ICD code S90.412S – Left great toe abrasion, sequela

Key Takeaways

S90.412S codes abrasion of the left great toe, sequela – a late-effect encounter, not treatment of the original wound

The 7th character ‘S’ applies only when today’s visit treats a condition caused by the original abrasion, not the abrasion itself

Sequela codes must be sequenced after the code for the specific sequela condition (scar, pain, contracture) – not listed first

Pabau’s claims management tools support accurate diagnosis code submission and denial tracking for superficial injury codes

ICD-10 code S90.412S: Quick-reference summary

The table below captures the essential facts coders and billing staff need before using this code on a claim.

What S90.412S covers: Exact clinical meaning

S90.412S describes a sequela encounter for an abrasion of the left great toe. Breaking that down matters, because each word in the descriptor carries a coding decision.

• Abrasion: A superficial wound caused by friction against a rough surface. The skin surface is disrupted but the full dermis is not penetrated. An abrasion is not a laceration (which involves a cut), not a contusion (bruising without skin break), and not an open wound (which moves to the S91 category). If the chart says “scrape,” “road rash,” or “friction burn to skin,” the S90 abrasion codes apply.
• Left great toe: Laterality (left) and site specificity (great toe, the first toe) are both required. “Left foot” is not specific enough – that maps to S90.812S. “Left toe” without specifying which toe maps to S90.412S only if the great toe is documented. Any ambiguity in the medical record (“toe injury, left”) requires a query to the treating provider before code assignment.
• Sequela: The patient is not being treated for the original abrasion. They are being treated for a condition – scar contracture, chronic pain, delayed tissue healing – that arose as a direct consequence of the original abrasion. The original injury is healed or resolved; its aftermath is now the clinical problem.

Understanding the 7th character ‘S’ (sequela)

The 7th character extension is where most coding errors on S90.412 occur. The ICD-10-CM Official Guidelines for Coding and Reporting (Section I.B.10) define three encounter types for injury codes, and they are mutually exclusive at any given visit.

S90.412A vs S90.412D vs S90.412S: Which to use

The correct 7th character depends on what condition is being treated at this specific encounter, not on how much time has passed since the original injury.

The pivot point: Ask “is the abrasion still the problem being treated today?” If yes, use A or D. If the abrasion has healed and today’s problem is a consequence it left behind, use S. Time elapsed is a clue, not the rule. A patient can still be in a D encounter six months after injury if the wound has not healed. A patient can reach a sequela encounter in six weeks if the wound healed quickly but left a painful scar.

Codes commonly confused with S90.412S

Four codes account for the majority of laterality, site, and encounter-type substitution errors on S90.412S claims.

A query to the treating provider resolves most of these before code assignment. Never assume laterality or site specificity from the operative side, wound photo labels, or clinical context alone – the documentation must state it explicitly.

Inclusions, exclusions, and coding notes

The S90 category covers superficial injuries of the ankle, foot, and toes. Its scope is narrower than it looks.

• Included under S90: Abrasions, blisters, contusions, superficial foreign bodies, and insect bites that do not penetrate the full dermis of the foot or toe.
• Excluded – open wounds: Any wound that penetrates through the skin requires codes from the S91 range (open wound of foot and toes). Using an S90 code when the chart clearly describes a laceration or puncture is an accuracy error that also exposes the claim to audit.
• External cause codes (V00-Y99): An additional external cause code may be reported with S90.412S to capture how the original injury occurred (e.g. W22.8XXS for striking against or struck by an unspecified object, sequela). Whether this is required depends on payer policy and care setting. Medicare does not mandate external cause codes on outpatient claims, but some commercial payers do. Check the payer’s local coverage determinations before submitting without one.

Documentation requirements for S90.412S

Five elements must appear in the medical record before S90.412S can be supported on a claim. Missing any one of them is enough for a payer to deny or downcode.

1. Laterality – explicit: The word “left” must appear in the documentation. “Left hallux” and “left first toe” are acceptable. “Left foot, great toe area” is marginal. “Left toe” without specifying which toe is insufficient.
2. Site specificity – great toe: “Great toe,” “hallux,” or “first toe” must be documented. “Foot,” “toe,” or “digit” without further specificity is not sufficient for S90.412S.
3. Wound type – abrasion: The original injury must be documented as an abrasion, scrape, or friction wound. If the original injury was a laceration, contusion, or puncture, S90.412 is not the correct code family for the original encounter, and sequela coding must reference the correct original injury code family.
4. Causal link – sequela to original abrasion: The chart for the current sequela encounter must explicitly connect today’s condition to the previous abrasion. Phrases such as “scar tissue resulting from prior left great toe abrasion,” “hypertrophic scar, sequela of left hallux abrasion in [month/year],” or “neuropathic pain, late effect of left great toe abrasion” establish the required link. A note that simply says “left great toe pain” with no reference to prior injury does not support sequela coding.
5. Treating provider attestation: The clinical note must be signed and dated by the treating provider. Unsigned notes or notes attributed to ancillary staff without co-signature do not meet CMS documentation standards for physician services.

Coders who use submitting a clean claim frameworks before submission catch most of these gaps before they reach the payer.

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Payer requirements and claim denial prevention for S90.412S

S90.412S is a billable code accepted by Medicare, Medicaid, and most commercial payers. Acceptance does not mean automatic payment. These payer-side considerations apply consistently.

• Secondary code required for the sequela condition: Under ICD-10-CM sequela coding convention, S90.412S is not sequenced first. The code for the specific sequela condition – hypertrophic scar (L91.0), scar contracture, chronic pain (G89.29), or delayed healing – is listed as the principal or first-listed diagnosis. S90.412S follows as a secondary code to identify the original injury. Submitting S90.412S as the only diagnosis code, with no sequela condition code, is the single most common denial trigger for this code.
• Prior authorization: Sequela codes for superficial injuries generally do not require prior authorization. If the sequela condition itself (e.g. a planned scar revision procedure) requires authorization, that is driven by the procedure code, not the diagnosis code.
• POA indicator: Present on admission indicators apply to inpatient claims only. For outpatient and office claims, POA is not applicable.
• External cause code (payer-specific): Some commercial payers require a V00-Y99 external cause code on sequela encounters to link today’s claim to the original injury event. Review the payer’s LCD or billing guidelines before submitting without one.

Pabau’s claims management software tracks denial patterns by code, so practices can identify whether S90.412S claims are denying for a sequencing issue, a documentation gap, or a missing secondary code. For US practices, Pabau integrates with Claim.MD for electronic claims submission via Claim.MD, enabling real-time eligibility checks and ERA receipt before manual follow-up is needed.

Top denial reasons for S90.412S and how to fix them

Reviewing denial management workflows in your practice helps catch these patterns before they accumulate. When denials for S90.412S cluster around the same root cause, that signals a documentation or workflow fix, not a one-off correction. Understanding the specific denial codes in medical billing that accompany these rejections (CO-4, CO-16, CO-50) pinpoints whether the issue is coding, documentation, or medical necessity.

Code sequencing rules for S90.412S

Sequela coding follows a specific sequencing convention in ICD-10-CM. Getting the order wrong is itself a denial cause, even when both codes are correct individually.

Correct sequence: Code for the sequela condition first, then S90.412S.

Worked example: A patient returns four months after a left great toe abrasion. The abrasion has fully healed but left a painful hypertrophic scar that now limits footwear. The correct code sequence is:

1. L91.0 (Hypertrophic scar) – the condition being treated today, listed first
2. S90.412S (Abrasion, left great toe, sequela) – identifies the original injury that caused the scar, listed second

An external cause sequela code from the V00-Y99 range may be added as a third code if the payer requires it or the facility policy mandates external cause reporting. The CMS ICD-10-CM coding guidelines and the CDC/NCHS ICD-10-CM tabular list both confirm this sequencing convention under the sequela/late effects guidance in Section I.B.10.

ICD-9-CM crosswalk for S90.412S

ICD-9-CM lacked both the laterality specificity and the encounter-type granularity that ICD-10-CM provides. The approximate legacy equivalent for a toe abrasion was 924.3 (Contusion of toe), which grouped abrasions, contusions, and superficial injuries together without distinguishing left from right or great toe from lesser toes.

This crosswalk is approximate. The AAPC Codify ICD-10-CM lookup and ICD List both provide General Equivalence Mapping (GEM) data for legacy-to-current conversions. Never treat an ICD-9-to-ICD-10 crosswalk as exact – the structural difference in specificity between the two systems means a one-to-one mapping rarely exists.

Conclusion

S90.412S is a narrow, highly specific code – and that specificity is exactly what makes it vulnerable to documentation gaps and sequencing errors. The most expensive mistake practices make is submitting S90.412S as the only diagnosis code on a sequela encounter, when ICD-10-CM convention requires the sequela condition code to lead.

Pabau’s claims management tools surface denial patterns by code so practices can fix systemic sequencing and documentation issues before they repeat. To see how the workflow handles ICD-10 code entry and claim submission together, book a demo.

Continue your research

Need to understand how clearinghouse submission works for ICD-10 codes? Claim.MD clearinghouse guide explains how electronic claims reach payers and how ERA remittances return denial reasons.

Want to reduce denials across your coding workflow? Medical billing fundamentals covers the full revenue cycle from code entry to payment posting.

Looking for tools to validate eligibility before submitting sequela claims? Insurance eligibility verification outlines how real-time checks catch coverage gaps before submission.

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