2026 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 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

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 2026 (October 1, 2025 through September 30, 2026) 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
  • Instability of joint of left knee
  • Instability of joint of right knee
  • Old disruption of ligament of knee

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 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About M23.51Overview

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, 2025 through September 30, 2026.

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, 565, 566, with relative weights from 0.7493 to 1.5436 depending on complications. Higher weights mean higher Medicare reimbursement.

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.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.