M08.879 ICD-10-CM Code: Other juvenile arthritis, unspecified ankle and foot
HCC Buddy Code Card
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Inflammatory polyarthropathies (M05-M14)
M08.879
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceOther juvenile arthritis, 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 specified or documented.
Buddy Insight
Other juvenile arthritis affecting unspecified ankle and foot represents chronic inflammatory disease requiring specialized management with potential for significant mobility impairment.
CMS-HCC V28
MappedHCC 93
RAF 0.175
CMS-HCC V24
MappedHCC 40
RAF 0.307
ACA/HHS
00
RAF 0
ESRD/PACE
MappedHCC 40
RAF 0.0
RXHCC
MappedHCC 83
RAF 0.0
Code Trumping
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Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M08.879 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M08.879 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M08.879 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M08.879 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M08.879 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M08.879 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M08.879 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.
Is M08.879 an HCC code?
Yes. M08.879 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24).
HCC Category Mapping
RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. 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.
MEAT Criteria for M08.879
For M08.879to 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 M08.879 during that encounter, not just copy-forwarded from a problem list.
What This Code Means
M08.879 is the ICD-10-CM diagnosis code for other juvenile arthritis, 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 specified or documented. M08.879 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, M08.879 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 93) with a community, non-dual, aged base RAF weight of 0.175. Under the older V24 model, M08.879 mapped to the same category but with a base RAF weight of 0.307, V28 recalibrated weights across the entire model. 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.
Use only when laterality cannot be determined; make every effort to obtain specific ankle/foot laterality from the medical record. Because M08.879 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 M08.879 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; make every effort to obtain specific ankle/foot laterality from the medical record
- •This unspecified code should be avoided when possible by querying the provider for laterality information
Clinical Significance
Other juvenile arthritis affecting unspecified ankle and foot represents chronic inflammatory disease requiring specialized management with potential for significant mobility impairment. This diagnosis indicates need for ongoing pediatric rheumatology care, immunomodulating therapy, and monitoring for growth and developmental complications in lower extremity function.
Documentation Requirements
- ✓Patient age at onset documented as under 16 years
- ✓Evidence of juvenile arthritis affecting ankle and/or foot joints
- ✓Documentation that laterality cannot be determined
- ✓Confirmation of other specified type of juvenile arthritis (not rheumatoid)
- ✓Physical examination showing joint inflammation in ankle/foot region
- ✓Supporting laboratory and imaging studies
- ✓Current treatment approach including disease-modifying agents
- ✓Assessment of ambulation and weight-bearing ability
Commonly Confused Codes
- •M08.871: Use when right ankle/foot is specifically documented
- •M08.872: Use when left ankle/foot is specifically documented
- •M08.0: Unspecified juvenile rheumatoid arthritis versus other juvenile arthritis
- •M25.579: Ankle/foot pain versus confirmed inflammatory arthritis
- •M06.9: Adult rheumatoid arthritis versus juvenile onset