What is ICD-10 code M00.021?

M00.021 is the ICD-10-CM diagnosis code for Staphylococcal arthritis, right elbow. A bacterial infection of the right elbow joint caused by Staphylococcus bacteria. It belongs to the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99). M00.021 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M00.021 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. M00.021 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. M00.021 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 M00.021 map to under V28?

M00.021 maps to CMS-HCC V28 HCC 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM M00.021: Staphylococcal arthritis

M00.021 maps to CMS-HCC V28 92. A source-labeled RAF reference is available. Documentation must support MEAT. MEAT criteria · RAF Calculator · HCC Buddy coding tools

ICD-10-CM Code View

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Digital ICD-10 code-book layout with official code detail, always-visible risk models, Code Trumping, and Buddy coding guidance.

Code lookupM00.021Effective 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)

M00.021

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

Staphylococcal arthritis, right elbow

A bacterial infection of the right elbow joint caused by Staphylococcus bacteria.

Buddy Insight

Staphylococcal arthritis of the right elbow is a serious bacterial joint infection (septic arthritis) requiring emergency treatment to prevent permanent joint damage.

CMS-HCC V28

Mapped

HCC 92

Bone/Joint/Muscle/Severe Soft...

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 055

HHS-HCC 055 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 39

Bone/Joint/Muscle Infections/...

Code-level coefficient reference

RXHCC

N/A

—

Not risk-adjusted for this model/period.

Not mapped

Code Book Path

Official

M00.0Staphylococcal arthritis and polyarthritis

M00.02Staphylococcal arthritis, elbow

M00.021Staphylococcal arthritis, right elbow

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M00.021 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M00.021 in this effective period.

Related Child Codes

Official

M00.022Staphylococcal arthritis, left elbow

M00.029Staphylococcal arthritis, unspecified elbow

Includes

Official

ICD-10-CM does not list Includes notes for M00.021 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M00.021 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M00.021 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M00.021 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M00.021 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Provider documentation identifying Staphylococcus as the causative organism (culture results, clinical diagnosis, or documented species)

Documentation of the affected joint with specific anatomical site

Laterality documented as right side

Clinical findings supporting joint infection (joint effusion, warmth, erythema, limited range of motion, fever)

MEAT Support

HCC Buddy guidance

Provider documentation identifying Staphylococcus as the causative organism (culture results, clinical diagnosis, or documented species)

Documentation of the affected joint with specific anatomical site

Laterality documented as right side

Clinical findings supporting joint infection (joint effusion, warmth, erythema, limited range of motion, fever)

Audit Caution

HCC Buddy guidance

Coding staphylococcal arthritis without confirmed Staphylococcus identification — if organism is unknown, use M00.9 (pyogenic arthritis, unspecified) instead

Failing to differentiate between Staphylococcus aureus and other Staphylococcus species when documentation is available — M00.0x covers all Staphylococcus species

Not coding associated conditions such as sepsis (A41.0x for Staphylococcal sepsis) or osteomyelitis when documented alongside the septic arthritis

Coding a single joint code when multiple joints are infected — use M00.09 (polyarthritis) when more than one joint is involved

Common Mistakes

HCC Buddy guidance

M00.12x — Pneumococcal arthritis of same joint site; differs by causative organism (Pneumococcus vs. Staphylococcus)

M00.22x — Streptococcal arthritis of same joint site; differs by causative organism (Streptococcus vs. Staphylococcus)

M00.82x — Arthritis due to other bacteria at same joint site; use when organism is identified but not Staphylococcus

M00.9 — Pyogenic arthritis, unspecified; use only when causative organism cannot be identified

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 M00.021 an HCC code?

Yes. M00.021 (Staphylococcal arthritis, right elbow) maps to HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.479. 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: M00.021 is billable and maps to V28 HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.

Code: M00.021
Description: Staphylococcal arthritis, right elbow
HCC (V28): HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
RAF reference coefficient: 0.479
Billable: Yes
Payment year: 2026

HCC Category Mapping

V28HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis

0.479

ESRDHCC 39, Bone/Joint/Muscle Infections/Necrosis

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 M00.021 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT Criteria for M00.021

For M00.021 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 M00.021 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M00.021 is the ICD-10-CM diagnosis code for staphylococcal arthritis, right elbow. A bacterial infection of the right elbow joint caused by Staphylococcus bacteria. M00.021 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, M00.021 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis (HCC 92) with a source-labeled community, non-dual, aged reference coefficient of 0.479. No V24 mapping is shown for M00.021; use the applicable model and payment year when reviewing the V28 mapping. 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. 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.

Verify documentation specifies right elbow as the affected joint. Because M00.021 maps to an HCC category, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) before the diagnosis is used for risk adjustment. 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 M00.021 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Verify documentation specifies right elbow as the affected joint
•Ensure Staphylococcus is identified as the causative organism

Clinical Significance

Staphylococcal arthritis of the right elbow is a serious bacterial joint infection (septic arthritis) requiring emergency treatment to prevent permanent joint damage. Staphylococcus is the most common causative organism in septic arthritis, and infection of the elbow joint carries risks of cartilage destruction, osteomyelitis, and systemic sepsis. Accurate site-specific coding is essential for risk adjustment and reflects the high acuity and resource needs of this condition.

Documentation Requirements

✓Provider documentation identifying Staphylococcus as the causative organism (culture results, clinical diagnosis, or documented species)
✓Documentation of the affected joint with specific anatomical site
✓Laterality documented as right side
✓Clinical findings supporting joint infection (joint effusion, warmth, erythema, limited range of motion, fever)
✓Synovial fluid analysis results or culture and sensitivity reports when available
✓Treatment documentation (antibiotics, joint aspiration, surgical drainage/washout)
✓Assessment of whether the infection is acute or chronic, and whether it is a primary infection or secondary to another source

Commonly Confused Codes

•M00.12x: Pneumococcal arthritis of same joint site; differs by causative organism (Pneumococcus vs. Staphylococcus)
•M00.22x: Streptococcal arthritis of same joint site; differs by causative organism (Streptococcus vs. Staphylococcus)
•M00.82x: Arthritis due to other bacteria at same joint site; use when organism is identified but not Staphylococcus
•M00.9: Pyogenic arthritis, unspecified; use only when causative organism cannot be identified