ICD-10 code S82.091N: Right patella type III nonunion

Key takeaways

ICD-10 code S82.091N reports an other fracture of the right patella at a subsequent encounter. The original open fracture was Gustilo type IIIA, IIIB, or IIIC, and it has reached nonunion.

The Gustilo grade is what the N character turns on. If the open fracture was type I or II, the nonunion code is S82.091M instead.

S82.091N is billable and valid for CMS claim submission in fiscal years 2026 and 2027. A closed patella fracture with nonunion takes S82.091K.

Nonunion is not delayed healing. On a type III open patella fracture, routine healing takes F, delayed healing takes J, and malunion takes R.

ICD-10 code S82.091N reports an other fracture of the right patella at a subsequent encounter. The original fracture was open, graded Gustilo type IIIA, IIIB, or IIIC, and the bone has failed to unite.

One letter is doing all of that work. Change the grade to type I or II and the code becomes S82.091M, a different injury with different documentation behind it. So the Gustilo grade is the first fact to confirm, ahead of the healing status.

What follows is the character set in full, the neighboring codes worth knowing, and the documentation a payer needs behind N.

ICD-10 code S82.091N describes a type III open patella fracture that never united

ICD-10 code S82.091N is a billable ICD-10-CM diagnosis code. Its full official description is: Other fracture of right patella, subsequent encounter for open fracture type IIIA, IIIB, or IIIC with nonunion.

That description is unchanged across the FY2026 and FY2027 code sets. Confirm it in the CDC/NCHS ICD-10-CM web tool or the CMS ICD-10-CM tabular list.

Four clinical facts sit inside that one code. The fracture is of the right patella, not the left and not an unspecified side. It was an open fracture, so bone or the fracture site communicated with the outside through the wound.

The Gustilo grade was type IIIA, IIIB, or IIIC, meaning extensive soft tissue damage or a vascular injury. And the bone has reached nonunion at a subsequent encounter, after active treatment ended.

Assign S82.091N only when the record supports all four.

The code hierarchy shows which notes S82.091N inherits

ICD-10-CM is hierarchical, and each level adds specificity. Reading the chain matters for one practical reason. Excludes notes and coding instructions attach at the category and block level, then apply to every code beneath them.

The rules that govern S82.091N sit several levels above it in the tabular list.

S82.091 on its own is not billable. It needs the 7th character, and because the base code is only six characters long, no placeholder X is required. Payers reject the stem code outright, so the full seven characters have to reach the claim form intact.

The 7th character is where S82.091 claims usually go wrong

That final letter carries the most billing-critical information in the code. It encodes three things at once.

The first is the encounter phase: initial, subsequent, or sequela. The second is the fracture type: closed, open type I or II, or open type IIIA to IIIC. The third is how the bone healed. For S82.091N, the answers are subsequent, open type IIIA/IIIB/IIIC, and nonunion.

The full set for S82.091 runs from A to S, though the letters I, L, and O are never used. ICD-10-CM avoids I and O because they read like the digits 1 and 0 on a claim form.

Here is every option, with the three-way split laid out.

Read the table in columns rather than rows and the logic falls out. Each fracture type owns a run of four subsequent-encounter characters. The order never changes: routine healing, delayed healing, nonunion, then malunion.

• Closed fracture: D, G, K, P
• Open type I or II: E, H, M, Q
• Open type IIIA, IIIB, or IIIC: F, J, N, R

Laid out as a grid, the whole set fits on one screen, and N stops being a letter you have to memorize.

AAPC’s ICD-10-CM code reference lists the same 16 extensions for the S82.091 stem.

Subsequent encounter means active treatment ended, not that this is visit two

Coders misapply encounter type more often than any other part of a fracture code. The ICD-10-CM Official Guidelines define it by treatment phase, not by visit number, and the difference has direct billing consequences.

• Initial encounter (A, B, C): The patient is still under active treatment. That covers the emergency department visit, the operative encounter, and every visit while active treatment continues. A third or fourth visit can still be an initial encounter.
• Subsequent encounter (D through R): Active treatment is finished. The patient returns for follow-up care such as wound checks, imaging review, hardware assessment, or rehabilitation.
• Sequela (S): The fracture episode is over, but a residual condition remains, such as stiffness, chronic pain, or deformity. Code the residual condition first, then S82.091S.

For S82.091N, the patient is past active treatment. Imaging or clinical assessment shows the right patella has stopped healing.

One caveat trips coders here. Say the surgeon performs a fresh operative procedure for the nonunion at this visit. That surgery treats the nonunion, so the encounter still takes N, the subsequent character. Initial-encounter characters belong to active treatment of the original fracture, not to a later revision.

Gustilo type III is the fact that separates S82.091N from S82.091M

The Gustilo-Anderson classification grades open fractures by wound size, contamination, and soft tissue damage.

ICD-10-CM borrows it directly, and the category note at S82 states that the open fracture designations are based on it. S82.091N belongs to the type III group only.

Two consequences follow from that table. First, ICD-10-CM collapses IIIA, IIIB, and IIIC into one 7th character group, so you never have to choose between them for coding purposes. The subgrade still belongs in the operative note, but it does not change the letter.

Second, and this is the error to watch, a type I or II open patella fracture with nonunion is S82.091M, not S82.091N. Malunion after a type I or II open fracture is S82.091Q. Neither of those is a type III code.

Nonunion, delayed healing, and malunion each take a different letter

Nonunion means the fracture has stopped healing. Orthopedic practice commonly treats a fracture as a nonunion when serial imaging shows no progressive healing over roughly six to nine months.

That threshold varies by bone and by institution. Check your own protocol or the orthopedic literature rather than assuming a single universal number.

Coding-wise, the distinction matters because each healing status carries its own character. For a right patella open type III fracture at a subsequent encounter, the four options are:

• Routine healing (F): The fracture is knitting on schedule. This is the ordinary follow-up visit.
• Delayed healing (J): Union is slower than expected but still progressing. Callus is forming on imaging, and the fracture is not yet a nonunion.
• Nonunion (N): Healing has stalled or never started. There is no progressive bridging bone. Treatment usually shifts to grafting, revision fixation, or bone stimulation.
• Malunion (R): The bone has united, but in a poor position. Alignment, rotation, or length is off.

Delayed healing and nonunion get confused constantly, because both describe a fracture that has not united. The clinical record has to draw the line. If the note describes progressing callus, J is correct.

If it describes a fracture line that has not changed across two or more imaging studies, N is the one to use.

What the chart must say to support a right patella nonunion claim

Six facts have to be on the chart before S82.091N holds up, and the Gustilo grade is the one that usually is not. Start with why these injuries are difficult in the first place.

The patella is a sesamoid bone sitting inside the quadriceps tendon, which is part of why open patella fractures behave badly. A type III injury usually comes from high-energy trauma, such as a motor vehicle collision or a fall onto a hard surface.

By the time nonunion is on the chart, the surgeon is typically weighing bone grafting, revision fixation, bone stimulation, or partial patellectomy.

None of that reaches the payer unless the note carries it. Run this checklist against every subsequent encounter you code with S82.091N.

• Laterality: Right patella, stated explicitly. Not “knee”, not “unspecified”.
• Fracture type: Open, documented at the time of the original injury.
• Gustilo grade: Type IIIA, IIIB, or IIIC, recorded in the original operative or emergency note and carried into the problem list.
• Encounter phase: Subsequent, meaning active treatment of the original fracture has finished.
• Healing status: Nonunion, backed by X-ray or CT showing no progressive bridging callus.
• Associated injuries: Any arterial repair, infection, or soft tissue reconstruction that needs its own code.

The Gustilo grade is the item that goes missing most often. It gets documented once, in the operative report, and then never repeats.

Six months later the follow-up note says “right patella fracture, nonunion” with no fracture type at all. A coder cannot assign N from that. Pulling the grade forward into the problem list at discharge solves it in one step.

External cause codes still belong on the subsequent encounter claim

Chapter 20 codes do not stop at the initial visit, and that trips people up. Report the external cause code for every encounter where you are treating the injury, and give it 7th character D for a subsequent encounter.

So a fall coded W19.XXXA at presentation becomes W19.XXXD at the nonunion follow-up.

Three companion code sets work differently. Place of occurrence (Y92), activity (Y93), and external cause status (Y99) are reported only at the initial encounter for the injury.

Repeating them on a follow-up claim is a common audit finding. It is easy to avoid once the rule sits on the team’s cheat sheet.

The full S82.091 family, and its left-side twin

Patients move through this family as the episode unfolds, from the initial open fracture code to whichever healing outcome the bone reaches.

Keeping the whole set in view makes the jump from one encounter to the next much less error-prone.

Two neighboring stems are worth knowing as well.

S82.001, S82.002, and S82.009 cover unspecified patella fractures. S82.01 through S82.04 cover the named patterns, meaning osteochondral, longitudinal, transverse, and comminuted displaced fractures. S82.09 is the “other” bucket, used when the record names a patella fracture that none of those patterns fit.

CPT codes that commonly travel with S82.091N

At a nonunion follow-up, the procedure performed drives CPT selection, and the diagnosis code supports medical necessity for it. The codes below show up most often on type III patella nonunion claims.

Verify each one against the current AMA codebook before you submit, since CPT is revised annually. The AMA CPT code set overview is the authoritative reference.

Global period is what to watch on this list. If the original fracture surgery is still inside its 90-day global period, an unrelated follow-up needs the right modifier. A return to the operating room for the nonunion needs modifier 78.

Check the surgery date before the claim goes out.

Six mistakes that send S82.091N claims back

Each of these turns up repeatedly on orthopedic audits. Fixing them upstream costs far less than working the appeal.

• Assigning N after a type I or II open fracture. This is the big one. N is reserved for Gustilo type IIIA, IIIB, and IIIC. A type I or II open patella fracture with nonunion is S82.091M. Read the original operative note, not the follow-up summary.
• Assigning N to a closed fracture. A closed right patella fracture with nonunion is S82.091K. Fracture type is fixed at the original injury and never changes later in the episode.
• Keeping the initial encounter code at follow-up. Coders often default to S82.091C, the code from the original injury. Once active treatment ends, the character has to move to the subsequent set.
• Coding nonunion when the note describes delayed healing. J means union is still progressing, just slowly. N means it has stopped. Assign N only on evidence of failed union.
• Coding nonunion when the note describes malunion. A patella that healed in poor alignment is S82.091R, not S82.091N. United but crooked is a different problem from not united at all.
• Dropping laterality. S82.091N is right side only. The left patella equivalent is S82.092N. Unspecified-side codes invite both a denial and an audit note.

When one of these does slip through, the remittance advice usually tells you which. Our guide to denial codes in medical billing maps the common CARC and RARC codes to the correction each one needs. That is the fastest route from a rejection to a clean resubmission.

Which Excludes notes apply, and which codes to add alongside

S82.091N inherits instructions from S82 and from the S80-S89 block. Check them against the rest of the diagnosis list before the claim leaves.

• Excludes1 at S82: traumatic amputation of lower leg (S88.-). An Excludes1 note means never code both. The amputation replaces the fracture as the injury descriptor.
• Excludes2 at S82: fracture of foot except ankle (S92.-), and periprosthetic fracture around an internal prosthetic ankle joint (M97.2) or knee implant (M97.1-). Excludes2 means the conditions differ, so you may report both when both are documented.
• Excludes2 at S80-S89: burns and corrosions (T20-T32), frostbite (T33-T34), and venomous insect bite or sting (T63.4). The block also excludes injuries of ankle and foot other than fracture of ankle and malleolus (S90-S99).
• Category note at S82: the open fracture designations follow the Gustilo classification. There is no separate add-on code for the grade, because the 7th character already carries it.
• Additional codes to consider: osteomyelitis (M86.-) if the nonunion is infected. Add a lower leg blood vessel injury code (S85.-) where a type IIIC fracture involved arterial repair.

That last point is easy to lose. Type IIIC is defined by arterial injury. If the vascular repair still matters clinically at this encounter, it needs its own code alongside S82.091N. New to this level of specificity? Our primer on medical billing covers how diagnosis and procedure codes support each other on a claim.

A 60-second check before the claim goes out

Run these seven questions over the claim. If any answer is no, the claim is not ready.

1. Does the record say right patella?
2. Does the original injury record say the fracture was open?
3. Does it name a Gustilo grade of IIIA, IIIB, or IIIC?
4. Has active treatment of the original fracture ended?
5. Does the clinician use the word nonunion, or cite imaging that shows it?
6. Is the code on the claim seven characters long, ending in N?
7. Is the external cause code present with 7th character D, and are Y92, Y93, and Y99 left off?

Keeping fracture codes intact from the note to the claim

Most S82.091N denials start as a documentation handoff problem. The grade was documented and the coder knew the rule. The detail simply did not survive the trip from the operative report to the claim form six months later. That is a systems issue, and software is where you fix it.

Pabau, practice management software built for healthcare practices, keeps the diagnosis attached to the record rather than to someone’s memory. Coders search an ICD-10 lookup library inside the EMR, so the seven-character code goes on the encounter at the point of care.

That code then pre-fills onto the claim instead of being retyped. Required-field validation runs before submission, so an incomplete code or a missing field surfaces while the claim is still yours to fix.

From there, Pabau’s claims management submits electronically through Claim.MD in the US, Healthcode in the UK, and Tyro in Australia. The dashboard then shows where each claim stands. Pabau does not decide whether N or M is correct. It keeps the code you chose intact all the way to the payer.

Keep the whole seven-character code on the claim

Pabau puts an ICD-10 lookup inside the EMR, pre-fills the code onto the claim, and checks required fields before you submit. See how it handles complex fracture follow-ups.

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Conclusion

S82.091N comes down to one distinction. The right patella was broken by a Gustilo type IIIA, IIIB, or IIIC open fracture. Active treatment has finished, and the bone has not united.

Change any one of those facts and the code changes with it. Type I or II shifts the letter to M, a closed fracture to K, delayed healing to J, and malunion to the R character.

If codes keep getting lost between the chart and the claim, fix it at the workflow level rather than the appeal level. Book a demo and see how Pabau carries a seven-character diagnosis from the encounter note straight through to submission.

Continue your research

Working a rejection on a fracture claim? Denial codes in medical billing explains the common CARC and RARC codes and the correction each one calls for.

New to the claim lifecycle? What is medical billing walks through how a diagnosis code, a procedure code, and the documentation behind them combine into a payable claim.

Seeing repeat denials across a whole code family? Denial management in healthcare covers how to spot the pattern, appeal effectively, and stop the same error recurring.

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