2027 ICD-10-CM Diagnosis Code M87.066Idiopathic aseptic necrosis of unspecified fibula

ICD-10-CM Codes›M00–M99›M86-M90›M87

ICD-10-CM M87.066
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

M87.066 is a billable ICD-10-CM diagnosis code for idiopathic aseptic necrosis of unspecified fibula. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 553 through 554. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 217 closely related codes. The code is flagged as an unspecified code, since codes identifying laterality exist in the same family. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Aseptic necrosis and osteonecrosis.

For Medicare Advantage risk adjustment, M87.066 maps to CMS-HCC Category 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis) under the V28 model, adding a risk factor of about 0.479 for a community, non-dual, aged beneficiary in payment year 2027.

Code Identity

ICD-10-CM Code
M87.066
Billable Status
Yes — Valid for Submission
Code Describes
Idiopathic aseptic necrosis of unspecified fibula
Short Description
Idiopathic aseptic necrosis of unspecified fibula
Same as the full description in the CMS dataset.
Parent Code
M87.06
Idiopathic aseptic necrosis of tibia and fibula

Code Classification

ChapterM00–M99Diseases of the musculoskeletal system and connective tissue
SectionM86-M90Other osteopathies
CategoryM87Osteonecrosis
This CodeM87.066Idiopathic aseptic necrosis of unspecified fibula

Code EditsBilling

Medicare Code Editor checks that affect claim validity for M87.066.

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.

Medicare Risk Adjustment (HCC)Billing

M87.066 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2027.

CMS-HCC V28 Category (Payment Model)
HCC 92— Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
Payment HCC · PY 2027 one of 609 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.479
community, non-dual, aged · ranges 0.471–0.632 across segments
Hierarchy
Top of its hierarchy
HCC 92 is not superseded by any other condition category
Prior Model (CMS-HCC V24)
HCC 39
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 39 · ESRD (V21): HCC 39 · ESRD (V24): HCC 39
ESRD V21 weights: 0.061 dialysis, 0.375–0.468 functioning graft · ESRD V24 weights: 0.092 dialysis, 0.431–0.578 functioning graft
Part D (RxHCC)
RxHCC 80 — Aseptic Necrosis of Bone
also risk-adjusts in the Part D prescription drug model (V08)

Source: CMS Payment Year 2027 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to M87.066: its own notes plus those printed at M87, block M86-M90, 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 M87 Osteonecrosis applies to 217 codes
  • avascular necrosis of bone

Excludes1

Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.

From M87 Osteonecrosis applies to 217 codes
  • juvenile osteonecrosis (M91-M92)
  • osteochondropathies (M90-M93)
From Block M86-M90 Other osteopathies applies to 732 codes
  • postprocedural osteopathies (M96.-)

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 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)

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From M87 Osteonecrosis applies to 217 codes
  • code to identify major osseous defect, if applicable (M89.7-)

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 M87.066, its category, or a range that includes it.

Code First 2

These codes say to code first a condition named in the note, and M87.066 is one of the conditions named.

  • M89.7 Major osseous defect
    aseptic necrosis of bone (M87.-) names M87.-, which includes this code
  • M89.7 Major osseous defect
    osteonecrosis (M87.-) names M87.-, which includes this code

Clinical ClassificationClinical

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

CCSR MUS030
Aseptic necrosis and osteonecrosis
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Osteonecrosis

    death of a bone or part of a bone, either atraumatic or posttraumatic.

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 M87.066 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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About M87.066Overview

What is the ICD-10 code for idiopathic aseptic necrosis of unspecified fibula?

The ICD-10-CM code for idiopathic aseptic necrosis of unspecified fibula is M87.066 (sometimes written as M87066). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is M87.066 (Idiopathic aseptic necrosis of tibia and fibula) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report idiopathic aseptic necrosis of unspecified fibula on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does M87.066 group to?

When idiopathic aseptic necrosis of unspecified fibula is the principal diagnosis on an inpatient stay, it groups to MS-DRG 554, 553, with relative weights from 0.8328 to 1.2492 depending on complications. Higher weights mean higher Medicare reimbursement.

Is M87.066 a CC or MCC?

CMS lists M87.066 as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 217 closely related codes in its exclusion list.

Can M87.066 be reported with a code from M96?

Not as a rule. The Excludes1 note at block M86-M90, which applies to M87.066, lists "postprocedural osteopathies (M96.-)". 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 HCC is M87.066?

M87.066 (idiopathic aseptic necrosis of unspecified fibula) maps to CMS-HCC Category 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis), commonly written as HCC 92, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 39 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 80.

Does M87.066 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, M87.066 adds a risk adjustment factor of about 0.479 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.471 to 0.632 depending on the payment segment). HCC 92 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 92 category page.