M00.861
BillableArthritis due to other bacteria, right knee
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M00.861 an HCC code?
Yes. M00.861 maps to Bone/Joint/Muscle Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis 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 M00.861
For M00.861to 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 M00.861 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M00.861 is the ICD-10-CM diagnosis code for arthritis due to other bacteria, right knee. Bacterial infection causing inflammation and swelling in the right knee joint, caused by bacteria other than the most common types. M00.861 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering infectious arthropathies (m00-m02).
Under the CMS-HCC V28 risk adjustment model, M00.861 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.209. Under the older V24 model, M00.861 mapped to the same category but with a base RAF weight of 0.482 — 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.
Verify bacterial organism documentation; if not specified, use M00.869 instead. Because M00.861 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 M00.861 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
Clinical Significance
Bacterial arthritis of the right knee is a serious infection of the largest weight-bearing joint that can rapidly lead to cartilage destruction and permanent disability. This condition requires immediate antibiotic therapy and often arthroscopic drainage to preserve joint function.
Documentation Requirements
- ✓Identification of 'other bacteria' as causative organism
- ✓Specific documentation of right knee joint involvement
- ✓Microbiological evidence supporting bacterial infection
- ✓Clinical findings of infectious arthritis
- ✓Documentation of systemic antibiotic treatment
- ✓Assessment of knee range of motion and stability
- ✓Laboratory markers of infection (WBC, ESR, CRP)
- ✓Exclusion of crystal arthropathy or mechanical derangement
Commonly Confused Codes
- •M00061 — Streptococcal arthritis of right knee (different organism)
- •M00016 — Staphylococcal arthritis of right knee (specific bacteria)
- •M06.861 — Other rheumatoid arthritis of right knee (autoimmune)
- •M17.11 — Unilateral primary osteoarthritis of right knee (degenerative)
- •M23.91 — Other internal derangement of right knee (mechanical)