What is ICD-10 code M02.361?

M02.361 is the ICD-10-CM diagnosis code for Reiter's disease, right knee. Reiter's disease affecting the right knee joint, a reactive arthritis that develops following an infection in another part of the body. M02.361 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M02.361 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. M02.361 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. M02.361 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does M02.361 map to under V28?

M02.361 maps to CMS-HCC V28 HCC 94 (Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM M02.361: Reiter's disease, right

M02.361 maps to CMS-HCC V28 94. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC Buddy coding tools

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Code lookupM02.361

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Infectious arthropathies (M00-M02)

M02.361

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

Reiter's disease, right knee

Reiter's disease affecting the right knee joint, a reactive arthritis that develops following an infection in another part of the body.

Buddy Insight

Reiter's disease affecting the right knee represents a major weight-bearing joint inflammatory arthropathy that significantly impacts mobility and functional independence.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 94

Systemic Lupus Erythematosus ...

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 057

HHS-HCC 057 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 40

Rheumatoid Arthritis and Infl...

Code-level coefficient reference

RXHCC

Mapped

HCC 83

Rheumatoid Arthritis and Othe...

Code-level coefficient reference

Code Book Path

Official

M02.3Reiter's disease M02.36Reiter's disease, knee M02.361Reiter's disease, right knee

Inclusion Terms

Official

Reactive arthritisInherited from M02.3

Excludes 2

Official

arthropathic psoriasis (L40.5-)Inherited from M00-M99
certain conditions originating in the perinatal period (P04-P96)Inherited from M00-M99
certain infectious and parasitic diseases (A00-B99)Inherited from M00-M99
compartment syndrome (traumatic) (T79.A-)Inherited from M00-M99
complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from M00-M99
congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from M00-M99
endocrine, nutritional and metabolic diseases (E00-E88)Inherited from M00-M99
injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from M00-M99
neoplasms (C00-D49)Inherited from M00-M99
symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from M00-M99

Related Codes

Official

M02.362Reiter's disease, left knee M02.369Reiter's disease, unspecified knee

Includes

Official

No Includes notes are included in this display for M02.361. Check the code and parent instructions in the Code Book.

Excludes 1

Official

Behçet's disease (M35.2)Inherited from M02
direct infections of joint in infectious and parasitic diseases classified elsewhere (M01.-)Inherited from M02
postmeningococcal arthritis (A39.84)Inherited from M02
mumps arthritis (B26.85)Inherited from M02
rubella arthritis (B06.82)Inherited from M02
syphilis arthritis (late) (A52.77)Inherited from M02
rheumatic fever (I00)Inherited from M02
tabetic arthropathy [Charcôt's] (A52.16)Inherited from M02

Code First

Official

underlying disease, such as:Inherited from M02
congenital syphilis [Clutton's joints] (A50.5)Inherited from M02
enteritis due to Yersinia enterocolitica (A04.6)Inherited from M02
infective endocarditis (I33.0)Inherited from M02
viral hepatitis (B15-B19)Inherited from M02

Use Additional

Official

No Use Additional Code instructions are included in this display for M02.361. Check the code and parent instructions in the Code Book.

Code Also

Official

No Code Also instructions are included in this display for M02.361. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Specific documentation of right knee joint involvement

Confirmed diagnosis of Reiter's disease with supporting clinical criteria

History of preceding bacterial infection (Chlamydia, enteric pathogens)

Physical examination findings of knee effusion, warmth, and range of motion loss

MEAT Support

HCC Buddy guidance

Specific documentation of right knee joint involvement

Confirmed diagnosis of Reiter's disease with supporting clinical criteria

History of preceding bacterial infection (Chlamydia, enteric pathogens)

Physical examination findings of knee effusion, warmth, and range of motion loss

Audit Caution

HCC Buddy guidance

Using unspecified knee code when right laterality is documented

Confusing with crystalline arthropathy (gout/pseudogout) which has different crystal deposits

Missing concurrent Achilles tendinitis or plantar fasciitis when present

Failing to document impact on ambulation and weight-bearing activities

Common Mistakes

HCC Buddy guidance

M06.061 — Rheumatoid arthritis of right knee has symmetric pattern and positive serology

M02.861 — Other reactive arthropathies of right knee lacks specific Reiter's diagnosis

M17.11 — Unilateral primary osteoarthritis of right knee is degenerative condition

M23.91 — Internal derangement of unspecified knee involves mechanical problems, not inflammation

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 M02.361 an HCC code?

Yes. M02.361 (Reiter's disease, right knee) maps to HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.268. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.

Coder answer: M02.361 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: M02.361
Description: Reiter's disease, right knee
HCC (V28): HCC 94 — Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders
RAF reference coefficient: 0.268
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 94, Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders

0.268

ESRDHCC 40, Rheumatoid Arthritis and Inflammatory Connective Tissue Disease

Not separately weighted

RxHCCHCC 83, Rheumatoid Arthritis and Other Inflammatory Polyarthropathy

Not separately weighted

These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. 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 context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.

Work M02.361 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for M02.361

For M02.361, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.

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

Coder workflow notes

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What This Code Means

M02.361 is the ICD-10-CM diagnosis code for reiter's disease, right knee. Reiter's disease affecting the right knee joint, a reactive arthritis that develops following an infection in another part of the body. M02.361 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, M02.361 maps to Systemic Lupus Erythematosus and Other Specified Systemic Connective Tissue Disorders (HCC 94) with a source-labeled community, non-dual, aged reference coefficient of 0.268. No V24 mapping is shown for M02.361; use the applicable model and payment year when reviewing the V28 mapping. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.

Confirm laterality is documented as right; if unspecified, use M02.369 instead. For M02.361, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. 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, source-labeled coefficient references, and MEAT documentation criteria for M02.361 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Confirm laterality is documented as right; if unspecified, use M02.369 instead
•Document the triggering infection (commonly chlamydia or dysentery) to support medical necessity and treatment decisions

Clinical Significance

Reiter's disease affecting the right knee represents a major weight-bearing joint inflammatory arthropathy that significantly impacts mobility and functional independence. This reactive arthritis condition typically requires aggressive immunosuppressive treatment and carries important implications for long-term disability and healthcare costs.

Documentation Requirements

✓Specific documentation of right knee joint involvement
✓Confirmed diagnosis of Reiter's disease with supporting clinical criteria
✓History of preceding bacterial infection (Chlamydia, enteric pathogens)
✓Physical examination findings of knee effusion, warmth, and range of motion loss
✓Synovial fluid analysis if arthrocentesis performed
✓Assessment of weight-bearing capacity and ambulatory function
✓Laboratory markers of systemic inflammation
✓Treatment regimen including DMARDs or biologic therapy

Commonly Confused Codes

•M06.061: Rheumatoid arthritis of right knee has symmetric pattern and positive serology
•M02.861: Other reactive arthropathies of right knee lacks specific Reiter's diagnosis
•M17.11: Unilateral primary osteoarthritis of right knee is degenerative condition
•M23.91: Internal derangement of unspecified knee involves mechanical problems, not inflammation