2026 ICD-10-CM Diagnosis Code M87.166Osteonecrosis due to drugs, unspecified fibula

ICD-10-CM Codes›M00–M99›M86-M90›M87

ICD-10-CM M87.166
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

M87.166 is a billable ICD-10-CM diagnosis code for osteonecrosis due to drugs, unspecified fibula. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 553 through 554. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family. Coders also document this condition as osteonecrosis of fibula. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Aseptic necrosis and osteonecrosis and Drug induced or toxic related condition.

Code Identity

ICD-10-CM Code
M87.166
Billable Status
Yes — Valid for Submission
Code Describes
Osteonecrosis due to drugs, unspecified fibula
Short Description
Osteonecrosis due to drugs, unspecified fibula
Same as the full description in the CMS dataset.
Parent Code
M87.16
Osteonecrosis due to drugs, tibia and fibula

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM86-M90Other osteopathies
CategoryM87Osteonecrosis
This CodeM87.166Osteonecrosis due to drugs, unspecified fibula

Code EditsBilling

Medicare Code Editor checks that affect claim validity for M87.166.

Unspecified codes
Unspecified codes exist in the ICD-10-CM classification for circumstances when documentation in the medical record does not provide the level of detail needed to support reporting a more specific code. However, in the inpatient setting, there should generally be very limited and rare circumstances for which the laterality (right, left, bilateral) of a condition is unable to be documented and reported. The following pages contain the list of unspecified ICD-10-CM diagnosis codes for which there is a more specific code to identify laterality (right, left, bilateral) within that code family.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Osteonecrosis of fibula
  • Osteonecrosis of fibula caused by drug

Clinical ClassificationClinical

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

CCSR MUS030
Aseptic necrosis and osteonecrosis
Default principal diagnosis: inpatient No · outpatient No
CCSR INJ030
Drug induced or toxic related condition
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Osteonecrosis

Osteonecrosis is a disease caused by reduced blood flow to bones in the joints. In people with healthy bones, new bone is always replacing old bone. In osteonecrosis, the lack of blood causes the bone to break down faster than the body can make enough new bone. The bone starts to die and may break down.

Read the full article at MedlinePlus

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

Convert M87.166 to ICD-9-CMHistory

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

ICD-9-CM
733.49 Asept necrosis bone NEC
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 M87.166Overview

Is M87.166 (Osteonecrosis due to drugs, tibia and fibula) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report osteonecrosis due to drugs, unspecified fibula on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does M87.166 group to?

When osteonecrosis due to drugs, unspecified fibula is the principal diagnosis on an inpatient stay, it groups to MS-DRG 553, 554, with relative weights from 0.8301 to 1.2963 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of M87.166?

Under the General Equivalence Mappings, osteonecrosis due to drugs, unspecified fibula converts to ICD-9-CM 733.49 (asept necrosis bone NEC). 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.