ICD-10 Code S42.343K: Displaced spiral fracture of humerus shaft

Key takeaways

ICD-10 Code S42.343K describes a displaced spiral fracture of the shaft of the humerus, unspecified arm, at a subsequent encounter with nonunion.

S42.343K is a billable, specific ICD-10-CM code valid for submission on HIPAA-covered claims. The 2026 edition became effective October 1, 2025.

The 7th character K marks a subsequent encounter where the fracture has gone to nonunion. That separates it from D for routine healing and G for delayed healing.

Use S42.341K for the right arm and S42.342K for the left arm whenever the record documents the side.

Practice management software like Pabau links diagnosis codes to procedure codes at the point of documentation, which keeps fracture claims consistent.

ICD-10 Code S42.343K is a billable diagnosis code for a displaced spiral fracture of the humeral shaft, unspecified arm. The 7th character K marks a subsequent encounter where the fracture has gone to nonunion.

Orthopedic, trauma, and physical therapy practices see it most often, because the 7th character has to be reselected at every follow-up visit.

S42.343K became valid with the 2026 ICD-10-CM edition, effective October 1, 2025. It is billable on its own, while its parent codes S42.3, S42.34 and S42.343 are not. Everything below assumes the fracture pattern documented at first presentation was a displaced spiral fracture.

Code details at a glance

Before applying S42.343K, confirm each field below. Submitting a code flagged as “not valid for submission” at the parent-code level is a guaranteed denial.

How the code breaks down, character by character

Each character in S42.343K carries a specific clinical meaning. Misreading a segment, particularly the 6th or 7th character, is how laterality and encounter-type errors enter the billing cycle.

The 6th character “3” carries two pieces of information at once: displacement and unspecified laterality. When the treating provider documents a side, use S42.341K for the right arm or S42.342K for the left arm. Choosing S42.343K when the side appears in the record signals a documentation problem rather than a valid code choice.

What the 7th character K means

The 7th character is where most fracture coding errors start. Six suffixes are available across the S42.3xx family, and each one describes a different healing status at the time of the visit. The same set applies to neighboring humerus and shoulder codes, including S42.223G for delayed healing and S42.131K for nonunion at the coracoid.

K is only appropriate once imaging or clinical assessment confirms that healing has ceased. Applying it before nonunion is established puts an inaccurate diagnosis on the claim, which is what payer audits look for. Rehabilitation teams often spot the transition from D to K when a patient presents for a delayed-healing workup.

Clinical overview: Displaced spiral fracture of the humeral shaft

Accurate coding depends on understanding the clinical picture. A displaced spiral fracture of the humeral shaft comes from a twisting force applied to the arm. That force creates a helical fracture line along the diaphysis, the mid-section of the bone, and the fragments shift out of anatomical position.

Nonunion occurs when the biological healing process stops before bony union is achieved. Risk factors include inadequate immobilization, poor vascular supply, infection, and comorbidities such as diabetes or osteoporosis. What remains is a persistent fracture gap that needs further intervention, usually surgical.

Common clinical documentation terms acceptable for S42.343K code selection include:

• Closed displaced spiral fracture of humeral shaft with nonunion
• Humeral shaft spiral fracture, nonunion, follow-up visit
• Diaphyseal humerus fracture, displaced, subsequent encounter, nonunion
• Spiral humerus shaft fracture, unspecified arm, failed healing

Providers in sports medicine practices and orthopedic trauma settings document these encounters most often. Delayed presentation and incomplete immobilization both raise nonunion rates in high-activity patients.

When to use S42.343K instead of a related code

The most common errors in this family involve laterality confusion and the wrong 7th character. This decision table covers the primary alternatives.

Fractures elsewhere in the humerus take their own codes. S42.409P covers malunion at the lower end, and S42.211P covers malunion after a surgical neck fracture. The CDC ICD-10-CM tool lists the full tabular hierarchy if you need to browse further.

Where S42.343K sits in the ICD-10-CM hierarchy

Knowing where S42.343K sits in the code tree prevents category-level submissions that payers reject for lack of specificity.

• S00-T88: Injury, poisoning, and certain other consequences of external causes
• S40-S49: Injuries to the shoulder and upper arm
• S42: Fracture of shoulder and upper arm
• S42.3: Fracture of shaft of humerus (not billable at this level)
• S42.34: Spiral fracture of shaft of humerus (not billable at this level)
• S42.343: Displaced spiral fracture of shaft of humerus, unspecified arm (not billable, requires 7th character)
• S42.343K: Billable specific code with 7th character K

S42.3 through S42.343 are parent codes that appear in the hierarchy but cannot be submitted on claims. Only codes with a valid 7th character are billable. The CMS ICD-10 codes page publishes the annual tabular list updates and valid code files.

Coding guidelines and documentation requirements

Section I.C.19.c of the ICD-10-CM Official Guidelines for Coding and Reporting governs fracture coding. Most code reference pages publish the descriptor and stop there, so here is what the guidelines actually require.

Encounter type is set by treatment status rather than by visit number. A patient who sees a new provider for active management of a nonunion uses suffix A for that visit. That holds even if months have passed since the original injury.

Key documentation requirements for S42.343K:

• Nonunion confirmed: Imaging must demonstrate failure of bony union at the fracture site, and the report or clinical note must reflect that finding
• Laterality absent or undocumentable: Use “unspecified arm” only when the side genuinely cannot be established from the clinical record
• Encounter type is subsequent: Active surgical or manipulative treatment at this visit requires suffix A, not K
• Displacement confirmed: The original fracture type must stay consistent with the pattern documented at first presentation

Practices using clinical documentation workflows that link imaging reports to the patient record cut the risk of 7th character mismatches. Review the encounter suffix at every visit, not only at first presentation.

Associated CPT codes for humerus shaft fracture treatment

This table covers the procedure codes most often paired with displaced humeral shaft fractures and nonunion repair. Verify payer coverage and reimbursement against the CMS Physician Fee Schedule before submission.

CPT 24430 and 24435 line up most directly with S42.343K, because both describe procedures triggered by established nonunion. CPT 24516 and 24515 usually appear with suffix A, when active surgical management is the reason for the visit. Anesthesia is reported separately, and 01730 covers closed humerus and elbow procedures.

How Pabau keeps fracture coding and claims in step

Most orthopedic practices split this work across two systems. Imaging reports and clinical notes sit in the patient record, and the coder rebuilds the diagnosis from scratch when the claim goes out. The suffix is the first thing to slip.

Pabau, our practice management software, keeps both in one place. The treatment note carries the imaging finding that establishes nonunion, and the diagnosis code travels with it into the claim. Your coder can see why K was chosen without opening a second system.

Pabau’s claims management software then pairs that diagnosis with the procedure code before submission. Fewer suffix mismatches reach the payer, so your team spends less time reworking denials on follow-up visits.

Streamline fracture coding and claims

Pabau connects clinical documentation to billing workflows for orthopedic and musculoskeletal practices. Code each encounter accurately and submit claims without the manual cross-referencing that leads to denials.

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Conclusion

The K suffix stands or falls on what the imaging shows. Before you use S42.343K, confirm the record documents that healing has stopped. Confirm too that this visit is follow-up care rather than active treatment.

Laterality is the other thing worth re-checking at each visit. If the side turns up anywhere in the chart, the specific code replaces the unspecified one and the claim gets stronger. Unspecified codes are a last resort, not a shortcut past a thin note.

Catching both at the point of documentation costs less than catching them in a denial letter. Book a demo to see how Pabau ties fracture documentation to the claim that leaves your practice.

Continue your research

Coding a fracture that is healing slowly rather than not at all? S52.033J walks through the delayed-healing suffix on a displaced olecranon fracture.

Documenting an open wound alongside the fracture? S41.021A covers a laceration with a foreign body at the shoulder on an initial encounter.

Assessing shoulder function during fracture follow-up? Full can test explains how to perform the test and how to read the result.

Want another worked example of a subsequent-encounter suffix? S33.4XXD applies the D suffix to a traumatic rupture of the symphysis pubis.

Billing anesthesia for a nonunion repair? 01744 covers anesthesia for elbow nonunion and malunion procedures.

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