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M23.4 vs S80

M23.4 (Loose body in knee) compared with S80 (Superficial injury of knee and lower leg), 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 M23.4 lists S80 under Excludes2, which marks them as distinct conditions.

Official rule
What is different?

The conditions named and chapter.M23.4 is “Loose body in knee”; S80 is “Superficial injury of knee and lower leg”. M23.4 sits in M00-M99 — Diseases of the Musculoskeletal System and Connective Tissue (M00-M99); S80 in S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88).

Registry fact

Can these codes be reported together?

Yes, when both are documented.M23.4 lists S80 under Excludes2: “current injury - see injury of knee and lower leg (S80-S89)”. 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. M23.4 carries 3 Excludes1 notes covering other codes; the side-by-side table quotes them.

Official rule

Is there an Excludes2 relationship?

Yes.M23.4’s tabular entry: “current injury - see injury of knee and lower leg (S80-S89)”. The note covers S80.

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?

Both are headers.Both are non-billable headers, and neither contains the other.

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

M23.4
Loose body in knee
↔
S80
Superficial injury of knee and lower leg

What we found

Yes, when both are documented.M23.4 carries an Excludes2 note covering S80: “current injury - see injury of knee and lower leg (S80-S89)”

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
M23.4

Loose body in knee

S80

Superficial injury of knee and lower leg

StatusDiffers
M23.4
Non-billable header

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

Report instead: M23.40, M23.41, M23.42

S80
Non-billable header

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

Report instead: S80.00XA, S80.00XD, S80.00XS, S80.01XA, S80.01XD

Excludes1Differs
M23.4
  • ankylosis (M24.66)
  • deformity of knee (M21.-)
  • osteochondritis dissecans (M93.2)
S80

None at this code

Excludes2Differs
M23.4
  • current injury - see injury of knee and lower leg (S80-S89)
  • recurrent dislocation or subluxation of joints (M24.4)
  • recurrent dislocation or subluxation of patella (M22.0-M22.1)
  • joints of the spine (M40-M54)
S80
  • superficial injury of ankle and foot (S90.-)
  • burns and corrosions (T20-T32)
  • frostbite (T33-T34)
  • injuries of ankle and foot, except fracture of ankle and malleolus (S90-S99)
  • insect bite or sting, venomous (T63.4)
CategoryDiffers
M23.4

M23 Internal derangement of knee

S80

Is itself a category

ChapterDiffers
M23.4

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

S80

S00-T88 — Injury, Poisoning and Certain Other Consequences of External Causes (S00-T88)

7th characterDiffers
M23.4

None at this code

S80
  • The appropriate 7th character is to be added to each code from category S80

No Code first, Use additional code, Code also and Includes 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