ICD-10 Code S43.121S: Right AC joint dislocation, sequela

Key Takeaways

S43.121S is a billable ICD-10-CM code for dislocation of the right acromioclavicular joint with 100%-200% displacement, sequela encounter

The 7th character S designates a sequela: a late-effect condition arising directly from the original AC joint dislocation, coded after active treatment is complete

Sequela coding requires two codes: the sequela condition sequenced first, followed by S43.121S; do not use S43.121S during active treatment

Pabau’s integrated clinical record and claims management software helps providers document laterality, displacement severity, and encounter type at the point of care

ICD-10 Code S43.121S: Code at a glance

Coders dealing with acromioclavicular joint injuries frequently need to distinguish between active treatment and late-effect visits. ICD-10 coding reference pages exist for many conditions, but AC joint codes carry specific displacement and laterality sub-classifications that trip up even experienced billers. ICD-10 Code S43.121S covers one of the most specific: dislocation of the right acromioclavicular joint, 100%-200% displacement, sequela encounter, valid for fiscal year 2026.

S43.121S became effective October 1, 2025 under the FY2026 ICD-10-CM update cycle. It is valid for HIPAA-covered transactions and can be submitted as a principal or secondary diagnosis code, subject to sequela sequencing rules. This reference covers the full code breakdown, 7th character guidance, hierarchy, related codes, and documentation requirements.

What does ICD-10 Code S43.121S mean?

Each segment of S43.121S carries clinical meaning. Breaking the code down by character set explains both the anatomy and the billing scenario it covers.

• S43: Category for dislocation and sprain of joints and ligaments of the shoulder girdle (S40-S49 range)
• S43.1: Dislocation of acromioclavicular joint (narrows to the AC joint specifically)
• S43.12: Dislocation with 100%-200% displacement (distinguishes severity from less-than-100% and greater-than-200%)
• S43.121: Right acromioclavicular joint (laterality specified)
• S43.121S: Sequela encounter (7th character S indicates a late effect of the original injury)

The 100%-200% displacement threshold corresponds clinically to a Grade III-IV AC separation in surgical classification systems. At this severity level, the coracoclavicular ligaments are fully disrupted. Providers coding shoulder injuries in sports medicine software environments encounter this range regularly when treating athletes with high-grade AC injuries that have progressed past the acute phase.

Understanding the 7th character: sequela (S)

The 7th character is the most clinically significant element of S43.121S. It determines which phase of care the encounter represents, and selecting the wrong one is a common reason for claim denial or audit flags.

All three S43.121 variants share the same anatomical description. The 7th character alone distinguishes the encounter type.

When to use S43.121S vs S43.121A vs S43.121D

Sequela (S) is not interchangeable with subsequent encounter (D). A subsequent encounter means the original injury is still being treated. A sequela means the original injury has resolved, but a new condition has developed as its direct result.

Per the CMS ICD-10-CM Official Guidelines, when coding sequela, the sequela condition is sequenced first, and the injury code with the 7th character S follows. Reversing the order is a sequencing error and will cause claim issues.

ICD-10-CM code hierarchy and parent codes

S43.121S sits within the S00-T88 injury block. Understanding the full hierarchy helps coders navigate related codes and avoid category-level errors. For broader context on how ICD-10 trauma code hierarchies are structured, see our reference on ICD-10 trauma code hierarchy.

Related ICD-10 codes for AC joint injuries

The S43.12x and S43.11x sub-classifications cover the full AC joint dislocation family by laterality and displacement severity. Providers coding both shoulders or billing for different severity grades will encounter these sibling codes regularly. Practices using chiropractic software with integrated diagnosis coding often need to navigate all three displacement categories.

Append the appropriate 7th character (A, D, or S) to any base code in the table. For example, S43.122S covers the same condition as S43.121S but on the left shoulder. Use the CDC/NCHS ICD-10-CM web tool to verify current code descriptions and validate sub-classifications against the official tabular list.

Distinguishing AC joint dislocation from AC joint sprain

One of the most common coding errors in shoulder girdle injuries is applying a sprain code (S43.5x) when the diagnosis supports a dislocation code (S43.12x). The distinction matters: payers treat them differently, and the documentation threshold differs between the two.

If imaging documentation states a specific displacement percentage, the dislocation code family (S43.12x for 100%-200%) is correct. If the note reads “AC joint sprain” without displacement measurement, S43.5x applies. Coders should query the provider when the note uses “separation” without quantifying the displacement, as this term is used informally for both conditions.

Documentation requirements for S43.121S

Supporting S43.121S requires more than the diagnosis alone. The clinical record must establish three elements for the code to survive audit review. Practices building structured encounter documentation in their claims management software can embed these prompts directly into the workflow.

• Laterality: The record must explicitly state “right” acromioclavicular joint. Bilateral or unspecified documentation does not support S43.121S.
• Displacement percentage: Imaging or clinical measurement must document 100%-200% displacement. The note should reference the measurement method (radiographic stress views are standard).
• Sequela linkage: The provider note must establish a causal connection between the current complaint and the prior dislocation. Language like “chronic shoulder instability as a sequela of [date] AC joint dislocation” satisfies this requirement.
• Original injury history: The medical record should reference when the original dislocation occurred. Coders relying on clinical record documentation systems benefit from having the original encounter date accessible within the same patient file.
• Sequela condition code: Per CMS guidelines, a code for the nature of the sequela is required and must be listed before S43.121S on the claim.

For reference on how the AAPC ICD-10-CM code lookup presents documentation guidance alongside code descriptions, cross-check the official tabular list notes against your payer’s local coverage determination. Physical therapy EMR workflows that carry forward prior injury history make the sequela linkage documentation far easier to produce at follow-up visits.

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Applicable To notes and index references

The ICD-10-CM Alphabetic Index provides multiple entry paths that lead to the S43.121 base code. Coders using index-first lookup (rather than direct code search) should be familiar with these routes. For broader context on ICD-10 diagnostic coding conventions, the WHO ICD-10 browser explains the classification structure behind the S43 category.

• Dislocation, acromioclavicular (joint) — navigate to displacement sub-classification, then to laterality
• Separation, acromioclavicular joint — cross-reference leads to S43.1x family
• Late effect, dislocation, shoulder — routes to sequela codes within S43
• Sequela, dislocation, acromioclavicular joint — direct index path to S43.121S with 7th character S

The Applicable To note at the S43 category level confirms that “acromioclavicular joint separation” is indexed under dislocation, not sprain. This supports using the S43.12x family when the clinical documentation uses separation language alongside displacement measurement. Occupational therapy providers managing shoulder rehabilitation cases will find this distinction relevant when coding for late-stage functional recovery. For occupational therapy software users, embedding index reference paths into documentation templates reduces lookup time at claim preparation.

Conclusion

Accurate use of ICD-10 Code S43.121S depends on three things: confirming the encounter is truly a sequela (not an active or follow-up visit), documenting the causal link between the current condition and the original AC dislocation, and sequencing the sequela condition code first on the claim. Missing any one of these steps creates claim exposure.

Pabau’s integrated sports medicine and orthopaedic practice tools carry clinical documentation through to billing without manual re-entry. Laterality, displacement severity, and encounter type captured during the consult flow directly to the claim, reducing the coding errors that sequela codes are especially prone to. To see how Pabau handles structured injury documentation across specialties, read our guide on compliance requirements for physiotherapy clinics or speak to the team.

Continue your research

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Managing compliance requirements for musculoskeletal and physical therapy practices? Mandatory compliance for physiotherapy clinics covers the documentation and regulatory obligations relevant to shoulder injury management.

Want to see how Pabau handles clinical records for sports medicine and orthopaedic workflows? Pabau’s client record feature keeps prior injury history, encounter dates, and laterality documentation in one accessible place for every follow-up visit.

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