ICD-10 code S52.209K: Ulna shaft fracture nonunion

Key takeaways

ICD-10 code S52.209K describes an unspecified fracture of the shaft of the unspecified ulna, subsequent encounter for closed fracture with nonunion.

The word “unspecified” here refers to the laterality and the fracture pattern, not to the bone. S52.209K is ulna-specific, and radius shaft fractures use the separate S52.3 codes.

The 7th character K marks a subsequent encounter for a closed fracture that has failed to unite. It separates nonunion from delayed healing (G) and malunion (P).

If the record documents the side, code S52.201K for the right ulna or S52.202K for the left ulna instead.

Practice management software like Pabau ties clinical notes to the billing record, so your coders can see the documented healing status at charge capture.

ICD-10 code S52.209K is the diagnosis code for an unspecified fracture of the shaft of the unspecified ulna, subsequent encounter for closed fracture with nonunion. It is a valid, billable ICD-10-CM diagnosis code accepted for claim submission.

The code appears in the current fiscal year tabular list maintained by the Centers for Medicare and Medicaid Services (CMS). It sits within ICD-10-CM category S52, which covers fractures of the forearm.

That category name is where S52.209K is most often misread. Subcategory S52.2 is the ulna shaft alone, so the code never stands in for a generic radius-or-ulna forearm fracture. Radius shaft fractures belong to a separate subcategory, S52.3.

Nonunion is a clinically distinct complication. The fracture has failed to heal after an appropriate healing period. That differs from healing slowly (delayed healing, character G) or healing in a misaligned position (malunion, character P). Selecting the correct 7th character is the single most common source of claim errors for this code family.

S52.209K code details at a glance

The table below summarizes the core reference data for this code as published in the ICD-10-CM tabular list.

Breaking down the code, character by character

Each character of ICD-10 code S52.209K carries specific clinical meaning. Reading the code position by position helps coders verify accuracy before submission. It also keeps code selection consistent across encounter types.

The digit 9 in S52.209 signals that laterality is unspecified. If the treating clinician documented which arm is involved, code S52.201K for the right ulna or S52.202K for the left. Those two codes are the only laterality siblings under S52.20.

Some payers require one of them when the record clearly identifies the side. The 5th character works the same way. When the record describes a spiral fracture, the code moves into subcategory S52.24, which holds codes such as S52.242J and S52.246H.

What the 7th character K means

The 7th character is the most clinically sensitive part of any fracture code. For S52 codes it records the treatment phase and the healing status of the fracture at the time of the encounter. Using the wrong 7th character is a leading cause of orthopedic claim denials.

Character K applies only when the fracture is closed. Open ulna shaft fractures carry their own characters, graded by the Gustilo-Anderson classification. An open type I or II fracture with nonunion takes character M at a subsequent encounter. Type IIIA, IIIB, and IIIC open fractures take character N.

Per ICD-10-CM Official Guidelines Section I.C.19.c, character K applies when the fracture has definitively failed to unite. This is typically confirmed by imaging at a follow-up visit showing absence of bridging callus or a persistent fracture line beyond the expected healing window. The National Center for Health Statistics (NCHS) maintains these guidelines in coordination with CMS.

Clinical information: Ulna shaft fracture nonunion

Nonunion of an ulna shaft fracture is a recognized orthopedic complication that requires separate clinical management from the initial fracture episode. Accurate patient records documenting the progression from initial injury to nonunion are essential for both clinical continuity and billing accuracy.

Common causes of ulna shaft fracture nonunion:

• Inadequate immobilization or early loading of the arm after the initial fracture
• Distraction at the fracture site (an excessive gap between bone fragments)
• Infection at or near the fracture site
• Poor vascular supply to the mid-shaft of the ulna
• Systemic factors including osteoporosis, smoking, diabetes, or nutritional deficiency
• Isolated ulna shaft (nightstick) fractures managed without fixation, where forearm rotation keeps loading the fracture site

Clinically, nonunion presents as persistent pain and functional limitation at the fracture site beyond the typical healing window. For ulna shaft fractures that window is generally 6 to 9 months, though it varies by patient and fracture pattern.

The imaging findings that confirm the diagnosis must be documented in the clinical record before character K is applied. Those findings include absent bridging callus, sclerotic fracture margins, or sealing of the medullary canal.

Includes, excludes, and applicable to notes

The S52 code block carries instructional notes that govern when S52.209K can and cannot be used. Understanding the Excludes1 and Excludes2 notes prevents unbundling errors and the claim rejections that follow them.

• Applicable to (S52.2): fractures of the ulna shaft, including nightstick fractures. The ulna component of a Monteggia fracture-dislocation has its own codes under S52.27-.
• Includes note: traumatic fractures of the ulna shaft. S52.209K is intended for acute traumatic fractures and their subsequent encounters, not pathological or stress fractures.
• Excludes1 (S52 block): traumatic amputation of forearm (S58.-). An Excludes1 note means the two conditions are mutually exclusive, so the codes are never reported together.
• Excludes2 (S52 block): fracture at wrist and hand level (S62.-), and periprosthetic fracture around an internal prosthetic elbow joint (M97.4). An Excludes2 code may be reported alongside S52.209K when both conditions are present.
• Note on anatomy: fractures of the upper end of the ulna use S52.0 codes, such as S52.022E, and the lower end uses S52.6 codes. S52.2, including S52.209K, covers the shaft only, and radius shaft fractures use S52.3.

Where the code sits in the hierarchy

S52.209K sits at the end of a seven-level code tree. Knowing the parent structure helps coders navigate the CDC/NCHS ICD-10-CM web tool and select the most specific applicable code.

1. S00-T88 — injury, poisoning, and certain other consequences of external causes
2. S50-S59 — injuries to the elbow and forearm
3. S52 — fracture of forearm
4. S52.2 — fracture of shaft of ulna
5. S52.20 — unspecified fracture of shaft of ulna
6. S52.209 — unspecified fracture of shaft of unspecified ulna, the non-billable parent
7. S52.209K — subsequent encounter for closed fracture with nonunion, billable

S52.209 on its own, without the 7th character, is not billable. ICD-10-CM requires a complete code including the appropriate 7th character for every fracture code in this block.

Related ICD-10-CM codes

The codes below are the ones coders most often choose between. The first group shares the parent S52.209 and differs only by 7th character. The last three cover the documented laterality options and the equivalent radius shaft code.

Coders at physical therapy practices managing fracture rehabilitation must confirm the encounter type at each follow-up visit. Verify current validity using the AAPC Codify ICD-10-CM lookup.

Documentation requirements for billing S52.209K

Billing S52.209K successfully requires more than selecting the right code. Payers, including Medicare and commercial insurers, apply medical necessity criteria that depend on what is documented in the clinical record at each subsequent encounter. Practices using claims management workflows should confirm these documentation elements are captured before submission.

• Bone and site: The note must identify the ulna shaft. A record that says only “forearm fracture” does not support S52.209K, because the code is ulna-specific.
• Confirmed nonunion diagnosis: The clinical note must state that nonunion has been confirmed, not merely suspected. “Concern for nonunion” does not support character K.
• Imaging findings: Radiology report or attending physician interpretation documenting absent bridging callus, a persistent fracture gap, or medullary sclerosis.
• Closed versus open: Character K covers closed fractures only. An open fracture with nonunion takes character M or N, depending on the Gustilo-Anderson type.
• Treatment phase: The record should clarify this is a follow-up encounter, not an initial evaluation of a newly identified fracture.
• Laterality: If the clinician can confirm which ulna is affected, use S52.201K for the right or S52.202K for the left. S52.209K is appropriate only when the side is genuinely undocumented.
• Mechanism of injury: Document the original mechanism, such as a fall or a direct blow to the forearm. This supports medical necessity and separates the injury from pathological and stress fracture categories.

The American Health Information Management Association (AHIMA) and the ICD-10-CM Official Guidelines agree on one point. The clinician of record owns the diagnosis documented in the medical record. Coders assign the code that best represents that documented diagnosis, not a provisional or assumed one.

How practice management software supports ICD-10 coding accuracy

Subsequent-encounter fracture coding is where claim errors compound. A patient with an ulna shaft nonunion typically attends multiple follow-up visits over several months, and the 7th character must be re-evaluated at each one.

Practices handling this at volume benefit from coding workflows that surface the patient’s current fracture status at the point of care. That includes sports medicine practices tracking athletes through fracture rehabilitation.

Practice management software like Pabau reduces S52.209K coding errors in three ways:

• Linked clinical documentation and billing: When the clinician’s note references imaging findings and confirms nonunion, the coder should see that context at charge capture. It should not sit in a separate system. Pabau’s digital clinical forms keep structured assessment data tied to the patient’s billing record.
• Encounter-type tracking: Recording whether a visit is initial, routine subsequent, or complicated subsequent stops teams from defaulting to character D when K or G applies.
• Audit trails for compliance: Practices subject to physical therapy regulatory requirements need audit trails. Each trail shows that a coding decision was supported by clinical evidence at the time of the encounter.

Integrated practice management software connects scheduling, clinical notes, and claim submission in one system. That narrows the distance between what is documented and what is billed. For background on how these codes are captured in claims data, see ResDAC.

Reduce claim errors on subsequent-encounter fracture codes

Pabau connects patient records, clinical notes, and billing workflows, so your team has the documentation it needs at every follow-up visit. See how orthopedic and physical therapy practices use Pabau to keep ICD-10-CM coding accurate.

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Conclusion

Ulna shaft nonunion is a clinically distinct and documentable complication, and ICD-10 code S52.209K is the code that captures it. Getting it right means naming the correct bone, confirming the fracture is closed, and evidencing the failed union. The difference between a paid claim and a denial often comes down to one character and one imaging report.

Pabau connects patient documentation to billing at every subsequent encounter, which cuts the 7th character errors behind orthopedic claim denials. To see how Pabau supports coding accuracy across your practice, book a demo.

Continue your research

Coding a follow-up where the fracture is healing slowly rather than failing to unite? S49.102G covers the delayed-healing 7th character and the documentation it needs.

Billing the late effects of a forearm injury? S51.801S explains how sequela coding differs from a subsequent encounter.

Working on the radius rather than the ulna? S52.133S walks through the radial neck codes and their laterality rules.

Documenting an open forearm fracture instead of a closed one? S52.131B shows how the Gustilo-Anderson type drives the 7th character.

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