2027 ICD-10-CM Diagnosis Code M23.51Chronic instability of knee, right knee

ICD-10-CM Codes›M00–M99›M20-M25›M23

ICD-10-CM M23.51
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M23.51 is a billable ICD-10-CM diagnosis code for chronic instability of knee, right knee. 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. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other specified joint disorders.

Code Identity

ICD-10-CM Code
M23.51
Billable Status
Yes — Valid for Submission
Code Describes
Chronic instability of knee, right knee
Short Description
Chronic instability of knee, right knee
Same as the full description in the CMS dataset.
Parent Code
M23.5
Chronic instability of knee

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM20-M25Other joint disorders
CategoryM23Internal derangement of knee
This CodeM23.51Chronic instability of knee, right knee

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Bilateral instability of joints of knees
  • Chronic disruption of cruciate ligament of right knee
  • Chronic instability of bilateral knee joints
  • Chronic instability of joint
  • Chronic instability of knee
  • Chronic instability of left knee joint
  • Chronic instability of right knee joint
  • Disruption of cruciate ligament of right knee joint
  • Instability of joint of left knee
  • Instability of joint of right knee
  • Old disruption of ligament of knee

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M23.51: its own notes plus those printed at M23, 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 M23 Internal derangement of knee applies to 111 codes

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 M23 Internal derangement of knee applies to 111 codes
  • 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)
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 M23.51, its category, or a range that includes it.

Excludes2 3

These codes carry an Excludes2 note naming M23.51: its condition is not part of those codes, and both may be reported when the patient has both.

  • M24.1 Other articular cartilage disorders
    internal derangement of knee (M23.-) names M23.-, which includes this code
  • S83 Dislocation and sprain of joints and ligaments of knee
    internal derangement of knee (M23.-) names M23.-, which includes this code
  • M24.2 Disorder of ligament
    internal derangement of knee (M23.5-M23.8X9) names M23.5-M23.8X9, which includes this code

Clinical ClassificationClinical

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

CCSR MUS007
Other specified joint disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Knee Injuries and Disorders

Your knee joint is made up of bone, cartilage, ligaments and fluid. Muscles and tendons help the knee joint move. When any of these structures is hurt or diseased, you have knee problems. Knee problems can cause pain and difficulty walking.

Read the full article at MedlinePlus

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

Convert M23.51 to ICD-9-CMHistory

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

ICD-9-CM
717.85 Old disrupt knee lig NEC
Approximate The match is approximate rather than exact.
ICD-9-CM
718.86 Jt derangement NEC-l/leg
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 M23.51Overview

What is the ICD-10 code for chronic instability of knee, right knee?

The ICD-10-CM code for chronic instability of knee, right knee is M23.51 (sometimes written as M2351). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M23.51 (Chronic instability of knee) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report chronic instability of knee, right knee on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M23.51 group to?

When chronic instability of knee, right knee 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 M23.51 be reported with M24.66?

Not as a rule. The Excludes1 note at M23, which applies to M23.51, lists "ankylosis (M24.66)". 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 M23.51?

Under the General Equivalence Mappings, chronic instability of knee, right knee converts to ICD-9-CM 717.85 (old disrupt knee lig NEC) and 718.86 (jt derangement NEC-l/leg). The mapping is approximate, so confirm the match fits the documentation.