ICD-10 code S66.527S: Laceration of intrinsic muscle, left little finger sequela

Key takeaways

ICD-10 code S66.527S means laceration of intrinsic muscle, fascia and tendon of the left little finger at wrist and hand level, sequela.

The sixth character carries the digit and the side, so S66.520 is the right index finger and only S66.527 is the left little finger.

S66.527S is billable in the FY2026 ICD-10-CM edition, effective October 1, 2025, and it is exempt from POA reporting.

Sequence the residual condition first and S66.527S second, as ICD-10-CM Official Guidelines section I.B.10 directs.

Practice management software like Pabau prompts providers to record laterality, injury date, and current deficit before the note leaves the room.

ICD-10 code S66.527S covers laceration of intrinsic muscle, fascia and tendon of left little finger at wrist and hand level, sequela. It applies once the laceration has healed and a lasting deficit remains. A patient who returns nine months after a glass injury, still unable to spread the little finger, is coded here.

The digit and the side live in the sixth character, and that is where this family is most often miscoded. S66.520 is the right index finger. Only S66.527 is the left little finger.

ICD-10 code S66.527S at a glance

S66.527S is a billable, specific ICD-10-CM code. The FY2026 edition took effect on October 1, 2025, and the code has not been revised since ICD-10-CM went live in 2015.

The descriptor above is the wording in the ICD-10-CM tabular list, which NCHS at the CDC maintains for the United States. You can confirm it in the CDC/NCHS ICD-10-CM web tool. CMS publishes the annual code files and the MS-DRG grouper that consumes them.

What S66.527S describes

S66.527S covers a healed laceration involving three tissue types in the left fifth digit: intrinsic muscle, fascia, and the tendons of those intrinsic muscles. The injury site is the wrist and hand level rather than the digit itself. The patient no longer needs wound care, but a deficit traceable to that laceration remains.

One distinction decides this code more often than laterality does. S66.5- is the intrinsic group only. A cut to a long flexor or extensor tendon running down from the forearm belongs elsewhere. The excludes-notes section below sets out where.

Intrinsic muscles that act on the little finger

Intrinsic muscles begin and end inside the hand. For the fifth digit that means the hypothenar group: abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi. The third palmar interosseous and the fourth lumbrical also act on this finger.

Damage here shows up as loss of finger spread, weak small-object pinch, and poor coordination in the ulnar side of the hand. Those are the deficits a sequela note should name, because they are what separates S66.527S from a healed wound with no residual effect.

Fascia at wrist and hand level

The palmar aponeurosis, the hypothenar fascia, and the proximal part of the digital flexor sheath are the fascial structures this code reaches. Fascial laceration matters clinically because scarring can tether the tissue planes around the hypothenar muscles. When that happens, code the scar or contracture as well, then report S66.527S after it.

Tendons included in this code

The tendons covered here belong to the intrinsic muscles above. That includes their insertions into the extensor hood and lateral bands of the fifth digit. They are short, they sit inside the hand, and they are easy to confuse with the extrinsic tendons crossing the same territory.

If the operative or emergency note names the flexor digitorum superficialis or profundus, the correct family is S66.1- rather than S66.5-. If it names the extensor digitorum slip to the little finger, the family is S66.3-.

Documenting which structure was cut is what keeps the coder out of the wrong subcategory. A structured clinical record makes that operative detail easy to retrieve years later.

Where S66.527S sits in the code hierarchy

Each character narrows the code by one decision: body region, then structure, then injury type, then digit and side, then encounter.

• S00-T88 injury, poisoning and certain other consequences of external causes.
• S60-S69 injuries to the wrist, hand and fingers.
• S66 injury of muscle, fascia and tendon at wrist and hand level.
• S66.5 injury of intrinsic muscle, fascia and tendon of other and unspecified finger at wrist and hand level.
• S66.52 laceration, as opposed to strain (S66.51), unspecified injury (S66.50), or other injury (S66.59).
• S66.527 left little finger, the digit and side that the sixth character fixes.
• S66.527S sequela, the encounter type that the seventh character fixes.

Only the last line is billable. S66.5, S66.52, and S66.527 are all non-specific codes that exist for navigation, and a claim carrying any of them will reject.

Understanding the seventh character: S for sequela

The seventh character records which encounter you are billing, not how severe the injury was. Getting it wrong is a common denial trigger on hand injury follow-up claims. Every code in category S66 takes one of three characters.

A sequela is a residual condition that remains after the acute phase has ended. ICD-10-CM Official Guidelines section I.B.10 sets the sequencing: code the residual condition first, then the sequela code. That means S66.527S rarely appears alone on a claim.

S66.527A vs S66.527D vs S66.527S: choosing the right encounter

• Use S66.527A when the wound is new and the clinician is treating it. First presentation, first repair, and the first assessment of the laceration all sit here.
• Use S66.527D while the injury is still healing. Suture removal, dressing changes, and splint adjustments after the repair are routine subsequent care.
• Use S66.527S once healing is complete and a deficit persists. Restricted little finger spread from tendon adhesion, or pain that began with the laceration, both qualify.

A quick test settles most cases. Wording such as healing wound in the assessment points to the D character. Wording such as sequela of prior laceration, or post-repair tendon adhesion, points to the S character. That distinction matters most in physical therapy practices that pick up grip rehabilitation months later.

Related and sibling codes

Most miscoding in this family is a one-digit slip. The table below holds the codes a coder is most likely to need next, with the exact descriptor for each.

Sixth-character finger map for the S66.52- series

The sixth character runs index to little, right before left, then two residual values. Read it once and the whole family becomes predictable.

Two errors follow from misreading this column. Picking S66.520S puts the claim on the right index finger, a different digit on the other hand. Picking S66.526S keeps the digit but flips the side. The same pattern runs through the flexor family at S66.12- and the extensor family at S66.32-. So S66.127 and S66.327 are also the left little finger.

Excludes notes and tabular instructions that apply to S66.527S

S66.527S carries no notes of its own. It inherits five from the levels above it, and every one of them changes what else goes on the claim.

• Code also, at category S66: any associated open wound, S61.-. A laceration usually breaks the skin, so an S61 code often belongs on the same claim.
• Type 2 Excludes, at category S66: sprain of joints and ligaments of wrist and hand, S63.-. Report both codes when both injuries are documented, so a wrist sprain such as S63.501D sits alongside S66.527S.
• Type 2 Excludes, at subcategory S66.5: injury of intrinsic muscle, fascia and tendon of thumb at wrist and hand level, S66.4-. A thumb injury alongside the little finger needs its own code.
• Type 2 Excludes, at block S60-S69: burns and corrosions T20-T32, frostbite T33-T34, and venomous insect bite or sting T63.4.
• Chapter note, at S00-T88: add a secondary external cause code from Chapter 20 to show how the injury happened. Add Z18.- as well if a foreign body was retained.

Note what is absent here. There is no Excludes1 anywhere in the chain above S66.527S, so nothing on this list is a never-code-together pairing.

Type 2 Excludes means the opposite. The two conditions can coexist, and each gets its own code when the record supports it. A cut nerve or blood vessel in the same hand works the same way, so S64.498S or S65.919S can sit on the claim too.

Clinical terminology that resolves to this code

ICD-10-CM publishes no approximate synonyms or inclusion terms under S66.52-, so the tabular list gives you nothing beyond the descriptor itself. Coders have to work from what providers actually write. These are the phrasings that resolve to S66.527S.

• Sequela of laceration of left little finger intrinsic muscle, fascia and tendon
• Late effect of left small finger intrinsic muscle laceration
• Left pinky hypothenar muscle laceration, healed with residual weakness
• Left fifth digit palmar fascia laceration at hand level, sequela
• Residual abduction deficit after left little finger laceration repair
• Post-repair intrinsic tendon adhesion, left little finger

None of these is a separate code. Each one still needs three confirmations before you assign S66.527S. The digit is the little finger, the side is left, and the encounter treats a residual effect rather than the wound.

Documentation requirements for S66.527S

A sequela claim lives or dies on the causal link. The note has to connect today’s complaint to a specific past laceration, and it has to name the digit and the side. Five elements carry most of that weight.

• The prior laceration, with a date: state that the current problem follows a laceration of the left little finger. A month and year is enough, and it is what an auditor looks for first.
• The current residual effect: name it specifically. Tendon adhesion, loss of finger abduction, muscle contracture, or scar tethering all work. Left hand pain on its own does not.
• Digit and side: left little finger, written out. A note that says hand or finger without either detail forces the unspecified code S66.529S.
• The structure and the level: record whether intrinsic muscle, fascia, tendon, or a combination was cut, and confirm the wrist and hand level. This is what separates S66.5- from S66.1- and S66.3-.
• Healing status: say that the acute phase is over. Wording such as the wound has healed and the patient now presents with is what justifies S over D.

Digital intake forms can collect the injury date, the affected side, and the current deficit before the clinician walks in. Clinical documentation software then keeps those answers in the note itself, which cuts the query list a coder sends back after the visit.

Billing and reimbursement guidance for a sequela claim

S66.527S is billable, but payment turns on sequencing and support rather than on the code itself. Payers look hard at these claims because the injury they name has already healed. Six points decide most outcomes.

• Sequence the residual condition first: common partners are M62.442 contracture of muscle in the left hand and M62.542 muscle wasting in the left hand. M25.642 stiffness of the left hand, M79.645 pain in left fingers, and L90.5 scar conditions also qualify. S66.527S follows whichever one leads.
• Never report an acute character alongside S: S66.527A and S66.527D both describe active treatment. Pairing either with S66.527S reads as a documentation conflict.
• Carry S through the external cause code: the Chapter 20 code takes the sequela character too. An A on the external cause code beside an S on the injury code is an easy edit to trip.
• Expect no fee schedule entry: an ICD-10-CM diagnosis code carries no payment rate. The Physician Fee Schedule prices the CPT and HCPCS services you bill, and S66.527S supports medical necessity for them.
• Know the inpatient grouping: S66.527S groups to MS-DRG 604 or 605 under MDC 09, trauma to the skin, subcutaneous tissue and breast. Most sequela encounters are outpatient, so this rarely applies.
• Check therapy caps before scheduling: some plans limit rehabilitation visits per diagnosis per year. Confirm the limit before booking a long course of occupational therapy or hand rehab.

Denials on sequela claims are almost always documentation problems wearing a coding costume. When the note names the original injury, roughly when it happened, and the deficit left behind, the claim usually holds. Capturing those three details during the visit costs far less staff time than reworking a denial later.

How Pabau supports accurate ICD-10 sequela coding

Sequela coding fails at the documentation stage rather than the coding stage. When a note never links the old laceration to today’s deficit, the coder must choose between an unspecified code and a query. Both cost money.

Practice management software like Pabau handles that upstream. Structured note templates prompt the provider for encounter type, injury history, and laterality while the patient is still in the room. The coder then works from a complete chart instead of chasing one.

Pabau’s client record keeps every encounter for a patient on one timeline, so the original repair and today’s rehab visit sit side by side. A coder can then prove the causal relationship without opening a second system.

Pabau Scribe, our AI scribe, drafts the note from the consultation itself. Anatomical detail stays in the record rather than in the clinician’s memory.

On the billing side, Pabau’s claims management software submits and tracks claims from the same record the clinician documented in. Nothing gets retyped, so the diagnosis codes on the claim match the note behind them.

Cut sequela denials with better documentation

Pabau’s clinical records, intake forms, and claims tools help your team capture laterality, injury history, and the current deficit at the point of care. Codes like S66.527S then submit right the first time.

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Conclusion

The hard part of S66.527S is not the seventh character. It is the sixth. Two coders can agree the encounter is a sequela and still land on different digits. S66.520 through S66.529 look almost identical on a screen. Read the sixth character against the finger map before you submit, every time.

Get that right and the rest follows. Sequence the residual condition first and S66.527S second, then give the external cause code the same seventh character. Add a note that names the injury date and the deficit left behind.

Practices that build those prompts into the visit stop losing time to queries. Book a demo to see how Pabau keeps injury history, laterality, and claims in one place.

Continue your research

Coding the open wound alongside the cut muscle? ICD-10 code S61.311S covers a left index finger laceration with nail damage from initial encounter to sequela.

Was the cut structure an extrinsic flexor? ICD-10 code S56.125S covers flexor tendon laceration of the right ring finger at forearm level.

Sprain rather than a laceration? ICD-10 code S63.615S walks through sequela sequencing for an unspecified sprain of the left ring finger.

Same digit, but the bone rather than the muscle? ICD-10 code S62.606K explains nonunion coding for a right little finger fracture.

Muscle laceration sequela at another site? ICD-10 code S76.129S applies the same sequela rules to a quadriceps muscle laceration.

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