M12.042
BillableChronic postrheumatic arthropathy [Jaccoud], left hand
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M12.042 an HCC code?
Yes. M12.042 maps to Reactive and Specified Arthropathies 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 M12.042
For M12.042to 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 M12.042 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M12.042 is the ICD-10-CM diagnosis code for chronic postrheumatic arthropathy [jaccoud], left hand. A chronic joint condition affecting the left hand that develops after rheumatic fever, characterized by reversible joint deformities without permanent damage to the joint structures. M12.042 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, M12.042 maps to Reactive and Specified Arthropathies (HCC 94) with a community, non-dual, aged base RAF weight of 0.000. Under the older CMS-HCC V24 model, M12.042 maps to Rheumatoid Arthritis and Inflammatory Connective Tissue Disease (HCC 40) with a community, non-dual, aged base RAF weight of 0.307. 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.
Confirm documentation specifies left hand involvement to differentiate from right-sided disease. Because M12.042 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 M12.042 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm documentation specifies left hand involvement to differentiate from right-sided disease
- •Link this diagnosis to a history of acute rheumatic fever when applicable
Clinical Significance
Chronic postrheumatic arthropathy affecting the left hand is a late sequela of rheumatic fever that can significantly compromise hand function and fine motor activities. This diagnosis requires comprehensive care addressing joint symptoms and functional preservation while maintaining cardiac surveillance due to underlying rheumatic heart disease risk.
Documentation Requirements
- ✓Documented history of rheumatic fever
- ✓Specific left hand joint involvement
- ✓Evidence of chronic, non-erosive joint deformity
- ✓Clinical examination showing hand abnormalities
- ✓Imaging studies confirming absence of erosions
- ✓Functional assessment of left hand dexterity
- ✓Concurrent cardiac evaluation and monitoring
- ✓Current medications and treatment effectiveness