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M08.979 ICD-10-CM Code: Juvenile arthritis, unspecified, unspecified ankle and foot

M08.979 maps to CMS-HCC V28 93. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC Buddy coding tools

ICD-10-CM Code View

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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)

M08.979

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

Juvenile arthritis, unspecified, unspecified ankle and foot

A type of arthritis that develops in children affecting the ankle and/or foot, but the specific side (left or right) is not documented or is bilateral.

Buddy the Bee presenting code insight

Buddy Insight

Juvenile arthritis affecting unspecified ankle and foot joints represents a chronic inflammatory condition that can significantly impact a child's mobility and participation in normal activities.

CMS-HCC V28

HCC 93

Code-level coefficient reference

CMS-HCC V24

Historical

Historical

Not used for CY2026 payment

ACA/HHS

HCC 056

Code-level coefficient reference

ESRD/PACE

HCC 40

Code-level coefficient reference

RXHCC

HCC 83

Code-level coefficient reference

Code Book Path

Official
M08.9Juvenile arthritis, unspecified
M08.97Juvenile arthritis, unspecified, ankle and foot
M08.979Juvenile arthritis, unspecified, unspecified ankle and foot

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M08.979 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M08.979 in this effective period.

Related Child Codes

Official
M08.971Juvenile arthritis, unspecified, right ankle and foot
M08.972Juvenile arthritis, unspecified, left ankle and foot

Includes

Official

ICD-10-CM does not list Includes notes for M08.979 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M08.979 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M08.979 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M08.979 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M08.979 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Patient age at onset (must be under 16 years old)
Evidence of chronic arthritis lasting 6 weeks or more
Ankle and/or foot involvement without laterality specification
Documentation of inflammatory signs and symptoms

MEAT Support

HCC Buddy guidance
Patient age at onset (must be under 16 years old)
Evidence of chronic arthritis lasting 6 weeks or more
Ankle and/or foot involvement without laterality specification
Documentation of inflammatory signs and symptoms

Audit Caution

HCC Buddy guidance
Using this code when laterality is documented elsewhere in record
Coding for ankle/foot pain without evidence of chronic inflammation
Not verifying patient meets age criteria for juvenile arthritis
Failing to establish chronicity (6+ weeks duration)

Common Mistakes

HCC Buddy guidance
M08.971/M08.972 — Use when right or left ankle/foot is specified
M08.99 — Multiple sites when more than ankle/foot involved
M08.4 — Pauciarticular juvenile rheumatoid arthritis
M25.579 — Ankle and foot pain without inflammatory arthritis

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 M08.979 an HCC code?

Yes. M08.979 (Juvenile arthritis, unspecified, unspecified ankle and foot) maps to HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.617. 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: M08.979 is billable and maps to V28 HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
M08.979
Description
Juvenile arthritis, unspecified, unspecified ankle and foot
HCC (V28)
HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
RAF reference coefficient
0.617
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
0.617
ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
Not separately weighted
RxHCCHCC 83, Rheumatoid Arthritis and Other Inflammatory Polyarthropathy
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 M08.979 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for M08.979

For M08.979 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 M08.979 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M08.979 is the ICD-10-CM diagnosis code for juvenile arthritis, unspecified, unspecified ankle and foot. A type of arthritis that develops in children affecting the ankle and/or foot, but the specific side (left or right) is not documented or is bilateral. M08.979 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering inflammatory polyarthropathies (m05-m14).

Under the CMS-HCC V28 risk adjustment model, M08.979 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a source-labeled community, non-dual, aged reference coefficient of 0.617. No V24 mapping is shown for M08.979; use the applicable model and payment year when reviewing the V28 mapping. 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. 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 laterality cannot be determined from available documentation. Because M08.979 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 M08.979 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

  • •Use only when laterality cannot be determined from available documentation
  • •Review imaging reports and clinical notes to determine if laterality can be specified

Clinical Significance

Juvenile arthritis affecting unspecified ankle and foot joints represents a chronic inflammatory condition that can significantly impact a child's mobility and participation in normal activities. This diagnosis requires comprehensive management to prevent joint damage and maintain functional independence during growth and development.

Documentation Requirements

  • ✓Patient age at onset (must be under 16 years old)
  • ✓Evidence of chronic arthritis lasting 6 weeks or more
  • ✓Ankle and/or foot involvement without laterality specification
  • ✓Documentation of inflammatory signs and symptoms
  • ✓Assessment of functional impact on ambulation
  • ✓Exclusion of other causes (infectious, traumatic)
  • ✓Current treatment plan and medication effectiveness
  • ✓Appropriate diagnostic imaging and laboratory studies

Commonly Confused Codes

  • •M08.971/M08.972: Use when right or left ankle/foot is specified
  • •M08.99: Multiple sites when more than ankle/foot involved
  • •M08.4: Pauciarticular juvenile rheumatoid arthritis
  • •M25.579: Ankle and foot pain without inflammatory arthritis
  • •M19.079: Osteoarthritis of ankle and foot, unspecified

Child Codes

M08.971Juvenile arthritis, unspecified, right ankle and foot
HCC 93
M08.972Juvenile arthritis, unspecified, left ankle and foot
HCC 93
M08.979Juvenile arthritis, unspecified, unspecified ankle and foot
HCC 93

Code Hierarchy

└M08Juvenile arthritis└M08.9Juvenile arthritis, unspecified└M08.97Juvenile arthritis, unspecified, ankle and foot└M08.979Juvenile arthritis, unspecified, unspecified ankle and foot
└M08.979Juvenile arthritis, unspecified, unspecified ankle and foot

Because M08.979 maps to an HCC category, the documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment.

M08.979 maps to CMS-HCC V28 category 93, Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. The mapping identifies a payment HCC category for M08.979. 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.

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