2026 ICD-10-CM Diagnosis Code S66.412SStrain of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level, sequela
S66.412S is a billable ICD-10-CM diagnosis code for strain of intrinsic muscle, fascia and tendon of left thumb 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 562 through 563. The code is exempt from POA reporting. Coders also document this condition as injury of intrinsic muscle of left thumb. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Injury, sequela.
Code Identity
Code Classification
Present on Admission (POA)Billing
S66.412S 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 left thumb
- Injury of intrinsic muscle of thumb
- Strain of intrinsic muscle of left hand
- Strain of intrinsic muscle of left thumb
- Strain of intrinsic muscle of thumb
- Strain 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 2026, published by CMS and the National Center for Health Statistics.
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
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
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Convert S66.412S to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About S66.412SOverview
Is S66.412S a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report strain of intrinsic muscle, fascia and tendon of left thumb 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 S66.412S mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the strain of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level itself has resolved, not the original event.
What MS-DRG does S66.412S group to?
When strain of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level, sequela is the principal diagnosis on an inpatient stay, it groups to MS-DRG 562, 563, with relative weights from 0.8955 to 1.4248 depending on complications. Higher weights mean higher Medicare reimbursement.
Is S66.412S 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 strain of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level, sequela on inpatient claims.
What is the ICD-9 equivalent of S66.412S?
Under the General Equivalence Mappings, strain of intrinsic muscle, fascia and tendon of left thumb at wrist and hand level, sequela converts to ICD-9-CM 905.7 (late effec sprain/strain). 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.
