ICD-10 code S52.253K: displaced comminuted fracture of ulnar shaft with nonunion

Key takeaways

ICD-10 code S52.253K describes a displaced comminuted fracture of the shaft of the ulna, unspecified arm, at a subsequent encounter for a closed fracture with nonunion.

S52.253K is a billable, specific ICD-10-CM code; the current fiscal-year edition took effect October 1, 2025.

The 7th character K means subsequent encounter for a closed fracture with nonunion — it never applies to an open fracture and never means malunion.

S52.253K belongs to the ulnar shaft fracture family (S52.2), not the radius shaft family (S52.3) — mixing up the two bones is the single most common error coders make on this code.

Practice management software like Pabau helps orthopedic and physical therapy practices capture laterality, closed-versus-open status, and healing status in the clinical record, so the coding team can select the right 7th character before a claim goes out.

ICD-10 code S52.253K describes a displaced comminuted fracture of the shaft of the ulna, unspecified arm, at a subsequent (follow-up) encounter for a closed fracture that has failed to heal, known as nonunion. It is not an open fracture code, a radius code, or a malunion code.

Coders mix up these three details because the S52 forearm family groups the radius and ulna into separate but similarly numbered subcategories, and the Gustilo-based 7th character set uses letters that look interchangeable at a glance. This page breaks down every character of the code, clarifies nonunion versus malunion and delayed union, and lists the documentation needed before submitting it.

Accurate fracture aftercare coding matters beyond compliance. Orthopedic and physical therapy practices managing these complex cases benefit from orthopedic practice management systems that keep clinical documentation and the coding workflow in the same record, so what a provider writes at a follow-up visit lines up with what a coder needs to select the right code.

ICD-10 code S52.253K: quick reference

ICD-10 code S52.253K is a billable, valid code under the current ICD-10-CM edition, effective October 1, 2025. The table below provides an at-a-glance summary for quick coder reference.

Breaking down ICD-10 code S52.253K character by character

Each character in ICD-10 code S52.253K carries a distinct clinical meaning. Coders unfamiliar with the S52 family frequently submit the wrong sibling code because they misread the 4th character (which bone) or the 7th character (encounter, closed/open status, and healing status). The table below decodes every position.

The “unspecified arm” designation (the 3 in S52.253) is appropriate only when the treating physician’s documentation does not specify right or left laterality. When laterality is documented, coders should use S52.251 (right arm) or S52.252 (left arm) instead. And because S52.2 (ulna) and S52.3 (radius) are separate categories with parallel numbering, always confirm which bone the physician documented as fractured before assigning either family.

Open versus closed fracture status in the S52.253 family

S52.253K itself is a closed fracture code. The Gustilo-Anderson classification, the standard surgical framework for grading open fractures by wound severity, contamination, and soft tissue involvement, only applies to the open-fracture siblings in this family (7th characters B, C, E, F, H, J, M, N, Q, and R). Per the CMS ICD-10-CM coding guidelines, coders assign what is documented, not what they infer, and a closed fracture never carries a Gustilo grade because there is no open wound to classify.

If the physician’s operative or emergency note documents an open wound at the fracture site, a different sibling code applies (see the sibling table below), and the Gustilo grade must come from the treating surgeon’s documentation, never from a coder’s inference. An open fracture also typically pairs with a debridement code such as CPT 11010 on the initial claim, which reinforces why the closed-versus-open distinction has to be settled before either code is selected. Sports medicine and orthopedic teams using sports medicine clinic software can document open-versus-closed status directly in the clinical record at the point of care, so this distinction never has to be reconstructed after the fact.

What is nonunion and how does it affect code selection?

Nonunion occurs when a fractured bone fails to heal at all, with no bony bridging visible across the fracture site on imaging within the expected healing window. It is distinct from two related conditions that coders must not conflate:

• Nonunion: the fracture failed to heal at all (7th character K for a closed fracture, M or N for an open fracture depending on Gustilo type)
• Malunion: the bone healed, but in an incorrect position (7th character P for a closed fracture, Q or R for an open fracture)
• Delayed union: healing is slower than expected but still progressing (7th character G for a closed fracture, H or J for an open fracture)

For ICD-10 code S52.253K, nonunion must be confirmed on imaging, typically a plain radiograph or CT scan, and documented by the treating provider as a confirmed finding. Coders cannot infer nonunion from a patient complaint of pain or limited range of motion alone.

Accurate differentiation between nonunion, malunion, and delayed union is a common failure point in fracture aftercare coding, and it is compounded on this code by the closed-versus-open distinction covered above. Both axes, healing status and openness, have to match the documentation independently before the 7th character is correct.

Understanding the 7th character in ICD-10 fracture codes

The 7th character is the most critical element in fracture coding accuracy. For shaft fracture codes in the S52 category, the 7th character encodes three pieces of information simultaneously: the encounter type (initial vs. subsequent vs. sequela), whether the fracture was open or closed (and, if open, the Gustilo type), and the healing status or complication. Other fracture regions use their own classification systems, such as the Danis-Weber classification for ankle fractures, but the same principle applies: the classification the physician documents, not the coder’s inference, drives the 7th character. The table below shows the full set of valid 7th characters for the S52.253 family.

Selecting K versus P is a frequent source of claim denials. K means the bone never healed. P means it healed, but crooked. The physician’s imaging report and clinical note must explicitly state one or the other. Coders who rely on the CDC/NCHS ICD-10-CM web tool can verify code descriptions and tabular notes directly to confirm the correct 7th character before submission.

Code hierarchy and parent codes

Understanding where ICD-10 code S52.253K sits in the ICD-10-CM hierarchy helps coders verify they are in the correct code family, and specifically in the ulna branch rather than the radius branch. The WHO ICD-10 browser provides the international classification context; the US ICD-10-CM adds clinical modification detail below the base codes.

• 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
• S52.25: Comminuted fracture of shaft of ulna
• S52.253: Displaced comminuted fracture of shaft of ulna, unspecified arm
• S52.253K: …subsequent encounter for closed fracture with nonunion

Physical therapy practices managing long-term fracture rehabilitation can benefit from physical therapy practice management platforms that connect clinical progress notes with the aftercare codes documented on each encounter date.

Sibling codes in the S52.253 family

ICD-10 code S52.253K belongs to the S52.253 sibling group. Selecting the wrong sibling, or reaching for the parallel radius code by mistake, is one of the most common fracture coding errors. The encounter type, open-versus-closed status, and healing status must all match the clinical documentation exactly before a 7th character is assigned.

When to use ICD-10 code S52.253K: documentation requirements

Five conditions must all be present and documented before ICD-10 code S52.253K is appropriate. Missing any one of them means a different code applies. Practices with strong HIPAA-compliant medical documentation workflows catch missing documentation before submission rather than after a denial.

• Confirmed displaced comminuted fracture of the shaft of the ulna: the fracture pattern must be documented as comminuted (multiple fragments) and displaced, and the fractured bone must be the ulna, not the radius. Nondisplaced variants and radius fractures map to different codes.
• Unspecified arm: laterality was not specified or documented in the physician’s note. If the record documents right or left, use S52.251K or S52.252K respectively.
• Subsequent encounter: this code is for follow-up visits only. The acute injury encounter uses the A 7th character (initial, closed fracture). Using K on an emergency department visit for the original injury is incorrect.
• Closed fracture confirmed: no open wound at the fracture site. If the physician documented an open fracture at any point in the episode, a different 7th character (E/F/H/J/M/N/Q/R, depending on Gustilo type and healing status) applies instead of K.
• Nonunion confirmed on imaging: the radiologist report or attending physician note must document nonunion, failure to heal, as a confirmed finding, not a suspicion, and not simply “slow to heal” (which is delayed union, character G).

Accurate medical form documentation at each follow-up visit is what makes these five conditions auditable. When documentation is incomplete, the coder must query the provider rather than assume.

Common coding errors and how to avoid them

ICD-10 code S52.253K has several specific error patterns that generate denials or audit flags. These are the most frequent mistakes across orthopedic and rehabilitation billing teams.

• Confusing the ulna with the radius: S52.2 (this code’s category) is the ulna; S52.3 is the radius. The two categories use parallel numbering, so a coder scanning quickly can land on the wrong bone entirely.
• Using an initial encounter code for follow-up visits: S52.253A (initial, closed) is correct at the trauma encounter. Every subsequent visit uses the appropriate subsequent-encounter character. Submitting A on a week-12 rehabilitation visit is a payer audit trigger.
• Confusing nonunion (K) with malunion (P): both are complications documented at a subsequent encounter for a closed fracture, but they are clinically and codologically distinct. Verify the imaging report before selecting the 7th character.
• Assigning an open fracture type when the fracture is closed: S52.253K carries no Gustilo grade. If a Gustilo type appears anywhere in the documentation, the fracture is open and a different 7th character applies.
• Using unspecified laterality when laterality is documented: if the record anywhere states “right ulna” or “left ulna,” the coder must use the specified laterality code, not the unspecified S52.253 parent.
• Skipping the 7th character entirely: submitting S52.253 without a 7th character produces an invalid, non-billable code. All S-section fracture codes require the 7th character to be billable.

The encounter-type logic is consistent across the entire ICD-10-CM injury chapter: A or initial characters are for the acute event; D through R characters are for aftercare, split by open/closed status and healing outcome; S is for sequela. The same framework applies to S52.253K.

Associated CPT codes for displaced comminuted fracture of the shaft of the ulna

ICD-10 diagnosis codes pair with CPT procedure codes on the same claim. For patients managed under ICD-10 code S52.253K, the associated CPT codes depend on what clinical service is being provided at the follow-up encounter. The table below lists common pairings. Verify current descriptors and reimbursement values through the AAPC Codify lookup or the current AMA CPT manual before submission.

CPT 25545 is specific to the ulnar shaft; it is not interchangeable with the distal-radius fixation codes (25607-25609), which apply to a different bone and a different anatomical region. The E/M level for a follow-up visit comes from medical decision making or time, not from how much the note says. Reimbursement amounts and bundling rules change annually, so verify each code against the current AMA CPT manual before using it on claims.

Coding and documentation workflow for orthopedic practices

Efficient fracture aftercare coding depends on a consistent intake and documentation workflow at each follow-up visit. Orthopedic practices that standardize their encounter note templates reduce the back-and-forth provider queries that delay claim submission. Reviewing physical therapy billing rules shows how the same documentation habits keep CPT and ICD-10 pairings audit-ready for orthopedic aftercare.

• Step 1 – Confirm the bone: is the fracture in the ulna (S52.2) or the radius (S52.3)? The two are separate categories with similarly structured but non-interchangeable codes.
• Step 2 – Confirm encounter type: is this the original injury visit or a follow-up? The answer determines initial vs. subsequent character assignment.
• Step 3 – Verify open vs. closed status: the operative or emergency record documents whether the fracture was open (and, if so, the Gustilo grade) or closed. This governs subsequent encounter coding throughout the care episode.
• Step 4 – Review current imaging: the radiology report must state the healing status, whether routine, delayed, nonunion, or malunion, before the coder selects the 7th character.
• Step 5 – Check laterality: right arm = S52.251K; left arm = S52.252K; unspecified = S52.253K. Default to specified when the record supports it.
• Step 6 – Pair with the appropriate CPT: match the procedure performed at this encounter with the correct procedure code. E/M level and procedure codes must reflect the documented work.

Using EHR integration for billing connects clinical notes directly to the coding workflow, so the coder has the surgical record, imaging report, and encounter note in one view when assigning the 7th character. This reduces the time spent chasing documentation across separate systems and lowers the risk of selecting the wrong sibling code, or the wrong bone entirely.

How Pabau supports fracture aftercare documentation and coding accuracy

Most fracture aftercare coding errors trace back to a mismatch between what happened at the visit and what made it into the record: the surgeon’s Gustilo grade never got typed up, the radiologist’s nonunion finding sat in a separate imaging system, or a follow-up note simply repeated the initial encounter’s language. Practice management software like Pabau prevents that mismatch by keeping the clinical documentation for each follow-up visit, laterality, open-versus-closed status, and the healing status confirmed on imaging, in one structured record tied to the encounter date.

That structured record is what a coder actually needs to choose between S52.253K, S52.253P, and S52.253D correctly, and to catch a radius-versus-ulna mix-up before it reaches a claim. Pabau does not submit or adjudicate US claims itself; instead, it gives your orthopedic or physical therapy practice’s existing billing workflow a complete, audit-ready clinical picture of the fracture at every stage of the care episode, so the coding decision is supported by documentation rather than guesswork.

Document fracture aftercare accurately from day one

Pabau's clinical documentation tools let orthopedic and physical therapy practices record laterality, open-versus-closed status, and healing status at every follow-up visit, so the coding team has everything needed to select the correct ICD-10 7th character before it reaches your billing workflow.

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Conclusion

ICD-10 code S52.253K is narrow, and it is narrow in a way that trips up coders in two directions at once: get the bone wrong (ulna, not radius) and you have the wrong category before you even reach the 7th character; get the healing status wrong (nonunion, not malunion) and a correctly identified fracture still lands on the wrong code. Neither error is obvious from the code string alone, which is exactly why both recur.

Treat the code as two independent checks rather than one lookup: confirm the fractured bone and its closed status from the operative or emergency record, then confirm the healing outcome from the current imaging report. When both check out, S52.253K is billable as written; when either does not, a sibling code, or an entirely different category, applies instead. Book a demo to see how Pabau helps orthopedic and physical therapy practices keep that documentation complete and accurate at every follow-up visit.

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