Orthopaedic ASC Site of Service Billing in 2027: What CMS's Inpatient-Only List Phase-Out Means for Your Revenue

The short answer

Orthopaedic ASC site of service billing is about to become one of the largest revenue variables an orthopaedic group controls. In the CY 2027 OPPS and ASC proposed rule published July 7, 2026, CMS proposed removing 637 more services from the Medicare inpatient-only (IPO) list and adding roughly 618 surgical procedures to the ASC Covered Procedures List, with the remaining IPO services scheduled for removal in CY 2028. For orthopaedics, that continues a migration that started when total knee arthroplasty came off the IPO list and later joined the ASC list, followed by total hip.

The practical effect for a group with 5 or more surgeons is that where a case is performed is becoming a clinical and financial decision rather than a regulatory one, and the professional fee, the facility fee, the payer contract, and the coding rules all change with the site. Groups that plan the site of service deliberately capture the ancillary facility revenue and protect the professional fee. Groups that let the site drift capture neither and add a new category of denials.

This guide covers what changed, how ASC billing differs mechanically from hospital outpatient and office billing, the coding traps that show up when ortho cases move, and the questions your CFO should be asking before January 1, 2027.

What CMS actually proposed for CY 2027

The proposed rule, published in the Federal Register on July 7, 2026 with a comment deadline of August 31, 2026 and most provisions effective January 1, 2027, contains four items that matter to orthopaedic groups.

‍The inpatient-only list is being retired. CMS proposed removing 637 additional services in CY 2027, roughly half of what remained, with the balance of about 801 services slated for CY 2028. That completes a three-year elimination of the IPO list. Once a procedure is off the list, Medicare no longer requires inpatient admission for payment, and the two-midnight expectation and medical necessity documentation carry the decision instead.

‍The ASC Covered Procedures List expands substantially. CMS proposed adding approximately 618 surgical procedures to the ASC list for CY 2027, including procedures coming off the IPO list. This is the mechanism that lets a physician-owned ASC bill Medicare a facility fee for cases it previously could not perform on Medicare patients at all.

‍Payment rates rise modestly. CMS proposed a 2.4 percent conversion factor update for both OPPS and the ASC payment system for CY 2027.

‍Site-neutral payment expands. CMS proposed applying physician fee schedule equivalent rates to imaging APCs 5521 through 5524 and composite imaging codes furnished in off-campus provider based departments, with an exemption for rural sole community hospitals. CMS estimated roughly 260 million dollars in savings. The direction of travel is unambiguous: the payment premium for performing a service in a hospital outpatient department keeps narrowing.

None of this is new territory for orthopaedics. Total knee arthroplasty came off the IPO list in 2018 and was added to the ASC Covered Procedures List in 2020. Total hip followed, coming off the IPO list in 2020 and onto the ASC list in 2021. CMS also revised its ASC list criteria in the CY 2021 rule in a way that made several hundred additional musculoskeletal services eligible. What CY 2027 does is finish the job across the rest of the surgical spectrum, which means spine, complex arthroplasty, and higher acuity musculoskeletal cases enter the same conversation.

Why site of service is a revenue decision, not a scheduling detail

The same CPT code pays three different amounts depending on where the case is performed, and it generates a different second revenue stream depending on who owns the facility.

‍The professional fee changes. Medicare pays a facility rate and a non-facility rate for most codes. When a surgeon performs a procedure in an ASC or a hospital, the practice is paid the facility rate, which carries lower practice expense RVUs because the facility, not the practice, supplies the staff, space, and supplies. When the same service is performed in the practice's own procedure room, the non-facility rate applies and the practice absorbs the cost. For minor procedures, injections, and small hand cases, moving a case out of the office to an ASC can reduce the practice's professional collections even as total system revenue rises. That is not a reason to keep cases in the office, but it is a reason to model the two revenue lines together rather than separately.

‍The facility fee changes hands. In a hospital outpatient department, the facility fee goes to the hospital. In an ASC the group owns or has equity in, it comes back to the group's owners. This is the entire economic case for the ortho ASC, and it is why the ASC Covered Procedures List expansion matters more to orthopaedic groups than to almost any other specialty. A total joint that previously had to go to the hospital because of the IPO list took the facility fee with it.

‍The payer mix behaves differently by site. Commercial contracts frequently pay ASC facility rates as a percentage of the hospital outpatient rate, and many carve out implant costs separately or not at all. A device intensive case with a poorly negotiated implant carve-out can lose money in the ASC even when the professional fee and volume look attractive. Model the implant cost against the contracted facility rate for every high-cost implant category before you move volume.

The billing mechanics that change when the case moves

Site of service migration introduces a set of rules that office-based and hospital-based billing teams are not always used to applying.

‍Place of service coding. Place of service 24 identifies the ambulatory surgical center. Place of service 22 is on-campus hospital outpatient and 19 is off-campus hospital outpatient. Place of service 11 is the office. A place of service that does not match the setting is one of the fastest ways to trigger a payment error, an overpayment recovery, or a payer audit, because it directly controls whether the facility or non-facility professional rate is applied.

‍Multiple procedure reductions apply on the facility side. Under the ASC payment system, when multiple surgical procedures are performed in the same session, the highest paying procedure is paid at 100 percent of the ASC rate and the additional procedures are generally paid at 50 percent. This is separate from the physician fee schedule multiple procedure reduction that applies to the surgeon's professional fee. Orthopaedic cases frequently involve multiple codes in a single session, so a group modeling ASC economics off the primary code alone will consistently overestimate facility revenue.

‍Device intensive procedures have their own logic. ASC payment for device intensive procedures includes a device portion calculated differently than the standard ASC rate. For arthroplasty and instrumented spine, the device offset is the difference between a viable case and a loss. Your ASC business office needs to be able to reconcile the device portion of each payment, not just the total.

‍The surgeon's documentation still drives both fees. The operative note supports the professional claim and, in an ASC the group owns, the facility claim as well. A note that is thin on approach, structures addressed, laterality, and implant detail now costs the group twice.

The coding traps that show up during migration

When ortho volume shifts sites, the denials that follow tend to cluster in five places.

‍Laterality and anatomic modifiers. RT, LT, and the finger and toe modifiers (FA, F1 through F9, TA, T1 through T9) become more consequential when a case is billed by two entities. A mismatch between the professional and facility claims on laterality is an automatic denial on at least one of them.

‍Modifier 59 and the X modifiers. NCCI procedure to procedure edits do not disappear because the setting changed. Orthopaedic sessions that combine arthroscopic procedures in the same compartment, or a debridement with a definitive procedure, still require a defensible distinct procedural service rationale. The 2027 expansion pulls more multi-procedure cases into the ASC, which raises exposure here.

‍Modifier 22 for increased procedural services. More complex cases moving to the ASC means more cases where the work substantially exceeded the typical service. Modifier 22 is only payable with documentation quantifying the additional work and time, and it requires a manual review that most practices never pursue. This is quiet revenue leakage in every group we look at.

‍Global period modifiers. As higher acuity cases migrate, the volume of related and unrelated postoperative encounters rises. Modifiers 24, 25, 57, 58, 78, and 79 have to be applied correctly or the practice either loses payable visits or invites an audit for unbundling.

‍Medical necessity and the two-midnight expectation. Removing a procedure from the IPO list does not mean every patient belongs in an ASC. It means the documentation now has to justify the setting. Patient selection criteria, comorbidity documentation, and the surgeon's stated expectation of the required stay become part of the compliance record.

What CFOs and COOs should do before January 1, 2027

Model your top 20 codes by site. For each high-volume CPT code, calculate the professional fee at the facility and non-facility rate, the ASC facility rate net of implant cost, and the hospital outpatient rate, by payer. Most groups discover that the ranking of profitable cases changes once implant cost is loaded in.

‍Audit your place of service accuracy now. Run a retrospective on the last two quarters. Any pattern of place of service mismatch is both a repayment exposure and an early warning that your billing workflow will not survive a larger volume shift.

‍Renegotiate ASC facility contracts before the list expands. Payers know what CY 2027 does. Groups that go into contracting with modeled case cost, implant cost, and expected volume by code do materially better than groups that accept a percentage-of-hospital-rate formula.

‍Tighten operative note templates for the cases you plan to move. Approach, laterality, structures treated, implant detail, time, and any factor supporting increased procedural services should be structured fields, not narrative afterthoughts. Groups like OrthoIndy and Midwest Orthopaedics at Rush that treat documentation structure as an operations problem rather than a physician behavior problem see the difference in clean claim rate within a quarter.

‍Decide who codes the facility claim. Practice coders and ASC coders are not interchangeable. If the group is standing up ASC billing for the first time, the staffing and training cost belongs in the ASC pro forma.

How autonomous coding changes the migration math

The reason site of service migration creates a coding problem is volume and variability. A group moving several hundred cases a year into a new setting is asking its coders to apply a different fee schedule logic, a different multiple procedure rule, a different place of service, and a second claim per case, usually without adding headcount. That is precisely the condition under which undercoding and modifier errors accelerate.

Maia's AutoCoder sits inside the EHR and reads the operative note and encounter documentation before a human coder opens the chart, recommending CPT and ICD-10 codes, modifiers, and the clinical justification that supports them. Because it is trained specifically on orthopaedic documentation rather than general medical coding, it flags the ortho-specific cases that drive the errors above: laterality and anatomic modifier mismatches, NCCI pairs that need a distinct service rationale, global period modifier selection, and operative notes that support modifier 22 but were never coded for it. Maia integrates with Athena, eClinicalWorks, Epic, ModMed, NextGen, and Tebra, so the workflow does not change when case volume moves between settings.

Frequently asked questions

What is the inpatient-only list and why does its removal matter to orthopaedic practices?‍

The Medicare inpatient-only list identifies services that Medicare will only pay for when furnished in an inpatient setting. Removing a procedure from the list makes it payable in the hospital outpatient department and, if CMS also adds it to the ASC Covered Procedures List, in an ambulatory surgical center. For orthopaedics, that determines whether the group's own ASC can perform a Medicare case and collect the facility fee. In the CY 2027 proposed rule CMS proposed removing 637 services, with the remaining services scheduled for CY 2028.

‍Does a procedure coming off the inpatient-only list automatically mean it can be done in an ASC?‍

No. Removal from the inpatient-only list makes a procedure payable in the hospital outpatient setting. It is only payable in an ASC if CMS separately adds it to the ASC Covered Procedures List. CMS proposed adding approximately 618 procedures to that list for CY 2027, but the two lists are governed by different criteria and should be checked separately for each code you plan to move.

‍How does the physician's payment change when a case moves from the office to an ASC?‍

The Medicare physician fee schedule pays a lower facility rate when the service is furnished in an ASC or hospital, because the practice is no longer bearing the practice expense. The practice must also report the correct place of service, 24 for an ASC, so the correct rate is applied. Groups with ASC ownership recover the difference and more through the facility fee, but the professional fee line will decline in isolation.

‍What is the multiple procedure reduction in the ASC setting?‍

When more than one covered surgical procedure is performed in the same ASC session, Medicare generally pays the highest paying procedure at 100 percent of its ASC rate and additional procedures at 50 percent. This is distinct from the multiple procedure reduction applied to the surgeon's professional fee under the physician fee schedule. Orthopaedic sessions commonly involve multiple procedures, so both reductions should be built into any ASC financial model.

‍What denials should we expect during a site of service transition?‍

The most common are place of service mismatches, laterality and anatomic modifier conflicts between the professional and facility claims, NCCI procedure to procedure edits on multi-procedure sessions, and medical necessity denials where documentation does not support the chosen setting. Auditing place of service accuracy and operative note structure before volume shifts prevents most of them.

‍When do these changes take effect?‍

CMS published the CY 2027 OPPS and ASC proposed rule on July 7, 2026, with a comment deadline of August 31, 2026. Most provisions are proposed to take effect January 1, 2027. The final rule is the operative document, so confirm the final code lists before committing 2027 case volume to a setting.

The bottom line

The regulatory constraint that kept a large share of orthopaedic surgical volume inside the hospital is being dismantled over the next two years. That is a revenue opportunity for groups that own or invest in an ASC and a coding risk for every group, because more settings and more complex cases mean more places for undercoding and modifier errors to hide. The work to do in the fourth quarter of 2026 is unglamorous: model your codes by site and payer, audit your place of service accuracy, tighten your operative note templates, and make sure your coding capacity scales with the volume you are about to move.

See how Maia's AutoCoder handles this automatically for orthopaedic practices. Book a demo at usemaia.com.