M87.173 ICD-10-CM Code: Osteonecrosis due to drugs, unspecified ankle
M87.173 is not a CMS-HCC payment code. MEAT criteria · RAF calculator · free HCC coding tools
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Other osteopathies (M86-M90)
M87.173
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceOsteonecrosis due to drugs, unspecified ankle
Death of bone tissue in the ankle caused by medication side effects when the specific side (left or right) is not documented.
Buddy Insight
Drug-induced osteonecrosis of unspecified ankle indicates medication-related bone death when laterality cannot be determined from documentation.
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
MappedHCC 39
RAF 0.401
ACA/HHS
MappedHCC 55
Varies by metal level
ESRD/PACE
MappedHCC 39
RAF 0.092
RXHCC
MappedHCC 80
RAF 0.204
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M87.173 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M87.173 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M87.173 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M87.173 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M87.173 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M87.173 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M87.173 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 M87.173 an HCC code?
Yes. M87.173 maps to Bone/Joint/Muscle Infections/Necrosis under the V24 model but is not retained in V28.
- Code
- M87.173
- Description
- Osteonecrosis due to drugs, unspecified ankle
- HCC (V28)
- No CMS-HCC V28 mapping
- RAF
- —
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 M87.173 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for M87.173
For M87.173 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 M87.173 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
M87.173 is the ICD-10-CM diagnosis code for osteonecrosis due to drugs, unspecified ankle. Death of bone tissue in the ankle caused by medication side effects when the specific side (left or right) is not documented. M87.173 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 older CMS-HCC V24 model, M87.173 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 is genuinely unspecified in the documentation. Because M87.173 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 M87.173 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use only when laterality is genuinely unspecified in the documentation
- •Attempt to obtain imaging reports or clinical notes that may clarify which ankle is affected
Clinical Significance
Drug-induced osteonecrosis of unspecified ankle indicates medication-related bone death when laterality cannot be determined from documentation. This condition represents significant functional impairment potential and requires comprehensive orthopedic management despite the side specification limitation.
Documentation Requirements
- ✓Documentation confirming ankle involvement in osteonecrosis
- ✓Specific causative medication or drug class identification
- ✓Imaging studies demonstrating ankle osteonecrosis
- ✓Assessment of joint function and weight-bearing capacity
- ✓Explanation for inability to determine affected ankle
- ✓Drug exposure history with temporal relationship to symptoms
- ✓Treatment approach addressing functional preservation
- ✓Provider confirmation of drug-induced etiology
Commonly Confused Codes
- •M87.171/M87.172: Use specific laterality when right/left is documented
- •M87.176: Unspecified foot involves broader foot structures
- •M87.273: Post-traumatic unspecified ankle requires injury history
- •M87.073: Idiopathic ankle osteonecrosis lacks drug causation
- •S93.4: Unspecified ankle sprain is acute soft tissue injury