2026 ICD-10-CM Diagnosis Code S66.912AStrain of unspecified muscle, fascia and tendon at wrist and hand level, left hand, initial encounter

ICD-10-CM Codes›S00–T88›S60-S69›S66

ICD-10-CM S66.912A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

S66.912A is a billable ICD-10-CM diagnosis code for strain of unspecified muscle, fascia and tendon at wrist and hand level, left hand, 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 562 through 563, 963 through 965. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Sprains and strains, initial encounter.

Code Identity

ICD-10-CM Code
S66.912A
Billable Status
Yes — Valid for Submission
Code Describes
Strain of unspecified muscle, fascia and tendon at wrist and hand level, left hand, initial encounter
Short Description
Strain of unsp musc/fasc/tend at wrs/hnd lv, left hand, init
Parent Code
S66.912
Strain of unspecified muscle, fascia and tendon at wrist and hand level, left hand

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 CodeS66.912AStrain of unspecified muscle, fascia and tendon at wrist and hand level, left hand, initial encounter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Pain of bilateral hands
  • Pain of left hand
  • Pain of right hand
  • Repetitive motion disorder of bilateral hands
  • Repetitive motion disorder of left hand
  • Repetitive motion disorder of right hand
  • Strain of muscle of left hand
  • Strain of muscle of left wrist
  • Strain of muscle of wrist
  • Strain of tendon of hand
  • Strain of tendon of left hand
  • Strain of tendon of left thumb
  • Strain of tendon of left upper limb
  • Strain of tendon of left wrist
  • Strain of tendon of wrist
  • Strain of thumb tendon
  • Traumatic tear of tendon of hand
  • Traumatic tear of tendon of left hand
  • Traumatic tear of tendon of left wrist region
  • Traumatic tear of tendon of wrist region

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 INJ024
Sprains and strains, 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 S66.912A to ICD-9-CMHistory

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

ICD-9-CM
842.00 Sprain of wrist NOS
Approximate The match is approximate rather than exact.
ICD-9-CM
842.10 Sprain of hand NOS
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 S66.912AOverview

Is S66.912A a billable code?

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

What does the 7th character A in S66.912A mean?

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

What MS-DRG does S66.912A group to?

When strain of unspecified muscle, fascia and tendon at wrist and hand level, left hand, initial encounter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 562, 563, 963, 964, 965, with relative weights from 0.8955 to 2.7338 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of S66.912A?

Under the General Equivalence Mappings, strain of unspecified muscle, fascia and tendon at wrist and hand level, left hand, initial encounter converts to ICD-9-CM 842.00 (sprain of wrist NOS) and 842.10 (sprain of hand NOS). 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.