2027 ICD-10-CM Diagnosis Code S66.422ALaceration of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level, initial encounter

ICD-10-CM Codes›S00–T88›S60-S69›S66

ICD-10-CM S66.422A
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

S66.422A is a billable ICD-10-CM diagnosis code for laceration of intrinsic muscle, fascia and tendon of left 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 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 564 through 566, 963 through 965. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 40 closely related codes. Coders also document this condition as injury of intrinsic muscle of left thumb. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Open wounds to limbs, initial encounter.

Code Identity

ICD-10-CM Code
S66.422A
Billable Status
Yes — Valid for Submission
Code Describes
Laceration of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level, initial encounter
Short Description
Lacerat intrinsic musc/fasc/tend l thm at wrs/hnd lv, init
Parent Code
S66.422
Laceration of intrinsic muscle, fascia and tendon of left 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 CodeS66.422ALaceration of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level, initial encounter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Injury of intrinsic muscle of left thumb
  • Injury of intrinsic muscle of thumb
  • Laceration of intrinsic muscle of left hand
  • Laceration of intrinsic muscle of left thumb
  • Laceration of intrinsic muscle of thumb
  • Laceration of left thumb
  • Laceration of muscle of left hand

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 2027, published by CMS and the National Center for Health Statistics.

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to S66.422A: its own notes plus those printed at S66, block S60-S69, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.

Excludes2

Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.

From S66 Injury of muscle, fascia and tendon at wrist and hand level applies to 540 codes
  • sprain of joints and ligaments of wrist and hand (S63.-)
From Block S60-S69 Injuries to the wrist, hand and fingers applies to 5,118 codes
  • burns and corrosions (T20-T32)
  • frostbite (T33-T34)
  • insect bite or sting, venomous (T63.4)
From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • code to identify any retained foreign body, if applicable (Z18.-)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From S66 Injury of muscle, fascia and tendon at wrist and hand level applies to 540 codes
  • any associated open wound (S61.-)

Notes

General instructions on how these codes are used.

From Chapter 19 (S00-T88) Injury, poisoning and certain other consequences of external causes applies to 41,187 codes
  • Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
  • The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.

7th Character

Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.

From S66 Injury of muscle, fascia and tendon at wrist and hand level applies to 540 codes
  • The appropriate 7th character is to be added to each code from category S66
Values for category S66 Encounter: Initial, Subsequent, Sequela
  • Ainitial encounter this code
  • Dsubsequent encounter
  • Ssequela

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name S66.422A, its category, or a range that includes it.

Excludes2 3

These codes carry an Excludes2 note naming S66.422A: its condition is not part of those codes, and both may be reported when the patient has both.

  • S56 Injury of muscle, fascia and tendon at forearm level
    injury of muscle, fascia and tendon at or below wrist (S66.-) names S66.-, which includes this code
  • S63 Dislocation and sprain of joints and ligaments at wrist and hand level
    strain of muscle, fascia and tendon of wrist and hand (S66.-) names S66.-, which includes this code
  • S66.5 Injury of intrinsic muscle, fascia and tendon of other and unspecified finger at wrist and hand level
    injury of intrinsic muscle, fascia and tendon of thumb at wrist and hand level (S66.4-) names S66.4-, which includes this code

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 S66.422A 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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About S66.422AOverview

Is S66.422A 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 thumb at wrist and hand level, initial encounter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What does the 7th character A in S66.422A mean?

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

What MS-DRG does S66.422A group to?

When laceration of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 564, 964, 965, 566, 565, 963, with relative weights from 0.7374 to 2.6361 depending on complications. Higher weights mean higher Medicare reimbursement.

Is S66.422A a CC or MCC?

CMS lists S66.422A as a CC (complication or comorbidity) for FY 2027. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 40 closely related codes in its exclusion list.

What is the ICD-9 equivalent of S66.422A?

Under the General Equivalence Mappings, laceration of intrinsic muscle, fascia and tendon of left 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.