2026 ICD-10-CM Diagnosis Code M21.70Unequal limb length (acquired), unspecified site

ICD-10-CM Codes›M00–M99›M20-M25›M21

ICD-10-CM M21.70
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M21.70 is a billable ICD-10-CM diagnosis code for unequal limb length (acquired), unspecified site. 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
M21.70
Billable Status
Yes — Valid for Submission
Code Describes
Unequal limb length (acquired), unspecified site
Short Description
Unequal limb length (acquired), unspecified site
Same as the full description in the CMS dataset.
Parent Code
M21.7
Unequal limb length (acquired)

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM21Other acquired deformities of limbs
This CodeM21.70Unequal limb length (acquired), unspecified site

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired unequal arm length
  • Acquired unequal limb length
  • Apparent shortening of leg
  • Distal shortening of arm
  • Distal shortening of leg
  • Proximal shortening of arm
  • Proximal shortening of leg
  • Short arm
  • Short leg
  • Shortening of middle section of arm
  • Shortening of middle section of leg
  • Telescoping of limb at hip
  • True shortening of leg

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
      • limb (acquired)
        • unequal length

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

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 M21.70 to ICD-9-CMHistory

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

ICD-9-CM
736.89 Oth acq limb deformity
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 M21.70Overview

Is M21.70 (Unequal limb length (acquired)) a billable code?

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

What MS-DRG does M21.70 group to?

When unequal limb length (acquired), unspecified site 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 M21.70?

Under the General Equivalence Mappings, unequal limb length (acquired), unspecified site converts to ICD-9-CM 736.89 (oth acq limb deformity). 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.