2027 ICD-10-CM Diagnosis Code M21.379Foot drop, unspecified foot

ICD-10-CM Codes›M00–M99›M20-M25›M21

ICD-10-CM M21.379
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M21.379 is a billable ICD-10-CM diagnosis code for foot drop, unspecified foot. 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. Coders also document this condition as acquired foot drop. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Acquired foot deformities.

Code Identity

ICD-10-CM Code
M21.379
Billable Status
Yes — Valid for Submission
Code Describes
Foot drop, unspecified foot
Short Description
Foot drop, unspecified foot
Same as the full description in the CMS dataset.
Parent Code
M21.37
Foot drop (acquired)

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM21Other acquired deformities of limbs
This CodeM21.379Foot drop, unspecified foot

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Acquired foot drop
  • Foot-drop

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M21.379: its own notes plus those printed at 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 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 M21.379, its category, or a range that includes it.

Excludes1 1

These codes carry an Excludes1 note naming M21.379: 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

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR MUS021
Acquired foot deformities
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Foot Injuries and Disorders

Each of your feet has 26 bones, 33 joints, and more than 100 tendons, muscles, and ligaments. No wonder a lot of things can go wrong. Here are a few common problems:

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert M21.379 to ICD-9-CMHistory

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

ICD-9-CM
736.79 Acq ankle-foot def 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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About M21.379Overview

What is the ICD-10 code for foot drop, unspecified foot?

The ICD-10-CM code for foot drop, unspecified foot is M21.379 (sometimes written as M21379). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M21.379 (Foot drop (acquired)) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report foot drop, unspecified foot on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M21.379 group to?

When foot drop, unspecified foot 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 M21.379 be reported with a code from Z89?

Not as a rule. The Excludes1 note at M21, which applies to M21.379, 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 M21.379?

Under the General Equivalence Mappings, foot drop, unspecified foot converts to ICD-9-CM 736.79 (acq ankle-foot def NEC). The mapping is approximate, so confirm the match fits the documentation.