What is ICD-10 code M86.161?

M86.161 is the ICD-10-CM diagnosis code for Other acute osteomyelitis, right tibia and fibula. A rapidly developing bone infection affecting the right shinbone and smaller bone of the lower leg. It belongs to the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99). M86.161 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M86.161 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. M86.161 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. M86.161 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.

What is the V28 vs V24 difference for M86.161?

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 M86.161, 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 should coders know when reporting M86.161?

Ensure documentation clearly specifies right tibia and fibula involvement before assigning this code Distinguish between acute, subacute, and chronic osteomyelitis as they have different code ranges Because M86.161 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.

2026 ICD-10-CM M86.161: Other acute osteomyelitis

ICD-10-CM Code View

HCC Buddy Code Card

Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupM86.161Effective 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)

M86.161

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

Other acute osteomyelitis, right tibia and fibula

A rapidly developing bone infection affecting the right shinbone and smaller bone of the lower leg.

Buddy Insight

Acute osteomyelitis affecting both tibia and fibula of the right lower leg represents a complex dual-bone infection with significant implications for weight-bearing and ambulation.

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

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

M86.1Other acute osteomyelitis

M86.16Other acute osteomyelitis, tibia and fibula

M86.161Other acute osteomyelitis, right tibia and fibula

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M86.161 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M86.161 in this effective period.

Related Child Codes

Official

M86.162Other acute osteomyelitis, left tibia and fibula

M86.169Other acute osteomyelitis, unspecified tibia and fibula

Includes

Official

ICD-10-CM does not list Includes notes for M86.161 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M86.161 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M86.161 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M86.161 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M86.161 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Specific documentation of right tibia and fibula involvement

Evidence of acute infection onset in lower leg bones

Clinical signs of dual bone infection

Imaging confirmation showing both tibia and fibula involvement

MEAT Support

HCC Buddy guidance

Specific documentation of right tibia and fibula involvement

Evidence of acute infection onset in lower leg bones

Clinical signs of dual bone infection

Imaging confirmation showing both tibia and fibula involvement

Audit Caution

HCC Buddy guidance

Coding separately for tibia and fibula when both documented together

Missing the dual bone involvement complexity

Confusing with single bone osteomyelitis codes

Failing to capture acute nature of infection

Common Mistakes

HCC Buddy guidance

M86121 — Acute hematogenous osteomyelitis of right tibia and fibula

M86661 — Chronic osteomyelitis with draining sinus of right tibia and fibula

M86261 — Subacute osteomyelitis of right tibia and fibula

S82.90XA — Unspecified fracture of right lower leg

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 M86.161 an HCC code?

Yes. M86.161 (Other acute osteomyelitis, right tibia and 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: M86.161 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: M86.161
Description: Other acute osteomyelitis, right tibia and 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

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 M86.161 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M86.161

For M86.161 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 M86.161 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

Get the V28 RAF + MEAT cheat sheet

One printable page: confirm a code's V28 HCC status, its RAF weight, and the MEAT your note needs to make it stick. Free, no card.

Free PDF. No card. Unsubscribe anytime.

What This Code Means

M86.161 is the ICD-10-CM diagnosis code for other acute osteomyelitis, right tibia and fibula. A rapidly developing bone infection affecting the right shinbone and smaller bone of the lower leg. M86.161 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, M86.161 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, M86.161 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.

Ensure documentation clearly specifies right tibia and fibula involvement before assigning this code. Because M86.161 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 M86.161 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Ensure documentation clearly specifies right tibia and fibula involvement before assigning this code
•Distinguish between acute, subacute, and chronic osteomyelitis as they have different code ranges

Clinical Significance

Acute osteomyelitis affecting both tibia and fibula of the right lower leg represents a complex dual-bone infection with significant implications for weight-bearing and ambulation. This condition requires aggressive treatment due to the critical role of these bones in lower extremity function.