ICD-10 code S64.31XS: Injury of digital nerve of right thumb, sequela

Key takeaways

S64.31XS is a billable ICD-10-CM code for injury of the digital nerve of the right thumb, coded as a sequela.

The 7th character ‘S’ applies only when the current condition is a documented late effect of a prior thumb nerve injury.

Sequela claims take two codes. The late-effect condition is sequenced first, then S64.31XS as the causative injury code.

Sibling codes S64.31XA and S64.31XD cover active treatment. Mixing them with the sequela code triggers denials.

Practice management software like Pabau captures ICD-10-CM codes inside the clinical note, so the sequela pairing is not missed at billing.

ICD-10 code S64.31XS is a billable ICD-10-CM diagnosis code for injury of the digital nerve of the right thumb, sequela. It is valid for fiscal year 2026, effective for discharges and patient encounters on or after October 1, 2025.

Use it when a patient presents with a documented late effect of a prior digital nerve injury to the right thumb. The active phase of treatment must already have concluded.

One rule decides most S64.31XS claims. The code never travels alone. The residual condition is sequenced first, and S64.31XS follows as the causative injury code.

Sequela is also the phase of care coders get wrong most often. The switch away from active treatment depends on what the record says, not on how much time has passed.

Code details at a glance

The table below summarizes the key metadata for S64.31XS, as confirmed by the CMS FY2026 tabular list and the CDC/NCHS ICD-10-CM official web tool.

Code hierarchy

Knowing where S64.31XS sits in the ICD-10-CM hierarchy helps coders pick the right parent category and apply the 7th character correctly. The full path from chapter to billable code is below.

S64.31 is not billable on its own. It serves as the parent code. The placeholder character “X” fills the 6th character position, because no further anatomical detail exists at that level.

That makes the full seven-character code S64.31XS the only billable form for a sequela encounter. For the placeholder rules themselves, use the Official Guidelines for Coding and Reporting, published annually by the NCHS.

What the 7th character ‘S’ means

ICD-10-CM uses 7th character extensions on injury codes to record the episode of care. For codes in the S60-S69 block, three options apply.

Key distinction: The 7th character “S” does not mean the injury is ongoing. It means the original injury has resolved and left a residual condition behind.

Per the ICD-10-CM Official Guidelines for Coding and Reporting (Section I.C.19), sequela coding takes two codes. The sequela condition comes first, followed by the injury code carrying the “S” extension. That second code is a frequent omission on submitted claims.

Sibling codes: S64.31XA and S64.31XD

All three codes under S64.31 carry the same anatomical detail and differ only in the episode of care. Choosing the wrong sibling is a common audit trigger. It happens most often when S64.31XS is applied to a patient who is still in active treatment.

Hand injuries generate a long tail of visits, so the encounter character has to change as the phase of care does. Rehab-heavy specialties feel this most, since a thumb nerve laceration can run through therapy for months. A practice running on physical therapy EMR or occupational therapy software can tie each visit type to the right 7th character.

• S64.31XA, initial encounter: Use it while the patient is receiving active treatment for the thumb nerve injury for the first time. Emergency visits, specialist consultations, and the first surgical repair all sit here.
• S64.31XD, subsequent encounter: Use it at follow-up visits where active treatment for the same injury continues. Wound re-evaluations, splint checks, and medication adjustments during healing fall here.
• S64.31XS, sequela: Use it once the original injury has healed or reached maximum medical improvement. The patient still has a residual condition caused by that injury, such as persistent paresthesia or reduced grip strength. Treatment at this visit targets the late effect.

Clinical description: Injury of digital nerve of right thumb

The digital nerves of the thumb are the paired proper palmar digital nerves running along its medial and lateral borders. They supply sensation to the volar surface of the thumb and to the nail bed.

Lacerations, crush injuries, and traction mechanisms cause most of these injuries, usually at work, in sport, or as a surgical complication. Damage to bone is coded separately, as with S62.630K for a displaced distal phalanx fracture.

When a right thumb digital nerve injury leaves a late effect that brings the patient back, that residual condition is what S64.31XS captures. Common sequelae include:

• Persistent numbness or paresthesia along the thumb’s volar surface
• Cold intolerance in the thumb
• Diminished two-point discrimination
• Chronic pain or allodynia at the original injury site
• Neuroma formation causing focal tenderness
• Reduced fine motor function in the right hand

The line between a sequela and an ongoing acute injury matters clinically and administratively. A patient 14 months past a laceration with persistent numbness, no open wound, and no acute inflammation is a sequela. A patient three weeks post-surgery who still needs wound care sits in the subsequent encounter phase, coded S64.31XD.

Approximate synonyms and alternate descriptions

The following terms map to S64.31XS in clinical documentation and coding lookups. Coders will meet these phrases in physician notes and should read them as valid documentation for this code:

• Sequela of injury of digital nerve of right thumb
• Late effect of right thumb digital nerve injury
• Right thumb nerve injury, late effect
• Chronic sequela, digital nerve right thumb
• Residual deficit following digital nerve injury of right thumb
• Post-traumatic neuropathy, right thumb digital nerve
• Sequelae of nerve injury at wrist and hand level, right thumb

These synonyms come from the approximate synonym index maintained in the CMS ICD-10-CM annual update files. When a note uses a term that is not on the list, confirm the anatomical detail before applying S64.31XS. Right thumb, digital nerve, and residual status all have to be present.

Documentation requirements for S64.31XS

Sequela coding is the ICD-10-CM category most often returned in post-payment audits. Three documentation elements are non-negotiable when using S64.31XS:

• Prior injury record: The chart must document the original digital nerve injury of the right thumb, including date, mechanism, and initial findings. A reference to earlier treatment records, a surgical note, or an emergency department report satisfies this.
• Nexus statement: The clinician has to link the current condition to the prior injury in words. “The patient’s thumb paresthesia is a sequela of the digital nerve laceration sustained on [date]” is the minimum.
• Current late-effect condition: The visit note must name the residual condition being evaluated or managed, such as paresthesia, numbness, neuroma, or cold intolerance. The word “sequela” on its own does not suffice.

Per AAPC ICD-10-CM coding resources, S64.31XS is reported as an additional code after the code for the late-effect condition. If the patient has post-traumatic neuralgia of the right thumb as a sequela, the neuralgia code leads and S64.31XS follows. Practices with HIPAA-compliant documentation workflows are better placed to capture that pairing while the patient is still in the room.

ICD-9-CM crosswalk

For historical billing review, payer crosswalk analysis, or legacy system mapping, the ICD-9-CM equivalents for S64.31XS are shown below. Per the General Equivalence Mappings published in the CMS ICD-10 transition files, there is no precise one-to-one match. ICD-9-CM did not use encounter-specific 7th character extensions.

Both ICD-9-CM codes are approximate equivalents only. The sequela concept in ICD-10-CM mapped loosely to ICD-9-CM late effect codes in the 9xx series, with no encounter-type differentiation. The WHO ICD-10 browser gives the international equivalent for work outside the US system.

How to use S64.31XS in medical billing and coding

Getting sequela coding right takes more than knowing the code exists. Two rules prevent most of the denials that follow when it is applied loosely.

Sequence the codes correctly

S64.31XS is not the primary diagnosis for the visit. The late-effect condition is sequenced first, and S64.31XS is listed as the additional causative injury code.

Reversing that order is the most common reason hand nerve sequela claims are rejected at adjudication. The same sequencing applies to other healed hand injuries, including S63.615S.

Do not apply the ‘S’ extension prematurely

Coders sometimes switch to S64.31XS as soon as a patient looks to have plateaued. The record has to state that the injury has resolved or reached maximum medical improvement.

While active treatment continues, S64.31XD stays correct and S64.31XS is wrong. Payers treat the early switch as potential upcoding, so it is worth a second look before submission.

How Pabau keeps sequela coding accurate at the point of care

In most practices, sequela claims are coded after the visit is over. A coder opens the finished note and hunts for three things. Those are the prior injury, the nexus statement, and the current late effect. One of them is usually missing, so the claim goes out a code short or waits in a query queue.

Practice management software like Pabau moves that decision into the note instead. Pabau’s claims management software supports structured diagnosis capture alongside the clinical record, so the sequence can be checked before the claim is submitted.

The prior injury also has to be reachable at the moment of coding. Patient record management keeps earlier treatment notes, photos, and operative reports on the same client file. The causal documentation then sits in front of whoever codes the visit.

The outcome is fewer single-code sequela submissions, fewer payer queries, and less rework for the billing team at month end.

Capture sequela codes while the patient is still in the room

Pabau puts ICD-10-CM code capture next to the clinical note, so the late-effect condition and the causative injury code are recorded together. Practices submit cleaner claims and spend less time reworking denials.

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Conclusion

S64.31XS is a small code with a strict evidentiary standard. It says that an injury is over and that something it caused is not. If the note cannot show both halves of that story, the code is the wrong one, whatever the calendar says.

The practical move is to settle the encounter character while the patient is in front of you, and to write the nexus sentence then. A coder inherits that decision instead of reconstructing it later.

Do that consistently and the paired late-effect code stops going missing, which is where most of these denials come from. Book a demo to see how Pabau captures ICD-10-CM codes and sequela documentation inside the clinical note.

Continue your research

Coding another hand injury that has healed? S63.615S applies the same sequela logic to a finger sprain.

Not sure the patient has left active treatment yet? S63.295D shows how the subsequent encounter character works in hand injuries.

Need the sequela rules for fracture care? S72.411S covers late-effect documentation after a femur fracture.

Coding a late effect after soft tissue trauma? S76.129S walks through the same two-code pairing for a muscle laceration.

Want the record to show when active treatment ended? Our patient discharge form gives you a dated close-out for the injury episode.

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