ICD-10 Code S32.402K: Left acetabulum nonunion

Key takeaways

ICD-10 Code S32.402K describes an unspecified fracture of the left acetabulum at a subsequent encounter where nonunion has occurred.

The 7th character K specifically designates a subsequent encounter for fracture with nonunion, distinguishing it from delayed healing (G) and sequela (S).

S32.402K is a fully billable, HIPAA-valid code for fiscal year 2026, covering October 1, 2025 through September 30, 2026.

Accurate documentation must confirm left-side laterality, nonunion via imaging, and that the encounter is a follow-up rather than initial active treatment.

Pabau’s claims management software helps orthopedic and physical therapy practices submit S32.402K and related fracture codes accurately.

ICD-10 Code S32.402K is the billable ICD-10-CM diagnosis code for an unspecified fracture of the left acetabulum at a subsequent encounter with fracture nonunion. The acetabulum is the cup-shaped socket of the hip joint. Nonunion means the fracture failed to unite within the expected healing timeframe.

This code is valid for HIPAA-covered electronic transactions from October 1, 2025 through September 30, 2026.

Denials for S32.402K claims rarely trace back to the clinical picture. The usual cause is a missing 7th character, an incorrect laterality, or an ambiguous encounter type. Any one of those turns a clean claim into a denial. Fracture codes like S82.422B demand the same character-by-character precision, and S32.402K is no exception.

What does S32.402K mean? Breaking down the code

Each character in S32.402K carries a specific clinical meaning. Understanding the structure prevents the most common coding errors. These include selecting the wrong laterality, choosing D instead of K, and submitting the 6-character parent code without the required 7th character extension.

The term “unspecified” in the code description refers to fracture type, not to the patient’s identity or anatomy. When the treating physician’s documentation does not classify the fracture as displaced or nondisplaced, coders must use the unspecified subtype.

This is a common documentation shortfall that thorough, current patient records can help prevent in future encounters.

Understanding the 7th character K for fracture nonunion

The 7th character is the defining distinction between fracture encounter codes. Getting it wrong is the most common reason S32.402 claims come back denied or downcoded.

According to the CMS ICD-10-CM coding guidelines, subsequent encounter codes apply once the patient has completed active treatment. At that point, the patient is receiving routine care during the healing or recovery phase.

The critical distinction between K and G is radiographic, not temporal. Delayed healing (G) means the fracture is still progressing toward union but more slowly than expected. Nonunion (K) means that progression has stopped and union is no longer occurring without intervention. Both are subsequent encounter codes, but they describe clinically different outcomes with different management implications.

S32.402K code hierarchy and acetabulum fracture classification

Understanding where S32.402K sits in the ICD-10-CM hierarchy helps coders navigate the tabular list. It also helps them select the correct parent category when a complete code is not immediately known.

The CDC/NCHS ICD-10-CM coding tool provides the full hierarchical navigation for every fiscal year.

Note that S32.402 is not itself a billable code. It requires a 7th character to be valid for claim submission. Submitting S32.402 without the K (or any other valid extension) will result in a rejection for code specificity.

Practices that use claims management software with built-in code validation can catch this class of error before submission.

Related and sibling codes to S32.402K

Coders regularly need to navigate between laterality variants, encounter types, and displaced versus nondisplaced fracture subtypes. The table below covers the most clinically relevant sibling codes.

For a full list of S32 acetabulum fracture codes, the AAPC ICD-10-CM code lookup provides searchable access to all variants.

Documentation sometimes specifies the anatomical wall: anterior, posterior, anterior column, posterior column, or dome. When it does, coders should use the more specific code instead of unspecified S32.402K. This same specificity principle applies to M16.4, where documentation detail alone decides which variant a coder can use.

When to use S32.402K: clinical coding guidelines for subsequent encounter fractures

The question coders must answer before selecting S32.402K is not just “has the fracture failed to heal?” but also “is this encounter still active treatment or has care transitioned to follow-up management?”

According to the ICD-10-CM Official Guidelines, Section I.C.19, subsequent encounter codes apply once the patient has received active treatment. Subsequent encounters are then for routine care. Payers, including HIPAA-covered Medicare and Medicaid programs, expect this distinction to be reflected in both the claim code and the supporting documentation.

S32.402K applies in these clinical scenarios:

• A patient returns to the orthopedic surgeon 4-6 months after initial acetabulum fracture repair, and imaging confirms absent bridging callus (radiographic nonunion)
• A physical therapy practice sees a patient for post-fracture rehabilitation, and the referring physician’s notes document confirmed nonunion of the left acetabulum
• An orthopedic follow-up visit where the surgeon documents that union has not occurred and additional intervention (bone grafting, revision fixation) is being considered
• A pain management follow-up where the working diagnosis remains an unhealed left acetabulum fracture with nonunion confirmed by CT or MRI

S32.402K should NOT be used when the patient is still in the initial active treatment phase, even if nonunion seems likely. As long as the encounter involves active treatment decisions (surgery planning, casting, acute management), 7th character A applies. The 7th character transitions from A to D/G/K based on the nature of the encounter, not on the number of visits.

Physical therapy and rehabilitation practices managing orthopedic patients benefit from physical therapy EMR software that supports accurate coding workflows across the full fracture recovery episode.

Includes, excludes, and coding notes for S32.402K

The S32 category carries instructional notes in the ICD-10-CM tabular list that apply to all codes within it, including S32.402K. Coders should review these notes each time they use a code from this category, as they affect sequencing and additional code requirements.

Applicable to S32

• A fracture not indicated as displaced or nondisplaced should be coded to displaced
• A fracture not indicated as open or closed should be coded to closed

Excludes1 (cannot be coded simultaneously with S32.402K)

• Transection of abdomen (S38.3)

Excludes2 (may be coded alongside S32.402K when both conditions exist)

• Fracture of hip NOS (S72.0-)

The Excludes1 note means that a transection of the abdomen (S38.3) cannot be coded alongside S32.402K, since the two conditions describe clinically distinct trauma patterns. The Excludes2 note works differently. Fracture of hip NOS (S72.0-) can be coded alongside S32.402K if both are documented. The acetabulum is the socket, while S72 codes cover the femoral head and neck.

These are separate structures that can each fracture independently. Coders managing high volumes of orthopedic cases can review T31.42 to see how category-level notes cascade through child codes elsewhere in the tabular list. Sports medicine practices that treat pelvic and acetabular injuries encounter this same distinction often.

Documentation requirements for accurate S32.402K coding

Claim denials for ICD-10 Code S32.402K almost always trace back to one of four documentation issues. Understanding each one helps practices build better intake and progress note templates that satisfy payer requirements at the first submission. The same documentation principles govern medical decision making for musculoskeletal practices.

1. Laterality confirmation

The note must explicitly state “left” acetabulum or “left hip.” A reference to “the acetabulum” or “the affected hip” without a laterality designation forces the coder to use an unspecified laterality code. That code is not the same as S32.402K. Left vs. right laterality must be clinically documented, not inferred from prior records.

2. Encounter type confirmation

The note should make clear that this is a follow-up visit, not an encounter for new or active fracture treatment. Language such as “returns for follow-up of left acetabulum fracture” or “subsequent visit for orthopedic management of left hip fracture” signals a subsequent encounter. That means a subsequent-encounter 7th character is appropriate, not an initial-encounter code.

3. Imaging evidence of nonunion

Nonunion is a radiographic finding, not a clinical judgment alone. The note must reference imaging such as an X-ray, CT, or MRI. It must also include a specific finding, such as absent bridging callus or persistent fracture lines without healing. Without an imaging reference, payers may challenge the nonunion designation and request K-to-D downcoding.

4. Fracture type documentation

The original operative or radiology report sometimes specifies the fracture as displaced or nondisplaced and identifies the anatomical wall: anterior, posterior, or column. When it does, the more specific code should replace S32.402K.

The “unspecified” designation is only appropriate when that detail is genuinely absent from all available records. Complete client records that carry forward the original fracture characterization reduce the frequency of unspecified coding over a patient’s treatment course.

How Pabau supports orthopedic and fracture billing workflows

Coding accuracy for fracture nonunion encounters depends on two things. The first is clean documentation at the point of care. The second is a claims workflow that validates codes before submission.

Practices managing post-fracture patients across extended episodes often deal with EHR integration challenges that create disconnects between clinical notes and billing records.

Pabau’s claims management software helps orthopedic, physical therapy, and sports medicine practices submit fracture-related codes, including ICD-10 Code S32.402K. Built-in validation, structured documentation templates, and direct payer connectivity catch errors before a claim goes out.

Practices can reduce the manual reconciliation burden that typically follows high-volume subsequent-encounter fracture billing.

Reduce fracture coding errors before they become denials

Pabau's claims management tools help orthopedic and physical therapy practices validate ICD-10 codes, document encounters accurately, and submit cleaner claims from day one.

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Conclusion

Fracture nonunion is a complex coding scenario in orthopedic billing. The complexity comes from the documentation it requires, not from the code itself. ICD-10 Code S32.402K is valid, billable, and HIPAA-accepted for FY2026. Holding up against payer scrutiny requires confirmed left-side laterality, a subsequent-encounter designation, and imaging-supported nonunion.

When documentation meets that standard, S32.402K flows through claims cleanly. When it does not, the most common outcome is a downcode to S32.402D or a denial for insufficient medical necessity. Practices that want to reduce that risk can look into practice management systems that connect clinical documentation directly to billing.

Book a demo to see how Pabau helps orthopedic and physical therapy practices code fracture encounters accurately from day one.

Continue your research

Need a reference for other fracture-adjacent ICD-10 codes? S37.502S covers a similarly complex sequela code requiring precise encounter documentation.

Looking for compliance guidance for musculoskeletal practices? Mandatory compliance for physiotherapy clinics outlines documentation standards that directly support accurate fracture coding.

Want to understand how practice software handles billing workflows? Practice management software explains how integrated billing and documentation tools reduce claim errors across specialties.

Billing for post-fracture mobility equipment? HCPCS Code E0117 covers the spring-assisted crutch coders often bill alongside a fracture recovery episode.

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