ICD code S31.031S – Puncture wound without foreign body of lower back and pelvis

Key takeaways

ICD-10 code S31.031S covers a puncture wound of the lower back and pelvis that reached the retroperitoneum, with no foreign body left in the wound. The 7th character S marks it as a sequela.

Two yes-or-no questions separate the four puncture wound codes in this group. Was a foreign body retained, and did the wound penetrate the retroperitoneum?

The anatomic site is identical in S31.030, S31.031, S31.040 and S31.041, so wound site and laterality never decide which one you pick.

The closest neighbor of S31.031S is S31.041S, which differs only on foreign body. S31.040S differs on both axes at once.

S31.031S is billable and HIPAA-valid for FY2026, from October 1, 2025 through September 30, 2026.

A sequela claim carries two codes: the residual condition first, then S31.031S as the cause.

Practice management software like Pabau keeps ICD-10 lookup and structured notes in the chart, so the penetration and foreign body details reach the claim.

ICD-10 code S31.031S: Definition and clinical description

ICD-10 code S31.031S is the billable ICD-10-CM diagnosis code for puncture wound without foreign body of lower back and pelvis with penetration into retroperitoneum, sequela. It is valid from October 1, 2025 through September 30, 2026 (FY2026), per the CDC/NCHS ICD-10-CM official code database.

Three separate facts are built into that description. “Without foreign body” means no object was retained in the wound. “Sequela” means today’s visit is for a late effect of that wound rather than for the wound itself.

“With penetration into retroperitoneum” means the wound track reached the retroperitoneal space behind the peritoneum. That space holds the kidneys, ureters, pancreas, and great vessels.

The code sits in category S31, open wound of abdomen, lower back, lumbar spine, pelvis, and external genitals. Retroperitoneal penetration is the clinically serious half of the description, because it puts retroperitoneal organs in the injury path. Only a note documenting that penetration supports the final digit 1 rather than 0.

7th character extensions for S31.031: A, D, and S

Once you have settled on S31.031, the 7th character is the last decision left. All three extensions share the same base description, including the retroperitoneal penetration, and only the encounter type changes. Picking the wrong character produces a denial that can only be fixed by resubmitting the claim.

Coders often reach for S31.031D when the wound itself has healed but the patient now presents with pain or scarring caused by it. That visit calls for S31.031S. Per Section I.B.10 of the FY2026 ICD-10-CM official guidelines, sequela coding applies once the acute phase is over.

When to use S31.031S: Sequela encounter guidelines

Sequela coding needs two things to be true at the same time. The original wound must be healed, and the current problem must be a direct result of it. A follow-up visit for an injury that is still being treated is a different scenario with a different 7th character.

• Use S31.031S when: the wound has healed and the patient presents with a residual condition traced to it. Scar contracture, retroperitoneal adhesions, chronic flank or low back pain, and nerve damage all qualify.
• Do not use S31.031S when: the wound is still open, actively treated, or in the healing phase. Report S31.031A or S31.031D instead.
• Sequence the residual condition first: code the late effect itself, then S31.031S as the cause. The sequela code is never listed first, per Section I.B.10 of the official guidelines.
• No time minimum applies: a sequela can appear right after healing or years later. What matters is that the acute phase is complete, not how long ago the injury happened.

ICD-10 code S31.031S versus S31.030S, S31.040S, and S31.041S

All four puncture wound codes for this region carry the same anatomic site, the lower back and pelvis. There is no site or laterality choice to make between them. They split on two yes-or-no questions instead, and each question changes a different digit. Laid out as a grid, the four codes sit in the four corners.

The grid explains the distances between the four codes. S31.041S is the one-step neighbor of S31.031S, because it shares the penetration status and differs only on the retained foreign body. S31.030S is the other one-step neighbor. The official descriptions below show how each combination reads on a claim.

A wound in this region that the record cannot type as a puncture does not belong in this group at all. Those fall to S31.000S and S31.001S, the unspecified open wound codes, split by the same penetration question. Lacerations use S31.01- and S31.02-, and open bites use S31.05-, each divided the same way.

What the record must prove

Every element of the code description has to be supported somewhere in the chart. Reviewers check four points before they accept a penetrating wound sequela claim.

• Wound type documented as a puncture: a note that says laceration, abrasion, or bite sends you to a different group of codes. The site and the penetration axis stay the same there.
• No retained foreign body: the exploration or imaging note should show that nothing remained in the wound. If an object was retained, code from S31.04- instead.
• Retroperitoneal penetration stated: an operative, imaging, or emergency note must record that the track reached the retroperitoneum. Without it, the sixth digit defaults to 0.
• Sequela relationship and residual condition: the clinician must link today’s problem to the healed wound, and that residual condition needs its own code, sequenced first.

An S31.031S claim is therefore a two-code claim. The residual condition comes first, then S31.031S as its cause. Leaving off the residual condition code is the most common reason these claims fail a records review.

Parent code hierarchy for S31.031S

S31.031S sits at the bottom of a defined hierarchical path. Walking down it is the fastest way to confirm you are in the right group before you attach a 7th character.

• S00-T88: Injury, poisoning, and certain other consequences of external causes (chapter level)
• S30-S39: Injuries to the abdomen, lower back, lumbar spine, pelvis, and external genitals (block level)
• S31: Open wound of abdomen, lower back, lumbar spine, pelvis, and external genitals (category level)
• S31.0: Open wound of lower back and pelvis (subcategory)
• S31.03: Puncture wound without foreign body of lower back and pelvis (wound type, foreign body status)
• S31.031: Puncture wound without foreign body of lower back and pelvis with penetration into retroperitoneum (parent, not billable)
• S31.031S: The same wound at the sequela stage (billable, this code)

Each decision lands on its own digit. The fifth digit carries wound type and foreign body status, the sixth carries retroperitoneal penetration, and the 7th character carries the encounter.

Parent code S31.031 is not billable on its own, because the subcategory requires a 7th character. Only the extended codes carrying A, D, or S can go on a claim.

Excludes notes and coding restrictions for S31

Category S31 carries one Excludes1 note and two Excludes2 entries. An Excludes1 violation is a hard claim error. An Excludes2 note says the two conditions are separate, so both may be reported when both are documented.

• Excludes1, never coded together: traumatic amputation of part of abdomen, lower back, and pelvis (S38.2-, S38.3-). If the injury is an amputation, the amputation code replaces the open wound code.
• Excludes2, may be coded together: open wound of hip (S71.0-). The hip is a separate site from the lower back and pelvis, so both can appear on one claim when both are documented.
• Excludes2, may be coded together: open fracture of pelvis (S32.1- through S32.9 with 7th character B). A pelvic open fracture and a puncture wound are distinct injuries and are reported separately.
• Code also: any associated wound infection. The infection is not part of S31.031S and needs its own code when the record documents it.

Only the amputation note blocks the code outright. The pelvic fracture and the hip wound may both be reported alongside it. Cross-reference the tabular list through the AAPC ICD-10-CM code lookup before you finalize any combination, since excludes notes change with each annual release.

External cause codes on a sequela claim

External cause codes record how the original injury happened. Most payers encourage them on traumatic wound claims, some state Medicaid programs require them, and workers’ compensation carriers expect them. A sequela claim without one can be pulled for manual review.

• W45-: Foreign body or object entering through skin. Use it when the puncture came from a nail, splinter, or tool, even where nothing was retained.
• W26-: Contact with knife, sword, or dagger. Use it for puncture wounds from bladed instruments.
• X99.-: Assault by sharp object. Use it when the puncture wound resulted from an assault.
• Y93-: Activity codes. Document what the patient was doing when the original injury occurred, such as Y93.89 for other specified activities.
• Y99-: External cause status. Record whether the injury happened at work (Y99.0), during leisure (Y99.8), or under another status.

On a sequela encounter, the external cause code takes the 7th character S as well, because it describes the same prior injury. An initial-encounter code such as W45.0XXA becomes W45.0XXS on the sequela claim.

ICD-9-CM crosswalk for S31.031S

Practices migrating legacy data, or reporting on records that predate the transition, need the backward mapping. The General Equivalence Mappings maintained by CMS are the official source for moving between ICD-9-CM and ICD-10-CM in either direction.

The acute open wound codes in the ICD-9-CM 879 range are not late effect codes, which makes them the wrong target for S31.031S. Because ICD-9-CM had no 7th character system, every sequela mapping stays approximate, so the GEM files should govern migration work.

Billing and reimbursement considerations

Sequela wound claims behave differently from active injury claims at the payer end. Five patterns account for most of the rejections, and each one is preventable at the point of coding.

• Denial trigger 1, active wound care billed as a sequela: a dressing change or wound management visit reads as an active encounter. Report S31.031D instead.
• Denial trigger 2, penetration not documented: if the record never states that the wound reached the retroperitoneum, an auditor will downgrade the claim to S31.030S. Documentation has to earn the sixth digit.
• Denial trigger 3, missing residual condition code: S31.031S alone does not tell the payer why the patient came in. Sequence the late effect first, then this code.
• Denial trigger 4, missing external cause code: most commercial payers flag sequela wound claims that arrive without one for manual review.
• Denial trigger 5, parent code submitted: S31.031 without a 7th character is rejected at adjudication. Only the fully extended codes are billable.
• Reimbursement note: these visits are usually outpatient E&M encounters. The documented complexity of the residual condition should match the E&M level billed.

Validation before submission is what keeps these claims moving. Clearinghouse edits catch a missing 7th character before the claim leaves the practice. Reviewing the denial codes billers see on wound sequela claims helps a billing team build prevention into its own process.

A clean claim matters more here than usual, because a records request adds weeks to the payment cycle. Tracking traumatic injury follow-up as its own segment also surfaces payer-specific denial patterns much faster.

Where Pabau fits into your wound coding workflow

A wrong code on this claim is almost always a documentation problem first. Suppose the note never records that the wound reached the retroperitoneum, or never confirms that it has healed. The coder falls back to a safer code, the claim goes out with the wrong sixth digit, and the denial lands weeks later.

Practice management software like Pabau closes that loop at the point of care. Its claims software for practices keeps ICD-10 lookup inside the patient record. Coders confirm S31.031S and its residual condition partner without leaving the chart.

• Structured note templates prompt the clinician to record wound depth and healed status at each visit. Those are the two details the sixth digit and the 7th character depend on.
• ICD-10 code lookup in the chart puts the four-code puncture wound group side by side. The foreign body and penetration questions then get answered deliberately, not by default.
• Clearinghouse validation through Claim.MD runs payer edits against the code combination and flags problems such as a missing 7th character before submission.
• Denial tracking by code shows billing managers which ICD-10 codes generate the most rejections, which turns coder education into a targeted exercise.

Urgent care, physical therapy, and surgical follow-up all see traumatic wound sequelae regularly. Catching the code before submission removes most of their back-end correction work.

Reduce ICD-10 coding errors at the source

Pabau’s claims management software includes built-in ICD-10 code lookup, structured clinical notes, and Claim.MD clearinghouse validation. Your team submits accurate wound sequela claims on the first attempt.

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Conclusion

Site specificity plays no part in this code. Two other facts decide it. One is whether an object stayed in the wound. The other is whether the track reached the retroperitoneum.

Both facts live in the operative or imaging note, not in the diagnosis line. So the fix for a denied S31.031S claim usually sits upstream of the coder. Give the clinician a place to record penetration and healed status, and the code stops being a judgment call.

Sequence the residual condition first, keep S31.041S and S31.030S straight as the one-step neighbors, and these claims stop coming back. Book a demo to see how wound sequela claims move from clinical note to submission in Pabau.

Continue your research

Need guidance on ICD-10 denial prevention? Denial management in healthcare covers the most common claim rejection patterns and how to address them systematically.

Submitting claims through a clearinghouse? Claim.MD clearinghouse overview explains how Pabau’s clearinghouse partner validates codes before payer submission.

Want to understand the full billing cycle? How superbills work in medical billing explains how ICD-10 codes flow from clinical documentation through to claim submission.

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