2026 ICD-10-CM Diagnosis Code M21.90Unspecified acquired deformity of unspecified limb

ICD-10-CM Codes›M00–M99›M20-M25›M21

ICD-10-CM M21.90
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M21.90 is a billable ICD-10-CM diagnosis code for unspecified acquired deformity of unspecified limb. 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
M21.90
Billable Status
Yes — Valid for Submission
Code Describes
Unspecified acquired deformity of unspecified limb
Short Description
Unspecified acquired deformity of unspecified limb
Same as the full description in the CMS dataset.
Parent Code
M21.9
Unspecified acquired deformity of limb and hand

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM21Other acquired deformities of limbs
This CodeM21.90Unspecified acquired deformity of unspecified limb

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired deformity of joint of lower limb
  • Acquired deformity of joint of upper limb
  • Acquired deformity of limb
  • Acquired deformity of lower limb
  • Acquired deformity of the wrist / hand
  • Acquired deformity of upper limb
  • Angulation deformity of lower limb
  • Deformity of fibrous joint
  • Deformity of limb
  • Deformity of lower limb
  • Deformity of upper limb
  • Joint deformity
  • Joint deviation
  • Multiple joint deformity

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Deformity
      • joint (acquired) NEC
    • Deformity
      • limb (acquired)

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

Convert M21.90 to ICD-9-CMHistory

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

ICD-9-CM
736.9 Acq limb deformity NOS
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 M21.90Overview

Is M21.90 (Unspecified acquired deformity of limb and hand) a billable code?

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

What MS-DRG does M21.90 group to?

When unspecified acquired deformity of unspecified limb 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 M21.90?

Under the General Equivalence Mappings, unspecified acquired deformity of unspecified limb converts to ICD-9-CM 736.9 (acq limb deformity NOS). 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.