ICD-10 code S81.009S: Unspecified open wound, unspecified knee

Key takeaways

ICD-10 code S81.009S covers an unspecified open wound of the unspecified knee, reported at a sequela visit.

It is a billable FY2026 code, effective October 1, 2025, and it is exempt from present on admission reporting.

The 7th character S separates a sequela visit from an initial encounter (A) and a subsequent encounter (D).

Assign it only when the original wound is documented as healed and the note ties the current condition to it.

Query the provider for laterality first, because S81.001S and S81.002S are more specific and payers prefer them.

ICD-10 code S81.009S is a billable diagnosis code for an unspecified open wound of the unspecified knee, reported as a sequela. It applies once the original wound has healed and the patient comes back for something that wound left behind. Scar contracture, chronic pain at the site, and restricted knee movement are the usual reasons for that visit.

This reference covers the code definition, the 7th character rules, and the full hierarchy. It also covers the sibling codes, the S81 excludes notes, and the documentation an assignment needs.

ICD-10 code S81.009S: Quick reference details

S81.009S is a billable, specific diagnosis code valid for reimbursement in the FY2026 ICD-10-CM edition. It became effective October 1, 2025. The code is also present on admission (POA) exempt, so inpatient facilities report no POA indicator for it.

What does ICD-10 code S81.009S mean?

S81.009S describes an open wound at the knee where neither the side nor the wound type is documented, coded at a sequela visit. An open wound is a break in the skin that exposes the tissue underneath. The code breaks into three parts: the site, the two unspecified qualifiers, and the 7th character.

The two unspecified qualifiers stand for two different missing details. The first is laterality, so “unspecified knee” means the record never says right or left. The second is wound character, so an “open wound” with no descriptor such as laceration, puncture, or bite defaults to unspecified. Query the provider for laterality whenever the record is unclear, since more specific codes exist and payers prefer them.

The 7th character S marks the encounter as a sequela visit. The patient is no longer in active treatment for the wound itself. What drives the visit is a lasting consequence of that earlier open knee wound. Coders in physical therapy practices and surgical follow-up settings meet this distinction constantly, and it drives a large share of 7th character errors.

Approximate synonyms accepted in documentation include sequela of open wound of knee, late effect of open wound of unspecified knee, and open wound knee sequela. All three map to the same code.

How the 7th character works for S81.009

Every code in the S81 category needs a 7th character extension, so the base code S81.009 is never billable on its own. The character tells the payer which phase of care is being reported. Picking the wrong one is a leading reason trauma codes are denied on first submission.

What is a sequela in ICD-10-CM?

A sequela is a condition that arises as a direct result of an earlier injury or illness, after that original condition has resolved. The ICD-10-CM official guidelines set the rule in Chapter 19, which covers injury, poisoning, and certain other consequences of external causes. The wound is no longer the focus of care, and what is being treated is the consequence.

ICD-9-CM called this a “late effect”. ICD-10-CM replaced that term with “sequela” throughout, and the mechanics stayed the same. The sequela code goes first. Second comes the code for the specific nature of the sequela, such as a scar contracture or a chronic pain code. Sequela codes in other chapters, including S12.14XS, follow the same two-code order.

S81.009S or S81.009D: which one fits the visit?

Use S81.009S once the wound has healed and the patient presents for a complication of it. The most common coder error is staying on the subsequent encounter code (D) long past the healing phase. Three things have to be true before you use S at that visit. The original wound is documented as healed, the current condition resulted from that wound, and the provider’s note links the two.

Use S81.009D while the wound is still healing and the provider is managing the wound itself. Use S81.009A at the first encounter, where active treatment begins. Knee wounds from contact sport often reach a sports medicine practice months later, once the skin has closed but movement has not come back. That visit is usually a therapy evaluation billed with CPT 97161.

Code hierarchy and classification for S81.009S

S81.009S sits within a six-level classification tree under the injury, poisoning, and external causes block. The hierarchy gives coders the anatomical context of the code. It also points to the neighboring codes worth reaching for once laterality or wound type turns up in the record.

Sibling and related codes under S81

The S81.009 base code has two siblings that differ only in laterality. When the record names the injured knee, use the laterality-specific code instead of the unspecified one. Laterality is something a provider’s note almost always carries once you query for it.

The wider S81 category also carries wound-type codes at the knee. Lacerations sit at S81.01x, puncture wounds without foreign body at S81.03x, puncture wounds with foreign body at S81.04x, and open bites at S81.05x. Each of those has its own laterality digits. Identify the wound type and the side before defaulting to the unspecified code. Repair work at the original visit is billed separately, with codes such as CPT 12002.

Neighboring categories cover injuries that are not open wounds. A superficial injury at the same site goes to S80, as with S80.812A. A knee wound that also damaged the popliteal artery carries its own sequela code, S85.099S. Open wound sequela codes exist for every body site, and the forearm version is S51.801S.

Coding guidelines and documentation requirements for S81.009S

Chapter 19 of ICD-10-CM sets the rules for sequela assignment, and five requirements have to be met before S81.009S goes on a claim. The CDC ICD-10-CM browser tool is the quickest way to confirm the current wording of any note quoted below. The same principles govern open wound sequela coding at other sites, including S51.801S.

• Healed original injury: The original open knee wound has to be documented as healed or resolved. If it is still healing, the visit is a subsequent encounter (D) rather than a sequela (S).
• Causal link documented: The provider’s note has to connect the current condition to the prior knee wound. A chronic pain complaint with no documented link to that injury does not support S81.009S.
• Sequela coded first: List the sequela code (S81.009S) first. Follow it with the code for the specific nature of the sequela, such as a scar, a pain code, or a contracture.
• No acute injury codes: Do not assign active injury codes for the same body site at a sequela visit. The original injury is healed, so coding it as active is a clinical inconsistency and an audit risk.
• External cause code: Assign an external cause code from the V-Y range to identify what caused the original injury, whenever the record supports one.

Excludes notes for the S81 category

The S81 category carries both an Excludes1 and an Excludes2 note, and both apply to every code beneath it, including S81.009S. They set which conditions can and cannot be coded alongside an S81 code.

Excludes1 (never coded together): open fracture of knee and lower leg (S82.- with 7th character B or C), and traumatic amputation of lower leg (S88.-). If the open wound came with an underlying open fracture, code the fracture instead, as with S82.422B. A traumatic amputation is coded from S88 alone, as with S88.929D.

Excludes2 (both may be coded when both are present): open wound of ankle and foot (S91.-). A patient who has a knee wound and a separate ankle wound gets a code from each category, because the two sites are distinct injuries.

Present on admission (POA) exempt status

S81.009S is POA exempt, so inpatient hospitals assign no POA indicator (Y, N, U, W, or 1) for it on UB-04 claims. Injury sequela codes are exempt as a class under CMS guidance. A sequela arose from a prior injury by definition, which makes a POA determination meaningless for the current admission.

Facilities should verify that status against the current fiscal year’s CMS ICD-10-CM code files. The exempt list is confirmed in each annual release, so check it when the fiscal year turns over.

How Pabau keeps sequela documentation and coding together

The code lookup is the easy part of an S81.009S claim. What trips practices up is the trail behind it. You need a note that proves the wound healed, a documented causal link, and a code that reaches the claim unchanged. Practice management software like Pabau holds all three on the same patient record.

A wound follow-up note has to state that the original wound closed and tie the current condition to it. A structured template prompts for both at the visit, well before anything reaches billing. Pabau’s digital intake and assessment forms carry those prompts inside the note itself, so nobody has to remember them.

Codes then have to move from the record to the claim without being retyped. Copying a code out of a lookup site into a separate billing system is where transcription errors creep in. Pabau’s claims management software pulls the diagnosis and procedure codes already on the patient record into a pre-filled claim, then submits and tracks it. Your coders still choose the codes.

A sequela note also needs the original injury visit in view while it is being written. Pabau’s clinical records link past encounters to the current one, so the provider can cite the first wound encounter without hunting for it. That leaves an auditable chain behind the code if a payer reviews the claim.

For code hierarchy browsing alongside that workflow, the AAPC Codify lookup remains useful. A reference tool confirms the code, and the practice management system is what carries it through to a paid claim.

Keep sequela notes and codes on one record

Pabau keeps the wound history, the sequela note, and the diagnosis code on the same patient record, then pre-fills the claim from it. Your team documents once and submits from the same place, so nothing is retyped between systems.

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Conclusion

S81.009S is a code you should reach for less often than you probably do. Two of its three unspecified elements are usually answerable from the chart. A single laterality query turns it into S81.001S or S81.002S. Treat the unspecified version as the fallback, not the default.

What decides the claim is the 7th character and the note behind it. If the wound has healed and the provider has written down why today’s problem traces back to it, S is correct and defensible. If either half is missing, no amount of code accuracy will hold the claim up on review.

The practices that get this right build the check into the visit rather than the audit. Book a demo to see how Pabau keeps sequela documentation, diagnosis codes, and claims on a single patient record.

Continue your research

Coding a lower limb amputation rather than a wound? ICD-10 code S78.922S walks through the sequela rules for a partial traumatic amputation of the thigh.

Need the repair code for the original wound visit? CPT code 13100 covers complex wound repair and the documentation that has to sit behind it.

Working on a sequela code outside the injury chapter? ICD-10 code S06.813S shows the same two-code sequencing applied to an internal carotid artery injury.

Assessing the knee that the wound left behind? The knee to wall test is a quick way to measure the range of movement a scarred knee has lost.

Billing an intermediate repair instead? CPT code 12054 explains how repair complexity and wound length decide which code applies.

Frequently asked questions