ICD code S84.801A – Injury of other nerves, lower leg, right side

Key takeaways

S84.801A is the billable FY2026 ICD-10-CM code for an initial encounter, and the parent S84.801 cannot be submitted.

‘Other nerves’ means the injured nerve is neither tibial (S84.0x), peroneal (S84.1x), nor cutaneous sensory (S84.2x).

Right-leg laterality must appear in the note, or the claim defaults to the unspecified S84.809A.

The 7th character A, D, or S follows the phase of care under ICD-10-CM Official Guidelines Section I.C.19.

Pabau’s claims management software flags an incomplete 7th character or a missing laterality before the claim reaches the clearinghouse.

ICD-10 Code S84.801A: Definition and clinical description

ICD-10 Code S84.801A describes an injury to a nerve at the lower leg level on the right side that ICD-10-CM classifies as “other.”

That means the injured structure is not the tibial nerve, not the common peroneal (fibular) nerve, and not a cutaneous sensory nerve. The code sits in the S84 category, injury of nerves at lower leg level. That category sits inside block S80-S89 (injuries to the knee and lower leg), under the S00-T88 injury chapter of ICD-10-CM as maintained by CMS.

The “other” designation is a residual slot rather than a name. S84.8x covers a nerve the note identifies, but which the alphabetic index does not route to the tibial, peroneal, or cutaneous sensory entries.

In practice that means motor branches, such as the nerve to the popliteus or a muscular branch supplying tibialis anterior. A saphenous or sural nerve injury does not belong here. Both are cutaneous sensory nerves, so they route to S84.2x instead.

Coders meet this code after acute trauma, a surgical complication, or a compression injury that does not point to one of the named nerve trunks.

S84.801A code details at a glance

The table below summarizes the key technical attributes of ICD-10 Code S84.801A for FY2026, verified against the CDC/NCHS ICD-10-CM tool.

Understanding the 7th character: A, D, and S for S84.801A

The 7th character in S84.801A designates the encounter type under ICD-10-CM Official Guidelines Section I.C.19. “Initial encounter” does not mean the first calendar visit to any provider. It means the patient is receiving active treatment for the injury.

A neurologist seeing the patient six weeks after the original trauma is still treating actively, provided the nerve injury is being managed. The 7th character A applies at that visit. Reaching for D too early is one of the documentation mismatches auditors flag most often on nerve injury claims.

A claim that pairs S84.801D with active nerve repair or neuroplasty triggers a medical necessity mismatch. Document the phase of care explicitly in the note. Write it plainly: “patient remains in active treatment for lower leg nerve injury.” That line supports the 7th character A at every visit where treatment continues.

ICD-10 code hierarchy for S84.801A

Understanding the hierarchy explains why S84.801 cannot be submitted as a standalone claim. Every code in the S84.8xx subgroup needs the 7th character to reach billable specificity. The full parent-to-child chain runs as follows.

Sibling codes: Left leg and unspecified

Laterality is not optional in ICD-10-CM. A claim submitted with the parent S84.801 instead of S84.801A will be rejected for incomplete coding. The three laterality variants under S84.80 are:

Clinical context: When to use S84.801A

S84.801A applies when the clinician names the injured nerve in the right lower leg. That nerve must fall outside the tibial, peroneal, and cutaneous sensory subgroups. The scenarios that reach this code most often involve motor branches and articular branches, which the index does not classify elsewhere.

The “initial encounter” requirement means active treatment is underway. ICD-10-CM assigns the 7th character by phase of care, not by visit count. A physical therapist treating the patient in week four of a rehabilitation program is still providing active treatment. S84.801D takes over when the plan shifts to routine monitoring.

• Motor branch injury to the nerve supplying tibialis anterior during a right tibial fracture repair
• Iatrogenic damage to an articular branch at the proximal right lower leg during knee or tibial surgery
• Compression neuropathy of a named motor branch under a tight cast on the right lower leg
• Blunt trauma to the right lower leg affecting a nerve the index does not route to S84.0x, S84.1x, or S84.2x

Documentation requirements for ICD-10 Code S84.801A

Four elements must appear in the clinical note to support ICD-10 Code S84.801A. When one is missing, the payer has grounds to deny the claim or request the full record. Build all four into your nerve injury note template.

• Laterality: the note must state “right leg” or “right lower extremity” explicitly. “Lower leg nerve injury” with no side documented defaults the coder to S84.809A, which payers often deny.
• Nerve specificity: the note must name the injured nerve and place it outside the tibial, peroneal, and cutaneous sensory subgroups. A phrase such as “motor branch to tibialis anterior, right leg” satisfies this. A bare “nerve injury, right lower leg” leaves the coder unable to rule out S84.01XA, S84.11XA, or S84.21XA.
• Encounter type: the note must support active treatment. Language such as “patient undergoing nerve conduction studies,” “initiating physical therapy for nerve injury,” or “referred for neuroplasty evaluation” establishes the initial encounter phase.
• Mechanism or clinical basis: trauma, surgical complication, or compression should be documented. This supports medical necessity, particularly when the claim also carries a nerve repair or neuroplasty CPT code.

Structured documentation catches these omissions before the claim is submitted, which cuts down on retrospective record requests. Thin documentation around nerve specificity is the leading reason an S84.801A claim converts to S84.809A at coding. The unspecified code then draws far more payer scrutiny.

Common coding pitfalls for lower leg nerve injury claims

The S84 category splits into five nerve subgroups: tibial (S84.0), peroneal (S84.1), cutaneous sensory (S84.2), other (S84.8), and unspecified (S84.9). Confusion between them generates a disproportionate share of denials on lower extremity nerve injury claims. The nerve the clinician names in the note decides the subgroup, and the subgroup decides the code.

• Submitting the non-billable parent S84.801: this code lacks a 7th character and every clearinghouse rejects it as incomplete. Code to the highest level of specificity, so S84.801A, S84.801D, or S84.801S.
• Confusing S84.801A with a peroneal nerve injury: the note may say “common peroneal nerve,” “fibular nerve,” or “foot drop from peroneal injury.” The right leg code is then S84.11XA. Using S84.801A on a documented peroneal injury loses specificity the note already supports.
• Confusing S84.801A with a tibial nerve injury: “tibial nerve” in the documentation routes to S84.01XA for the right leg. S84.8xx is a residual subgroup for nerves outside the named trunks.
• Coding a saphenous or sural nerve injury to S84.8x: both are cutaneous sensory nerves, so a right leg injury routes to S84.21XA rather than S84.801A.
• Wrong 7th character timing: switching from A to D before active treatment ends. The encounter type follows the phase of care, not the calendar. Premature use of D can produce medical necessity denials for ongoing treatment.
• Omitting laterality and defaulting to S84.809A: unspecified codes carry higher audit risk, and many commercial payers auto-deny them for elective or scheduled procedures. Document right or left in every nerve injury note.

Related ICD-10 codes for lower leg nerve injury

Coders working with S84.801A routinely meet the following adjacent codes. Picking the wrong one is the most common audit trigger in this code family, and the named nerve variants cause most of it. The AAPC ICD-10-CM code reference provides searchable crosswalks for each of these.

Associated CPT codes for S84.801A lower leg nerve injuries

S84.801A is a diagnosis code only, so it pairs with CPT procedure codes to complete a billable claim. The codes below are commonly submitted alongside it for nerve repair, evaluation, and rehabilitation. Every pairing is subject to NCCI edits and individual payer policy, so check current guidelines before submission. Our CPT codes reference carries the full descriptor for each one.

Pabau submits CPT and ICD-10 pairs electronically through Claim.MD, our US clearinghouse partner. The integration routes CMS-1500 and 837P claims to over 4,000 US payers and runs eligibility checks before the appointment. It also returns Electronic Remittance Advice, so staff can see how each nerve injury claim settled. For practices with high lower leg injury volume, submitting a clean claim on the first pass depends on validating the pair first.

How Pabau supports accurate ICD-10 coding for nerve injuries

Coding accuracy for S84.801A rests on three things. The note has to capture the clinical detail, and the coder needs a validated code reference. The claim then has to reach the payer with the 7th character and laterality intact. Pabau’s claims management software handles all three.

Built-in ICD-10-CM validation flags an incomplete code before the claim batch is finalized, including a parent code sent without its 7th character. Structured notes built on Pabau’s digital form templates prompt the clinician for laterality and nerve specificity at the point of care. Coders query back less often as a result.

For practices submitting through a clearinghouse, the Claim.MD integration passes denial reason codes back into the workflow. Staff can see which claim line triggered the rejection instead of reopening the whole batch.

Reduce nerve injury claim denials before they happen

Pabau’s claims management software validates ICD-10-CM codes, including 7th character completeness and laterality, before each claim reaches the clearinghouse. See how it works for your practice.

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Conclusion

S84.801A is a narrow code, and the narrowness is the point. It earns its place only when the note names a nerve in the right lower leg. That nerve must be one the index will not send to S84.0x, S84.1x, or S84.2x. Reach for it on a saphenous or peroneal injury and you have swapped a specific code for a vaguer one.

That makes the fix a documentation job rather than a coding job. If the note names the nerve and the side, the code follows on its own and the 7th character is the only judgment left. If it does not, no amount of care at the coding desk recovers the specificity, and the claim drifts toward S84.809A.

Put the prompt in the template rather than in the coder’s memory. Book a demo to see how Pabau validates the 7th character and laterality on every nerve injury claim before it leaves your practice.

Continue your research

Need a framework for tracking claim denials by code? Denial codes in medical billing breaks down the most common remittance advice codes and how to respond to each one.

Billing nerve injury claims through a clearinghouse? Electronic remittance advice (ERA) explained covers how 835 files return denial reasons so you can act on them by claim line.

Want to verify insurance eligibility before the appointment? Insurance eligibility verification outlines the real-time checks that prevent coverage surprises on lower leg injury claims.

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