M05.662 ICD-10-CM Code: Rheumatoid arthritis of left knee with involvement of other organs and systems
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)
M05.662
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceRheumatoid arthritis of left knee with involvement of other organs and systems
Rheumatoid arthritis affecting the left knee with systemic complications involving other organs or body systems.
Buddy Insight
This code represents systemic rheumatoid arthritis affecting the left knee with organ system involvement, indicating advanced inflammatory disease with significant patient morbidity.
CMS-HCC V28
MappedHCC 93
RAF 0.617
CMS-HCC V24
MappedHCC 40
RAF 0.421
ACA/HHS
MappedHCC 56
Varies by metal level
ESRD/PACE
MappedHCC 40
RAF 0.058
RXHCC
MappedHCC 83
RAF 0.222
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M05.662 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M05.662 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M05.662 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M05.662 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M05.662 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M05.662 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M05.662 in this effective period.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
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 M05.662 an HCC code?
Yes. M05.662 (Rheumatoid arthritis of left knee with involvement of other organs and systems) maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic 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 0.617. It is billable for payment year 2026.
Coder answer: M05.662 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
- M05.662
- Description
- Rheumatoid arthritis of left knee with involvement of other organs and systems
- HCC (V28)
- HCC 93 — Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders
- RAF
- 0.617
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 M05.662 in the Code Book — tabular path, V28 RAF, and MEAT checklist →
MEAT Criteria for M05.662
For M05.662 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 M05.662 during that encounter, not just copy-forwarded from a problem list.
Coder workflow notes
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What This Code Means
M05.662 is the ICD-10-CM diagnosis code for rheumatoid arthritis of left knee with involvement of other organs and systems. Rheumatoid arthritis affecting the left knee with systemic complications involving other organs or body systems. M05.662 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, M05.662 maps to Rheumatoid Arthritis and Other Specified Inflammatory Rheumatic Disorders (HCC 93) with a community, non-dual, aged base RAF weight of 0.617. Under the older CMS-HCC V24 model, M05.662 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 left knee is the affected site; this code encompasses both joint and systemic disease manifestations. Because M05.662 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 M05.662 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm left knee is the affected site; this code encompasses both joint and systemic disease manifestations.
- •If patient has bilateral knee involvement, assign both M05.661 and M05.662 to capture complete clinical picture.
Clinical Significance
This code represents systemic rheumatoid arthritis affecting the left knee with organ system involvement, indicating advanced inflammatory disease with significant patient morbidity. The systemic component elevates this beyond simple arthritis to a complex multi-system condition requiring intensive management.
Documentation Requirements
- ✓Confirmation of rheumatoid arthritis diagnosis affecting the left knee
- ✓Documentation of organ or system involvement beyond the knee joint
- ✓Evidence of extra-articular manifestations (cardiovascular, pulmonary, etc.)
- ✓Laboratory support for RA diagnosis (RF, anti-CCP, inflammatory markers)
- ✓Clinical assessment documenting systemic disease activity
- ✓Specific identification of affected organ systems beyond joints
- ✓Clear relationship between systemic involvement and rheumatoid arthritis
Commonly Confused Codes
- •M05662 vs M17.12: M17.12 is unilateral primary osteoarthritis of left knee
- •M05662 vs M25.562: M25.562 is left knee pain without inflammatory component
- •M05662 vs M05661: Wrong laterality (right vs left knee)
- •M05662 vs M06.9: M06.9 lacks the required organ involvement specification
- •M05662 vs M13.162: M13.162 is monoarthritis not elsewhere classified