ICD code S52.221N – Displaced transverse fracture of shaft of right ulna

Key takeaways

S52.221N is the billable ICD-10-CM code for a displaced transverse fracture of the right ulna shaft. It applies at a subsequent encounter for an open type IIIA, IIIB, or IIIC fracture with nonunion.

The 7th character N is valid only when the record documents both a Gustilo type III open fracture and nonunion.

Parent code S52.221 carries no 7th character, so payers reject it outright. Use N only at follow-up visits where nonunion is confirmed.

A missing Gustilo subtype at the initial encounter rules out N at every later encounter, so query it early.

Practice management software like Pabau flags missing documentation before submission, so orthopedic teams send cleaner fracture claims.

ICD-10 Code S52.221N: Definition and clinical description

ICD-10 Code S52.221N identifies a displaced transverse fracture of the shaft of the right ulna.

It applies at a subsequent encounter, where the fracture was classified as an open type IIIA, IIIB, or IIIC and has since developed nonunion. It is a fully billable ICD-10-CM diagnosis code, valid for the FY2026 edition and effective October 1, 2025.

The clinical picture behind the code is a severe open forearm fracture that has failed to heal. This reference covers the code structure, the Gustilo criteria, and the definition of nonunion. It also covers the documentation each element needs and the rest of the S52.221 family.

Code details at a glance

Use the table below for a quick reference to the key attributes of S52.221N before diving into the clinical detail.

Breaking down the code: S52.221 and the 7th character N

Every character in S52.221N carries clinical meaning. Misreading any segment produces a code that points to a different fracture, encounter type, or healing status entirely.

The full 7th character set for S52.221 is large. Coders commonly confuse N with adjacent characters. The table below maps all encounter/healing-status options so you can verify the right selection against what is documented.

Laid out as a grid, the same set is far easier to check. The wound status runs down one axis and the healing status runs across the other.

Three conditions must all be true for S52.221N to be correct. Miss any one of them and a different 7th character applies.

• The fracture involves the right ulna shaft in a displaced transverse pattern.
• The encounter is a follow-up visit, not the original treatment visit.
• The open fracture was documented as Gustilo type IIIA, IIIB, or IIIC, with nonunion confirmed.

Understanding the Gustilo classification (types IIIA, IIIB, IIIC)

The Gustilo-Anderson classification is the accepted grading system for open fracture severity. Gustilo and Anderson described it in 1976, and it was later refined to add the type III subcategories. For S52.221N, the physician must document one of the three type III subtypes. The ICD-10-CM tabular does not accept a generic “type III” without a subtype for 7th character selection.

The Gustilo subtype has to appear in the operative report or clinical note from the initial encounter. Coders cannot infer the subtype from wound size alone.

If the original record says only “open fracture” with no Gustilo classification, ICD-10-CM Official Guidelines Section I.C.19.c defaults the fracture to closed. That means 7th character A, D, G, K, P, or S, depending on the encounter type. A missing classification at the initial encounter rules out S52.221N at every subsequent encounter.

What counts as nonunion, and when does it apply?

Nonunion means the fracture has failed to heal within the expected timeframe, with no radiographic evidence of bridging callus or progressive healing. A fracture is generally considered nonunion when healing has not occurred after roughly six months. The treating physician makes that call from imaging and clinical assessment, since ICD-10-CM guidelines set no fixed timeframe.

Distinguishing nonunion from the other two abnormal healing statuses is essential for 7th character selection. The wrong character produces a billable but clinically inaccurate code, which can trigger a medical necessity audit. Accurate clinical notes at each follow-up visit are the most reliable defense against coding disputes and post-payment reviews.

Malunion (7th character R) and nonunion (7th character N) are mutually exclusive. Malunion implies healing has occurred, just improperly. Nonunion means no consolidation. Reviewing the imaging report alongside the physician note at each encounter is the most reliable way to confirm which status applies.

Subsequent encounter: What the N suffix means for billing

Claims for orthopedic fracture follow-up care are among the most frequently denied for incorrect encounter-type coding. The “subsequent encounter” designation covers any visit after the patient has received active, definitive treatment and has moved into routine care. It is not a count of visits.

That includes ongoing monitoring, physical therapy referrals, cast changes, and complication management such as nonunion treatment. Correct encounter-type coding also reduces the automated rejections triggered by conflicting date-of-service logic.

Understanding medical billing fundamentals for traumatic injury codes helps practices recognize when the encounter type shifts. Clinical context decides that transition, not the calendar date. Once the patient enters a phase of routine monitoring or complication management, subsequent encounter codes apply.

• Initial encounter (A, B, C): Use during active, definitive treatment for the fracture. That includes emergency care, surgical fixation, and casting at the first treating facility.
• Subsequent encounter (D through R): Use for follow-up visits once active treatment is underway. That covers cast removal, hardware removal, physical therapy oversight, and nonunion management.
• Sequela (S): Use for late effects of a healed fracture, such as post-traumatic arthritis developing years after the injury resolved.

Laterality: Right, left, and unspecified ulna

S52.221N specifies the right ulna. Displaced transverse ulna shaft fractures split across three codes by side. Payers frequently reject the unspecified-laterality option when the record makes the side clear.

Use S52.223N only when the clinical documentation genuinely does not specify which arm was injured. Payers including Medicare apply medical necessity edits that flag laterality-unspecified codes when the claim includes procedures that are anatomically specific. The site of surgery or casting documented in operative or procedure notes typically makes laterality determinable.

Documentation requirements for accurate S52.221N coding

Clean claims for ICD-10 Code S52.221N depend on documentation that covers every element of the code description. Missing a single element forces the coder to a less specific code, which may not support medical necessity for the billed procedures. Build the elements below into the encounter template, so none of them has to be reconstructed later.

• Laterality: Right or left ulna must be explicitly documented.
• Fracture pattern: Transverse fracture specifically (not oblique, comminuted, or spiral).
• Displacement: Displaced vs nondisplaced must be stated — nondisplaced transverse ulna shaft fractures code to S52.224 (right) or S52.225 (left).
• Open vs closed: The record must state that the fracture was open. Undocumented, it defaults to closed under Official Guidelines Section I.C.19.c.
• Gustilo type: IIIA, IIIB, or IIIC must be documented, not simply “type III” or “open fracture.”
• Healing status: Nonunion must be explicitly documented — ideally with radiographic confirmation referenced in the note.
• Encounter type: Follow-up visit for ongoing management (subsequent encounter), not active initial treatment.

The CMS ICD-10 coding resources page publishes the ICD-10-CM Official Guidelines for Coding and Reporting, which is the authoritative source for all fracture coding rules. Section I.C.19 covers traumatic fractures specifically and should be reviewed alongside this reference.

Related ICD-10 codes for displaced transverse ulna shaft fractures

Understanding the full S52.221 family and its adjacent codes prevents miscoding when the clinical scenario is similar but slightly different. Review the CDC/NCHS ICD-10-CM official code lookup tool to verify current descriptions for any of the following codes, as effective dates vary.

The 7th character logic in S52 fracture codes mirrors the rest of Chapter 19. The same grid reading transfers directly to the radius shaft codes in S52.3, which carry an identical character set.

Common coding errors and how to avoid them

Claims billed with S52.221N are rejected or audited when documentation does not support the code’s specificity. The errors below are the ones most frequently flagged in orthopedic and musculoskeletal billing. Reading the denial codes a payer returns tells you which of them your practice keeps repeating.

ICD-10-CM coding guidelines for fractures (official guidance)

The ICD-10-CM Official Guidelines for Coding and Reporting, Section I.C.19.c govern all traumatic fracture coding. Key rules that affect S52.221N include the following.

• Default to closed: When documentation does not specify open vs closed, code the fracture as closed per Official Guidelines Section I.C.19.c.
• Open fracture Gustilo requirement: For open fractures, the Gustilo type must be documented to select the correct open fracture 7th character. Without it, default to closed.
• Multiple fracture sequencing: When multiple fractures are coded, sequence based on severity. The AAPC ICD-10-CM code reference provides guidance on sequencing rules for multiple simultaneous fractures.
• Encounter type continuity: Where several providers share the care, each one codes the encounter type from its own scope of treatment. A specialist managing nonunion at a follow-up visit uses subsequent encounter codes, whatever another provider is treating.

The WHO ICD-10 browser gives the international classification context for musculoskeletal injury codes. For US billing, reference the ICD-10-CM (Clinical Modification) maintained by CDC/NCHS instead. Only the CM version carries the 7th character extensions that make codes like S52.221N possible.

How claims management software prevents fracture coding denials

A fracture coding error usually surfaces after the payer sends the claim back. The coder appends a 7th character from the follow-up note, while the initial operative report sits in another system. Nobody confirms that a Gustilo subtype was ever recorded.

Practice management software like Pabau keeps the full course of care in one patient record. The initial encounter note, the imaging report, and every follow-up sit side by side. Its claims management software checks a claim for missing documentation before it leaves the practice, then tracks which codes come back denied.

On a nonunion claim that hinges on a subtype documented months earlier, one record is the difference between a clean submission and a query cycle. Coders read the history instead of reconstructing it.

Simplify orthopedic and fracture billing with Pabau

Pabau’s claims management tools help orthopedic and musculoskeletal practices build cleaner claims and track denial patterns. Your team spends less time on rework and more time on patient care.

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Conclusion

ICD-10 Code S52.221N covers a narrow scenario. The patient has a displaced transverse fracture of the right ulna shaft, seen at follow-up. The fracture was originally classified as Gustilo type IIIA, IIIB, or IIIC, and nonunion is now confirmed. All three conditions have to be documented before the code is defensible.

The element that fails most often is the Gustilo subtype, and it fails at the initial encounter rather than at the visit being coded. If the original operative note says only “open fracture”, character N is off the table for every encounter that follows. Send that query while the record is still fresh.

Get the encounter template right once and the 7th character stops being a judgment call. Book a demo to see how Pabau keeps fracture documentation and claim coding in step across a full course of care.

Continue your research

Want the codes a payer sends back when a claim like this fails? Denial codes in medical billing maps the common rejection reasons to the documentation that fixes them.

Need the wider claim workflow around a diagnosis code? What is medical billing walks through how a coded encounter becomes a paid claim.

Looking to cut denials across your orthopedic billing? Denial management in healthcare covers how to build denial prevention in from the coding stage.

Tracking what fracture follow-up care actually collects? What is revenue cycle management explains where coding accuracy shows up in the numbers.

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