2026 ICD-10-CM Diagnosis Code S66.021ALaceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand level, initial encounter

ICD-10-CM Codes›S00–T88›S60-S69›S66

ICD-10-CM S66.021A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S66.021A is a billable ICD-10-CM diagnosis code for laceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand 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. Coders also document this condition as laceration of flexor tendon of right thumb. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Open wounds to limbs, initial encounter.

Code Identity

ICD-10-CM Code
S66.021A
Billable Status
Yes — Valid for Submission
Code Describes
Laceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand level, initial encounter
Short Description
Lacerat long flexor musc/fasc/tend r thm at wrs/hnd lv, init
Parent Code
S66.021
Laceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand level

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionS60-S69Injuries to the wrist, hand and fingers
CategoryS66Injury of muscle, fascia and tendon at wrist and hand level
This CodeS66.021ALaceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand level, initial encounter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Laceration of flexor tendon of right thumb
  • Laceration of right thumb
  • Laceration of tendon of right hand
  • Laceration of tendon of thumb

Coding GuidelinesGuidance

The appropriate 7th character is to be added to each code from block Injury of muscle, fascia and tendon at wrist and hand level (S66). 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

Hand Injuries and Disorders

No matter how old you are or what you do for a living, you are always using your hands. When there is something wrong with them, you may not be able to do your regular activities.

Read the full article at MedlinePlus

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

Convert S66.021A to ICD-9-CMHistory

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

ICD-9-CM
881.22 Opn wound wrist w tendon
Approximate The match is approximate rather than exact.
ICD-9-CM
882.2 Open wound hand w tendon
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 S66.021AOverview

Is S66.021A a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report laceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand level, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in S66.021A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for laceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand level, such as an emergency visit or first evaluation.

What MS-DRG does S66.021A group to?

When laceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand 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 S66.021A?

Under the General Equivalence Mappings, laceration of long flexor muscle, fascia and tendon of right thumb at wrist and hand level, initial encounter converts to ICD-9-CM 881.22 (opn wound wrist w tendon) and 882.2 (open wound hand w tendon). 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.