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M90.539 ICD-10-CM Code: Osteonecrosis in diseases classified elsewhere, unspecified forearm

M90.539 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 · free HCC coding tools

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Code lookupM90.539

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

M90.539

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

Osteonecrosis in diseases classified elsewhere, unspecified forearm

Death of bone tissue in the forearm (side not specified) caused by another disease or condition affecting the body.

Buddy the Bee presenting code insight

Buddy Insight

Secondary osteonecrosis of unspecified forearm indicates bone tissue death resulting from an underlying systemic condition, requiring comprehensive medical management.

OverviewRisk ModelsCode BookDocumentationAuditNotesEdition comparison

CMS-HCC V28

HCC 92

Coefficient HCC 92: 0.479 (Community Non-Dual Aged (CNA))

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 055

Code-level coefficient reference

ESRD/PACE

HCC 39

Code-level coefficient reference

RXHCC

HCC 80

Code-level coefficient reference

Code Book Path

Official
M90.5Osteonecrosis in diseases classified elsewhereM90.53Osteonecrosis in diseases classified elsewhere, forearmM90.539Osteonecrosis in diseases classified elsewhere, unspecified forearm

Inclusion Terms

Official

No inclusion terms are included in this display for M90.539. 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

Official
M90.531Osteonecrosis in diseases classified elsewhere, right forearmM90.532Osteonecrosis in diseases classified elsewhere, left forearm

Includes

Official

No Includes notes are included in this display for M90.539. 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

Official

No Use Additional Code instructions are included in this display for M90.539. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for M90.539. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance
Documentation of underlying disease process causing the secondary osteonecrosis
Clinical evidence of bone necrosis in forearm location
Imaging confirmation of osteonecrotic changes (MRI, bone scan, or CT)
Provider documentation establishing causal relationship to primary disease

MEAT Support

HCC Buddy guidance
Documentation of underlying disease process causing the secondary osteonecrosis
Clinical evidence of bone necrosis in forearm location
Imaging confirmation of osteonecrotic changes (MRI, bone scan, or CT)
Provider documentation establishing causal relationship to primary disease

Audit Caution

HCC Buddy guidance
Using when laterality is documented but coder defaults to unspecified
Failing to code the underlying causative disease condition
Coding based on radiologic findings without clinical correlation
Missing the requirement for established causal relationship to classified disease

Common Mistakes

HCC Buddy guidance
M87.039 — Primary osteonecrosis of unspecified forearm, not disease-related
M90.532 — Same condition but specifically left forearm rather than unspecified
M90.531 — Same condition but specifically right forearm rather than unspecified
M86.139 — Chronic osteomyelitis of unspecified forearm, which involves infection rather than necrosis

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 M90.539 an HCC code?

Yes. M90.539 (Osteonecrosis in diseases classified elsewhere, unspecified forearm) 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: M90.539 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
M90.539
Description
Osteonecrosis in diseases classified elsewhere, unspecified forearm
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

V28HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
0.479
ESRDHCC 39, Bone/Joint/Muscle Infections/Necrosis
Not separately weighted
RxHCCHCC 80, Aseptic Necrosis of Bone
Not separately weighted

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 M90.539 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for M90.539

For M90.539, 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

M90.539 is the ICD-10-CM diagnosis code for osteonecrosis in diseases classified elsewhere, unspecified forearm. Death of bone tissue in the forearm (side not specified) caused by another disease or condition affecting the body. M90.539 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, M90.539 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 M90.539; 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.

Use only when the specific side (left or right) is not documented in the medical record. For M90.539, 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 M90.539 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Use only when the specific side (left or right) is not documented in the medical record
  • •Query the provider if laterality is missing, as it affects specificity of coding

Clinical Significance

Secondary osteonecrosis of unspecified forearm indicates bone tissue death resulting from an underlying systemic condition, requiring comprehensive medical management. This diagnosis reflects significant medical complexity and ongoing care needs that substantially impact risk stratification and resource allocation.

Documentation Requirements

  • ✓Documentation of underlying disease process causing the secondary osteonecrosis
  • ✓Clinical evidence of bone necrosis in forearm location
  • ✓Imaging confirmation of osteonecrotic changes (MRI, bone scan, or CT)
  • ✓Provider documentation establishing causal relationship to primary disease
  • ✓Current management plan for both underlying condition and osteonecrosis
  • ✓Assessment of functional limitations or complications
  • ✓Exclusion of primary or traumatic causes of bone necrosis
  • ✓Treatment response documentation or progression monitoring

Commonly Confused Codes

  • •M87.039: Primary osteonecrosis of unspecified forearm, not disease-related
  • •M90.532: Same condition but specifically left forearm rather than unspecified
  • •M90.531: Same condition but specifically right forearm rather than unspecified
  • •M86.139: Chronic osteomyelitis of unspecified forearm, which involves infection rather than necrosis
  • •M79.3: Panniculitis of forearm, which is soft tissue inflammation rather than bone death

Child Codes

M90.531Osteonecrosis in diseases classified elsewhere, right forearm
HCC 92
M90.532Osteonecrosis in diseases classified elsewhere, left forearm
HCC 92
M90.539Osteonecrosis in diseases classified elsewhere, unspecified forearm
HCC 92

Code Hierarchy

└M90Osteopathies in diseases classified elsewhere└M90.5Osteonecrosis in diseases classified elsewhere└M90.53Osteonecrosis in diseases classified elsewhere, forearm└M90.539Osteonecrosis in diseases classified elsewhere, unspecified forearm
└M90.539Osteonecrosis in diseases classified elsewhere, unspecified forearm

Also searched as

  • M90 539
  • M90539

For M90.539, 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.

M90.539 maps to CMS-HCC V28 category 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for M90.539. Review its source-labeled HCC coefficient above, check the RAF Calculator with complete member context for CMS-HCC V28 PY2026, and confirm the documentation the chart needs before the code is submitted. HCC Buddy shows no RAF score unless every required source and calculation check passes.

Work M90.539 in HCC Buddy

Open M90.539 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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