ICD-10 Code S52.356R: Malunion after an open radius fracture

Key takeaways

ICD-10 Code S52.356R describes a nondisplaced comminuted fracture of the radial shaft, unspecified arm. It applies at a subsequent encounter for an open type IIIA, IIIB, or IIIC fracture with malunion.

The 7th character R marks a subsequent encounter after a Gustilo type III open fracture. It tells the payer the bone healed with malunion.

Malunion (7th character R) is clinically distinct from nonunion (7th character K, M, or N). Malunion means the bone healed, but in the wrong position.

Practice management software like Pabau helps orthopedic and sports medicine practices submit S52.356R and related fracture codes accurately on CMS-1500 and UB-04 claim forms.

ICD-10 Code S52.356R is a billable ICD-10-CM diagnosis code for a nondisplaced comminuted fracture of the shaft of the radius, unspecified arm. It applies at a subsequent encounter, after an open fracture graded Gustilo type IIIA, IIIB, or IIIC. The bone has healed, but in the wrong position.

Here is the full ICD-10-CM description. Nondisplaced comminuted fracture of shaft of radius, unspecified arm, subsequent encounter for open fracture type IIIA, IIIB, or IIIC with malunion.

The code is valid for the 2026 ICD-10-CM edition, effective October 1, 2025. According to CMS ICD-10-CM coding resources, it can be submitted on both a CMS-1500 and a UB-04 claim form.

Code details at a glance

The table below is a quick-reference summary of S52.356R for coders and clinicians checking billing eligibility.

Orthopedic and sports medicine practices managing follow-up fracture care should confirm the 7th character before submission. Encounter-type mismatches are an avoidable source of denials.

What each part of the code description means

Each part of the description carries a distinct clinical meaning. Knowing what each one asks for makes the right code obvious.

• Nondisplaced: The fracture fragments stayed in their anatomical position. The bone broke but did not shift out of alignment at the time of injury. Displaced fractures are the contrast, where fragments separate or override.
• Comminuted: The bone shattered into three or more fragments at the fracture site. Comminuted fractures usually follow high-energy trauma such as motor vehicle accidents, falls from height, and industrial injuries.
• Shaft of radius: The fracture sits along the diaphysis, the mid-section of the radius on the thumb side of the forearm. This is not the distal end at the wrist or the proximal end at the elbow.
• Unspecified arm: The treating physician’s documentation did not say whether the fracture involved the right or left forearm. When laterality is documented, use S52.354_ (right) or S52.355_ (left) instead.
• Subsequent encounter: The patient is no longer in the acute phase. The 7th character shows this visit falls after the active treatment period, during follow-up and management of fracture healing.
• Open fracture type IIIA, IIIB, or IIIC: The original injury involved a wound communicating with the fracture site. The Gustilo-Anderson system grades that wound as type III, the most severe category.
• Malunion: The fracture has healed, but the bone segments united out of alignment. The healing process completed and the anatomical result is poor.

Practices running physical therapy documentation for post-fracture rehabilitation should confirm the encounter type before assigning this or any S52 code. The character has to match the current phase of care.

The 7th character R and fracture encounter types

The 7th character in ICD-10-CM fracture codes is not optional. It separates an initial fracture visit from a subsequent encounter that carries a healing complication.

Getting it wrong is one of the most common reasons fracture claims are rejected. The same character logic runs through the rest of the S00-T88 injury chapter, including codes such as S12.690B.

For S52.356, the valid 7th characters and their meanings are set out below.

The 7th character R therefore captures a very specific scenario. The patient had a high-energy open fracture graded Gustilo III and received acute care.

At a later visit, imaging or clinical assessment confirms the bone healed out of proper alignment. The character tracks both the phase of care and the healing outcome at once.

Gustilo classification for open fractures: Types IIIA, IIIB, and IIIC

The Gustilo-Anderson classification was first published in the Journal of Bone and Joint Surgery (Gustilo and Anderson, 1976). It grades open fractures by wound size, soft tissue damage, periosteal stripping, contamination, and vascular injury.

ICD-10-CM encodes the Gustilo type directly into the 7th character, so the grading decides the code. Type I and type II wounds share one set of characters, as S82.016B shows. All three type III subtypes share another.

S52.356R applies when the original fracture was graded Gustilo IIIA, IIIB, or IIIC. ICD-10-CM does not separate the three subtypes in the 7th character, so the coder does not have to choose between them.

What the record must support is type III. Wound length alone will not settle the subtype either. IIIA, IIIB, and IIIC turn on soft tissue coverage and arterial injury, not on how long the wound measured.

What is malunion and how does it affect code selection?

Malunion means the fracture healed, but the bone united in the wrong position. That one distinction decides whether you assign S52.356R or S52.356N. Practices using structured clinical documentation capture healing status at every follow-up, which keeps the choice straightforward.

• Malunion (7th character R for Gustilo III): The fracture fragments have united, but the bone consolidated in an abnormal position. Radiographs show callus formation and bony continuity with incorrect alignment. Healing finished, and the alignment is the problem.
• Nonunion (7th character N for Gustilo III): The fragments failed to unite after a sufficient healing period, typically six to nine months. Radiographs show a persistent fracture gap, sclerotic margins at the bone ends, or a pseudarthrosis. No callus bridges the fracture.
• Delayed healing (7th character J for Gustilo III): The fracture is still healing, but more slowly than expected. This sits between routine healing and nonunion.
• Routine healing (7th character F for Gustilo III): Healing is progressing normally at the subsequent encounter. No complication of healing is documented.

For S52.356R specifically, the documentation must state or clearly imply that the fracture healed in malposition. A note reading “fracture healed with angular deformity” or “malunion of radial shaft, open fracture Gustilo IIIB” supports the code.

Vague notes such as “follow-up open radius fracture” are not enough and should prompt a provider query.

When to use the subsequent encounter designation

The most common coding error on fracture follow-up visits involves the initial encounter characters. Coders keep using A, B, or C long after the acute phase has ended. Medical records compliance rules are unambiguous here. The 7th character must reflect the current phase of care, not the original injury.

• Initial encounter (A, B, or C): Use for every visit during the active or definitive treatment phase, including cast application, surgical fixation, and inpatient care. A patient can have several initial encounter visits while active treatment continues.
• Subsequent encounter (D through R): Use once the patient has moved into the healing phase. That covers follow-up cast changes, physical therapy referrals, and wound checks after discharge from acute care. S52.356R falls in this group.
• Sequela (S): Use for conditions that arise as a direct result of a previous fracture, once the fracture itself is fully resolved. Chronic pain or functional limitation after a malunion is coded as sequela, the same way S81.009S handles a resolved knee wound.

One practical rule settles most cases. If the treating physician is still managing the fracture itself, this is a subsequent encounter. That covers adjusting fixation, monitoring bone healing, and treating the malunion.

Once the fracture is resolved and the patient presents with a residual condition, that is sequela. Practice management software that tracks encounter phase across a multi-visit episode makes the call easier.

S52.356R code hierarchy and parent codes

Knowing where S52.356R sits in the ICD-10-CM hierarchy makes the adjacent codes easier to navigate. Digital intake forms used at the point of care should capture the same level of detail the hierarchy demands.

Related ICD-10-CM codes in the S52.356 family

S52.356R is one member of the S52.356 code family. The table below lists the sibling codes coders compare it against most often. A different arm, a different Gustilo type, or a different healing outcome sends you to one of these instead.

S52.354_ and S52.355_ cover the same fracture with documented laterality. The right arm takes S52.354R and the left arm takes S52.355R. When the physician documents which arm broke, use the laterality code rather than S52.356R.

Documentation requirements for accurate coding

Accurate assignment of S52.356R depends on what the record actually says at the time of the encounter. The CDC ICD-10-CM tool confirms the elements built into the code’s full description.

• Fracture type: Documentation must specify comminuted, meaning multifragment or shattered. “Radius fracture” alone is not enough.
• Displacement status: The note must indicate nondisplaced. If displacement status is not documented and cannot be inferred, ICD-10-CM defaults to displaced. Code from the displaced comminuted family instead: S52.351_ (right), S52.352_ (left), or S52.353_ (unspecified).
• Anatomical location: Shaft, or diaphysis, of the radius. Not the distal radius (Colles or Smith), not the radial head, not the radial neck.
• Laterality: If the treating physician documents right or left arm, use S52.354_ or S52.355_ respectively. Use S52.356_ only when the arm is genuinely unspecified in the documentation.
• Open versus closed: The note must state the fracture was open and document the wound. An open fracture designation needs physician documentation, never coder inference.
• Gustilo classification: Documentation must specify type IIIA, IIIB, or IIIC, or at minimum type III with qualifying characteristics. Without a documented Gustilo type, the coder cannot assign the R character.
• Encounter type: The note must support that this is a follow-up visit, not the initial definitive treatment visit.
• Healing status (malunion): Imaging or clinical findings documenting that the fracture has united in improper alignment. The physician’s note should use the word “malunion” or describe equivalent findings such as angulation, rotational deformity, or a shortened radius.

When any of these elements is missing, query the provider rather than assume. The AAPC code lookup is a useful second check on the S52 family before submission.

Common coding errors to avoid with S52.356R

S52.356R is a high-specificity code, and every component of its description is a potential error point. The mistakes below show up most often in audit findings for open fracture coding.

A consistent medical forms framework is what keeps capture habits steady across a team.

• Using initial encounter codes at follow-up visits: Continuing to assign S52.356C after the acute treatment phase has ended. Every visit after discharge from active fracture treatment needs a subsequent encounter character in the D to R range. In payer audits this is among the most frequently cited fracture coding errors.
• Confusing malunion with nonunion: Assigning S52.356N when the documentation describes a malunion, or the reverse. Malunion means the bone healed in the wrong position. Nonunion means the bone did not heal. Two different outcomes, two different codes.
• Omitting the Gustilo type: Assigning a code with the R character without confirmed documentation of Gustilo III classification. If the original wound documentation does not specify a Gustilo type, query the provider before assigning R.
• Ignoring laterality when documented: Assigning S52.356R when the physician’s note clearly identifies the right or left forearm. Use S52.354R or S52.355R when laterality is available. Payers increasingly deny claims where documented specificity is missing from the submitted code.
• Confusing sequela with subsequent encounter: Assigning the S character for ongoing fracture management. Sequela applies only after the fracture episode is fully resolved and a residual condition remains. While the fracture itself is still being managed, subsequent encounter applies.

How Pabau keeps fracture encounter coding accurate

In many orthopedic practices, the encounter phase lives in someone’s memory. The chart says follow-up, the last claim said S52.356C, and the character gets copied forward. The denial arrives three weeks later.

Pabau keeps the whole injury episode in one patient record. Every follow-up note sits beside the operative report, the imaging, the wound documentation, and the code you last billed.

Pabau Scribe drafts that note from the consultation itself. Healing status gets written down while the physician is still looking at the images.

From there, claims management maps the diagnosis straight onto the encounter, so nobody retypes a seven-character code from a printout. Your coders spend their time on the queries that matter, and fewer claims come back over a mismatched 7th character.

Manage fracture coding and claims in one place

Pabau's claims tools help orthopedic and sports medicine practices submit codes like S52.356R on CMS-1500 and UB-04 forms. Fewer encounter-type mismatches mean fewer denials.

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Conclusion

Finding S52.356R is the easy part. Proving that the record supports all seven of its characters is what decides whether the claim survives a payer review.

So move the check upstream, into the visit. If the physician names the Gustilo type and the healing status in the note, the coder never has to query. The character stops being a guess.

One trade-off is worth remembering. The unspecified-arm codes are legitimate, but only when the arm genuinely is not documented. Reaching for S52.356R out of habit costs you the specificity that S52.354R or S52.355R would have carried. Book a demo to see how Pabau tracks encounter phases across a full fracture episode.

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