S66.325A
Laceration of extensor muscle, fascia and tendon of left ring finger at wrist and hand level, initial encounter
S66.325A (also written S66325A) is a billable ICD-10-CM diagnosis code for laceration of extensor muscle, fascia and tendon of left ring finger at wrist and hand level, initial encounter. It is part of the FY2027 code set, effective October 1, 2026. It is one of the 540 codes in category S66 (Injury of muscle, fascia and tendon at wrist and hand level). Its 7th character, A, means initial encounter. Its coding notes include a Use additional code instruction, a Code also instruction and 7 Excludes2 entries.
7th character
Category S66 requires a 7th character.
Guidelines tips
From the FY2027 Official Guidelines. ICD10Ref adds no rules of its own.
The 7th character depends on whether the patient is in active treatment, not on who sees the patient. An aftercare Z code is not used for injury aftercare.
Each injury gets its own code unless a combination code exists, with the most serious injury first. Superficial injuries at the same site as a more severe injury are not coded. Injuries during medical care are coded as complications.
Use additional code
Add the listed code as a secondary code, if known.
Also from chapter/block level (1 note)
- code to identify any retained foreign body, if applicable (Z18.-)
Code also
Two codes may be needed to describe the condition. This note gives no sequencing order.
Excludes2
Not included here. Both codes may be reported if the patient has both conditions.
- Injury of extensor muscle, fascia and tendon of thumb at wrist and hand level (S66.2-)
- sprain of joints and ligaments of wrist and hand (S63.-)
Also from chapter/block level (5 notes)
- birth trauma (P10-P15)
- obstetric trauma (O70-O71)
Care settings
How CMS programs treat this code. These are CMS claim edits and list entries, not coverage or eligibility rules.
Home Health Primary
Accepted as the primary (principal) diagnosis on a home health claim. The Home Health Grouper assigns it to the Wound clinical group.
Source: CMS Home Health Grouper Software v07.2.26, effective October 1, 2026Hospital CC
Counts as a complication or comorbidity (CC) when reported as a secondary diagnosis on an inpatient claim. It does not count when the principal diagnosis is one of the 40 codes in its exclusion list. Some MS-DRGs also ignore a CC or MCC that defines the DRG.
Source: CMS MS-DRG Definitions Manual v44, effective October 1, 2026, Appendix CNotes
Also from chapter/block level (2 notes)
- 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.