M23.5 vs M40

M23.5 (Chronic instability of knee) compared with M40 (Kyphosis and lordosis), 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 · NCD code lists 2026-01 · LCD export September 20, 2026 · All releases and sources

Summary

These codes can be reported together when both conditions are documented, because M23.5 lists M40 under Excludes2, which marks them as distinct conditions.

Official rule

What is different?

The conditions named.M23.5 is “Chronic instability of knee”; M40 is “Kyphosis and lordosis”.

Registry fact

Can these codes be reported together?

Yes, when both are documented.M23.5 lists M40 under Excludes2: “joints of the spine (M40-M54)”. 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. M23.5 carries 3 Excludes1 notes and M40 carries 3 Excludes1 notes covering other codes; the side-by-side table quotes them.

Official rule

Is there an Excludes2 relationship?

Yes.M23.5’s tabular entry: “joints of the spine (M40-M54)”. The note covers M40.

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

M23.5

Chronic instability of knee

↔

M40

Kyphosis and lordosis

What we found

Yes, when both are documented.M23.5 carries an Excludes2 note covering M40: “joints of the spine (M40-M54)”

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 Excludes2 Check 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

	M23.5Chronic instability of knee	M40Kyphosis and lordosis
Billing status	Non-billable header Report instead: M23.50, M23.51, M23.52	Non-billable header Report instead: M40.00, M40.03, M40.04, M40.05, M40.10
Classification	M00-M99 — Diseases of the Musculoskeletal System and Connective Tissue (M00-M99)	M00-M99 — Diseases of the Musculoskeletal System and Connective Tissue (M00-M99)
Definition	Chronic instability of knee is a non-billable ICD-10-CM category code (M23.5).	Kyphosis and lordosis is a non-billable ICD-10-CM category code (M40).
Excludes1	ankylosis (M24.66) deformity of knee (M21.-) osteochondritis dissecans (M93.2)	congenital kyphosis and lordosis (Q76.4) kyphoscoliosis (M41.-) postprocedural kyphosis and lordosis (M96.-)
Excludes2	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)	—
Code first	—	underlying disease

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.

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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