ICD-10 code S42.436B: Nondisplaced avulsion fracture, unspecified humerus

Key takeaways

ICD-10 code S42.436B describes a nondisplaced avulsion fracture of the lateral epicondyle of the unspecified humerus, initial encounter for open fracture

The word unspecified in S42.436B refers to laterality, so use S42.434B for the right humerus and S42.435B for the left when the side is documented

The 7th character B is mandatory and marks an open fracture at the initial encounter, while A marks a closed one

When documentation does not specify displaced or nondisplaced, ICD-10-CM Official Guidelines default to nondisplaced coding

Practice management software like Pabau ties the diagnosis code to the clinical note, so laterality and encounter type reach the claim unchanged

ICD-10 code S42.436B is the diagnosis code for a nondisplaced avulsion fracture of the lateral epicondyle of the unspecified humerus, initial encounter for open fracture. It is the code you reach for when the record documents everything except which arm was injured.

That makes S42.436B both a valid billable code and a documentation warning. Payers accept it, but a run of unspecified-laterality claims invites review, so treat every use as a prompt to query the provider.

Clinical description: Nondisplaced avulsion fracture of the lateral epicondyle

The lateral epicondyle sits on the distal lateral surface of the humerus, just proximal to the elbow joint. It serves as the attachment point for the forearm extensor muscles and the radial collateral ligament complex.

An avulsion fracture happens when a tendon or ligament pulls a bone fragment away from the main bone. The break comes from traction, not from direct impact.

At the lateral epicondyle, this usually follows forceful contraction of the forearm extensor group or acute valgus stress at the elbow. Throwing athletes, manual laborers, and patients who fall on an outstretched arm are the typical presentations. Confirm the code text against the AAPC ICD-10-CM code reference before you submit.

The nondisplaced descriptor means the fragment has separated but has not moved far from its original position. The fragment stays approximated to the donor site on the lateral humerus, which usually favors conservative management over surgical fixation.

Throwing athletes and manual workers turn up with this injury most often. Sports medicine software keeps the mechanism, the injured side, and the imaging on one patient record.

What unspecified humerus means in S42.436B

Unspecified humerus means the record does not state which arm was injured. It is a laterality placeholder, not a clinical finding, and it is never the code for a bilateral injury.

The S42.43 subcategory splits six ways before the 7th character is added:

• S42.431 — Displaced fracture (avulsion) of lateral epicondyle of right humerus
• S42.432 — Displaced fracture (avulsion) of lateral epicondyle of left humerus
• S42.433 — Displaced fracture (avulsion) of lateral epicondyle of unspecified humerus
• S42.434 — Nondisplaced fracture (avulsion) of lateral epicondyle of right humerus
• S42.435 — Nondisplaced fracture (avulsion) of lateral epicondyle of left humerus
• S42.436 — Nondisplaced fracture (avulsion) of lateral epicondyle of unspecified humerus

So S42.436B covers an open-fracture initial encounter for a nondisplaced avulsion where the side was never recorded. If the note, the operative report, or the imaging order names a side, code S42.434B or S42.435B instead.

Laterality is almost always recoverable from an elbow fracture record. Query the provider before you settle for S42.436B, because unspecified codes attract medical necessity review and slow payment.

Displaced vs. nondisplaced: The default coding rule

The ICD-10-CM Official Guidelines for Coding and Reporting (Section I.C.19) set a clear default. When the documentation does not say whether a fracture is displaced or nondisplaced, code it as nondisplaced.

That default is why S42.436B, rather than the displaced code S42.433B, applies whenever the provider’s note is silent on displacement. Coders should not assume displacement from imaging findings alone unless the treating provider documents it.

Understanding the 7th character B: Initial encounter for open fracture

The 7th character is not optional in S42 codes. It is required on every submission and sets both the clinical context and the encounter type for reimbursement. For S42.436, the available 7th characters span initial encounters, subsequent encounters, and sequela.

The B character applies only when the treating provider documents that the fracture is open. Open means a wound connects the external environment to the fracture site. These injuries carry higher infection risk and usually need more intensive initial management than closed fractures.

Key rule for the initial encounter: a patient can have more than one initial encounter. Transferring care to a different facility during active treatment does not end the initial phase. The 7th character A or B holds for as long as the provider is actively managing the acute fracture. Once care shifts to monitoring the healing, the encounter type moves to D, G, K, or P instead. The same suffix logic drives S42.489P, where the P marks a malunion found at a later visit.

S42.436 code family: All variants

S42.436 is the parent stem for a nondisplaced avulsion fracture of the lateral epicondyle where laterality is not documented. Each variant adds the 7th character to specify encounter type and healing status. Confirm the exact code against the CDC/NCHS ICD-10-CM web tool for the current fiscal year.

Practices handling high volumes of orthopedic injury claims can cut 7th character errors with structured claims management software. It connects the diagnosis code directly to claim generation.

Synonyms and look-alike diagnoses

Providers rarely write the code description word for word. These phrases in a chart all point to the S42.43 family, and the last three point somewhere else entirely.

• Lateral epicondylar avulsion — maps to S42.43-, with the 7th character set by encounter type
• Avulsion of the extensor origin at the elbow — the extensor tendons attach at the lateral epicondyle, so this is the same injury
• Chip fracture of the lateral epicondyle — still an avulsion mechanism, so S42.43- applies
• Medial epicondyle fracture — a different site with its own family, S42.44-, often documented as Little Leaguer’s elbow
• Lateral condyle fracture — a separate injury coded to S42.45-, not S42.43-, and easy to confuse in a rushed chart
• Lateral epicondylitis or tennis elbow — an overuse tendinopathy with no fracture, coded to M77.1-

ICD-10-CM humerus fracture coding guidelines (S42)

The CMS ICD-10-CM Official Guidelines for Coding and Reporting (Section I.C.19) govern all traumatic fracture coding, including the S42 category. These are the rules that decide code selection.

• Default to nondisplaced: a note that is silent on displacement is coded nondisplaced, so S42.436B stands and the displaced code S42.433B does not.
• Laterality first, unspecified last: code S42.434B for the right humerus and S42.435B for the left. S42.436B is only for records that never name a side.
• Fracture type must be documented: avulsion is a specific mechanism. The provider should document the mechanism or morphology, and coders should not infer avulsion from imaging alone.
• 7th character governs all submissions: no S42 code is billable without it. A claim submitted with only S42.436 and no suffix will reject.
• Open fracture classification: the Gustilo-Anderson grade is common in orthopedic notes, but ICD-10-CM does not require it in the 7th character for these codes. B only requires documentation that the fracture is open.
• External cause codes: Chapter 20 codes for cause, place, and activity are not nationally required. Many payers and trauma registries still expect them alongside a fracture code.

The same rules govern the rest of the S42 category, including shaft codes like S42.343K. Practices running the rehabilitation half of the episode can build the same prompts into their rehab documentation workflows.

Documentation requirements for accurate coding

Six documentation elements decide whether S42.436B is the right code. Miss one and you are left with a less specific code or a query to the treating provider.

Teams building structured clinical note templates can explore clinical documentation workflows that prompt for laterality, encounter type, and fracture status at the point of care. Prompting for the side at the moment of the exam is the single change that keeps unspecified codes off your claims.

Related ICD-10 codes and when to use them instead

S42.436B sits inside a dense family of lateral epicondyle and lower humerus fracture codes. Picking the wrong sibling is one of the most common sources of claim rejection in orthopedic billing.

Proximal humerus fractures sit one subcategory away and follow the same 7th-character pattern, as S42.212D shows. Check every candidate against the current fiscal-year code set before you commit to one.

Three coding scenarios for S42.436B

The same injury produces three different codes depending on what the chart says. These worked examples show where S42.436B belongs and where it does not.

Scenario 1: Open avulsion with no side recorded

A patient arrives at the emergency department after a fall from a ladder. The physician documents an open wound over the elbow with an avulsion fracture of the lateral epicondyle, and no displacement is described. Nothing in the note, the triage record, or the imaging order names an arm.

Code: S42.436B. The nondisplaced default applies, the fracture is open, and this is the first active treatment encounter. Send a provider query so the next claim can carry a laterality-specific code. Immobilization supplies dispensed at that visit bill separately, under codes such as A4566.

Scenario 2: The same injury with the side documented

Identical presentation, except the physician writes left elbow in the assessment. Laterality is now on the record, so the unspecified code no longer applies.

Code: S42.435B, the left-humerus equivalent. Coding S42.436B here would understate the specificity your documentation already supports.

Scenario 3: Follow-up visit six weeks later

The patient from scenario 1 returns for a healing check. Active treatment has ended, radiographs show routine healing, and the record still does not name a side.

Code: S42.436D. The 7th character moves from B to D because the encounter is now monitoring rather than active treatment.

Common coding errors and how to avoid them

Five errors cause most of the claim rejections on this code. Each one is avoidable with a careful documentation review.

• Reading the 6 as left: the digit before the 7th character carries both displacement and laterality. S42.436 is nondisplaced and unspecified, S42.435 is nondisplaced and left, and S42.434 is nondisplaced and right.
• Using S42.436B when the side is documented: the unspecified code is a last resort. If the chart names an arm anywhere, code S42.434B or S42.435B and expect fewer medical necessity reviews.
• Using S42.436A instead of S42.436B: the most common substitution error. S42.436A is for closed fractures, so an open wound communicating with the fracture site makes S42.436B the only correct choice.
• Using a displaced code without documented displacement: if the note does not say displaced, the default is nondisplaced. Coding S42.433B from a radiologist’s remark that the fragment looks slightly shifted risks audit exposure.
• Using an initial-encounter code for a follow-up visit: once care shifts to monitoring, the 7th character must change to a subsequent-encounter value. Repeating S42.436B at every visit inflates denial rates and attracts audits.

Practices managing follow-up coding across the S42 family can lean on the structured workflows in a physical therapy EMR. These are built around musculoskeletal care episodes, where the 7th character changes more than once.

How Pabau supports accurate ICD-10 coding workflows

Most 7th character and laterality errors start between the note and the claim. A provider documents an open avulsion fracture of the left lateral epicondyle clearly. The coder works in a separate billing system, re-keys the diagnosis, and lands on the unspecified code. Another common slip is picking A when the fracture was open. Each one costs a rework cycle.

Practice management software like Pabau connects clinical note creation directly to diagnosis code assignment in one workflow. Structured note templates prompt providers for the fields that decide the code: laterality, displacement status, open or closed status, and encounter context. The code then flows into claim generation instead of being retyped, so a single character cannot quietly change what you bill.

Orthopedic and sports medicine practices handling high volumes of fracture encounters can see the approach in Pabau’s practice management software. Teams carrying a heavy post-encounter note burden can also look at Pabau Scribe, our AI scribe. It records the consult and structures the note automatically.

Reduce fracture code denials with structured documentation

Pabau connects clinical notes directly to diagnosis code workflows, prompting providers for laterality, displacement status, and encounter type before the claim is generated. See how it works for orthopedic and sports medicine practices.

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Conclusion

S42.436B is billable, current for FY 2026, and specific on everything except the side of the body. It encodes a nondisplaced avulsion fracture of the lateral epicondyle of the unspecified humerus at an initial encounter for an open fracture.

Treat it as a temporary answer. Query the provider, then move to S42.434B or S42.435B once the side is on the record. Switch the 7th character as soon as active treatment ends. The two errors worth guarding against are choosing A over B, and reading the 6 in S42.436 as left.

For practices where coding accuracy directly affects revenue, Pabau keeps diagnosis codes synchronized with the clinical note from first encounter through claim submission. To see how it works in an orthopedic or sports medicine setting, book a demo.

Continue your research

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Need to code a late effect rather than an active injury? S42.126S shows how the sequela character works on a shoulder fracture.

Working on clavicle claims rather than humerus ones? S42.032S sets out the documentation a displaced lateral end fracture needs.

Billing an aspiration alongside the fracture visit? CPT 20604 explains the small joint reimbursement rules.

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