2026 ICD-10-CM Diagnosis Code S56.321ALaceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level, initial encounter

ICD-10-CM Codes›S00–T88›S50-S59›S56

ICD-10-CM S56.321A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S56.321A is a billable ICD-10-CM diagnosis code for laceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 564 through 566, 963 through 965. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Open wounds to limbs, initial encounter.

Code Identity

ICD-10-CM Code
S56.321A
Billable Status
Yes — Valid for Submission
Code Describes
Laceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level, initial encounter
Short Description
Lacerat extn/abdr musc/fasc/tend of r thm at forarm lv, init
Parent Code
S56.321
Laceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS50-S59Injuries to the elbow and forearm
CategoryS56Injury of muscle, fascia and tendon at forearm level
This CodeS56.321ALaceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level, initial encounter

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Injury of muscle, fascia and tendon at forearm level (S56). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INJ012
Open wounds to limbs, initial encounter
Default principal diagnosis: inpatient Yes · outpatient Yes

Patient EducationClinical

Arm Injuries and Disorders

Of the 206 bones in your body, three of them are in your arm: the humerus, radius, and ulna. Your arms are also made up of muscles, joints, tendons, and other connective tissue. Injuries to any of these parts of the arm can occur during sports, a fall, or an accident.

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert S56.321A to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
881.20 Open wnd forearm w tendn
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About S56.321AOverview

Is S56.321A a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report laceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in S56.321A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for laceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level, such as an emergency visit or first evaluation.

What MS-DRG does S56.321A group to?

When laceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 564, 565, 566, 963, 964, 965, with relative weights from 0.7493 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of S56.321A?

Under the General Equivalence Mappings, laceration of extensor or abductor muscles, fascia and tendons of right thumb at forearm level, initial encounter converts to ICD-9-CM 881.20 (open wnd forearm w tendn). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.