M90.561 ICD-10-CM Code: Osteonecrosis in diseases classified elsewhere, right lower leg
M90.561 maps to CMS-HCC V28 92. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Other osteopathies (M86-M90)
M90.561
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceOsteonecrosis in diseases classified elsewhere, right lower leg
Bone death (osteonecrosis) in the right lower leg caused by another disease. The bone tissue in the lower leg dies as a secondary effect of an underlying condition.
Buddy Insight
Secondary osteonecrosis of the right lower leg represents bone death in the tibia or fibula caused by an underlying classified disease, requiring comprehensive medical management.
CMS-HCC V28
MappedHCC 92
Coefficient HCC 92: 0.479 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 055
Code-level coefficient reference
ESRD/PACE
MappedHCC 39
Code-level coefficient reference
RXHCC
MappedHCC 80
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for M90.561. Check the code and parent instructions in the Code Book.
Excludes 2
Official- arthropathic psoriasis (L40.5-)Inherited from M00-M99
- certain conditions originating in the perinatal period (P04-P96)Inherited from M00-M99
- certain infectious and parasitic diseases (A00-B99)Inherited from M00-M99
- compartment syndrome (traumatic) (T79.A-)Inherited from M00-M99
- complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from M00-M99
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from M00-M99
- endocrine, nutritional and metabolic diseases (E00-E88)Inherited from M00-M99
- injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from M00-M99
- neoplasms (C00-D49)Inherited from M00-M99
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from M00-M99
Related Codes
Includes
OfficialNo Includes notes are included in this display for M90.561. Check the code and parent instructions in the Code Book.
Excludes 1
Official- postprocedural osteopathies (M96.-)Inherited from M86-M90, M90
- osteochondritis, osteomyelitis, and osteopathy (in):Inherited from M86-M90, M90
- cryptococcosis (B45.3)Inherited from M86-M90, M90
- diabetes mellitus (E08-E13 with .69-)Inherited from M86-M90, M90
- gonococcal (A54.43)Inherited from M86-M90, M90
- neurogenic syphilis (A52.11)Inherited from M86-M90, M90
- renal osteodystrophy (N25.0)Inherited from M86-M90, M90
- salmonellosis (A02.24)Inherited from M86-M90, M90
- secondary syphilis (A51.46)Inherited from M86-M90, M90
- syphilis (late) (A52.77)Inherited from M86-M90, M90
Code First
Official- underlying disease, such as:Inherited from M90.5
- caisson disease (T70.3)Inherited from M90.5
- hemoglobinopathy (D50-D64)Inherited from M90.5
Use Additional
OfficialNo Use Additional Code instructions are included in this display for M90.561. Check the code and parent instructions in the Code Book.
Code Also
OfficialNo Code Also instructions are included in this display for M90.561. Check the code and parent instructions in the Code Book.
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 M90.561 an HCC code?
Yes. M90.561 (Osteonecrosis in diseases classified elsewhere, right lower leg) maps to HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.479. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: M90.561 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
- M90.561
- Description
- Osteonecrosis in diseases classified elsewhere, right lower leg
- HCC (V28)
- HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
- RAF reference coefficient
- 0.479
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work M90.561 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for M90.561
For M90.561, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- 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
Coder workflow notes
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What This Code Means
M90.561 is the ICD-10-CM diagnosis code for osteonecrosis in diseases classified elsewhere, right lower leg. Bone death (osteonecrosis) in the right lower leg caused by another disease. The bone tissue in the lower leg dies as a secondary effect of an underlying condition. M90.561 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, M90.561 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis (HCC 92) with a source-labeled community, non-dual, aged reference coefficient of 0.479. No V24 mapping is shown for M90.561; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Requires a secondary diagnosis code for the underlying disease causing the osteonecrosis. For M90.561, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, and MEAT documentation criteria for M90.561 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Requires a secondary diagnosis code for the underlying disease causing the osteonecrosis
- •Laterality is specified as right; do not use this code for left-sided or bilateral involvement
Clinical Significance
Secondary osteonecrosis of the right lower leg represents bone death in the tibia or fibula caused by an underlying classified disease, requiring comprehensive medical management. This diagnosis significantly impacts risk adjustment modeling due to potential mobility limitations and complex care coordination needs.
Documentation Requirements
- ✓Clear documentation of underlying disease causing secondary osteonecrosis
- ✓Specific identification of right lower leg (tibia/fibula) involvement
- ✓Radiological evidence of bone necrosis (MRI, bone scan, or CT imaging)
- ✓Clinical correlation between primary disease and secondary bone death
- ✓Current management plan for both underlying condition and osteonecrosis
- ✓Assessment of weight-bearing status and mobility limitations
- ✓Provider statement confirming secondary rather than primary cause
- ✓Documentation of treatment response and complication monitoring
Commonly Confused Codes
- •M87.061: Primary osteonecrosis of right tibia, not secondary to disease
- •M90.569: Same condition but unspecified lower leg rather than specifically right
- •M86.161: Chronic osteomyelitis of right tibia involving infection rather than necrosis
- •S82.91XA: Fracture of right lower leg, which is traumatic rather than disease-related
- •M25.561: Pain in right lower leg, which is symptomatic rather than structural pathology