Why it matters in orthopedics
Many orthopedic services have strict coverage rules: arthroscopy for knee osteoarthritis under NCD 150.9, knee braces under DME MAC LCD L33318, injections with frequency limits, and therapy above the annual KX modifier threshold when it is not medically necessary. If Medicare denies one of these services and you did not give a valid ABN in advance, you generally cannot bill the patient. In WISeR states, CMS also expects an ABN when a non-affirmed service goes ahead; see our WISeR guide.
How it works
When it is required: before items or services Medicare usually covers but may deny as not reasonable and necessary (including experimental care and services beyond frequency limits), custodial care, and outpatient therapy above the threshold that is not medically necessary.
When it is optional: for services Medicare never covers by statute or that are not a Medicare benefit. A voluntary notice informs the patient but does not change liability.
When it cannot be used: for Medicare Advantage or Part D patients, in emergencies or under duress, to bill patients for units denied under Medically Unlikely Edits, or to charge for parts of a bundled service.
How to deliver it: before the service, early enough for the patient to consider options, with the specific item, the reason Medicare may not pay and a good-faith cost estimate. The patient picks an option and signs, and you keep a copy for 5 years.
Which form: since May 12, 2026, notifiers must use the version marked “Exp. 03/31/2029” (OMB 0938-0566).
Modifier | When to use it |
|---|---|
GA | You expect a medical-necessity denial and have a signed, required ABN on file |
GZ | You expect a medical-necessity denial but did not obtain an ABN |
GX | You gave a voluntary notice for a service excluded by statute or not a Medicare benefit |
GY | The service is excluded by statute or is not a Medicare benefit |
Orthopedic example
A 70-year-old patient with severe (Outerbridge grade IV) knee osteoarthritis asks for arthroscopic debridement after counseling about alternatives. NCD 150.9 makes debridement for severe osteoarthritis nationally noncovered, so the practice completes an ABN that names the procedure, explains that Medicare does not pay for it in severe arthritis and estimates the cost. The patient selects Option 1 and signs, and the surgeon’s claim goes out with modifier GA.
Common denial triggers
No ABN, or one signed after the service, leaves the practice liable for a medical-necessity denial (see CARC CO-50).
Routine or blanket ABNs given to every patient are invalid, except in limited cases such as frequency-limited or experimental services.
A vague reason, a missing cost estimate or an outdated form version can invalidate the notice.
The wrong modifier, such as GZ when a valid ABN exists, misreports liability. Our review of common orthopedic claim denials covers related denial codes.
How to prevent or fix
Build ABN triggers into scheduling for services with known NCD, LCD or frequency limits. Use the current CMS-R-131, write a specific reason and a reasonable cost estimate, and explain the form before the patient signs. Append GA when a valid ABN is on file. If Medicare pays after the patient has paid you, refund the patient within 30 days of the remittance. Confirm unusual situations with your MAC or compliance team.
Frequently asked questions
Do I need an ABN for a service Medicare never covers?
No. You don’t need to notify the patient before providing items or services that Medicare never covers by statute or that are not a Medicare benefit. You may still give a voluntary notice so the patient understands they will be responsible for payment; in that case the patient does not have to choose an option or sign. Bill these services with modifier GY, adding GX when you gave a voluntary notice.
Can an ABN be used for Medicare Advantage patients?
No. The ABN applies only to Original Medicare (fee-for-service) patients. CMS states that advance written notices of noncoverage are not used for items and services provided under Medicare Part C or Part D. For Medicare Advantage patients, follow the plan’s own coverage and notice rules before asking a patient to accept financial responsibility for a service the plan may not cover, and confirm the process with the plan.
How long must a practice keep signed ABNs?
CMS requires notifiers to keep ABNs for 5 years from the date of care delivery when no other state law requirement applies. Keep every notice record, including those where the patient declined care, refused to choose an option or refused to sign. If you deliver the notice electronically, offer the patient a paper copy and retain your own copy, whether it was signed on paper or electronically.
Which ABN form version is current?
As of October 2026, the current Form CMS-R-131 shows an expiration date of March 31, 2029, under OMB control number 0938-0566. Notifiers have had to use this version since May 12, 2026, when the prior version expired. Check the expiration date printed at the bottom of the form, and download English, Spanish and large-print versions from CMS’s ABN page.
Guides that cover this term
WISeR Model: Which Orthopedic Services Need Medicare Prior Authorization?
In six states, Medicare’s WISeR Model adds prior authorization or pre-payment review for knee scopes, epidural injections and spine procedures.
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The Most Common Orthopedic Claim Denials in 2026, and How to Prevent Them
Ten orthopedic denial types, the CARCs behind them, their root causes and how to prevent them, plus when to appeal or correct and resubmit.
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Related terms
Sources
Medicare Advance Written Notices of Non-coverage (MLN006266) — CMS Medicare Learning Network, May 2025
FFS ABN — CMS, accessed October 14, 2026
Form Instructions: Advance Beneficiary Notice of Non-coverage (ABN) — CMS, OMB 0938-0566
Updated Advance Beneficiary Notice of Noncoverage (ABN) Form Now Available! — CGS Administrators (Medicare Administrative Contractor), March 19, 2026
NCD 150.9 Arthroscopic Lavage and Arthroscopic Debridement for the Osteoarthritic Knee — CMS Medicare Coverage Database, accessed October 14, 2026
This entry is educational and is not legal, coding-compliance or billing advice. Payer rules change often, so confirm requirements with the payer before you bill. CPT® is a registered trademark of the American Medical Association; code descriptions here are Rette’s plain-language summaries.