ICD code S42.213P – Displaced surgical neck humerus malunion

Key takeaways

S42.213P is the billable ICD-10-CM code for an unspecified displaced surgical neck humerus fracture, subsequent encounter for fracture with malunion.

The seventh character P means malunion, not sequela. The sequela character for this code family is S, which gives S42.213S.

P is a subsequent-encounter character, so S42.213P is normally the first-listed diagnosis. No sequela-first sequencing rule applies to it.

S42.213 takes seven valid seventh characters: A, B, D, G, K, P and S. No other letter is valid for this code.

Practice management software like Pabau validates required claim fields before submission and tracks the denial reason codes that come back.

ICD-10 code S42.213P: full description and code status

ICD-10 code S42.213P is a billable, valid ICD-10-CM diagnosis code confirmed active for FY2025 and FY2026. It sits in the S42 branch of the ICD-10-CM code set, which groups fractures of the shoulder and upper arm. The table below shows the full code path and the key reference data.

Per the CMS ICD-10 codes page, S42.213P carries no age or sex edit restrictions. The code is not a manifestation code, and the guidelines do not push it into a secondary position. On a malunion encounter it normally leads the claim.

What S42.213P covers: anatomy and clinical scope

The surgical neck of the humerus is the narrow region just below the greater and lesser tuberosities, where the shaft meets the humeral head. It is the most common site for proximal humerus fractures, particularly in older patients after low-energy falls. “Unspecified displaced” means the record confirms displacement but never states the direction.

S42.213P describes a later stage of that injury. Active treatment has finished, the bone has united, and the union sits in a faulty position. Malunion at the surgical neck usually shows up as one of the following:

• Varus angulation of the humeral head, the most common pattern after a displaced two-part fracture
• Rotational malalignment that limits external rotation and overhead reach
• Greater tuberosity displacement that blocks abduction and causes impingement
• Shortening of the proximal humerus with altered deltoid tension
• Head-shaft angular deformity that narrows the subacromial space

The malunion itself needs no separate diagnosis code. The seventh character P carries it, so S42.213P states both the original fracture and its faulty union in one code. Conditions that sit on top of the malunion, such as post-traumatic arthritis or stiffness, are coded additionally.

The seventh character P: subsequent encounter with malunion

The P seventh character marks a subsequent encounter for a fracture that united with malunion, not a sequela. That is a frequent misreading, and it changes claim sequencing.

Section I.C.19.c of the ICD-10-CM Official Guidelines has coders assign the acute fracture code with the correct seventh character for aftercare. S42.213P is normally the first-listed diagnosis. Section I.B.10’s sequela rule covers the S character instead: S42.213S, with the late effect coded first and the injury code second.

S42.213 supports seven valid seventh characters, shown below with their full meaning and typical sequencing.

Open and closed fractures are separated only at the A and B characters. From D onward the descriptor drops that distinction, so S42.213P covers a healed open fracture as well as a closed one. C, E, F, H, J, M, N, Q and R belong to the expanded Gustilo set, used on the forearm, femur and leg. None of those letters is valid on S42.213; a claim carrying one is rejected as invalid.

Malunion, sequela and aftercare: choosing between P, S and D

The most frequent error on S42.213 claims is picking the wrong subsequent-encounter character. D gets used out of habit for any follow-up visit, and S gets used whenever a visit feels like a late effect.

Two clinical facts settle it. Has the bone united, and is the fracture still being managed? The chart below runs both questions across every seventh character S42.213 takes.

The practical difference is sequencing. S42.213P leads its claim, so the coder does not need a second diagnosis to make it valid. S42.213S cannot lead a claim, because Section I.B.10 requires the late effect first. Reversing that order on an S claim is a compliance problem. Applying the S rule to a P claim buries a sound primary diagnosis behind something else.

Malunion and nonunion of the surgical neck of the humerus

Malunion and nonunion drive most of the confusion between S42.213P and S42.213K. One clinical test separates them. A fracture site that is still mobile, with no bridging callus, is a nonunion and takes the K character. Bone that has consolidated but healed in poor alignment is a malunion and takes the P character. Put simply, K means the bone never finished healing, while P means it finished healing wrong.

Malunion and nonunion are among the most audited distinctions in orthopedic fracture coding. The two conditions carry different procedure implications, different medical necessity thresholds, and different CPT pairings.

Payer edit systems cross-reference the procedure code against the diagnosis code. Billing a bone-graft CPT against S42.213P usually triggers a medical necessity edit. So does a corrective osteotomy billed against S42.213K without supporting notes.

Excluded and related conditions

Several fracture types sit outside the S42.213P code family. Knowing which ones prevents miscoding and reduces claim-level compliance findings.

• Periprosthetic fractures (M97.3-): a fracture around an existing shoulder implant is coded M97.31X- or M97.32X-. S42.213P does not cover fractures involving prosthetic components.
• Pathological fractures (M84.42-): a fracture caused by bone disease uses the M84 category. Its malunion counterpart is M84.421P, M84.422P or M84.429P, not S42.213P.
• Physeal (growth plate) fractures: Salter-Harris fractures of the proximal humerus fall under S49.0-, and the malunion character there is S49.001P through S49.099P.
• Sequela of the same fracture (S42.213S): once the fracture episode has closed and only a residual condition remains, the S character applies rather than P.

Open fractures are not excluded. S42.213 separates open from closed only at the initial encounter, with A for closed and B for open. From the subsequent-encounter characters onward the descriptor drops the distinction, so S42.213P covers a malunited open fracture too.

Conditions commonly reported alongside S42.213P are the problems the malunion is causing. The usual companions are post-traumatic osteoarthritis of the shoulder (M19.111, M19.112, M19.119) and osteonecrosis of the humerus due to previous trauma (M87.221, M87.222). Shoulder stiffness (M25.611, M25.612) and chronic pain due to trauma (G89.21) also appear often. Soft-tissue injuries from the original event may be reported too, such as rotator cuff strain (S46.01-) or axillary nerve injury (S44.31X-, S44.32X-).

Clinical documentation requirements for S42.213P

Payer auditors reviewing an S42.213P claim look for five documentation elements. Missing any one of them creates grounds for denial or recoupment. The CDC/NCHS ICD-10-CM coding tool confirms the descriptor, but only the note can show that this patient has a malunited fracture.

The five elements auditors expect in the record are:

1. Prior fracture identified: the note names a displaced fracture of the surgical neck of the humerus. It also gives the date of injury or points to the earlier encounter. Imaging alone does not establish the history.
2. Union with malunion stated: the note says the fracture has united and that the union is in a faulty position. Radiology findings support that statement but do not replace it.
3. Active treatment has ended: P is a subsequent-encounter character, so the record must show the initial treatment phase is over. An encounter still delivering acute fracture care takes A or B.
4. Deformity described: the note characterizes the malunion as varus, valgus, rotational, angular or shortened, ideally with a measurement. Auditors use this to judge medical necessity for corrective surgery.
5. Laterality addressed: if the side is known, a side-specific code is expected. S42.211P and S42.212P are the right and left versions, and switching to the unspecified code raises edit-system flags.

Documentation prompts that ask the physician for each element at the point of care reduce coder queries. They also stop claims leaving the practice without adequate support. When the record names the right humerus, S42.211P is the code to submit instead of S42.213P.

Three coding scenarios for S42.213P

The seventh character is chosen from the state of the bone at that visit, not from how long ago the injury happened. These three scenarios show how the same patient history produces three different codes.

1. Malunion found at follow-up. A 74-year-old treated in a sling for a displaced surgical neck fracture returns at 14 weeks. Imaging shows union with 40 degrees of varus angulation, and abduction is limited. The note does not record the side, and the query goes unanswered. Code S42.213P as the first-listed diagnosis.
2. Malunion plus post-traumatic arthritis. The same patient returns six months later. The surgeon documents the malunion and post-traumatic glenohumeral arthritis, and plans an arthroplasty. Code S42.213P first, then M19.119 for the arthritis. Both conditions are being treated at this visit, so both belong on the claim.
3. Residual stiffness after a well-aligned union. A fracture healed in good alignment three years ago. The patient now attends for shoulder stiffness alone, with no fracture care planned. This is a sequela, so code M25.619 first and S42.213S second. S42.213P does not apply, because there is no malunion.

The third scenario is where most S42.213P errors start. A visit that feels like a late effect is not automatically a sequela encounter. The malunion character stays in play for as long as the malunited fracture is what the clinician is managing.

Payer requirements and prior authorization

Medicare and commercial payers treat S42.213P as a subsequent-encounter fracture claim. Medical necessity review focuses on the deformity and the functional loss it causes. Prior authorization depends on the associated procedure. Corrective osteotomy for malunion and shoulder arthroplasty for end-stage post-traumatic arthritis both need prior authorization from most Medicare Advantage plans and commercial insurers.

Claim.MD, Pabau’s US clearinghouse partner, runs real-time eligibility checks before the visit. Claim status tracking then shows where each submitted claim sits with the payer, and electronic remittance advice reports what was paid. That matters on S42.213P claims, because payer edits commonly flag unspecified laterality and mismatched encounter characters before payment.

For Medicare fee-for-service claims, no Local Coverage Determination currently restricts S42.213P itself. Restrictions sit at the procedure level. Any surgery paired with S42.213P must meet the payer’s medical necessity criteria, with documented functional impairment, failed conservative management, and a described deformity.

Common claim denial reasons for S42.213P

S42.213P denials cluster around a small set of correctable errors. Most are either a wrong seventh character or a note that never states the malunion. Tracking these patterns lifts first-pass acceptance, and it starts with mapping each denial reason to its coding cause.

• S submitted where P belongs: the coder reads P as sequela, files S42.213S instead, and then sequences it behind an unrelated diagnosis. The claim fails clinical review because the note describes a malunion, not a residual condition.
• P submitted where S belongs: the fracture healed in good alignment and the visit treats a late effect only. The record shows no malunion, so the payer denies on clinical support grounds.
• Malunion never stated in the note: the physician records deformity or poor function but never says the fracture united in a faulty position. Payers request records and deny.
• D carried forward out of habit: the coder uses the routine-healing character on every follow-up visit, including the one where malunion was diagnosed. This understates the encounter and misroutes the medical necessity review.
• Laterality inconsistency: S42.213P goes out for a patient whose earlier claims carry S42.211P or S42.212P. Payers holding the prior claim expect the same side.
• Acute-care CPT on a subsequent encounter: a primary fracture fixation code is billed against S42.213P. A malunion claim needs a malunion-appropriate procedure, an evaluation code, or a therapy code.

A clean S42.213P claim means confirming all six points above before it leaves the practice. A pre-submission checklist built into the workflow catches most of them at source rather than after the denial.

CPT codes commonly paired with S42.213P

The CPT code submitted alongside S42.213P has to match a subsequent-encounter malunion visit, not an acute fracture event. Billing primary fracture fixation against a malunion diagnosis creates a medical necessity mismatch that payers flag on adjudication. Practices that also bill therapy alongside orthopedic care should check the therapy evaluation code just as carefully.

For practices billing shoulder arthroplasty or osteotomy against S42.213P, each step stays traceable from prior authorization through remittance posting. The AAPC ICD-10-CM code lookup provides further crosswalk data for checking CPT-to-ICD-10 pairing against payer policy.

How Pabau helps orthopedic practices code malunion encounters

In most orthopedic practices the seventh character is chosen at the end of the day, from a note the coder reads hours after the visit. If the physician wrote “healed, still deformed” rather than “united with malunion”, the coder either queries or guesses. Queries slow the claim down. Guesses show up later as denials on codes like S42.213P.

Practice management software like Pabau moves that decision to the point of care. Custom clinical forms prompt the surgeon for union status, deformity type and laterality while the patient is still in the room. Those answers land in the patient record as structured fields. The coder then opens a note that already carries the three facts an S42.213P claim needs.

From there, the claims management software in Pabau validates the required claim fields before submission and tracks what comes back. Denials are grouped by reason code, so a practice can see which reasons drive its S42.213P rejections. The result is fewer reworked claims and a shorter path from visit to payment.

Reduce claim denials on fracture malunion codes

Pabau’s claims management tools help orthopedic and sports medicine practices submit cleaner ICD-10 fracture claims. Track denial reason codes, and fix revenue leaks before they turn into write-offs.

Book a demo

Conclusion

S42.213P is straightforward once the seventh character is read correctly. P means the fracture united in a faulty position, which makes this a subsequent-encounter code and the first-listed diagnosis for that visit. The sequela code for the same fracture is S42.213S, and only on that claim does the late effect come first.

Three habits cause most of the trouble. A note stops at “healed” without saying how the bone united. A side is left unspecified even though the chart names it. An acute-care procedure code goes out against a malunion diagnosis. All three are fixed at the point of documentation, not in the appeals queue.

Pabau puts the union, deformity and laterality prompts in the note itself, then tracks the denial reason codes that come back on claims like these. To see how that fits your orthopedic workflow, book a demo.

Continue your research

Is the right side documented on your malunion claim? ICD-10 code S42.211P covers the same fracture and malunion on the right humerus.

Need to decode the denial that just came back? Denial codes in medical billing explains the reason codes payers return and what each one asks for.

Dealing with recurring denial patterns across your orthopedic claims? Denial management in healthcare explains how to build a systematic denial tracking and appeals workflow.

Want to understand how claim submission works end to end? Clean claim submission walks through the elements every claim must have before it leaves the practice.

Frequently asked questions