2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

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 2027 (October 1, 2026 through September 30, 2027) 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
  • Unequal length of lower limbs
  • Unequal length of lower limbs due to acquired shortening
  • Unequal length of upper limbs

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M21.70: its own notes plus those printed at M21.7, M21, block M00-M25, block M20-M25, and Chapter 13. A note printed at a category, block or chapter applies to every code under it.

Includes

Further defines, or gives examples of, the content of the category.

From Block M00-M25 applies to 2,249 codes
  • Disorders affecting predominantly peripheral (limb) joints

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From M21 Other acquired deformities of limbs applies to 124 codes
  • acquired absence of limb (Z89.-)
  • congenital absence of limbs (Q71-Q73)
  • congenital deformities and malformations of limbs (Q65-Q66, Q68-Q74)

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From M21 Other acquired deformities of limbs applies to 124 codes
  • acquired deformities of fingers or toes (M20.-)
  • coxa plana (M91.2)
From Block M20-M25 Other joint disorders applies to 719 codes
From Chapter 13 (M00-M99) Diseases of the musculoskeletal system and connective tissue applies to 6,687 codes
  • arthropathic psoriasis (L40.5-)
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • compartment syndrome (traumatic) (T79.A-)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)

Notes

General instructions on how these codes are used.

From M21.7 Unequal limb length (acquired) applies to 17 codes
  • The site used should correspond to the shorter limb
From Chapter 13 (M00-M99) Diseases of the musculoskeletal system and connective tissue applies to 6,687 codes
  • Use an external cause code following the code for the musculoskeletal condition, if applicable, to identify the cause of the musculoskeletal condition

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name M21.70, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming M21.70: they are not reported together with it, unless the two conditions are unrelated.

  • M23 Internal derangement of knee
    deformity of knee (M21.-) names M21.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About M21.70Overview

What is the ICD-10 code for unequal limb length (acquired), unspecified site?

The ICD-10-CM code for unequal limb length (acquired), unspecified site is M21.70 (sometimes written as M2170). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

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, 566, 565, with relative weights from 0.7374 to 1.4909 depending on complications. Higher weights mean higher Medicare reimbursement.

Can M21.70 be reported with a code from Z89?

Not as a rule. The Excludes1 note at M21, which applies to M21.70, lists "acquired absence of limb (Z89.-)". An Excludes1 note means the excluded code is never reported together with this one; the only exception is when the two conditions are unrelated to each other (Official Guidelines, Section I.A.12.a).

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.