What is ICD-10 code M87.266?

M87.266 is the ICD-10-CM diagnosis code for Osteonecrosis due to previous trauma, unspecified fibula. Death of bone tissue in the smaller bone of the lower leg (fibula) caused by previous trauma, but the specific side (left or right) is not specified or documented. M87.266 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M87.266 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. M87.266 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. M87.266 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does M87.266 map to under V28?

M87.266 maps to CMS-HCC V28 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis). The category number and label come from the CMS-HCC V28 model file for payment year 2026.

What does M87.266 pay in RAF?

M87.266 carries a community, non-dual, aged (CNA) RAF weight of 0.479 under CMS-HCC V28 for payment year 2026. The weight comes from the CMS V28 relative-factor file, not a hand-typed table.

What is the V28 vs V24 difference for M87.266?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. For M87.266, V28 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis at RAF 0.479 while V24 mapped to Bone/Joint/Muscle Infections/Necrosis at RAF 0.401. Both models can still appear in legacy data and in payer-specific lookback periods.

What documentation supports M87.266?

Use only when laterality cannot be determined from available documentation; attempt to obtain clarification from provider This unspecified code is less preferred; strive to code to the most specific laterality when possible Because M87.266 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score. See the MEAT criteria checklist at /meat-criteria for what Monitor, Evaluate, Assess, or Treat looks like in a note. MEAT is generic documentation evidence, not a payer-specific rule.

2026 ICD-10-CM M87.266: Osteonecrosis due

M87.266 maps to CMS-HCC V28 92 (RAF 0.479). Documentation must support MEAT. MEAT criteria · RAF calculator · free HCC coding tools

ICD-10-CM Code View

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Code lookupM87.266Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Other osteopathies (M86-M90)

M87.266

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Osteonecrosis due to previous trauma, unspecified fibula

Death of bone tissue in the smaller bone of the lower leg (fibula) caused by previous trauma, but the specific side (left or right) is not specified or documented.

Buddy Insight

Unspecified fibular osteonecrosis following trauma represents bone death in the lateral support structure of the lower leg, which can affect ankle stability and gait mechanics.

CMS-HCC V28

Mapped

HCC 92

Bone/Joint/Muscle/Severe Soft...

RAF 0.479

CMS-HCC V24

Mapped

HCC 39

Bone/Joint/Muscle Infections/...

RAF 0.401

ACA/HHS

Mapped

HCC 55

HHS-HCC 55

Varies by metal level

ESRD/PACE

Mapped

HCC 39

Bone/Joint/Muscle Infections/...

RAF 0.092

RXHCC

Mapped

HCC 80

Bone/Joint/Muscle Infections/...

RAF 0.204

Code Book Path

Official

M87.2Osteonecrosis due to previous trauma

M87.26Osteonecrosis due to previous trauma, tibia and fibula

M87.266Osteonecrosis due to previous trauma, unspecified fibula

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M87.266 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M87.266 in this effective period.

Related Child Codes

Official

M87.261Osteonecrosis due to previous trauma, right tibia

M87.262Osteonecrosis due to previous trauma, left tibia

M87.263Osteonecrosis due to previous trauma, unspecified tibia

M87.264Osteonecrosis due to previous trauma, right fibula

M87.265Osteonecrosis due to previous trauma, left fibula

Includes

Official

ICD-10-CM does not list Includes notes for M87.266 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M87.266 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M87.266 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M87.266 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M87.266 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Documentation of fibula involvement without specified laterality

Clear history of previous trauma to lower leg area

Evidence of bone necrosis in fibular structures

Justification for unspecified laterality (bilateral involvement or unclear documentation)

MEAT Support

HCC Buddy guidance

Documentation of fibula involvement without specified laterality

Clear history of previous trauma to lower leg area

Evidence of bone necrosis in fibular structures

Justification for unspecified laterality (bilateral involvement or unclear documentation)

Audit Caution

HCC Buddy guidance

Using unspecified laterality when documentation clearly indicates right or left

Failing to establish traumatic etiology versus other secondary causes

Confusing fibular with tibial osteonecrosis

Missing bilateral involvement that would justify unspecified laterality

Common Mistakes

HCC Buddy guidance

M87.264 — Osteonecrosis due to previous trauma, right fibula (when laterality is documented)

M87.265 — Osteonecrosis due to previous trauma, left fibula (when laterality is documented)

M87.263 — Osteonecrosis due to previous trauma, unspecified tibia (different bone)

M87.366 — Other secondary osteonecrosis, unspecified fibula (non-traumatic cause)

Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →

Is M87.266 an HCC code?

Yes. M87.266 (Osteonecrosis due to previous trauma, unspecified fibula) maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis under V24), with a community non-dual aged RAF of 0.479. It is billable for payment year 2026.

Coder answer: M87.266 is billable and maps to V28 HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: M87.266
Description: Osteonecrosis due to previous trauma, unspecified fibula
HCC (V28): HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
RAF: 0.479
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis

0.479

V24HCC 39, Bone/Joint/Muscle Infections/Necrosis

0.401

ESRDHCC 39, Bone/Joint/Muscle Infections/Necrosis

0.092

RxHCCHCC 80, Bone/Joint/Muscle Infections/Necrosis

0.204

Each model's RAF is its CMS base weight for that model's standard population, so weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

Work M87.266 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M87.266

For M87.266 to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
EEvaluate: test results, medication response, or physical findings reviewed by the provider
AAssess: explicit mention in the assessment or plan with acknowledgment of status
TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed M87.266 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M87.266 is the ICD-10-CM diagnosis code for osteonecrosis due to previous trauma, unspecified fibula. Death of bone tissue in the smaller bone of the lower leg (fibula) caused by previous trauma, but the specific side (left or right) is not specified or documented. M87.266 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering other osteopathies (m86-m90).

Under the CMS-HCC V28 risk adjustment model, M87.266 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.479. Under the older CMS-HCC V24 model, M87.266 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 39) with a community, non-dual, aged base RAF weight of 0.401. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Use only when laterality cannot be determined from available documentation; attempt to obtain clarification from provider. Because M87.266 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.

HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for M87.266 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Use only when laterality cannot be determined from available documentation; attempt to obtain clarification from provider
•This unspecified code is less preferred; strive to code to the most specific laterality when possible

Clinical Significance

Unspecified fibular osteonecrosis following trauma represents bone death in the lateral support structure of the lower leg, which can affect ankle stability and gait mechanics. This condition requires ongoing orthopedic monitoring and may impact overall lower extremity function.

Documentation Requirements

✓Documentation of fibula involvement without specified laterality
✓Clear history of previous trauma to lower leg area
✓Evidence of bone necrosis in fibular structures
✓Justification for unspecified laterality (bilateral involvement or unclear documentation)
✓Assessment of ankle stability and function
✓Current pain levels and mobility status
✓Treatment modalities and effectiveness
✓Impact on gait and weight-bearing capacity

Commonly Confused Codes

•M87.264: Osteonecrosis due to previous trauma, right fibula (when laterality is documented)
•M87.265: Osteonecrosis due to previous trauma, left fibula (when laterality is documented)
•M87.263: Osteonecrosis due to previous trauma, unspecified tibia (different bone)
•M87.366: Other secondary osteonecrosis, unspecified fibula (non-traumatic cause)
•M84.369A: Stress fracture, unspecified fibula (acute injury, not chronic necrosis)