ICD code S82.855N – Nondisplaced trimalleolar fracture, left leg, open fracture nonunion

Key takeaways

S82.855N is a billable ICD-10-CM code for a nondisplaced trimalleolar fracture of the left lower leg with nonunion. It applies at follow-up visits when the original fracture was open type IIIA, IIIB or IIIC.

The 7th character N combines a subsequent encounter, nonunion, and an open type IIIA, IIIB or IIIC fracture at injury. K covers nonunion of a closed fracture, and M covers open type I or II.

Documentation must confirm a trimalleolar fracture of the left ankle, nondisplaced at injury, the open fracture type, a follow-up visit, and imaging evidence of nonunion. Missing any element risks denial.

Pabau’s claims management software routes S82.855N claims through Claim.MD for eligibility checks and clearinghouse validation before submission.

ICD-10 Code S82.855N: Quick reference table

ICD-10 Code S82.855N reports a nondisplaced trimalleolar fracture of the left lower leg that has not healed, seen at a follow-up visit. The original injury was an open fracture, Gustilo type IIIA, IIIB or IIIC. Use this table to confirm the code’s attributes before submitting a claim. All details reflect the current ICD-10-CM tabular list published by CMS and NCHS.

Full descriptor breakdown: What each character in S82.855N means

Every character in S82.855N carries a specific clinical meaning. Misreading one character is enough to produce a wrong code and a denied claim. The breakdown below traces the code from its category to its 7th character extension.

A trimalleolar fracture breaks three parts of the ankle: the medial malleolus, the lateral malleolus and the posterior malleolus of the tibia. Nondisplaced means the fragments stayed in anatomical alignment at the time of injury.

Within S82.85, the final digit before the 7th character records both displacement and side. Digits 1 to 3 are displaced fractures, and digits 4 to 6 are nondisplaced.

Understanding the 7th character N: Subsequent encounter for nonunion

The 7th character N signals three things at once. The patient is at a follow-up visit, the fracture has not healed, and the original fracture was open type IIIA, IIIB or IIIC.

Per ICD-10-CM Official Guidelines Section I.C.19.a, subsequent encounters are visits after active treatment, while the patient is in the healing or recovery phase. Nonunion means imaging or clinical examination confirms healing has stalled.

S82.855 takes 16 possible 7th characters. The table below lists each one, with the encounter type and the fracture type at injury it applies to.

The choice between K, M and N depends only on the fracture type recorded at the initial encounter. Internal fixation hardware plays no part in it. A nonunion after a closed fracture takes K, and open type I or II takes M instead.

Open type IIIA, IIIB or IIIC takes N as the 7th character. The guidelines code a fracture not documented as open or closed as closed, which makes K the default. The grid below places N among the 12 subsequent-encounter characters for S82.855.

S82.855N in context: Laterality and adjacent code variants

The S82.85 subcategory contains six codes that differ by laterality and displacement. There is no bilateral code, so a patient with trimalleolar fractures of both ankles gets one code per side. The table below shows the full matrix with the N extension.

Laterality must match the physician note. If the note says “left ankle” and the claim carries S82.854N (right, nondisplaced), payer edits flag the mismatch. The CDC/NCHS ICD-10-CM web tool lets coders confirm laterality sub-codes directly against the official tabular list.

Codes commonly confused with S82.855N

Several codes share most of their characters with S82.855N but differ in one critical dimension. The table below shows the most frequently confused codes and the single factor that distinguishes each.

ICD-10-CM coding guidelines for fracture nonunion: Applying S82.855N correctly

ICD-10-CM Official Guidelines Section I.C.19 governs 7th character assignment for fracture codes. For S82.855N, the coder must satisfy four conditions.

1. Confirm the encounter is not the first active treatment visit. The 7th character N belongs to the subsequent encounter group. If the patient is receiving initial active treatment for the open fracture, such as debridement or fixation, the correct 7th character is C.
2. Confirm healing failure is documented. Nonunion requires evidence, typically serial X-rays or a CT scan showing no bridging callus and a persistent fracture line. Most payers expect imaging support, not a clinical statement alone.
3. Confirm the fracture was open type IIIA, IIIB or IIIC at injury. The Gustilo type comes from the initial encounter record, usually the emergency or operative note. A closed fracture takes K as its 7th character, while open type I or II takes M instead.
4. Confirm laterality and displacement from the original injury documentation. The nondisplaced designation describes the fracture at the time of injury, not its current radiographic appearance. If the fracture was nondisplaced at diagnosis, it stays nondisplaced for all subsequent encounter coding.

Documentation requirements for S82.855N

The physician note supporting S82.855N must contain all of the following elements. A claim missing any one of them is open to denial.

• Identification of the fracture as trimalleolar (medial, lateral and posterior malleolus)
• Clear documentation that the involved limb is the left leg
• Confirmation that the fracture was nondisplaced at injury
• The open fracture classification at injury: Gustilo type IIIA, IIIB or IIIC
• Statement or evidence that this is a follow-up visit, not initial active treatment
• Imaging report or clinical documentation confirming nonunion

CPT codes commonly billed with S82.855N

When S82.855N is the primary diagnosis, the accompanying CPT code describes the specific service rendered at that encounter. Payers cross-reference the CPT and ICD-10 pair for medical necessity. Using claims management software with a built-in ICD-10 catalog reduces CPT-ICD mismatch errors before the claim leaves the practice.

The table below lists the CPT codes most often paired with this diagnosis.

Verify CPT-ICD pairings against current CMS National Correct Coding Initiative (NCCI) edits before submitting. The AAPC Codify ICD-10-CM lookup provides crosswalk data showing which CPT codes payers accept alongside specific ICD-10 codes.

Payer requirements and prior authorization for fracture nonunion

Medicare and most commercial payers apply heightened scrutiny to nonunion claims because of the potential for extended treatment and surgical intervention. Understanding what each payer needs before you submit saves the back-and-forth of appeals. The medical billing process for nonunion cases typically involves more documentation than routine fracture follow-up.

• Imaging proof: Plain X-ray at minimum; CT scan preferred by many commercial payers when surgical intervention is planned. The radiology report must describe the trimalleolar fracture and confirm absent or inadequate callus formation.
• Prior conservative treatment record: Medicare and most commercial plans expect documentation of conservative management before approving surgical repair or bone stimulator use. Absence of a treatment timeline is a frequent denial reason.
• Prior authorization for surgical repair: Surgical treatment, including repair of a nonunion, often requires prior authorization. Submit the auth request with the imaging report, clinical notes, and S82.855N as the primary diagnosis.
• Bone stimulator (electrical or ultrasound): Medicare covers electrical stimulators under NCD 150.2 and ultrasound stimulators under NCD 150.3. Both are national coverage policies. Document a nonunion of at least 3 months with no progressive healing on serial X-rays. Check your MAC for any added local policy before seeking authorization.

Practices billing nonunion codes regularly should keep a payer-specific matrix of authorization rules, built around a documented prior authorization process. Good billing compliance requirements documentation reduces denials and protects against audit exposure.

Common claim denial reasons for ICD-10 Code S82.855N and how to avoid them

Denial patterns for S82.855N are consistent across payers. Most trace back to one of six root causes. Payers return each one as a claim adjustment reason code, explained in our medical billing denial codes guide. The table below shows each denial type with the corrective action that prevents recurrence.

Practices that submit through a Claim.MD clearinghouse connection catch many of these errors before adjudication. Eligibility checks can also show whether the payer requires prior authorization, which helps prevent the missing authorization denial. Effective denial management workflows for orthopedic practices track denial reason codes by ICD-10 code so recurring patterns surface quickly.

How Pabau catches S82.855N claim errors before submission

Nonunion fracture claims carry higher audit risk than routine subsequent encounter submissions. A clearinghouse validation step before claims leave the EHR catches the CPT-ICD mismatches, missing modifiers and laterality errors that generate denials.

Pabau, the practice management and billing platform we build, integrates with Claim.MD, a US clearinghouse that connects practices to commercial and government payers. Claims submitted through the clean claim workflow run edits against NCCI and payer-specific rules before reaching the payer.

Electronic remittance advice and CARC denial reason codes post automatically. Billing staff can spot a failed S82.855N claim and recode it the same day, instead of waiting for an Explanation of Benefits in the mail.

Stop chasing S82.855N denials after the fact

Pabau integrates with Claim.MD to validate ICD-10 codes, run eligibility checks, and catch CPT-ICD mismatches before claims leave your practice. See how it works for orthopedic and physical therapy billing teams.

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Conclusion

ICD-10 Code S82.855N fits one narrow scenario. The patient returns with a nondisplaced trimalleolar fracture of the left ankle that has not healed, after an open type IIIA, IIIB or IIIC injury.

Before you code it, pull the initial encounter note for the Gustilo type and the latest imaging report for nonunion. Those two documents decide between N, K and M, and between nonunion and malunion. Get them right, and the claim stands up to payer edits and audits.

Pabau’s built-in ICD-10 catalog and Claim.MD integration catch the most common S82.855N errors before they reach the payer. To see how it works for orthopedic and physical therapy billing workflows, book a demo.

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