Identity

ICD-10-CM Code
M21.831
Billable Status
Yes — Valid for Submission
Code Describes
Other specified acquired deformities of right forearm
Short Description
Other specified acquired deformities of right forearm
Same as the full description in the CMS dataset.
Parent Code
M21.83
Other specified acquired deformities of forearm

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM21Other acquired deformities of limbs
This CodeM21.831Other specified acquired deformities of right forearm

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired deformity of wrist
  • Acquired varus deformity of joint of bilateral wrist regions
  • Acquired varus deformity of joint of upper limb
  • Acquired varus deformity of wrist
  • Bilateral radioulnar synostosis
  • Bilateral radioulnar synostosis following traumatic injury
  • Left acquired varus deformity of wrist region joint
  • Left radioulnar synostosis
  • Radioulnar synostosis following traumatic injury
  • Radioulnar synostosis of left forearm following traumatic injury
  • Radioulnar synostosis of right forearm following traumatic injury
  • Right acquired varus deformity of wrist region joint
  • Right radioulnar synostosis

Clinical ClassificationClinical

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

CCSR MUS023
Acquired deformities (excluding foot)
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 M21.831 to ICD-9-CMHistory

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

ICD-9-CM
736.09 Forearm deformity 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 M21.831Overview

Is M21.831 (Other specified acquired deformities of forearm) a billable code?

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

What MS-DRG does M21.831 group to?

When other specified acquired deformities of right forearm is the principal diagnosis on an inpatient stay, it groups to MS-DRG 564, 565, 566, with relative weights from 0.7493 to 1.5436 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M21.831?

Under the General Equivalence Mappings, other specified acquired deformities of right forearm converts to ICD-9-CM 736.09 (forearm deformity 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.