M86.40 ICD-10-CM Code: Chronic osteomyelitis with draining sinus, unspecified site
M86.40 maps to CMS-HCC V28 92 (RAF 0.479). Documentation must support MEAT. 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)
M86.40
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceChronic osteomyelitis with draining sinus, unspecified site
A chronic bone infection with an open drainage tract or sinus when the specific location on the body is not documented.
Buddy Insight
Chronic osteomyelitis with draining sinus at an unspecified site represents a severe, persistent bone infection complicated by an open drainage tract, indicating treatment-resistant disease.
CMS-HCC V28
MappedHCC 92
RAF 0.479
CMS-HCC V24
MappedHCC 39
RAF 0.401
ACA/HHS
MappedHCC 55
Varies by metal level
ESRD/PACE
MappedHCC 39
RAF 0.092
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M86.40 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M86.40 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M86.40 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M86.40 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M86.40 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M86.40 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M86.40 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 M86.40 an HCC code?
Yes. M86.40 (Chronic osteomyelitis with draining sinus, unspecified site) 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: M86.40 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
- M86.40
- Description
- Chronic osteomyelitis with draining sinus, unspecified site
- HCC (V28)
- HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
- RAF
- 0.479
- 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 M86.40 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for M86.40
For M86.40 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 M86.40 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
M86.40 is the ICD-10-CM diagnosis code for chronic osteomyelitis with draining sinus, unspecified site. A chronic bone infection with an open drainage tract or sinus when the specific location on the body is not documented. M86.40 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, M86.40 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, M86.40 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.
The presence of a draining sinus is a key distinguishing feature of this code category. Because M86.40 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 M86.40 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •The presence of a draining sinus is a key distinguishing feature of this code category
- •Query provider for anatomical site if not clearly documented
Clinical Significance
Chronic osteomyelitis with draining sinus at an unspecified site represents a severe, persistent bone infection complicated by an open drainage tract, indicating treatment-resistant disease. The presence of a draining sinus significantly complicates treatment and increases risk for recurrent infection and systemic complications.
Documentation Requirements
- ✓Documentation of chronic osteomyelitis with confirmed draining sinus
- ✓Evidence of chronicity (>6 weeks duration or recurrent episodes)
- ✓Description of draining sinus tract characteristics
- ✓Imaging findings showing chronic osteomyelitic changes
- ✓Clinical evidence of persistent drainage from bone infection
- ✓Laboratory findings supporting chronic infectious process
- ✓Treatment history addressing both infection and drainage
- ✓Absence of specific anatomical site documentation
Commonly Confused Codes
- •M86.60: Other chronic osteomyelitis, unspecified site, lacks drainage
- •M86.30: Chronic multifocal osteomyelitis, lacks drainage component
- •M86.10: Acute osteomyelitis, differs by chronicity
- •L02.9: Cutaneous abscess, unspecified, superficial vs bone involvement
- •M86.50: Other chronic hematogenous osteomyelitis, lacks drainage