C40.31 ICD-10-CM Code: Malignant neoplasm of short bones of right lower limb
C40.31 maps to CMS-HCC V28 21. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software
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FY 2026 Apr update / Neoplasms (C00-D49) / Malignant neoplasms of bone and articular cartilage (C40-C41)
C40.31
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceMalignant neoplasm of short bones of right lower limb
Cancer that starts in the small bones of the right leg or foot, such as the ankle or foot bones.
Buddy Insight
Primary malignant neoplasm of the short bones (tarsals, metatarsals) of the right lower limb.
CMS-HCC V28
MappedHCC 21
Coefficient HCC 21: 0.671 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 010
Code-level coefficient reference
ESRD/PACE
MappedHCC 10
Code-level coefficient reference
RXHCC
MappedHCC 22
Code-level coefficient reference
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for C40.31. Check the code and parent instructions in the Code Book.
Excludes 2
OfficialNo Excludes 2 notes are included in this display for C40.31. Check the code and parent instructions in the Code Book.
Related Codes
Includes
Official- malignant neoplasm of cartilage (articular) (joint)Inherited from C40-C41
- malignant neoplasm of periosteumInherited from C40-C41
Excludes 1
Official- malignant neoplasm of bone marrow NOS (C96.9)Inherited from C40-C41
- malignant neoplasm of synovia (C49.-)Inherited from C40-C41
Code First
OfficialNo Code First sequencing instructions are included in this display for C40.31. Check the code and parent instructions in the Code Book.
Use Additional
Official- code to identify major osseous defect, if applicable (M89.7-)Inherited from C40
Code Also
OfficialNo Code Also instructions are included in this display for C40.31. Check the code and parent instructions in the Code Book.
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 C40.31 an HCC code?
Yes. C40.31 (Malignant neoplasm of short bones of right lower limb) maps to HCC 21, Lymphoma and Other Cancers under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.671. 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: C40.31 is billable and maps to V28 HCC 21, Lymphoma and Other Cancers. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- C40.31
- Description
- Malignant neoplasm of short bones of right lower limb
- HCC (V28)
- HCC 21 — Lymphoma and Other Cancers
- RAF reference coefficient
- 0.671
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
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 C40.31 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for C40.31
For C40.31, 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
C40.31 is the ICD-10-CM diagnosis code for malignant neoplasm of short bones of right lower limb. Cancer that starts in the small bones of the right leg or foot, such as the ankle or foot bones. C40.31 sits in the ICD-10-CM chapter for neoplasms (c00-d49), within the section covering malignant neoplasms of bone and articular cartilage (c40-c41).
Under the CMS-HCC V28 risk adjustment model, C40.31 maps to Lymphoma and Other Cancers (HCC 21) with a source-labeled community, non-dual, aged reference coefficient of 0.671. 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 right side laterality is documented; this code is specific to right lower limb short bones. For C40.31, 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 C40.31 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Confirm right side laterality is documented; this code is specific to right lower limb short bones
- •Short bones include tarsals and metatarsals; ensure distinction from long bone malignancies
Clinical Significance
Primary malignant neoplasm of the short bones (tarsals, metatarsals) of the right lower limb. Foot and ankle bone cancers are rare and may present as persistent swelling or pain often mistaken for trauma or infection. Accurate laterality coding is important for surgical planning and risk adjustment documentation.
Documentation Requirements
- ✓Right-side laterality explicitly documented
- ✓Specific short bone involved (calcaneus, talus, navicular, cuboid, cuneiform, metatarsal)
- ✓Histologic type from biopsy (chondrosarcoma, Ewing sarcoma, osteosarcoma)
- ✓Primary vs. metastatic origin confirmed
- ✓Imaging findings (radiograph, MRI, CT) supporting the diagnosis
- ✓Treatment plan and current disease status
Commonly Confused Codes
- •C40.32: Short bones of LEFT lower limb; laterality differentiator
- •C40.30: Short bones of UNSPECIFIED lower limb; avoid when right side is documented
- •C40.21: Long bones of right lower limb; different anatomic axis
- •C49.21: Malignant neoplasm of connective and soft tissue of right lower limb; for soft tissue sarcomas, not bone