ICD-10 code S42.242P: 4-Part fracture of surgical neck of left humerus

Key takeaways

ICD-10 code S42.242P covers a 4-part fracture of the surgical neck of the left humerus, subsequent encounter with malunion.

The code is valid for HIPAA-covered transactions in FY2026, which runs from October 1, 2025 through September 30, 2026.

The 7th character ‘P’ marks a fracture that healed in a non-anatomical position. Nonunion is a different outcome and takes the character ‘K’.

S42.242 on its own is non-billable, so the full seven-character code has to reach the claim.

Practice management software like Pabau helps orthopedic and physical therapy practices document encounter type and laterality before a claim goes out.

ICD-10 code S42.242P is a billable ICD-10-CM diagnosis code. Its full official description is 4-part fracture of surgical neck of left humerus, subsequent encounter for fracture with malunion. You use it once active fracture treatment has ended and the physician has documented that the bone healed out of alignment.

The code is valid for HIPAA-covered electronic transactions in fiscal year 2026. That period runs from October 1, 2025 through September 30, 2026. This page covers the 7th character system, the sibling codes, the documentation payers look for, and the errors that trigger claim edits.

S42.242 without a 7th character is non-billable. A full seven-character code has to reach the payer before the claim can process. Validity for HIPAA transactions is also not a promise of payment, because coverage policies vary by plan.

Clinical description: 4-part fracture of the surgical neck of the left humerus

The surgical neck of the humerus is the narrowed region just below the greater and lesser tuberosities. It is anatomically distinct from the anatomical neck, which sits immediately below the humeral head. Fractures here account for a large share of proximal humerus injuries, particularly in older adults after low-energy falls.

A 4-part fracture, as described by the Neer classification, involves four separate fragments. Those are the humeral head, the greater tuberosity, the lesser tuberosity, and the humeral shaft. This configuration disrupts the blood supply to the humeral head. It carries a higher risk of avascular necrosis than a 2- or 3-part fracture.

Surgical management often involves open reduction and internal fixation, known as ORIF, or shoulder arthroplasty. Treatment decisions rest with the treating clinician and sit outside the scope of this coding reference.

• Typical patients: Adults over 60, with osteoporosis as a frequent contributing factor
• Mechanism: Low-energy falls in older patients, and high-energy trauma in younger ones
• Left vs. right laterality: S42.242P specifies the left side, and S42.241P codes the equivalent right-side fracture
• Neer classification: A 4-part grouping based on fragment count and displacement
• Common treatments: ORIF with a proximal humerus locking plate, hemiarthroplasty, or reverse total shoulder arthroplasty

Malunion at this site often leaves lasting loss of shoulder range of motion, so these patients come back for repeated follow-up visits. Whether those visits are logged in a physical therapy EMR or in occupational therapy software, each one needs its encounter type recorded before billing.

The malunion diagnosis itself must also be in the record before S42.242P or any sibling code can be assigned.

Understanding the 7th character ‘P’

ICD-10-CM fracture codes use a 7th character to record the type of encounter. Without it, S42.242 is incomplete and cannot go out as a billable claim. The character ‘P’ has a narrow meaning that sets it apart from the characters next to it.

What malunion means: Malunion is a fracture that healed, but in a non-anatomical position, leaving altered alignment, angulation, or rotation. Nonunion is the opposite outcome, where the fragments never unite at all.

Assign ‘P’ from the physician’s documented diagnosis, not from your own reading of the imaging. Per the ICD-10-CM Official Guidelines, the 7th character has to reflect the encounter as documented.

In fracture coding, “initial encounter” does not mean the first time the patient saw a physician. It means the period when the patient is receiving active treatment for the fracture. Once the fracture is considered healed, even in a malunited position, later visits take a subsequent-encounter character.

The ‘P’ extension keeps the same meaning across the rest of the humerus families. Another humerus malunion code such as S42.489P reads exactly the same way. What changes between those codes is the anatomy and the laterality, never the definition of malunion.

S42.242P code hierarchy and parent codes

Knowing where S42.242P sits in the ICD-10-CM tabular list helps you check a code choice before it goes out. Each level narrows the anatomy first, then the laterality, then the encounter.

The right-side equivalent is S42.241, with the same set of 7th characters, and S42.249 covers the unspecified side. Laterality has to be documented before you can pick S42.242P over S42.241P or S42.249P. Where the record does not support a 4-part pattern, the unspecified surgical-neck family that includes S42.212D applies instead.

Sibling codes: All S42.242 variants by encounter type

The codes below all share the same anatomical base, a 4-part fracture of the surgical neck of the left humerus. Only the 7th character changes. Picking the wrong sibling is the most common source of claim edits for this fracture.

K vs. P: ‘K’ records nonunion, where the fragments never united. ‘P’ records malunion, where the bone united in the wrong position. Those two are the pair most often confused at audit, especially when a chart notes complicated healing without naming the outcome.

Only the treating physician’s documented diagnosis settles it, so query the chart rather than infer from imaging. Where the physician has documented nonunion, S42.242K is the code that belongs on the claim.

How to use S42.242P: Coding guidelines and documentation requirements

The ICD-10-CM Official Guidelines for Coding and Reporting, maintained by the National Center for Health Statistics and CMS, govern how S42.242P is applied. Practices running claims management software that understands encounter-type logic cut the manual review a coder faces on complex fracture follow-ups.

1. Confirm the encounter type: S42.242P is a subsequent-encounter code. The patient must already have had active treatment for the fracture. The current visit has to be ongoing care, not the visit where treatment began.
2. Verify the malunion diagnosis: The physician has to state malunion in the record. A note reading “healed fracture” with nothing about alignment does not support the ‘P’ character. The clinical documentation needs the word malunion, or a description of bone healed in a non-anatomical position.
3. Confirm left-side laterality: The record has to name the left humerus. Where laterality is missing, S42.249P covers the unspecified side, though payers increasingly reject unspecified laterality on extremity fractures.
4. Confirm the fracture part count: The record has to support four fragments. A 2-part or 3-part fracture belongs in a different sub-category, S42.22x or S42.23x respectively.
5. Check payer-specific requirements: Some plans ask for prior authorization or extra documentation on malunion management. FY2026 validity is not a guarantee of payment.

Digital intake forms and visit notes that capture fracture history, laterality, and healing status head off most malunion coding errors. Accurate encounter-type documentation is also the first thing an auditor looks for when a subsequent-encounter claim is questioned.

Common coding errors and how to avoid them

Most denials on this code trace back to one of five errors. Each one has a fix that happens before the claim goes out, not after the denial arrives.

• Using S42.242P for an initial encounter: ‘P’ is strictly a subsequent-encounter designator. Applying it at the visit where active treatment starts produces a clinical logic mismatch and a likely rejection. Surgery, casting, and closed reduction all count as active treatment, so they take ‘A’ for closed or ‘B’ for open.
• Confusing malunion (P) with nonunion (K): Malunion means the fracture healed out of position. Nonunion means it never united. Both are subsequent-encounter complications, and both are clinically distinct. Coding ‘P’ against a documented nonunion is an inaccurate diagnosis code and a common audit trigger. Check the patient care management record for the physician’s own wording.
• Omitting or assuming laterality: S42.242P specifies the left side. Where the record does not say left, query the physician instead of assuming. Laterality errors are a leading cause of orthopedic claim edits.
• Submitting S42.242 without a 7th character: The parent code is incomplete and non-billable as submitted. Some EHR systems autofill the base code and leave the extension off, so check the claim before it goes.
• Defaulting to ‘D’ after surgery: Follow-up visits after ORIF or arthroplasty still take S42.242P where the operative notes document malunion. Surgery on its own does not make the healing routine.

ICD-9-CM to ICD-10-CM crosswalk for S42.242P

Mapping between ICD-9-CM and ICD-10-CM is approximate rather than a direct equivalence. ICD-9-CM used fewer specificity levels and did not consistently capture laterality or fracture part count. As ResDAC notes, the move to ICD-10 expanded fracture code specificity sharply, so one ICD-9 code can map to several ICD-10 codes.

Use these entries for legacy reconciliation and audit trails only. Do not lean on an ICD-9 predecessor to validate a current ICD-10-CM selection. AAPC’s code lookup carries crosswalk references, and the CDC’s ICD-10-CM tool is the authority for the current code set.

How Pabau keeps encounter type and laterality in the record

In most practices the coder learns about a malunion after the fact. The operative note says one thing, the follow-up note says another, and the query goes back to the physician a week later.

Practice management software like Pabau puts those fields in the note itself. Laterality, fragment count, and healing outcome are captured as structured entries at the visit, not reconstructed from free text later. Every follow-up encounter stays attached to the same patient record, so the encounter type is obvious when the claim is built.

Records stay in one HIPAA-compliant system, so the imaging notes, the operative report, and the coding detail are never in separate tools. When a payer questions an S42.242P claim, the support is already assembled.

Reduce fracture coding errors with better documentation

Capture the encounter type, laterality, and healing outcome at the visit. Coders get what they need before the claim is built, so fewer denials come back.

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Conclusion

S42.242P is a narrow code, and that is what makes it easy to get wrong. It holds up only when the record names a documented malunion, a subsequent encounter, and the left side.

The fix sits upstream of billing. Build the note so those three facts are there the first time, and the coding decision stops being a judgment call. Book a demo to see how Pabau captures encounter type and laterality at the point of care.

Continue your research

Coding the nonunion outcome instead? S42.242K covers the same fracture where the fragments never united.

Need the humeral shaft equivalent? S42.343K handles a displaced spiral shaft fracture that has gone to nonunion.

Working on a distal humerus claim? S42.475G covers a left transcondylar fracture with delayed healing.

Coding a sequela rather than a complication? S42.126S shows how the ‘S’ extension works on a shoulder girdle fracture.

Assessing shoulder strength at follow-up? Full can test walks through the procedure and how to read the result.

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