HCPCS code L1843: Knee orthosis, single upright, prefabricated

Key Takeaways

HCPCS code L1843 describes a prefabricated single-upright knee orthosis (KO) with adjustable flexion and extension joint, customized to fit a specific patient by an individual with expertise.

Medicare covers L1843 under LCD L33318 when the beneficiary is ambulatory and meets at least one of three qualifying medical necessity criteria.

L1843 has required Medicare prior authorization since August 12, 2024, and as of December 1, 2024 only PDAC-verified products may be billed under this code.

Pabau’s claims management software helps DME suppliers and orthotists track documentation, prior authorization status, and proof of delivery requirements in one place.

HCPCS code L1843 is a Medicare billing code for a prefabricated single-upright knee orthosis with an adjustable flexion and extension joint, customized to fit a specific patient. It is billed by DME suppliers and orthotists under Medicare Part B and carries specific coverage, documentation, and prior authorization requirements. This guide covers the code description, Medicare coverage criteria under LCD L33318, documentation and face-to-face requirements, related codes, and the ICD-10 diagnosis codes commonly paired with L1843 claims.

HCPCS code L1843: Full code description and device specifications

The official long descriptor for HCPCS code L1843, as maintained by CMS, reads:

Knee orthosis (KO), single upright, thigh and calf, with adjustable flexion and extension joint (unicentric or polycentric), medial-lateral and rotation control, with or without varus/valgus adjustment, prefabricated item that has been trimmed, bent, molded, assembled, or otherwise customized to fit a specific patient by an individual with expertise.

The short descriptor used by PDAC and on claim forms is “KO SINGLE UPRIGHT PRE CST,” where “PRE” stands for prefabricated and “CST” for customized. Every element of the long descriptor is a billing requirement: if the device delivered lacks any one of these components, a different code applies.

Key device characteristics that must be present to bill L1843:

• Single upright: One structural upright (Compare L1845, which requires two uprights).
• Thigh and calf components: The brace spans both segments of the leg, securing above and below the knee joint.
• Adjustable flexion and extension joint: The hinge allows range-of-motion adjustment, either unicentric (single pivot) or polycentric (multi-pivot).
• Medial-lateral and rotation control: The design provides coronal and rotational stability.
• With or without varus/valgus adjustment: Optional unloading capability is covered either way.
• Prefabricated, customized to fit: The device was manufactured off-the-shelf but physically modified (trimmed, bent, molded, assembled) by a qualified individual. This distinguishes L1843 from custom-fabricated code L1844.

Only products listed in the PDAC DMECS (Durable Medical Equipment Coding System) as verified for L1843 may be billed under this code. Suppliers using products not verified by PDAC risk claim denial and potential audit exposure.

Medicare coverage criteria for L1843 under LCD L33318

Medicare Part B covers HCPCS code L1843 as a durable medical equipment benefit when medical necessity criteria under LCD L33318 (Knee Orthoses) are met. LCD L33318 applies to all Medicare Administrative Contractor (MAC) jurisdictions and sets the baseline coverage standard. Palmetto GBA, CGS Medicare, and Noridian may each have supplemental guidance, but LCD L33318 governs.

Under LCD L33318, a knee orthosis with single upright, adjustable flexion and extension joint, medial-lateral and rotation control (codes L1843, L1845, L1851, L1852) is covered when the beneficiary is ambulatory and at least one of the following criteria is met:

• Criterion 1: The beneficiary has objective clinical documentation of moderate to severe knee instability due to a ligamentous laxity or musculotendinous insufficiency.
• Criterion 2: The beneficiary has objective clinical documentation of a condition causing weakness or absence of knee muscles or ligaments, such as post-surgical status, neurological condition, or musculoskeletal condition.
• Criterion 3: The beneficiary has objective clinical documentation supporting pain relief and functional improvement in a knee with significant degenerative disease (e.g., osteoarthritis of the knee) that limits ambulation.

The ambulatory status requirement is a firm coverage condition. A non-ambulatory beneficiary does not meet LCD L33318 criteria, regardless of diagnosis.

Palmetto GBA summarizes the coverage pathway clearly: prefabricated codes L1832, L1833, L1843, L1845, L1851, and L1852 each have two potential paths to coverage, with the treating practitioner’s clinical documentation serving as the foundation for both.

Documentation requirements for L1843 billing

Documentation is the most common denial trigger for L1843 claims. The medical record must support every coverage criterion before the device is delivered. Retroactive documentation cannot make up for records that were incomplete at the time of delivery.

The following documents must be in the billing file for L1843:

• Written Order Prior to Delivery (WOPD): A detailed written order from the treating practitioner must be obtained before the orthosis is dispensed. Effective for dates of service on or after August 12, 2024, L1843 requires a WOPD. The WOPD must include the patient’s name, date, treating practitioner’s name and signature, code, and description of the item.
• Face-to-Face (F2F) examination: Also effective August 12, 2024, a face-to-face clinical evaluation by the treating practitioner is required before the order is written. The F2F must be documented in the medical record and must support the medical necessity of the orthosis.
• Proof of Delivery (POD): The supplier must retain a signed delivery confirmation. For shipped items, a signed shipping receipt or equivalent is acceptable.
• Continued need documentation: If the beneficiary continues to use the device beyond the initial dispensing period, documentation of continued need must be obtained at required intervals.
• Beneficiary authorization: The beneficiary (or authorized representative) must sign acknowledging receipt of the device.

Noridian’s Documentation Checklist for Knee Orthoses (updated September 20, 2024) explicitly lists L1843 and L1845 as subject to F2F and WOPD requirements effective for DOS on or after August 12, 2024. This checklist is the reference standard for Noridian jurisdiction suppliers. Using digital intake and documentation forms helps suppliers capture all required fields at the point of care rather than chasing paperwork after the fact.

Prior authorization requirements for L1843

Prior authorization is a billing prerequisite for L1843 under Medicare. CMS added L1843 to the Required Prior Authorization (PA) program under Policy Article A52465, with an effective date of August 12, 2024. Claims for L1843 with dates of service on or after that date that do not have an affirmative prior authorization decision will not be paid. Separately, effective December 1, 2024, only products with a completed PDAC coding-verification review may be billed under L1843.

The CMS Required PA program for lower limb orthoses covers L1843 along with related codes L1832, L1845, and L1851.

Beginning December 1, 2024, the DME MACs also require a PDAC coding-verification review for L1843 and L1951 (publication COPE162443). As of that date, only products published on the PDAC Product Classification List may be billed under these codes. This coding-verification step is separate from, and does not replace, the prior authorization requirement.

How the Required PA process works for L1843:

1. Submit the PA request to the MAC before delivering the device. The request must include the written order, clinical documentation supporting medical necessity, and F2F documentation.
2. Receive an affirmative PA decision. The MAC reviews the submission against LCD L33318 criteria and issues an approval or provisional denial.
3. Deliver the device and submit the claim. Include the PA approval number on the claim. Claims without a matching PA decision are automatically rejected.
4. Retain all documentation. The PA approval does not guarantee payment if the delivered item differs from what was approved or if the claim contains errors.

Suppliers billing across multiple MAC jurisdictions should verify jurisdiction-specific submission portals and timelines with CGS, Noridian, or Palmetto GBA directly, as PA submission workflows vary by MAC.

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L1843 vs L1845 and related knee orthosis codes

Choosing the wrong code is a common and costly error in DMEPOS knee orthosis billing. HCPCS code L1843 sits within a family of related knee orthosis codes, and each has distinct device requirements. The table below summarizes the key distinctions for the codes most frequently confused with L1843.

The single-versus-double upright distinction between L1843 and L1845 is the most frequent code selection error. Both codes share identical joint, medial-lateral, and varus/valgus requirements, and the upright count is the only differentiator.

Audit reviewers check this against the product’s PDAC listing. Billing L1843 for a device that is PDAC-verified as L1845 is an incorrect claim regardless of clinical intent.

L1851 and L1852 are sometimes confused with L1843 and L1845. L1851 and L1852 share the single and double upright structure but their code descriptors differ in the specific control features required. Review the PDAC verification for the specific product being dispensed, not just the general device category, before selecting a code. For orthosis coding outside the knee, see our guides to HCPCS code L1971 (Prefabricated ankle-foot orthosis) and, on the surgical side, CPT code 27447 (Total knee arthroplasty).

ICD-10 diagnosis codes commonly used with L1843

Every L1843 claim must be supported by an ICD-10-CM diagnosis code that meets LCD L33318 medical necessity criteria. The diagnosis code alone does not establish coverage; the underlying clinical documentation must support the specific criterion met.

Commonly paired ICD-10 codes for L1843 claims include:

• M17.11 (Primary osteoarthritis, right knee)
• M17.12 (Primary osteoarthritis, left knee)
• M17.31 (Post-traumatic osteoarthritis, right knee)
• M17.32 (Post-traumatic osteoarthritis, left knee)
• M23.206 (Derangement of unspecified meniscus due to old tear or injury, right knee)
• M23.611 (Other spontaneous disruption of anterior cruciate ligament of right knee)
• M25.361 (Other instability, right knee)
• G82.20 (Paraplegia, unspecified, when bilateral weakness affects knee musculature)

Diagnosis codes must reflect the condition supported by the F2F examination and documented in the treating practitioner’s notes. Billing M17.11 when the clinical record documents only ligamentous laxity with no osteoarthritis findings is a documentation mismatch that creates audit risk. For meniscus-related claims, our guide to ICD-10 code S83.241 (Medial meniscus tear, right knee) shows how laterality and chronicity drive code selection. The relationship between procedure codes and diagnosis codes is always a crosswalk of clinical reality, not administrative convenience.

For a closer look at diagnoses frequently paired with knee-orthosis claims, see our guides to ICD-10 code M17.12 (Left knee osteoarthritis) and ICD-10 code M25.561 (Right knee pain), both of which map to LCD L33318 medical necessity criteria.

Billing and reimbursement guidance for L1843

Fee schedule amounts for L1843 vary by MAC jurisdiction and are updated annually by CMS. Suppliers should verify current allowed amounts directly through the CMS Durable Medical Equipment fee schedule rather than relying on third-party fee tables, which may be outdated.

Key billing considerations for L1843:

• PA is required before delivery. Claims for L1843 with DOS on or after August 12, 2024 without a corresponding affirmative PA decision will be rejected, not just denied. Rejected claims cannot be appealed; they must be resubmitted once PA is obtained.
• PDAC product verification. Only submit L1843 when the specific product dispensed has a PDAC coding verification confirming L1843 applicability. Suppliers can verify products through the Palmetto GBA DMECS portal.
• Modifier usage. When applicable, use modifiers (such as KX for documentation on file, or GA for signed ABN on file) as required by the MAC. The KX modifier signals that documentation supporting medical necessity criteria is in the billing file.
• One unit per claim. L1843 is billed per orthosis. Bilateral claims require documentation of bilateral medical necessity and correct claim form completion.
• Assignment of benefits. Most DMEPOS suppliers participating in Medicare must accept assignment for covered items, including L1843.

Pabau’s claims management software gives DME suppliers and physical therapy practices a structured way to track PA submission dates, approval numbers, and documentation completeness before submitting to Medicare. For practices also managing allied health procedure codes across multiple payers, centralizing claims workflows reduces the risk of missing jurisdiction-specific requirements. Teams new to therapy claims can also review our guide to physical therapy billing for CPT, units, and Medicare rules.

Practical workflow: Billing L1843 from referral to claim

Many billing errors with L1843 happen not from ignorance of the rules but from breakdowns in coordination between the prescribing clinician, the DME supplier, and the billing team. A clear step-by-step process prevents most of those breakdowns.

1. Receive the referral and verify eligibility. Confirm Medicare Part B active coverage, deductible status, and any secondary payer information before committing to the order.
2. Obtain the F2F documentation from the treating practitioner. The face-to-face examination note must predate the written order. Request it in writing and retain it in the billing file immediately.
3. Obtain the Written Order Prior to Delivery (WOPD). Confirm the order includes all required elements: Patient name, date, practitioner name and signature, HCPCS code L1843, and item description.
4. Submit the prior authorization request to the MAC. Include the WOPD, F2F note, and clinical documentation supporting LCD L33318 criteria. Allow adequate processing time before scheduling delivery.
5. Verify PDAC product eligibility. Confirm the specific product being dispensed is PDAC-verified for L1843 through the Palmetto GBA DMECS portal before delivery.
6. Deliver the device and obtain POD. Have the beneficiary or authorized representative sign the delivery confirmation. Retain the signed POD in the file.
7. Submit the claim. Include the PA approval number, modifier KX, applicable ICD-10 diagnosis code, and complete claim data. Submit to the appropriate MAC within the filing deadline.

Practices billing physical therapy alongside DME can link their clinical documentation workflows using physical therapy EMR software that supports structured clinical notes aligned with LCD criteria. Therapy teams should also confirm they are applying Medicare time rules correctly, as covered in our guide to the Medicare 8-minute rule. The treating practitioner’s documentation is the single most important variable in L1843 claim success.

LCD and policy article references for L1843

Three CMS documents govern most L1843 coverage and billing decisions. Billing teams should bookmark all three and verify they are using the current version, as LCDs and policy articles are revised without formal notice periods.

• LCD L33318 (Knee Orthoses): The national coverage determination governing medical necessity criteria for L1843 and related codes. Maintained by CMS. Access via the CMS Medicare Coverage Database.
• Policy Article A52465 (Knee Orthoses): The companion policy article to LCD L33318. Contains the Required Prior Authorization listing and billing instructions. Confirmed: L1843 added to Required PA effective August 12, 2024.
• MAC-specific documentation checklists: Noridian, CGS, and Palmetto GBA each publish documentation checklists aligned with LCD L33318. The Noridian checklist (updated September 20, 2024) explicitly lists the F2F/WOPD requirements for L1843.

Compliance teams at DME suppliers should build an internal policy that cross-references all three documents and flags when policy article updates have been issued. Pabau’s compliance management tools support practices in maintaining audit-ready documentation across multiple regulatory requirements. For practices also navigating HIPAA obligations alongside DME billing compliance, HIPAA compliance for medical offices covers the documentation retention requirements that overlap with Medicare audit standards.

ACHC (Accreditation Commission for Health Care) also added L1843 to its F2F/WOPD tracking list, effective April 2026, confirming that accreditation bodies are aligned with CMS program requirements for this code.

Conclusion

HCPCS code L1843 carries significant billing complexity: Prior authorization is required before delivery, face-to-face documentation requirements apply from August 2024, and only PDAC-verified products qualify. Suppliers who treat these requirements as optional paperwork will face rejected claims and audit exposure.

Pabau’s claims management software gives DME suppliers and orthotics practices the workflow infrastructure to track PA status, documentation completeness, and proof of delivery without relying on manual checklists. To see how Pabau handles DMEPOS billing workflows end to end, book a demo.

Continue your research

Managing physical therapy documentation alongside DME billing? Physical therapy EMR software supports structured clinical notes that align with LCD L33318 medical necessity criteria.

Need to streamline prior authorization tracking? Claims management software helps track PA approvals, modifier requirements, and submission deadlines across multiple payers.

Billing other HCPCS codes alongside L1843? Procedure code fee schedule guides cover fee schedule lookup strategies for DMEPOS and allied health billing teams.

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