ICD-10 code S52.236N: Nondisplaced oblique ulna fracture

Key takeaways

S52.236N reports a nondisplaced oblique fracture of the ulna shaft, side unspecified. It applies at a subsequent encounter for an open Gustilo III fracture with nonunion.

The 7th character N carries three facts at once. The visit is a follow-up, the fracture was graded Gustilo IIIA, IIIB, or IIIC, and it has not united.

S52.2 is the ulna shaft category. Radius shaft fractures sit under S52.3, so the radius twin of this code is S52.336N.

Only the treating physician can state the Gustilo type and the nonunion diagnosis. A coder cannot read either one off the wound size or the imaging.

Reach for the unspecified side only when the record genuinely lacks it. Query the physician first, because payers read a default as thin documentation.

ICD-10 code S52.236N covers a nondisplaced oblique fracture of the ulna shaft, with the side unspecified. It applies at a subsequent encounter, after an open Gustilo type IIIA, IIIB, or IIIC fracture has failed to unite. The code is billable and valid for FY2026, so it can carry a claim on its own.

Three facts have to sit in the record before you use it. The physician must name the ulna, state the Gustilo type, and document the nonunion. Miss one and the claim comes back, because payers audit long-running nonunion care closely. The rest of this page works through the 7th character, the sibling codes, and the documentation that keeps the claim moving.

What S52.236N covers, and why it’s billable

S52.236N is a valid, billable ICD-10-CM diagnosis code. It is not a header or a placeholder, so it needs no companion code to reach the specificity payers want. Here is the code in full.

Three clinical conditions have to be true at the same time before the code fits. The record needs a nondisplaced oblique fracture pattern, an open wound graded Gustilo IIIA, IIIB, or IIIC, and a confirmed nonunion at that visit. All three come from the treating physician. That combination is what makes S52.236N one of the harder fracture codes to assign.

Every word in the description changes the code

Read the official description as seven separate decisions rather than one long phrase. Each one points at a different digit, and each one is a place the code can go wrong.

• Nondisplaced: the fragments stay in anatomical alignment. The fracture line runs through the bone, but the fragments have not moved. Displaced fractures sit out of alignment and usually need reduction.
• Oblique: the fracture line runs at an angle across the shaft, roughly 30 to 45 degrees. ICD-10-CM keeps oblique separate from transverse, which runs straight across, and from spiral.
• Shaft of ulna: the diaphysis, meaning the long middle section between the two ends of the bone. Ulna shaft fractures sit under S52.2x. The lower end falls under S52.6x and the upper end under S52.0x.
• Unspecified: the 6th character 6 says the record does not name the right or left ulna. It is not a default setting. Use it only when the side is genuinely absent from the documentation.
• Subsequent encounter: the patient is still under active treatment, but the initial phase has passed. Subsequent encounters take 7th characters D through R, and they cover every follow-up visit.
• Open fracture type IIIA, IIIB, or IIIC: the injury involved a wound exposing the bone, graded as high severity under the Gustilo-Anderson system.
• Nonunion: the fracture has stopped healing. Nonunion is its own clinical finding, separate from malunion, which heals crooked, and delayed union, which is still moving toward union.

Chapter 19 runs on the CMS ICD-10-CM guidelines. They tell you to pick the encounter type from the purpose of the visit, not the calendar. A patient seen 18 months after the injury for nonunion care is still at a subsequent encounter.

The 7th character is where these claims go wrong

Most S52.236 errors land on the final digit. Open fractures in the S52 category use an extended set of 7th characters, so the shorter closed-fracture options do not apply here.

Two questions settle the character at any follow-up visit. How was the fracture graded, and how is it healing? The grid below crosses the two.

Take a patient seen 11 months after a Gustilo IIIB ulna shaft fracture. Imaging shows no union, and the surgeon documents nonunion at that visit. The pattern was oblique and nondisplaced, and the note never names the arm. That set of facts lands on S52.236N.

Swap any one of those facts and the character moves. K means a closed-fracture nonunion. M means an open type I or II nonunion. Choose either one for this patient and the code contradicts the operative note, which is exactly what a payer looks for on review.

Only the physician can grade the Gustilo type

The Gustilo-Anderson grade comes from the surgeon, never from the coder. It is the standard system for scoring how severe an open fracture is, and the type has to appear in the operative or clinical note. A wound description on its own will not support the N character.

Type I wounds measure under 1 cm and type II wounds fall between 1 cm and 10 cm, both with limited soft tissue damage. The type III grades cover the high-energy injuries most likely to end in nonunion, through lost blood supply, contamination, and stripped periosteum. The StatPearls open fracture management review sets out how surgeons separate the grades at debridement.

How S52.236N differs from its nearest siblings

S52.236N belongs to the S52.23 oblique ulna shaft group, and its neighbors differ by a single character. Knowing which one moves where saves a query later.

One distinction is worth stating plainly, because it is the costliest mix-up in this family. S52.236N is an ulna code. The matching radius code is S52.336N, since radius shaft fractures sit in the separate S52.3 subcategory. Put the ulna code on a radius fracture and the claim names the wrong bone.

The split between S52.236N and S52.236J is clinical rather than administrative. Delayed healing means the fracture is still moving toward union. Nonunion means it has stopped and will not heal without intervention. The physician has to say which one applies, because a coder cannot make that call.

The notes that decide when this code applies

The S52 block carries instructional notes that govern when you can report S52.236N. Reading them first heads off the rejections that follow a bundling error.

• Applicable to (S52.2): fractures of the ulnar shaft, including nightstick fractures. The ulna part of a Monteggia fracture-dislocation has its own codes under S52.27-.
• Includes: traumatic fractures of the ulnar shaft. The code covers acute traumatic injury and its follow-up visits, not pathological or stress fractures.
• Excludes1 (S52 block): traumatic amputation of forearm (S58.-). An Excludes1 note means the two conditions never happen together, so the codes never appear on the same claim line.
• Excludes2 (S52 block): fracture at wrist and hand level (S62.-), plus periprosthetic fracture around an internal prosthetic elbow joint (M97.4-). An Excludes2 code may be reported alongside S52.236N when both conditions are present.
• Coding conventions: a fracture not documented as displaced or nondisplaced defaults to displaced. A fracture not documented as open or closed defaults to closed. Open fracture designations follow the Gustilo classification.
• Both-bone forearm fractures: a broken ulna and radius need two codes, one from S52.2 and one from S52.3, each carrying its own 7th character.

Where S52.236N sits in the ICD-10-CM hierarchy

S52.236N sits seven levels down the tree. Reading it from the top shows you which digit to change when you need to move sideways.

• S00-T88: Injury, poisoning and certain other consequences of external causes
• S50-S59: Injuries to the elbow and forearm
• S52: Fracture of forearm (radius and ulna)
• S52.2: Fracture of shaft of ulna
• S52.23: Oblique fracture of shaft of ulna
• S52.236: Nondisplaced oblique fracture of shaft of unspecified ulna
• S52.236N: Subsequent encounter for open fracture type IIIA, IIIB, or IIIC with nonunion

Each level adds one qualifier: the bone, the site within it, the pattern, the displacement status, then the side. The 7th character layers encounter type and healing status on top. Our ICD-10-CM code library indexes the neighboring entries if you need to work across the family. Codes change every October, so check validity in the CDC/NCHS ICD-10-CM web tool at the start of each fiscal year.

The ICD-9 crosswalk only gets you close

Legacy claims, audits, and older records sometimes still need an ICD-9-CM equivalent. The CMS General Equivalence Mapping files map S52.236N approximately to ICD-9-CM code 733.82, nonunion of fracture. Treat that mapping as a starting point rather than a conversion.

• Code 733.82 captures nonunion broadly. It carries no detail on fracture pattern, bone site, displacement status, or open fracture classification.
• Mapping 733.82 back the other way produces several candidate ICD-10-CM codes. It cannot tell you whether the ulna or the radius was the injured bone.
• Older episodes of care still surface in secondary billing, so verify any mapping against the official CMS files rather than a commercial lookup tool.

What the record has to say before you code

Payers reviewing an S52.236N claim look for seven specific elements. Miss one and you get a medical necessity denial or a request for records. These claims draw more scrutiny than routine fracture follow-up, because the care runs long and costs more.

Auditors read those elements against each other. A note that states nonunion but never names a Gustilo type will not support the N character, however complete the rest of the record looks.

Run this check before the claim goes out

Rejected S52.236N claims usually fail on one of six checks. Run them in order, before the claim leaves the practice.

• The note names the ulna, not just the forearm.
• The pattern reads oblique, and the record says nondisplaced.
• A Gustilo type of IIIA, IIIB, or IIIC appears in the physician’s own words.
• The physician has written nonunion or failed union at this visit, not delayed union.
• The visit is documented as follow-up care rather than initial active treatment.
• Laterality is absent from the whole record, and a physician query has already come back empty.

Clear all six and the claim travels the ordinary route. It leaves the practice, passes the clearinghouse edits, and reaches the payer with the supporting documentation already lined up behind it. Fail one, and the work moves to the back end, where an appeal costs far more than a query would have.

Five errors that get these claims denied

S52.236N carries a high rate of avoidable claim errors. Five patterns account for most of the denials and physician queries on these claims.

• Coding the radius instead of the ulna: a note that says only “forearm shaft fracture” sends coders to S52.336N as often as S52.236N. Query the physician for the named bone before you assign either one.
• Using K instead of N for a Gustilo III nonunion: character K means the original fracture was closed. On an open Gustilo III injury it contradicts the operative report, and the claim fails medical necessity review.
• Confusing nonunion with malunion: malunion means the fracture healed in the wrong position, while nonunion means it never healed. S52.236N is the nonunion code. Malunion of the same fracture takes character R.
• Defaulting to unspecified laterality: coders reach for S52.236N when the side is documented but buried in the chart. Per AAPC’s ICD-10-CM coding resources, unspecified codes belong only where the side is absent from all available documentation.
• Missing Gustilo documentation: assigning N without a stated type is a clinical inference. Payers will request the operative note and deny the claim if the type is not there. Escalate to a physician query first.

A quarterly review of S52.23x denials shows which of the five is happening in your practice. Good denial management turns that pattern into a workflow fix rather than a standing rework queue.

How practice management software keeps these claims clean

In most orthopedic and trauma practices, nonunion claims get coded from free-text operative notes. A coder reads the note, hunts for the Gustilo type, and raises a query when it is missing. That loop adds days to the claim, and it leaves the 7th character exposed at audit.

Practice management software like Pabau moves those details into the note itself. Structured clinical templates prompt the physician at the point of care. The note asks for the bone, the pattern, the displacement status, the side, the Gustilo type, and the union status. The coder then works from a complete record instead of chasing one.

Pabau’s claims management software then checks the claim before it leaves the practice. Eligibility and clean-claim validation run against the Claim.MD clearinghouse, so payer-level problems surface while you can still fix them. Fewer resubmissions on complex fracture claims means the money arrives sooner.

Fewer coding denials on complex fracture claims

Pabau prompts clinicians for the Gustilo type, laterality and union status while they write the note, then validates the claim before it reaches the payer. Orthopedic and trauma practices use it to cut rework on nonunion and open fracture cases.

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Conclusion

Start with the bone. S52.236N is an ulna shaft code, and its radius twin is S52.336N. From there, the code only holds up if the physician’s own words carry the Gustilo grade and the nonunion. N is not interchangeable with K or M, and an unspecified side is a last resort rather than a shortcut.

Practices that stop losing money on these claims are the ones that fix the note, not the ones that appeal faster. Book a demo to see how Pabau prompts for the Gustilo type and validates the claim before it reaches the payer.

Continue your research

Coding the displaced version of this fracture? ICD-10 code S52.233F covers the displaced oblique ulna shaft fracture at a subsequent encounter.

Need the documentation rules behind fracture coding? Medical billing compliance guidance covers the standards that keep complex diagnosis codes out of the denial pile.

Seeing the same denials on fracture claims every month? Denial management in healthcare sets out the workflow fixes that address systemic rejection patterns.

Wondering how a clearinghouse checks a diagnosis code? Medical claims clearinghouse overview explains how pre-submission scrubbing catches errors before they reach the payer.

Looking for a repeatable clean claim process? Clean claim submission requirements details what payers check at adjudication and how to meet it consistently.

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