Orthopedic billing: global periods, injection modifiers, and assistant surgeon rules.

THE BOTTOM LINE

Orthopedics stacks more billable events into one episode of care than almost any other outpatient specialty: an office visit, imaging, an injection, a cast, DME, and possibly a 90-day global package, all for the same patient inside a short window. Every one of those has a bundling relationship with the others.

The denials concentrate in three places: E/M visits inside a global period, joint injections billed with a same-day visit, and assistant surgeon claims on codes that were never going to pay an assistant.

That last one has a rule most reference material states backward, and it is worth reading carefully because getting it wrong means either denied claims or a case booked with an assistant who cannot be paid.

Definitions and frequently used terms

Global surgical period. The window during which related pre-operative, intra-operative, and post-operative care is included in the surgical payment. 90 days for major procedures, 0 or 10 days for many minor procedures and injections.

Global surgical package. What the payment covers. For a 90-day global, the window is actually 92 days: one preoperative day, the day of surgery, and the 90 days following.

Assistant-at-surgery payment policy indicator. A number assigned to each CPT code in the Medicare Physician Fee Schedule Relative Value File that determines whether an assistant can be paid at all, independent of medical necessity.

Restorative treatment. Reduction or manipulation of a fracture or dislocation. The threshold for a global fracture care code.

L-codes and A-codes. HCPCS Level II. L-codes are orthotics and prosthetics. A-codes are medical supplies.

CARC and RARC. Claim Adjustment Reason Code and Remittance Advice Remark Code. The CARC gives the category, the RARC the detail.

Global periods and the modifiers that go with them

Get this framework right and a large share of orthopedic denials disappear, because most of them are a modifier choice made without knowing what the modifier does to the global clock.

Modifier 24. Unrelated E/M during the postoperative period. Requires documentation showing why the visit is unrelated, with a distinct ICD-10 code. The modifier alone does not carry it.

Modifier 25. Significant, separately identifiable E/M on the same day as a procedure.

Modifier 57. The decision for surgery, made at an E/M visit the day before or the day of a major procedure. Frequently forgotten, and it is the reason that pre-op visit gets bundled when it should not be.

Modifier 58. Staged or related procedure planned at the time of the original surgery. Starts a new postoperative period.

Modifier 78. Unplanned return to the operating or procedure room for a related complication. Pays the intraoperative portion only and does not start a new global period.

Modifier 79. Unrelated procedure by the same physician during the postoperative period. Paid in full and starts a new global period.

Those last three get confused constantly. The distinction that matters operationally is that 78 does not reset the clock and 58 and 79 do. If you are tracking global periods in the PM system, that is the field the modifier choice has to update.

SAVE this as a workflow rule: log the surgery date and the window end date by patient and by procedure, and require staff to confirm the window before coding any subsequent visit or procedure. This is the single highest-yield front-end control in the specialty.

E/M during a global period

When a patient returns inside a global period for something unrelated, modifier 24 is required and the note has to state the unrelated diagnosis explicitly with its own ICD-10 code.

Without both, the payer's system treats the visit as bundled and you get CARC 97 ("The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated"), often with RARC M144 ("Pre/post-operative care payment is included in the allowance for the surgery/procedure").

Missing or unsupported modifier 24 is among the most common causes of E/M denials during orthopedic global periods. I want to be straight with you about that sentence: you will see a specific figure attached to this claim, usually 30%, attributed to AAPC audit data. I could not find that dataset, and AAPC does not publish specialty denial-attribution statistics of that kind. The pattern is real. The number is not one I can stand behind, so I am not going to put it in front of you as though it were.

Joint injections

The tiers, with the paired ultrasound-guided version of each:

• 20600 / 20604 small joint or bursa
• 20605 / 20606 intermediate joint or bursa
• 20610 / 20611 major joint or bursa (for example shoulder, hip, knee, subacromial bursa)

NOTE: the second code in each pair is not an alternative for the same joint size. It is the with ultrasound guidance, with permanent recording and reporting version. 20610 and 20611 are not interchangeable, and CPT's language is "major joint or bursa," not "large joint."

IMPORTANT: do not bill 76942 separately with 20600 through 20611. CPT instructs against reporting ultrasound guidance separately with these codes. When ultrasound guidance with permanent recording is performed, that is what the 20604, 20606, and 20611 codes exist for. Billing 76942 alongside is a bundling denial you generated yourself.

The same-day E/M question

Payers bundle the pre-injection assessment into the injection code by default, because some assessment is inherent to every injection. Modifier 25 unbundles a significant, separately identifiable E/M.

The test is practical. If the patient was scheduled in advance for the injection and no separate exam was performed, the E/M should not be billed at all. AAPC's guidance says it plainly: if the patient comes in for a scheduled injection and you do not perform a separate exam, do not bill an E/M in addition to the injection.

When there genuinely was separate work, document the history, exam, and decision-making for it in a section distinct from the injection procedure note.

The drug line

Units have to match the HCPCS descriptor exactly. J3301 is triamcinolone acetonide per 10 mg, so 40 mg administered is 4 units. J7325 is a hyaluronan or derivative per 1 mg.

Payer policies vary on whether specific hyaluronic acid products are separately payable or bundled, particularly under Medicare Advantage plans applying step therapy or product-specific limits.

SAVE: build a unit-conversion table for every injectable you use, cross-checked against the current HCPCS descriptor, and review it when descriptors change. Unit mismatches produce CARC 16 ("Claim/service lacks information or has submission/billing error(s)") and they are entirely mechanical to prevent.

Fracture care: three paths, not two

This is described as a binary in most reference material and it is actually three options. The missing one costs practices money.

Path 1: global fracture care code. Report this when the physician performed restorative treatment, meaning a reduction or manipulation, and will provide the full global package of follow-up care. CMS, CPT, AAOS, and the American College of Emergency Physicians are aligned on this.

Path 2: fracture care code with modifier 54. Restorative treatment was performed but follow-up care is being transferred to someone else. Modifier 54 means surgical care only. This is the case that gets billed wrong most often, usually as E/M plus casting, which undervalues the reduction the physician actually performed.

Path 3: E/M plus the cast or strapping application code. No restorative treatment performed and the physician is not assuming global care. A splint applied with no reduction, patient referred elsewhere.

Document explicitly whether a reduction or manipulation was performed and whether the treating physician intends to provide all subsequent care. Those two facts select the path.

NOTE on code ranges: the CPT fracture and dislocation series for the forearm and wrist is 25500 through 25695. You will sometimes see a narrower range quoted; that is not a real CPT grouping.

Casting and strapping

Only the initial cast, splint, or strapping application at the time of initial fracture treatment is inherently bundled into the fracture care code.

A replacement cast during the global period is separately reportable with modifier 58 when it is medically necessary: structural damage, loss of fit, contamination, or skin integrity risk. Payers will not pay for a cast change because the patient did not like the color, and documenting the actual clinical reason is what separates the two.

NOTE on the codes usually cited here: 29075 is a cast (elbow to finger), 29125 is a static short arm splint, and 29280 is strapping of the hand or finger. Calling all three "casting codes" is imprecise enough to send someone to the wrong code. Say cast, splint, or strapping.

Assistant at surgery, where the usual explanation is backward

Every CPT code carries an assistant-at-surgery payment policy indicator in the Medicare Physician Fee Schedule Relative Value File. That indicator determines whether an assistant can be paid at all, independent of how medically necessary the assistant was.

IMPORTANT: here are the actual definitions.

• 0 = Payment restriction applies unless supporting documentation establishes medical necessity. Documentation can overcome this one.
• 1 = Statutory payment restriction. Medicare may not pay an assistant at surgery. Documentation cannot overcome this.
• 2 = No payment restriction. An assistant may be paid, with no special documentation required.
• 9 = Concept does not apply.

You will very commonly see 0 and 1 stated the other way around, with 0 described as the automatic denial and 1 as the one documentation fixes. That is exactly inverted. 1 is the wall. 0 is the one you can document your way through. 2 needs nothing.

Getting this backward has two costs. You book cases with an assistant on indicator 1 codes and the claim will never pay, or you skip documentation on indicator 0 codes and lose payment you were entitled to.

The payment amounts

An assistant at surgery is paid 16% of the amount otherwise applicable for the surgical payment, per Claims Processing Manual Chapter 12, Section 20.4.3.

A PA, NP, or clinical nurse specialist billing modifier AS is paid 85% of that 16%, which works out to 13.6% of the surgeon's fee schedule amount.

Knowing those numbers changes the staffing conversation, because "we can bill an assistant" and "we will collect 13.6%" are different facts.

The modifiers

• 80 assistant surgeon
• 81 minimum assistant surgeon
• 82 assistant surgeon when a qualified resident surgeon is not available
• AS PA, NP, or CNS serving as assistant at surgery

Modifier 82 specifically requires documentation of why a qualified resident was unavailable, which in a teaching setting often means a stated across-the-board policy.

SAVE this as a scheduling step: check the assistant-at-surgery indicator in the current CY 2026 Relative Value File before the case is booked, not before the claim goes out. The indicator, not the clinical need, controls payability, and by the time you are billing it is too late to have that conversation with the surgeon.

NOTE: you will see 63030 (lumbar laminotomy with decompression) and 22551 (anterior cervical discectomy and fusion) cited as examples of codes that prohibit an assistant. I could not confirm either carries a restrictive indicator, and both are routinely billed with paid assistants. Look up the current indicator for your own high-volume codes rather than relying on a remembered example.

The 2026 payment picture

The CY 2026 Physician Fee Schedule final rule (CMS-1832-F), effective January 1, 2026, set two conversion factors: $33.5675 for qualifying APM participants and $33.4009 for non-qualifying participants, up 3.77% and 3.26% from the CY 2025 factor of $32.3465.

NOTE: those increases are less durable than they look. Each factor is built from a small statutory update, a one-year 2.5% statutory increase that expires, and a budget neutrality adjustment. Do not model 2027 off the 2026 baseline without accounting for the one-year piece coming back out.

CMS also finalized a 2.5% efficiency adjustment reducing work RVUs and the corresponding intra-service time for nearly all non-time-based procedural and diagnostic codes, based on a five-year lookback at the Medicare Economic Index productivity adjustment. Exempt: time-based codes including E/M, care management, behavioral health, telehealth-list codes, maternity global codes, and new CY 2026 codes.

For orthopedics, AMGA's analysis puts the weighted impact of the efficiency adjustment at close to a 1.5% decrease in work RVUs, concentrated in procedural and imaging-heavy codes rather than E/M.

IMPORTANT, because the 1.5% figure is the friendliest number in that document: the same AMGA analysis shows orthopedic surgery at -3% in the facility setting and a combined provider-plus-hospital orthopedic department impact of -2.9%. If you are modeling a hospital-based or ASC-heavy practice, use those figures rather than the 1.5%.

CMS also changed indirect practice expense allocation for facility-based services, assigning work RVUs used to allocate indirect PE to facility RVUs at one-half the amount allocated to non-facility PE RVUs. That disproportionately affects hospital-based and ASC orthopedic procedures relative to office-based evaluation and injection work.

Prior authorization and peer-to-peer

MRI prior authorization is one of the highest-friction categories in this specialty, and the reason is usually documentation rather than genuine non-coverage.

A 2023 study published in Orthopedics found that nearly all peer-to-peer reviews for CT and MRI prior authorization denials for orthopedic specialists were approved. That is PMID 37921528, DOI 10.3928/01477447-20231027-08, and it is worth citing the study directly rather than a vendor summary of it.

The practical read: if a physician-to-physician conversation flips almost all of these, the initial denial was usually about what was in the request rather than whether imaging was warranted.

So put the conservative treatment history in the initial authorization request. Physical therapy duration, NSAID trial, injections already performed, dates and outcomes. Commercial payers, including major Blue Cross Blue Shield plans, commonly require a documented conservative treatment course before authorizing advanced imaging or joint replacement. Check the specific payer's medical policy, because the required duration varies and a request that is thirty days short of their threshold denies exactly like a request with nothing in it.

DME, braces, and splints

Orthopedics carries a supply and DME component most surgical specialties do not manage in-house.

L-codes describe orthotic and prosthetic devices, like knee braces and spinal orthoses. A-codes generally describe medical supplies. Billing a brace under the wrong family is a common denial, and so is billing any DME item without a signed physician order and proof of delivery on file.

Confirm the code family against the specific device's HCPCS description before submission rather than relying on how the item is categorized in your inventory system.

The denial patterns you will actually see

E/M during a global period without modifier 24 | CARC 97, RARC M144. Fix at the scheduler and in the note, with a distinct unrelated diagnosis.

Joint injection with same-day E/M missing modifier 25 | CARC 97, CARC 4 ("The procedure code is inconsistent with the modifier used"). Fix by documenting separately identifiable work, or by not billing the E/M when there was none.

Drug units not matching the dose | CARC 16. Fix with the unit-conversion table.

Fracture care billed globally without qualifying restorative treatment | CARC 97, CARC 16. Fix by choosing among the three paths above, including modifier 54.

Replacement cast without modifier 58 or documented necessity | CARC 97, CARC 50 ("These are non-covered services because this is not deemed a 'medical necessity' by the payer"). Fix by recording the clinical reason.

Assistant surgeon on a restricted code | CARC 54 ("Multiple physicians/assistants are not covered in this case"), CARC 236 ("This procedure or procedure/modifier combination is not compatible with another procedure or procedure/modifier combination provided on the same day according to the National Correct Coding Initiative or workers compensation state regulations/fee schedule requirements"). Fix at scheduling by checking the indicator.

NOTE on CARC 4: you will see it glossed as "modifier missing or inconsistent with the procedure code." The current X12 text is just "The procedure code is inconsistent with the modifier used." The missing-modifier clause is legacy phrasing, so do not quote it in an appeal.

Practices that prevent the denial

1. Track every global period by patient, procedure, and start date, with the window end date visible to scheduling.
2. Document a distinct unrelated diagnosis for every E/M inside a global period. The modifier does not do the work by itself.
3. Separate the injection note from the E/M note whenever modifier 25 is applied.
4. Maintain a drug unit-conversion table cross-checked against current HCPCS descriptors.
5. Compile conservative treatment history before submitting any advanced imaging authorization, not after the denial.
6. Verify the assistant-at-surgery indicator before the case is booked, using the current Relative Value File.
7. Record the specific clinical reason for every cast or splint replacement, structural or skin-related rather than preference.

Frequently asked questions

Why do E/M visits during a global period keep denying after a knee replacement? Usually a missing or unsupported modifier 24. The fix is both coding and documentation: the note has to state a clearly unrelated diagnosis with its own ICD-10 code, not just carry the modifier. This shows up as CARC 97, often with RARC M144.

Can we bill an E/M on the same day as a joint injection? Only when a significant, separately identifiable evaluation was performed beyond the assessment inherent to the injection, with modifier 25 on the E/M. If the visit was scheduled purely for the injection and no separate exam happened, do not bill the E/M.

What is the difference between modifiers 58, 78, and 79? 58 is a staged or related procedure planned at the time of the original surgery and starts a new postoperative period. 78 is an unplanned return to the OR for a related complication, pays the intraoperative portion only, and does not restart the global. 79 is an unrelated procedure during the postoperative period, paid in full, and starts a new global period.

When do we bill global fracture care versus E/M plus casting? Global fracture care requires restorative treatment (reduction or manipulation) and that the same physician will provide all subsequent care. If restorative treatment was performed but follow-up is being transferred, use the fracture care code with modifier 54 for surgical care only. If no restorative treatment was performed and you are not assuming global care, bill E/M plus the cast or strapping application code.

Can we bill a replacement cast during the global period? Yes, with documented medical necessity such as damage, loss of fit, contamination, or skin integrity risk, using modifier 58 on the replacement cast, splint, or strapping code with a supporting diagnosis. Patient preference does not qualify.

Why do assistant surgeon claims deny on spine cases even with strong documentation? Because the code's assistant-at-surgery payment policy indicator, not the documentation, controls payability. Indicator 1 is a statutory restriction and no documentation overcomes it. Indicator 0 is the one supporting documentation can overcome. Indicator 2 permits an assistant with nothing extra. Check the indicator in the current Relative Value File before booking the case.

How much does an assistant at surgery actually pay? 16% of the amount otherwise applicable for the surgical payment. A PA, NP, or CNS billing modifier AS is paid 85% of that 16%, so 13.6% of the surgeon's fee schedule amount.

Why was our MRI prior authorization denied when the patient clearly needs imaging? Most commercial and Medicare Advantage payers require a documented course of conservative treatment before approving advanced imaging for musculoskeletal complaints, and the denial usually reflects what was missing from the request rather than a coverage judgment. The 2023 Orthopedics study on peer-to-peer review supports that read, since nearly all of these were approved once a physician-to-physician conversation happened.

What is the difference between L-codes and A-codes? L-codes are orthotic and prosthetic devices. A-codes are generally medical supplies. Confirm the family against the device's HCPCS description, and make sure a signed physician order and proof of delivery are on file before billing either.

Do orthopedic surgeons bill physical therapy? Most refer out. When a practice runs in-house therapy, those codes bill separately from the surgeon's E/M and procedural codes, with their own documentation supporting medical necessity and frequency, and distinct from the global surgical package.

How we work on this at ROI

Orthopedic denials repeat because the same three or four decisions get made without the information that would have made them differently.

• The platform ingests 835 and 837 files from any clearinghouse or EHR export and flags global period modifier denials, joint injection bundling, and assistant surgeon indicator conflicts into the right categories.
• Global period windows are tracked by patient and procedure so modifier selection happens with the dates in view.
• The EDI Code Intelligence Lab carries every CARC and RARC common in orthopedics with fix, appeal, and prevention guidance.
• The appeal template library includes global period modifier appeals, MRI prior authorization overturns, and assistant surgeon documentation frameworks.

If you want to see where your own denials concentrate first, the revenue health assessment is free.

“Orthopedic billing rewards practices that build global period and modifier discipline into the front end. Every missing modifier 24 is preventable at the scheduler. Every assistant surgeon indicator is knowable before the case is booked. A denial in this specialty is almost always something that could have been caught before the claim went out.”

Mindy Corbett, CSPO, CPC, CPB, CPPM, Founder, Revenue Optimization & Intelligence

Two things worth checking this week

1. Pull the assistant-at-surgery indicators for your top ten spine and complex joint codes from the current Relative Value File. If your team has been working from the inverted version of the 0 and 1 rule, this is where it shows up.
2. Check whether your fracture care workflow includes modifier 54. If every transferred-care case is being billed as E/M plus casting, you are giving away the reduction.

If something here does not match what your payers are doing, tell me. I would rather fix the guide than have the next person work from it and get stuck.

Sources

1. Centers for Medicare & Medicaid Services. CY 2026 Medicare Physician Fee Schedule Final Rule Fact Sheet (CMS-1832-F). https://www.cms.gov/newsroom/fact-sheets/calendar-year-cy-2026-medicare-physician-fee-schedule-final-rule-cms-1832-f
2. Federal Register. CY 2026 Payment Policies Under the Physician Fee Schedule (indirect practice expense allocation). https://www.federalregister.gov/documents/2025/11/05/2025-19787/medicare-and-medicaid-programs-cy-2026-payment-policies-under-the-physician-fee-schedule-and-other
3. AMGA. Unpacking the 2026 Physician Fee Schedule. https://www.amga.org/getmedia/2d845474-6427-4991-9aab-671e53320657/amga_consulting_infographic_medicare_v4.pdf
4. Centers for Medicare & Medicaid Services. Medicare Claims Processing Manual, Pub. 100-04, Chapter 12, including Section 20.4.3 (assistant at surgery) and Section 30.6.6 (global surgery). https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/clm104c12.pdf
5. Centers for Medicare & Medicaid Services. Global Surgery Booklet (MLN907166). https://www.cms.gov/files/document/mln907166-global-surgery-booklet.pdf
6. Centers for Medicare & Medicaid Services. Medicare Physician Fee Schedule Relative Value Files (assistant-at-surgery payment policy indicators). https://www.cms.gov/medicare/payment/fee-schedules/physician/pfs-relative-value-files
7. Centers for Medicare & Medicaid Services. Physician Assistants: assistant-at-surgery payment. https://www.cms.gov/medicare/payment/fee-schedules/physician-fee-schedule/advanced-practice-non-physician-practitioners/physician-assistants-pas
8. Orthopedics. Nearly All Peer-to-Peer Reviews for CT and MRI Prior Authorization Denials for Orthopedic Specialists Are Approved (2023). PMID 37921528. https://pubmed.ncbi.nlm.nih.gov/37921528/
9. American Academy of Orthopaedic Surgeons. Coding and Reimbursement Resources. https://www.aaos.org/quality/coding-and-reimbursement/
10. AAPC. Joint Injection With E/M? Append -25 in These Instances. https://www.aapc.com/codes/coding-newsletters/my-orthopedic-coding-alert/joint-injection-with-em-append-25-in-these-instances-article
11. AAPC. ED Fracture Care Redux. https://www.aapc.com/blog/29726-ed-fracture-care-redux/
12. Centers for Medicare & Medicaid Services. NCCI Policy Manual, Chapter 4 (musculoskeletal system). https://www.cms.gov/medicare/coding-billing/national-correct-coding-initiative-ncci-edits/medicare-ncci-policy-manual
13. X12.org. Claim Adjustment Reason Codes. https://x12.org/codes/claim-adjustment-reason-codes