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M12.042 ICD-10-CM Code: Chronic postrheumatic arthropathy [Jaccoud], left hand

M12.042 maps to CMS-HCC V28 94 (RAF 0.268). 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) / Inflammatory polyarthropathies (M05-M14)

M12.042

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

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.

Buddy the Bee presenting code insight

Buddy Insight

Chronic postrheumatic arthropathy affecting the left hand is a late sequela of rheumatic fever that can significantly compromise hand function and fine motor activities.

CMS-HCC V28

HCC 94

RAF 0.268

CMS-HCC V24

HCC 40

RAF 0.421

ACA/HHS

HCC 57

Varies by metal level

ESRD/PACE

HCC 40

RAF 0.058

RXHCC

HCC 83

RAF 0.222

Code Book Path

Official
M12.0Chronic postrheumatic arthropathy [Jaccoud]
M12.04Chronic postrheumatic arthropathy [Jaccoud], hand
M12.042Chronic postrheumatic arthropathy [Jaccoud], left hand

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M12.042 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M12.042 in this effective period.

Related Child Codes

Official
M12.041Chronic postrheumatic arthropathy [Jaccoud], right hand
M12.049Chronic postrheumatic arthropathy [Jaccoud], unspecified hand

Includes

Official

ICD-10-CM does not list Includes notes for M12.042 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M12.042 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M12.042 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M12.042 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M12.042 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance
Documented history of rheumatic fever
Specific left hand joint involvement
Evidence of chronic, non-erosive joint deformity
Clinical examination showing hand abnormalities

MEAT Support

HCC Buddy guidance
Documented history of rheumatic fever
Specific left hand joint involvement
Evidence of chronic, non-erosive joint deformity
Clinical examination showing hand abnormalities

Audit Caution

HCC Buddy guidance
Confusing laterality documentation (left vs right)
Using unspecified codes when laterality is clearly stated
Not confirming required rheumatic fever history
Mistaking for other inflammatory hand conditions

Common Mistakes

HCC Buddy guidance
M12.041 — Right hand involvement instead of left
M12.049 — Unspecified hand when left is documented
M05.742 — Rheumatoid arthritis of left hand
M25.542 — Pain in left hand without arthropathy

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 M12.042 an HCC code?

Yes. M12.042 (Chronic postrheumatic arthropathy [Jaccoud], left hand) maps to Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders under the CMS-HCC V28 risk adjustment model (and Rheumatoid Arthritis and Inflammatory Connective Tissue Disease under V24), with a community non-dual aged RAF of 0.268. It is billable for payment year 2026.

Coder answer: M12.042 is billable and maps to V28 HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code
M12.042
Description
Chronic postrheumatic arthropathy [Jaccoud], left hand
HCC (V28)
HCC 94 — Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders
RAF
0.268
Billable
Yes
Payment year
2026

HCC Category Mapping

V28HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders
0.268
V24HCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
0.421
ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
0.058
RxHCCHCC 83, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease
0.222

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 M12.042 in the Code Book — tabular path, V28 RAF, and MEAT checklist →

MEAT Criteria for M12.042

For M12.042 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 M12.042 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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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 Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders (HCC 94) with a community, non-dual, aged base RAF weight of 0.268. 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 0.421. 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

Commonly Confused Codes

  • •M12.041: Right hand involvement instead of left
  • •M12.049: Unspecified hand when left is documented
  • •M05.742: Rheumatoid arthritis of left hand
  • •M25.542: Pain in left hand without arthropathy
  • •M19.042: Primary osteoarthritis of left hand

Child Codes

M12.041Chronic postrheumatic arthropathy [Jaccoud], right hand
HCC 94
M12.042Chronic postrheumatic arthropathy [Jaccoud], left hand
HCC 94
M12.049Chronic postrheumatic arthropathy [Jaccoud], unspecified hand
HCC 94

Code Hierarchy

└M12Other and unspecified arthropathy└M12.0Chronic postrheumatic arthropathy [Jaccoud]└M12.04Chronic postrheumatic arthropathy [Jaccoud], hand└M12.042Chronic postrheumatic arthropathy [Jaccoud], left hand
└M12.042Chronic postrheumatic arthropathy [Jaccoud], left hand

Because M12.042 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.

M12.042 maps to CMS-HCC V28 category 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders. See the ICD-10 to HCC mapping hub for how the V28 crosswalk works. Because M12.042 carries a payment HCC, you can see what it adds to a RAF score and check the documentation the chart needs before it is submitted.

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Open M12.042 in the Code Book for the full Index-to-Tabular path, MEAT checklist, and V28 HCC mapping, or in the Encoder to code from a keyword search. Pro includes 7 days to try everything, no card required.

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