2026 ICD-10-CM Diagnosis Code S66.521SLaceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level, sequela

ICD-10-CM Codes›S00–T88›S60-S69›S66

ICD-10-CM S66.521S
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S66.521S is a billable ICD-10-CM diagnosis code for laceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level, sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 604 through 605. The code is exempt from POA reporting. Coders also document this condition as injury of intrinsic muscle of index finger. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury, sequela.

Code Identity

ICD-10-CM Code
S66.521S
Billable Status
Yes — Valid for Submission
Code Describes
Laceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level, sequela
Short Description
Lacerat intrns musc/fasc/tend l idx fngr at wrs/hnd lv, sqla
Parent Code
S66.521
Laceration of intrinsic muscle, fascia and tendon of left index finger 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 CodeS66.521SLaceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level, sequela

Present on Admission (POA)Billing

S66.521S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Injury of intrinsic muscle of index finger
  • Laceration of index finger
  • Laceration of intrinsic muscle of index finger
  • Laceration of intrinsic muscle of index finger of left hand
  • Laceration of intrinsic muscle of left hand
  • Laceration of left index finger
  • Laceration of muscle of left hand
  • Left index finger intrinsic muscle injury

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 INJ073
Injury, sequela
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 S66.521S to ICD-9-CMHistory

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

ICD-9-CM
906.1 Late eff open wnd extrem
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 S66.521SOverview

Is S66.521S a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report laceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level, sequela on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character S in S66.521S mean?

The final character S makes this a sequela code: it reports a lingering problem that remains after the laceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level itself has resolved, not the original event.

What MS-DRG does S66.521S group to?

When laceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 604, 605, with relative weights from 0.9160 to 1.4721 depending on complications. Higher weights mean higher Medicare reimbursement.

Is S66.521S exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for laceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level, sequela on inpatient claims.

What is the ICD-9 equivalent of S66.521S?

Under the General Equivalence Mappings, laceration of intrinsic muscle, fascia and tendon of left index finger at wrist and hand level, sequela converts to ICD-9-CM 906.1 (late eff open wnd extrem). 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.