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M23.5 ICD-10-CM Code: Chronic instability of knee

Billing Status: NO. This is a non-billable ICD-10-CM code: report a more specific billable code beneath it.

Coding at a Glance

Tabular directives
3 Excludes1 · 4 Excludes2

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for M23.5 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2027Effective: October 1, 2026

Trace:FY2027 changesChange historyRelease, file and checksum

Notes without a marker are published on M23.5 itself; “inherited from” names the category or block whose note applies here.

Excludes1 — Not Coded Here

Conditions generally not reported together with this code (Excludes1) -- an error unless the two conditions are documented as unrelated to each other (ICD-10-CM Official Guidelines, Section I.A.12.a).

Source: inherited from M23

Excludes2 — Not Included Here

Conditions not covered by this code, but which may be reported alongside it when both are present.

Coder workflow for M23.5

MedCoder structured workflow — derived from this code’s own official record

Before you code M23.5

  1. M23.5 is not reportable as written. Select the more specific code beneath it that the documentation supports. Codes are reported to the highest level of specificity the classification provides (Guidelines I.B.2).

    ReviewM23.50, M23.51, M23.52

    See the relationships section · Guide: How to choose an ICD-10-CM code →

  2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with M23.5. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

    See the official tabular notes

Choose the right path

  1. Does the documentation support one of the more specific codes beneath M23.5?
    Yes → Select that code and continue the checks below on its own page.
    No → M23.5 cannot be reported as written; query for the specificity its subcategory needs.

    ReviewM23.50, M23.51, M23.52

  2. Does the documentation support a condition named in M23.5’s Excludes1 note?
    Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
    No → Continue.

    ReviewM24.66, M21, M93.2

Consider M23.5. Then confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement
Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).
Acuity
Acute or chronic as documented; when both are documented and separate codes exist, both are reported with the acute code first (Guidelines I.B.8).

Official instructions as workflow

  • Excludes1 — check before selecting M23.5(3 notes)

    Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with M23.5: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

    CompareM24.66, M21, M93.2

    See the official tabular notes · Guidelines I.A.12.a

  • Excludes2 — not part of M23.5(4 notes)

    Coding workflow: The conditions named in this note are not included in M23.5. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

    CompareM24.4

    See the official tabular notes · Guidelines I.A.12.b

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Documentation: Both the condition M23.5 describes and a condition named in its Excludes1 note are documented for the same encounter.

Coding question: Can both codes be reported?

Path: Review the Excludes1 note and the excluded code, and look for a provider statement on whether the two conditions are related.

Reason: Excludes1 means the two are not coded together; the exception is when the record shows the conditions are unrelated to each other (Guidelines I.A.12.a).

ReviewM24.66, M21, M93.2

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Don’t confuse M23.5 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of M23.5 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

  • M24.66— Excludes1 conflict (Excludes1 — generally not reported together)

    Not coded here — the tabular list excludes this pair for the same encounter.

    Not reported together with this code, except where the two conditions are documented as unrelated.

    What moves you there: Documentation of ankylosis moves the case to M24.66; the two are not reported together unless documented as unrelated.

    Full comparison: M23.5 vs M24.66 →

  • M21— Excludes1 conflict (Excludes1 — generally not reported together)

    Not coded here — the tabular list excludes this pair for the same encounter.

    Not reported together with this code, except where the two conditions are documented as unrelated.

    What moves you there: Documentation of deformity of knee moves the case to M21; the two are not reported together unless documented as unrelated.

    Full comparison: M23.5 vs M21 →

  • M93.2— Excludes1 conflict (Excludes1 — generally not reported together)

    Not coded here — the tabular list excludes this pair for the same encounter.

    Not reported together with this code, except where the two conditions are documented as unrelated.

    What moves you there: Documentation of osteochondritis dissecans moves the case to M93.2; the two are not reported together unless documented as unrelated.

    Full comparison: M23.5 vs M93.2 →

  • S80— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of current injury - see injury of knee and lower leg adds S80; it is not part of this code and both may be reported when both are documented.

    Full comparison: M23.5 vs S80 →

  • S89— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of current injury - see injury of knee and lower leg adds S89; it is not part of this code and both may be reported when both are documented.

    Full comparison: M23.5 vs S89 →

  • M24.4— Excludes2 relationship (Informational)

    Distinct conditions — both may be reported.

    A distinct condition — both may be reported when both are documented.

    What moves you there: Documentation of recurrent dislocation or subluxation of joints adds M24.4; it is not part of this code and both may be reported when both are documented.

    Full comparison: M23.5 vs M24.4 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Code Overview

Chronic instability of knee is a non-billable ICD-10-CM category code (M23.5). A more specific billable subcode must be selected for claims submission.

MedCoder summary Summary composed by MedCoder from this code's official ICD-10-CM record. The tabular instructional notes themselves appear verbatim below.

Verify Before Coding

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name M23.5 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 3 Excludes2 notes across 2 chapters: M24.1 — Other articular cartilage disorders (via M23.-), M24.2 — Disorder of ligament (via M23.-), S83 — Dislocation and sprain of joints and ligaments of knee (via M23.-).

These codes’ tabular lists name this diagnosis as distinct — both may be reported when both are documented.

Related Codes

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main terms “Derangement”, “Instability”; these codes share that main term but sit in a different category of the Tabular List.

F48.8 — Other specified nonpsychotic mental disorders (nervous), F60.3 — Borderline personality disorder (emotional), M24.10 — Other articular cartilage disorders, unspecified site (joint, articular cartilage), M24.11 — Other articular cartilage disorders, shoulder (joint, articular cartilage, shoulder), M24.12 — Other articular cartilage disorders, elbow (joint, articular cartilage, elbow), M24.13 — Other articular cartilage disorders, wrist (joint, articular cartilage, wrist), M24.14 — Other articular cartilage disorders, hand (joint, articular cartilage, hand), M24.15 — Other articular cartilage disorders, hip (joint, articular cartilage, hip), M24.17 — Other articular cartilage disorders, ankle and foot (joint, articular cartilage, foot), M24.19 — Other articular cartilage disorders, other specified site (joint, articular cartilage, specified site NEC), M24.80 — Other specific joint derangements of unspecified joint, not elsewhere classified (joint, specified type NEC), M24.81 — Other specific joint derangements of shoulder, not elsewhere classified (joint, specified type NEC, shoulder), M24.82 — Other specific joint derangements of elbow, not elsewhere classified (joint, specified type NEC, elbow), M24.83 — Other specific joint derangements of wrist, not elsewhere classified (joint, specified type NEC, wrist), M24.84 — Other specific joint derangements of hand, not elsewhere classified (joint, specified type NEC, hand joint), M24.85 — Other specific joint derangements of hip, not elsewhere classified (joint, specified type NEC, hip), M24.87 — Other specific joint derangements of ankle and foot, not elsewhere classified (joint, specified type NEC, ankle), M24.89 — Other specific joint derangement of other specified joint, not elsewhere classified (joint, specified type NEC, specified site NEC), M24.9 — Joint derangement, unspecified (joint), M25.30 — Other instability, unspecified joint (joint), +14 more

Contextual Map

Every relationship of M23.5 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run M23.5 with these 3 related codes in Claim Check

Hierarchy

Referenced by Excludes2 notes

Nearest codes (40)

Change history

  • FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Common coding questions

Can M23.5 be billed directly?

No. M23.5 (Chronic instability of knee) is a non-billable ICD-10-CM category code. A more specific billable subcode must be selected based on clinical documentation.

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data
CMS/CDC ICD-10-CM FY2027 tabular list, index and tables, effective October 1, 2026 Release, file and checksum · Publisher’s page
Claim edits Official source data
CMS Definitions of Medicare Code Edits — v44.0 (October 2026) Release, file and checksum · Publisher’s page
Change history and date-of-service validity Official source data
CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page
Comparisons, relationships and the contextual map MedCoder structured relationship
Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears
Summary and FAQ answers MedCoder explanation
Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Cite this page

Reference this page in a research guide, syllabus or article. The release is included because code content changes each year.

MedCoder.ai. "M23.5 — Chronic instability of knee." ICD-10-CM FY2027. https://medcoder.ai/icd10/code/m23.5-chronic-instability-of-knee

Change history

  • FY2016 — October 1, 2015
    In the code set at ICD-10-CM adoption
    Chronic instability of knee

No changes since FY2016 — additions, deletions, description changes and billable-status changes are tracked through FY2027, and none are recorded for this code. Note changes are tracked from FY2027 only.

Nearest Codes in This Family

Official ICD-10-CM classifications closest to M23.5 in its code family, with their registry titles.

View all codes in the M23 family