ICD-10 code S52.042Q: Open left ulna fracture with malunion

Key takeaways

ICD-10 code S52.042Q covers a displaced fracture of the coronoid process of the left ulna. It applies to a subsequent encounter for an open fracture type I or II with malunion.

S52.042Q is a billable, specific ICD-10-CM code valid for FY2026 claims (effective October 1, 2025).

The seventh character Q means open type I or II with malunion. Closed-fracture malunion takes P, and open type IIIA, IIIB, or IIIC malunion takes R.

Q is also the default malunion character when the record documents an open fracture but never states its Gustilo type.

Practice management software like Pabau pre-fills claims from the patient record and checks that required claim fields are complete. Submission runs through integrated clearinghouses, including Claim.MD for US payers.

ICD-10 code S52.042Q covers a displaced fracture of the coronoid process of the left ulna. It applies when that fracture healed out of position after an open type I or II wound.

Below you’ll find the code’s structure, the seventh-character logic, the documentation payers expect, and the mistakes that keep sending it back.

S52.042Q spells out four clinical facts at once

The long description reads: Displaced fracture of coronoid process of left ulna, subsequent encounter for open fracture type I or II with malunion.

Laterality, displacement, wound type, and healing outcome all sit inside that one string. Leave any of the four out of the note and the code moves elsewhere.

S52.042Q is billable and specific, so it goes onto a claim form exactly as written, with no further expansion. The FY2026 edition took effect on October 1, 2025, and the code appears in the CMS ICD-10-CM tabular list.

Confirm the effective date before you submit, because the October 1 update can retire a code you used last year.

The seventh character Q carries most of the meaning

Q says one thing. It marks a subsequent encounter for an open type I or II fracture that healed with malunion.

Every fracture code in the S52 category ends in a seventh character. That letter sets the encounter phase, the wound type, and the healing outcome. Nothing else in the code makes up for choosing the wrong one.

Here is the full seventh-character set for S52.042, a displaced fracture of the coronoid process of the left ulna.

Q sits where malunion meets an open type I or II wound. A closed fracture that healed crooked takes P instead, and an open type IIIA, IIIB, or IIIC wound takes the R character.

Reporting E or H on a documented malunion understates the complication. It also hides the work done at that visit. The CDC ICD-10-CM tool carries the official tabular list, fiscal year by fiscal year.

Q needs a Gustilo type I or II wound behind it

The open-fracture characters in S52 follow the Gustilo-Anderson classification, so the surgeon’s wound description picks the letter.

• Type I: a wound under 1 cm, clean, with minimal soft-tissue damage.
• Type II: a wound wider than 1 cm, with moderate soft-tissue damage and no heavy contamination.
• Type III: a high-energy injury with extensive soft-tissue damage, split into IIIA, IIIB, and IIIC.

Only the first two of those reach Q. Type III malunion belongs to R.

A useful default also sits in the Official Guidelines. When the record documents an open fracture but never states a Gustilo type, you code from the type I or II characters. Those are B, E, H, M, and Q, so a malunion with no wound type on the chart still lands on Q.

Why a first visit with you can still be a subsequent encounter

The seventh character follows the phase of treatment, so the visit count is irrelevant. That rule comes from the ICD-10-CM Official Guidelines for Coding and Reporting, and it trips up coders constantly.

• Initial encounter (A, B, C): active treatment, which covers the emergency visit, surgery, casting, and any visit that actively manages the fracture. An open type I or II wound takes B here.
• Subsequent encounter (D through R): the healing and recovery phase, once active treatment has finished. On an open type I or II wound, E covers routine healing, H delayed healing, M nonunion, and Q malunion.
• Sequela (S): a late effect, meaning a condition that remains after the acute phase of the fracture ends.

Picture a patient who returns six weeks after coronoid repair. Imaging confirms malunion of an open type I fracture, so that visit codes to S52.042Q.

The original emergency room encounter was S52.042B. Encounter type does not reset when a new provider picks the patient up, so the physical therapist treating post-malunion stiffness reports Q as well.

Rehab teams working from a physical therapy EMR should put healing status in the note itself, not only in the imaging report. The coder reads the note first.

Malunion means the bone healed in the wrong position

Malunion describes a fracture that united shortened, angulated, or rotated beyond acceptable limits. Nonunion is a different outcome, because there the bone never united at all.

Delayed healing is different again, since the bone is simply slower than expected.

On an open type I or II fracture those two outcomes take M and H, which leaves Q to malunion alone. At the coronoid process, malunion usually appears as residual angular deformity of the proximal ulna. That deformity limits elbow flexion, or pronation and supination.

Documentation has to establish the malunion before you can code it. Any one of these will do that:

• imaging that shows healed but malaligned bone on X-ray or CT
• the physician’s assessment, using malunion, malalignment, or healed in an incorrect position
• functional notes describing restricted motion that the malunion explains

Clinical inference is not enough on its own. Without imaging or a provider statement, Q will not survive a review.

Why a malunited coronoid process costs the patient motion

Malunion here reshapes the elbow’s hinge, so the joint stops tracking properly. The patient loses part of the flexion arc, and often some pronation and supination too.

The coronoid process is a triangular bony projection on the front of the proximal ulna. It forms the lower part of the trochlear notch, which meets the humeral trochlea to make that hinge. Because it resists the ulna sliding backward, it also keeps the joint stable and limits hyperextension.

These fractures make up roughly 10 to 15% of all elbow fractures. They often arrive alongside a radial head fracture or an elbow dislocation, the pattern surgeons call the terrible triad. Contact and throwing sports produce plenty of them, so sports medicine practices see the injury often.

Displaced means the fragment moved far enough to disturb the joint surface. In an open injury the wound connects to that fracture site, which raises infection risk and makes alignment harder to hold.

Heal both together out of position and the joint surfaces no longer match, which brings impingement and a higher long-term osteoarthritis risk.

So the follow-up code carries clinical weight, not just administrative weight. A coder who knows what coronoid malunion does to an elbow is likelier to spot it in a progress note.

S52.042Q sits at the end of a five-level chain

S52.042Q is the billable tip of a hierarchy that starts with the whole injury chapter. Knowing the levels above it helps when documentation is partial, because guidance written at the S52 level flows down to every child code.

S52.042 on its own is not a valid billable code. The tabular list requires a seventh character on every S52 fracture code, so a truncated claim rejects on arrival.

A quick look at the AAPC code lookup settles it, listing S52.042Q as the submission format for this scenario.

Three sides and three wound types sit beside this code

S52.042Q belongs to a laterality triplet, so a vague note has two other places to land. Coders working without a documented side should know all three.

Laterality is not optional in ICD-10-CM. Reporting S52.043Q when the record clearly names a side trips a specificity flag with many payers, so use S52.042Q whenever the left side is documented.

This subcategory also has no S52.049 series, which makes S52.043Q the only unspecified-side option here.

Wound type then splits the same left-sided malunion three ways.

Other outcomes on the same open type I or II injury include S52.042E for routine healing and S52.042M for nonunion. Each needs its own documentation.

The same character logic runs through every fracture chapter, which is why which is why S72.414P and S72.435M read the same way on the femur.

Five facts have to be in the note before you code Q

Each fact maps to a piece of the code, so a missing one usually points at a different code.

• Laterality: the left side named in the clinical note or the imaging report.
• Displacement: the fracture described as displaced, and sited at the coronoid process rather than the olecranon.
• Open wound: an open fracture confirmed at the fracture site, with the Gustilo type wherever the surgeon recorded it.
• Healing outcome: malunion stated by the provider, or imaging that shows healed but malaligned bone.
• Treatment phase: evidence that active treatment has ended and this visit falls in the healing phase.

Two guideline defaults cover the smaller omissions. A fracture not documented as open or closed is coded as closed, and a fracture not documented as displaced or nondisplaced is coded as displaced.

Neither default rescues a note that never mentions malunion, so that fact has to come from the provider.

How an S52.042Q claim gets from the note to the payer

Assigning the code is one step in a longer route. Here is the trip a malunion claim makes after the patient goes home.

1. The provider records laterality, wound type, and healing status in the visit note.
2. The coder assigns S52.042Q, plus the evaluation and management or procedure code for the work done.
3. Billing builds the CMS-1500, or its electronic equivalent, the 837 file.
4. A claims clearinghouse screens that file for format errors and missing fields, then routes it to the payer.
5. The payer adjudicates and returns a remittance with the payment, or with a reason it will not pay.

Two things derail this claim more than anything else. One is a note that never says whether the fracture was open. The other is a seventh character that contradicts the imaging report.

Either one comes back as one of the usual denial codes, weeks after the visit.

A short check before submission catches most of that:

• the seventh character on the claim matches the character in the coding note
• the diagnosis pointer ties S52.042Q to the right service line
• the imaging report is on file and ready to send if the payer asks
• every required claim field is complete, including any authorization number
• the code is still valid in the current fiscal year

Scrubbing for a clean claim before the file leaves the practice saves a round trip. If a denial has already landed, work it through your denial management process instead of resubmitting the same character and hoping.

The guidelines that decide a malunion claim

Fracture coding sits in Section I.C.19 of the ICD-10-CM Official Guidelines for Coding and Reporting. Five rules do most of the work on an S52.042Q claim.

• Encounter type drives the seventh character. The phase of treatment decides it, not the visit number. A patient who returns months later with malunion is still in the subsequent-encounter phase.
• Malunion has to be documented. Q cannot rest on a coder’s inference. The provider states malunion, or describes it in terms the imaging supports.
• Wound type picks the character column. Q applies only to an open type I or II fracture. Closed malunion takes P, and open type IIIA, IIIB, or IIIC malunion takes R.
• An unspecified Gustilo type defaults to type I or II. An open fracture with no stated type codes from the B, E, H, M, and Q column.
• Code any associated condition too. Post-traumatic osteoarthritis of the left elbow, M19.122, is reported additionally where the malunion caused it.

The guidelines are republished with every annual code update, which is where outdated references cause trouble. Any EMR software you rely on should refresh its ICD-10 tables each October, so a retired code never reaches a claim.

Which CPT codes travel with coronoid fracture care

S52.042Q is a diagnosis code, so the procedure codes beside it depend on what happened at the encounter. These turn up most often across a coronoid fracture’s treatment course:

• 24685: open treatment of an ulnar fracture at the proximal end, such as the olecranon or coronoid process, including internal fixation when performed.
• 24675: closed treatment of an ulnar fracture at the proximal end, with manipulation.
• 11010 to 11012: debridement at an open fracture site, chosen by the deepest tissue layer treated.

Those procedures usually sit on the initial treatment encounter, which carries the B character. A malunion follow-up is likelier to bring an evaluation and management code, imaging, or therapy codes.

Where the injury reached the humeral condyle as well, 24582 may join the claim.

Corrective surgery for the malunion is coded from the operative report. Read the descriptor in the current AMA CPT manual before you submit.

Six mistakes that send S52.042Q straight back

Most denials on this code trace to the same short list.

• Swapping P and Q. P is the closed-fracture malunion character, and Q belongs to an open type I or II fracture.
• Using a closed-column character on an open fracture. D, G, and K all describe closed fractures, so none of them fits an open type I or II injury.
• Reaching for S52.049Q. That code does not exist, and unspecified laterality is S52.043Q.
• Dropping the seventh character. S52.042 on its own is invalid, so the claim rejects.
• Assigning Q without documented malunion. A follow-up visit on its own supports E, not Q.
• Coding the wound type from the triage note. Where the operative report states a different Gustilo type, the operative report wins.

How Pabau keeps the fracture detail attached to the claim

Most fracture coding errors begin as documentation errors. The note records a follow-up visit, but never says whether the original fracture was open, or which Gustilo type the wound met. Then the coder picks a seventh character without the one fact that decides it.

Practice management software like Pabau keeps that detail on the patient record instead of spread across scanned reports. Digital forms capture wound type, laterality, and healing status at the point of care, in fields a coder can find later.

Claims management then builds the claim from that record, so nobody retypes the codes already attached to the visit. Built-in ICD-10-CM and CPT lookup libraries refresh with each official release, which means the code you search is the current one.

Before the send button unlocks, Pabau checks that every required claim field is complete. US practices submit through the Claim.MD integration, which also handles eligibility checks, claim status, and remittance posting. Your billing team stops chasing wound descriptions weeks after the fact.

Send fracture claims with the detail already attached

Pabau pre-fills claims from the patient record, keeps ICD-10-CM and CPT lookup libraries current, and checks required fields before you submit. US claims go out through the Claim.MD integration.

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Conclusion

Coronoid malunion is a specific, documentable outcome, and S52.042Q is the code that says so. One letter carries the whole distinction. Q means the wound was open at Gustilo type I or II, and the bone healed out of line. P, E, and M each tell a different story about the same elbow.

So the work sits upstream of the claim. Capture the wound type and the healing status while the patient is still in the room, and the seventh character stops being a guess.

Pabau then pre-fills the claim from that record, checks that required fields are complete, and submits electronically to payers in the US, UK, and Australia. Book a demo to see how that shortens the trip from clinical note to paid claim.

Continue your research

Coding an open fracture somewhere else? S72.345C runs the same open-wound character logic on the femoral shaft.

Billing a fracture you treated without surgery? 23620 covers closed treatment of a greater humeral tuberosity fracture.

Same arm, different injury? 25676 walks through open treatment of a distal radioulnar dislocation.

Billing a facial or hand tissue transfer? CPT code 14041 covers adjacent tissue transfer on the face, neck, hands, or feet for defects up to 30 square centimeters.

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