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M21.221 vs M91.2

M21.221 (Flexion deformity, right elbow) compared with M91.2 (Coxa plana), from the official CMS tabular data.

Current data releases:ICD-10-CM FY2027 · ICD-10-PCS FY2027 · HCPCS October 2026 · MS-DRG v44 · Medicare Code Editor v44.0 · NCCI PTP Q4 2026 · MUE Q4 2026 · NCD code lists 2026-01 · LCD export September 28, 2026 · All releases and sources

Summary

These codes can be reported together when both conditions are documented, because M21.221 lists M91.2 under Excludes2, which marks them as distinct conditions.

Official rule
What is different?

The conditions named and billing status.M21.221 is “Flexion deformity, right elbow”; M91.2 is “Coxa plana”. M91.2 is a non-billable header; M21.221 is billable.

Registry fact

Can these codes be reported together?

Yes, when both are documented.M21.221 lists M91.2 under Excludes2: “coxa plana (M91.2)”. Excludes2 marks distinct conditions that may both be reported when both are documented.

Official ruleGuide: Excludes1 vs Excludes2

Is there an Excludes1 relationship?

None.Neither entry carries an Excludes1 note that names the other code. M21.221 carries 3 Excludes1 notes and M91.2 carries 2 Excludes1 notes covering other codes; the side-by-side table quotes them.

Official rule

Is there an Excludes2 relationship?

Yes.M21.221’s tabular entry: “coxa plana (M91.2)”. The note covers M91.2.

Official ruleGuide: Excludes1 vs Excludes2

Is one more specific?

Not comparable.The codes sit in different categories; specificity is only comparable within one category.

Is one a parent or header code?

One is a header.M91.2 is a non-billable header, but M21.221 is not one of its subdivisions.

Registry fact

Are there sequencing instructions?

None.Neither entry carries a Code First or Use Additional Code note that names the other.

Official rule

Are there other coding relationships?

None found.No laterality, encounter-phase, Table of Neoplasms, Table of Drugs and Chemicals, or history-versus-active-disease relationship links these codes.

MedCoder-derived

Official rule: a tabular instructional note or a section of the ICD-10-CM Official Guidelines, quoted as published. Registry fact: the codes’ own published attributes (titles, billable status, position in the hierarchy, code set). MedCoder-derived: a reading MedCoder computes from those facts; it is not itself a rule. How to read the labels

Can these codes be reported together?

Informational

Excludes2 relationship

M21.221
Flexion deformity, right elbow
↔
M91.2
Coxa plana

What we found

Yes, when both are documented.M21.221 carries an Excludes2 note covering M91.2: “coxa plana (M91.2)”

Excludes2 marks distinct conditions — both may be reported when both are documented.

What to review

Report both only when the documentation supports both conditions; otherwise report the one documented.

Guide: Excludes1 vs Excludes2Check these on a claim

Why it matters

An Excludes2 note means the excluded condition is not part of the code above it, but a patient can have both. Report both when both are documented.

Source / rule

CMS ICD-10-CM tabular instructional notes

Official guidance behind these answers

  • Section I.A.12.b — Excludes2 · applies to: Excludes2

    A type 2 Excludes note represents “Not included here.” An excludes2 note indicates that the condition excluded is not part of the condition represented by the code, but a patient may have both conditions at the same time. When an Excludes2 note appears under a code, it is acceptable to use both the code and the excluded code together, when appropriate.

    ICD-10-CM Official Guidelines FY2027

Quoted from the ICD-10-CM Official Guidelines for Coding and Reporting in effect for the release shown. The tabular notes above are the code-level instruction; these sections are the convention that says how such a note is applied. Source document (CMS PDF) · Release and checksum

Side by side

Similar descriptions do not make codes interchangeable. The documentation and the official instructions decide which code applies.

Official descriptionDiffers
M21.221

Flexion deformity, right elbow

M91.2

Coxa plana

StatusDiffers
M21.221
Billable
M91.2
Non-billable header

A header is not reported on a claim; a code beneath it is.

Report instead: M91.20, M91.21, M91.22

Excludes1Differs
M21.221
  • acquired absence of limb (Z89.-)
  • congenital absence of limbs (Q71-Q73)
  • congenital deformities and malformations of limbs (Q65-Q66, Q68-Q74)
M91.2
  • slipped upper femoral epiphysis (nontraumatic) (M93.0-)
  • postprocedural chondropathies (M96.-)
Excludes2Differs
M21.221
  • acquired deformities of fingers or toes (M20.-)
  • coxa plana (M91.2)
  • joints of the spine (M40-M54)
M91.2

None at this code

CategoryDiffers
M21.221

M21 Other acquired deformities of limbs

M91.2

M91 Juvenile osteochondrosis of hip and pelvis

ChapterSame for both

M00-M99 — Diseases of the Musculoskeletal System and Connective Tissue (M00-M99)

IncludesDiffers
M21.221

None at this code

M91.2
  • Hip deformity due to previous juvenile osteochondrosis

No Code first, Use additional code, Code also and 7th character note at either code.

Notes are the code’s own tabular entry, quoted as published. A note that names the other code is the one the verdict above rests on. In a row that differs, notes every code shares are dimmed.

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Derived from the official CMS ICD-10-CM tabular data (FY2027). A coding-rule comparison, not billing advice: payer-specific edits and medical-necessity policy are outside its scope. All data sources