2026 ICD-10-CM Diagnosis Code M21.751Unequal limb length (acquired), right femur

ICD-10-CM Codes›M00–M99›M20-M25›M21

ICD-10-CM M21.751
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M21.751 is a billable ICD-10-CM diagnosis code for unequal limb length (acquired), right femur. 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. Coders also document this condition as acquired deformity of right thigh. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Acquired deformities (excluding foot).

Code Identity

ICD-10-CM Code
M21.751
Billable Status
Yes — Valid for Submission
Code Describes
Unequal limb length (acquired), right femur
Short Description
Unequal limb length (acquired), right femur
Same as the full description in the CMS dataset.
Parent Code
M21.75
Unequal limb length (acquired), femur

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM21Other acquired deformities of limbs
This CodeM21.751Unequal limb length (acquired), right femur

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired deformity of right thigh
  • Unequal lower limb length due to acquired shortening of right femur

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

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 M21.751 to ICD-9-CMHistory

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

ICD-9-CM
736.81 Unequal leg length
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 M21.751Overview

Is M21.751 (Unequal limb length (acquired), femur) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report unequal limb length (acquired), right femur on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M21.751 group to?

When unequal limb length (acquired), right femur 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 M21.751?

Under the General Equivalence Mappings, unequal limb length (acquired), right femur converts to ICD-9-CM 736.81 (unequal leg length). 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.