2026 ICD-10-CM Diagnosis Code M21.859Other specified acquired deformities of unspecified thigh

ICD-10-CM Codes›M00–M99›M20-M25›M21

ICD-10-CM M21.859
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M21.859 is a billable ICD-10-CM diagnosis code for other specified acquired deformities of unspecified thigh. 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
M21.859
Billable Status
Yes — Valid for Submission
Code Describes
Other specified acquired deformities of unspecified thigh
Short Description
Other specified acquired deformities of unspecified thigh
Same as the full description in the CMS dataset.
Parent Code
M21.85
Other specified acquired deformities of thigh

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM21Other acquired deformities of limbs
This CodeM21.859Other specified acquired deformities of unspecified thigh

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired coxa valga
  • Acquired coxa vara
  • Acquired external femoral torsion
  • Acquired internal femoral torsion
  • Coxa valga
  • External rotation of lower limb
  • Hip held in external rotation
  • Hip joint deformity in external rotation
  • Torsion of femur
  • Varus deformity of hip
  • Windswept hip deformity

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

Clinical InformationClinical

  • Coxa Valga

    hip deformity in which the angle between the femoral neck and its shaft is increased. it may be congenital, acquired, or developmental.

Patient EducationClinical

Leg Injuries and Disorders

Your legs are made up of bones, blood vessels, muscles, and other connective tissue. They are important for motion and standing. Playing sports, running, falling, or having an accident can damage your legs. Common leg injuries include sprains and strains, joint dislocations, and fractures (broken bones).

Read the full article at MedlinePlus

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Convert M21.859 to ICD-9-CMHistory

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

ICD-9-CM
736.39 Acq hip 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 M21.859Overview

Is M21.859 (Other specified acquired deformities of thigh) a billable code?

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

What MS-DRG does M21.859 group to?

When other specified acquired deformities of unspecified thigh 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 M21.859?

Under the General Equivalence Mappings, other specified acquired deformities of unspecified thigh converts to ICD-9-CM 736.39 (acq hip 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.