In the world of podiatry, the surgical suite is where the most life-changing work happens—but the billing office is where that work is either rewarded or lost. For many podiatric surgeons, the period following a procedure is a “black hole” of uncaptured revenue and compliance risks.
This blog will take you through some of the best hacks that you can apply to your billing and coding practices to get the maximum result. Reading this guide will help you optimize revenue cycle management (RCM) for foot surgery. Here is a deep dive into the high stakes of post-op billing and why getting this section right is the foundation of a healthy practice.
Understanding the Global Surgical Package (GSP) in Podiatry
In the complex world of podiatric medicine, the Global Surgical Package (GSP) is a reimbursement policy used by Medicare and private payers to consolidate all services associated with a surgical procedure into a single payment. This “all-inclusive” price covers the entire surgical experience, from the moment you prep the patient to the final follow-up visit. Mastering the GSP is the difference between a clean claim and a “duplicate service” denial.
The 0, 10, and 90-Day Rules: Where Your Procedures Fall
The “Global Period” refers to the timeframe during which all routine care related to a surgery is considered pre-paid. In podiatry, most procedures fall into one of three buckets:
0-Day Global (Minor Procedures)
These are simple, “in-and-out” services where the global period ends the same day as the procedure.
Example: Simple incision and drainage (I&D) of a superficial abscess.
10-Day Global (Minor Surgeries)
This is common for less invasive podiatric interventions. The day of surgery is Day 0, followed by 10 days of “bundled” care.
Example: Partial or Total Nail Avulsion/Matrixectomy (CPT 11730, 11750).
90-Day Global (Major Surgeries)
These involve significant structural work or “bone work.” The package includes one day of pre-operative care and 90 days of post-operative follow-up.
Example: Bunion Corrections (CPT 28296), Hammertoe Repairs (CPT 28285), or Triple Arthrodesis.
What’s Included: The “All-In” List
When you bill a surgical CPT code, the insurance company assumes you are being paid for a specific bundle of work. This includes:
Pre-operative Visits
Any evaluation performed by the surgeon on the day of a minor surgery, or the day before/day of a major surgery, results in the decision to operate.
The Intra-operative Work
This is the procedure itself, including local anesthesia, digital blocks, and the surgical technique.
Routine Post-operative Care
All visits during the global period are part of “normal” recovery. This includes checking the incision site, discussing the surgery with the family, and monitoring healing.
Supplies
Most routine surgical supplies used during the procedure are included in the facility or practice payment.
The “Bundle” Concept: The Trap of “Incident-To” Services
A frequent point of frustration for podiatry billers is the Bundle Concept. Payers view certain post-op activities as “incidental” to the surgery. This means they are mathematically accounted for in the primary surgical fee and cannot be unbundled for extra payment.
Routine Dressing Changes
If a patient comes in five days after a bunionectomy for a simple dressing change, this is bundled. You cannot bill an E/M code or a supply code for the gauze and tape.
Suture/Staple Removal
Removing stitches is considered a standard part of the post-operative healing process. Even if a medical assistant performs the removal, it is not separately billable.
K-Wire Removal
In many podiatric surgeries (like hammertoe repairs), K-wire removal is bundled into the global package unless the wire is removed in the Operating Room under general anesthesia.
The Hack
If you are performing a service during the global period that is not routine—such as treating a new injury on a different toe or managing a severe, unexpected surgical complication in the OR—you must use Modifiers 24, 78, or 79 to “break” the bundle and secure payment.
Master the Modifiers: The Keys to Post-Op Revenue
Providers need to know that in podiatric surgery, the global period doesn’t have to mean a complete freeze on revenue. While routine care is bundled, “non-routine” services are frequently performed but often go unbilled due to a fear of denials. The strategic use of CPT modifiers is the only way to signal to payers that a service is distinct from the global package.
Mastering these four modifiers is essential to accurately capture legitimate revenue during the post-operative phase.
Modifier 58: Staged or Related Procedure
Modifier 58 is used when a procedure performed during the global period was planned or anticipated at the time of the original surgery. This is common in complex podiatric cases where a single surgical procedure isn’t sufficient to resolve the issue.
Podiatry Example
You perform an initial debridement of a severe diabetic foot ulcer (CPT 11042) and explicitly document in the operative report that the patient will return in 14 days for a secondary, “staged” debridement or a skin graft.
Key Requirement
The service must be more extensive than the original or a planned follow-up “stage” of the therapy.
Modifier 78: Unplanned Return to the Operating Room
Modifier 78 is used for a related procedure that was unplanned and requires a return to the Operating Room (OR). This usually involves treating a complication that arose from the initial surgery.
Podiatry Example
A patient develops a deep post-operative infection 20 days after a triple arthrodesis. The infection is severe enough that the patient must be taken back to the OR for an unplanned Incision and Drainage (I&D).
Revenue Note
Unlike other modifiers, Modifier 78 pays only the “intra-operative” portion of the procedure (usually about 70–80% of the allowable fee) because pre- and post-op care is still covered under the original surgery’s global period.
Modifier 79: Unrelated Procedure by the Same Physician
Modifier 79 is used when you perform a procedure during a global period that is entirely unrelated to the original surgery. This modifier “breaks” the global bond for that specific claim.
Podiatry Example
You are currently in a 90-day global period for a bunionectomy on the right foot. Two weeks later, the patient comes in with a painful, infected ingrown toenail on the left hallux that requires a permanent matrixectomy (CPT 11750).
Key Requirement
Use different ICD-10 diagnosis codes and anatomical modifiers (e.g., T5 for the right foot vs. TA for the left) to clearly demonstrate the lack of relation.
Modifier 24: Unrelated E/M Service During a Global Period
While the previous modifiers apply to procedures, Modifier 24 applies to Evaluation and Management (E/M) office visits. It tells the payer: “I am seeing the patient for a new problem, not a post-op check-up.”
Podiatry Example
A patient is in the global postoperative period after hammertoe correction. During their follow-up, they ask you to look at a suspicious lesion on their ankle or a new onset of plantar fasciitis.
The Documentation Rule
Your progress note must be “split.” You should clearly document the routine post-op check (non-billable) and then create a distinct section for the new problem (billable with Modifier 24). The diagnosis for the E/M must be different from the surgical diagnosis.
Modifier Summary Table for Podiatry RCM
| Modifier | Type of Service | Relationship to Surgery | Planned? |
| 58 | Procedure | Related | Yes (Planned) |
| 78 | Procedure | Related (Complication) | No (Unplanned) |
| 79 | Procedure | Unrelated | N/A |
| 24 | E/M Visit | Unrelated | N/A |
Common Podiatric Surgical Scenarios & Coding Solutions
Applying billing theory to the clinic floor requires a deep understanding of specific podiatric CPT codes. Below are three of the most common surgical scenarios and the coding solutions needed to protect your bottom line.
Bunionectomies (CPT 28296–28299)
Bunion repairs are high-value procedures with 90-day global periods. The most common billing errors occur not with the surgery itself, but with the ancillary services provided during follow-up.
Post-Op X-rays (CPT 73620/73630)
Routine X-rays taken to “check healing” during the global period are generally not separately billable by the surgeon if they are part of standard protocol. However, if an X-ray is ordered for a suspected complication (such as a displaced screw or a new injury), it may be billable.
Durable Medical Equipment (DME)
CAM boots (L4360/L4361) or surgical shoes (L3260) provided to the patient are not bundled into the surgical package. You can bill these separately.
The Professional Tip
Ensure the DME dispensing date is the day of surgery or later, and that your documentation supports the medical necessity of the specific device.
Hammertoe Corrections (CPT 28285)
Hammertoe surgery often involves the use of a K-wire for stabilization. The billing question always arises: Can I bill for taking it out?
In-Office Removal
If you pull a K-wire in the office during the 90-day global period, it is considered bundled routine post-operative care. You cannot bill a separate procedure code or an E/M visit for this.
Removal in the OR
It’s important to remember that if the wire breaks or becomes deep-seated, requiring the patient to return to the Operating Room for removal under anesthesia, you may be able to bill for the removal using Modifier 78 (unplanned return to the OR).
Amputations and Debridements
High-risk diabetic follow-up or limb salvage surgery involves high-frequency care that often blurs the lines of the global period.
Amputations (CPT 28820/28825)
These carry a 90-day global period. Routine wound checks are bundled.
Debridements (CPT 11042–11044)
These are considered “minor” but often require a “staged” approach.
The Coding Solution
If you know a diabetic ulcer will require multiple cleanings over several weeks, use Modifier 58 for the subsequent debridements to show they were part of a planned, staged therapeutic process.
High-Risk Necessity
Document comorbid conditions like Peripheral Vascular Disease (PVD) or Neuropathy. If the patient develops a new ulcer on a different site during the global period of an amputation, use modifier 24 for the E/M and modifier 79 for the new debridement.
Podiatric Global Period Cheat Sheet
For a better and more helpful understanding, the following table illustrates the common CPT codes and scenarios for their use:
| Procedure Type | Common CPT | Global Days | Billable Extras? |
| Bunionectomy | 28296 | 90 Days | DME, Unrelated E/M |
| Hammertoe | 28285 | 90 Days | DME, Cast Supplies |
| Matrixectomy | 11750 | 10 Days | Antibiotics, New Injuries |
| I&D (Abscess) | 10060 | 0 Days | Follow-up E/M (Next Day) |
Documenting for Medical Necessity
In the eyes of a medical auditor, if it isn’t documented, it didn’t happen. When billing during a global period, your clinical notes must do more than record a patient visit; they must actively “defend” the claim by demonstrating that the service was separate from the surgical package. The medical necessity document does this exact job by classifying the medical intervention as compulsory and required to save the patient’s life.
How to Write “Modifier 24” Notes That Survive a Medicare Audit
Modifier 24 is among the most scrutinized codes by Medicare Recovery Audit Contractors (RACs). To ensure your unrelated Evaluation and Management (E/M) service is paid and retained, your documentation must follow the “Split-Note” approach:
The Clinical Wall
Clearly separate the routine post-op check from the new issue. Use a heading like “Post-Operative Evaluation (Non-Billable)” followed by a second heading titled “New/Unrelated Complaint: [Issue Name] (Billable with Modifier 24).”
Distinct History & Exam
You must document a separate History of Present Illness (HPI) and Physical Exam (PE) that focuses solely on the new problem.
The Decision-Making Trail
The medical decision-making (MDM) section must demonstrate that you evaluated a condition that was not a complication of the surgery and did not require the use of the surgical site.
The Importance of Distinct Diagnoses (ICD-10)
The single biggest reason for “Global Period” denials is using the same ICD-10 code for the post-op visit as for the surgery. To separate care, you must utilize distinct diagnostic coding:
The Primary Surgical Diagnosis
This should be listed in the chart, but should not be linked to the new E/M service or procedure code.
The “New” Diagnosis
Use a specific ICD-10 code for the unrelated issue. For example, if the surgery was for a Bunion (M21.611), and the patient presents with Plantar Fasciitis (M72.2), ensure the Plantar Fasciitis code is the primary link for the Modifier 24 claim.
Using Anatomical Modifiers (T1–TA) to Prove Distinction
In podiatry, the “where” is just as important as the “what.” Using Level II HCPCS anatomical modifiers provides an immediate, machine-readable signal to the insurance company that you are working on a different part of the body.
Anatomical Separation
If you performed surgery on the Right Hallux (T5), any unrelated service on the Left Hallux (TA) or the Right Lesser Toes (T6–T9) must be clearly flagged.
Example Scenario
A patient is in the global period after hammertoe correction of the Left 2nd Toe (T1). They return because of an ingrown nail on the Left Hallux (TA).
The Code: 11750 (Matrixectomy)
The Modifiers: 79 (Unrelated procedure) + TA (Anatomical location)
The Audit Defense
When an auditor sees a claim with a different anatomical modifier than the original surgery, the likelihood of an automatic denial drops significantly because the physical distinction is clear.
Billing for Post-Op Complications vs. Routine Care
For foot and ankle surgeons, one of the most significant areas of revenue loss in podiatry is the failure to distinguish between “routine healing” and “medical complications.” While the Global Surgical Package covers the former, the latter often qualifies for additional reimbursement—provided you understand the “Return to OR” requirement.
When Does a Complication Become a Billable Event?
A complication becomes billable the moment the care required exceeds the “typical” post-operative follow-up described in the CPT guidelines. However, the treatment location determines how you are paid.
In-Office Complications
If you treat a minor complication (like a superficial stitch abscess or minor skin irritation) in the office during the global period, you generally cannot bill for the procedure. Medicare considers in-office treatments of surgical complications to be included in the global fee.
The Exception
If the complication is severe enough to require a significant, separate Evaluation and Management (E/M) service that is unrelated to the “normal” recovery, you may be able to bill an office visit with Modifier 24, though this is highly scrutinized.
The “Return to OR” Rule: Modifier 78
The most important rule in surgical complication billing is the Return to the Operating Room (OR). Under CPT guidelines, if a complication requires a return to the OR (or a formal procedure room within a hospital or ASC), it is a billable event.
Office vs. OR
If you perform an Incision and Drainage (I&D) of a deep post-op infection in your office exam room, it is bundled (non-billable). If you take the same patient to the OR for an I&D, it is billable with Modifier 78.
Reimbursement Impact
Modifier 78 allows you to capture the “intra-operative” portion of the surgical fee. Because the global period of the original surgery stays in effect, you do not get paid for the pre-op or post-op work, but you do get paid for the surgical intervention itself.
Handling Specific Podiatric Scenarios: Infections and Non-Unions
Podiatric surgeons frequently encounter two specific hurdles: infections and nonunion (failure of bone healing).
Post-Operative Infections
Routine: Redness that clears with a simple oral antibiotic prescription during a scheduled check-up is bundled.
Significant: A deep space infection requiring debridement or hardware removal in the OR. Use the appropriate CPT for debridement or hardware removal with Modifier 78.
Non-Union Scenarios
If a bunionectomy or fusion fails to heal (non-union) and you decide to perform a revisional surgery during the 90-day global period, this is a “related” but “new” procedure.
The Coding: Use Modifier 58 (staged or more extensive procedure) if the revision was anticipated as a possibility, or Modifier 78 if it was an unplanned trip to the OR to fix the failing union.
Quick Logic Check for Complications
The following table provides a snapshot of the complications your practice may face and how to handle them:
| Scenario | Location | Modifier | Billable? |
| Suture Abscess | Office | N/A | No (Bundled) |
| Deep Hematoma | Operating Room | 78 | Yes (Intra-op only) |
| Planned Revision | Operating Room | 58 | Yes (Full fee) |
| New Infection (Other foot) | Office | 24 / 79 | Yes (Unrelated) |
Durable Medical Equipment (DME) and Post-Op Supplies
In podiatry, the surgical fee covers the “work,” but it rarely covers the “hardware” used to protect that work. Billing for Durable Medical Equipment (DME) is a vital revenue stream that remains separate from the Global Surgical Package. However, because DME falls under HCPCS Level II coding and is often managed by a different payer department (DMEPOS), specific rules must be followed to avoid denials.
Billing for CAM Boots, Surgical Shoes, and Orthotics
Most post-operative offloading devices are billable even if dispensed during a 10-day or 90-day global period. Each device has a specific “L-code” that must be used.
CAM Walkers/Boots (L4360 / L4361)
Used for significant offloading after reconstructive surgery or fractures.
Coding Tip
Use L4361 for a pneumatic (air-pump) boot and L4360 for a non-pneumatic version.
Post-Op Surgical Shoes (L3260)
Frequently used after forefoot surgery, such as bunionectomies or matrixectomies.
Custom Orthotics (L3000)
If a patient requires custom inserts to maintain the surgical correction (common after flatfoot or cavus foot reconstruction), these are billable as prosthetic devices.
The “Dispensing Date” vs. Global Period Rules
A common reason for DME denials is a “date of service” conflict. To ensure the payer recognizes the equipment as a separate entity from the surgery:
Date of Service
The date of service on the DME claim should be the date the patient actually received the item.
Place of Service (POS)
If dispensed in your office, use POS 11. If the patient is provided the boot in the hospital/ASC, but you are the one billing for it, ensure your billing software reflects the correct facility setting to avoid “Inpatient” overlaps.
The Decision to Purchase
Documentation must state why the specific device is medically necessary for post-operative stabilization rather than just “routine care.”
Navigating “Same or Similar” DME Denials
Medicare and private payers generally cover only one “functional” device per limb every five years. This leads to the dreaded “Same or Similar” denial.
The Conflict
If a patient received a CAM boot from an Urgent Care or ER for a sprain three months ago, and you dispense a new one after surgery today, the claim will likely be denied.
The Solution
* The CMN (Certificate of Medical Necessity): You must document that the previous device is no longer functional, does not fit the post-surgical dressing, or provides a different level of stabilization required for surgical recovery.
Modifier RA
In some cases, when replacing a device, the RA modifier (Replacement) may be required.
Advanced Beneficiary Notice (ABN)
For Medicare patients, always have an ABN on file if you suspect they recently received a similar device. This allows you to bill the patient directly if Medicare denies the claim.
DME Quick-Reference Table
| Item | HCPCS Code | Global Bundle? | Key Modifier |
| Pneumatic CAM Boot | L4361 | No (Billable) | LT / RT (Anatomical) |
| Surgical Shoe | L3260 | No (Billable) | KX (Requirements met) |
| Custom Orthotics | L3000 | No (Billable) | RT / LT |
| A6203 (Gauze/Tape) | N/A | Yes (Bundled) | Do not bill separately |
The Role of Technology in Post-Op RCM
In a high-volume podiatry practice, relying on manual memory to track global periods is a recipe for revenue leakage. Modern revenue cycle management (RCM) thrives on automation and integrated technology to ensure that every billable second is captured while maintaining strict compliance.
Leveraging EMR Alerts to Flag Global Periods
The most effective way to prevent “accidental” bundling is to have your Electronic Medical Record (EMR) do the heavy lifting.
Automated Tracking
Top-tier podiatry EMRs can be configured to trigger a “Global Period Alert” the moment a patient’s chart is opened. For example, if a patient is on day 45 of a 90-day bunionectomy global, a pop-up should notify the provider and the front desk.
Task Management
These alerts prompt the doctor to specify the nature of the visit. If the visit is unrelated, the EMR can automatically prompt the user to attach Modifier 24, ensuring the claim isn’t sent out as a standard—and therefore deniable—follow-up.
Automating the Scrubbing of Surgical Claims
“Claim scrubbing” is the process of checking a claim against thousands of payer rules before it ever reaches the insurance company. Technology allows for:
Conflict Detection
Automated scrubbers identify “Anatomical Mismatches.” If you bill for a procedure on the left foot (TA) but the EMR shows the global period is for the right foot (T5), the system will flag the need for Modifier 79 before the claim is submitted.
CCI Edit Integration
The system automatically checks the National Correct Coding Initiative (NCCI) edits to ensure that the codes being billed together aren’t considered “mutually exclusive” or part of a larger bundle.
Telehealth in the Post-Op Period
Telehealth has become a staple for quick post-op checks, but billing rules remain identical to those for in-person visits. Here’s how you can leverage it to bill patients.
Routine Follow-up via Video
If you jump on a 5-minute video call to look at a patient’s surgical incision to ensure it’s healing well, this is bundled. You cannot bill an E/M code (like 99212) because it is considered part of the routine post-op care.
The Billable Exception
Telehealth is billable during the global period only if it meets the criteria for Modifier 24. For example, if a post-op patient schedules a virtual visit to discuss new-onset gout in a different joint or to review lab results unrelated to the surgery, you can bill the appropriate telehealth E/M code with Modifier 24.
Synchronous Requirement
Remember that for the visit to be billable, it must be a real-time, audio-visual interaction. A simple “secure message” or “photo text” check-in does not qualify as a billable telehealth visit.
Tech Integration Checklist for Podiatry RCM
This table demonstrates a short overview for providers for technology integration, its function, and what type of financial benefits they can obtain:
| Technology Tool | Function | Financial Benefit |
| EMR Global Tracker | Auto-flags 10/90 day windows | Prevents “free” work on unrelated issues |
| Claim Scrubber | Validates Modifiers (24, 58, 78, 79) | Reduces denial rates by ~30% |
| Anatomical Mapping | Matches T-modifiers to diagnosis | Ensures audit-proof documentation |
| Telehealth Portal | Facilitates remote unrelated E/M | Increases patient access and billable volume |
Avoiding the Audit: Compliance and Oversight
In the world of podiatric billing, an audit isn’t just a stressful inconvenience; it’s a significant financial threat that can result in massive “clawbacks” of previously paid revenue. As a surgical specialty, podiatry is frequently targeted by Recovery Audit Contractors (RACs) and Unified Program Integrity Contractors (UPICs). Staying under the radar requires a proactive approach to compliance.
Common Red Flags for RAC Audits in Podiatry
Auditors use data analytics to find outliers. If your billing patterns deviate significantly from the national average, your practice will likely be flagged for a manual review. Common triggers include:
Modifier 24 Overuse
High frequencies of billable E/M visits during a 90-day global period are a major red flag. Auditors look for “template-cloning” where every post-op patient somehow has an “unrelated” issue.
Anatomical Inconsistency
Billing a procedure on a specific digit (e.g., T5) while the diagnosis code points to a different toe or the wrong foot.
Upcoding Minor Procedures
Frequently billing a “simple” matrixectomy (11730) as a “permanent” matrixectomy (11750) without sufficient documentation of chemical or surgical destruction of the matrix.
Lack of Medical Necessity for DME
Dispensing high-cost CAM walkers (L4361) for minor conditions where a surgical shoe (L3260) would have sufficed.
Internal Auditing: How to “Spot-Check” Your Surgical Billing
You shouldn’t wait for a letter from a player to find mistakes. Implementing a Quarterly Internal Audit (QIA) allows you to catch and correct errors before they become systemic.
The “Quarterly Spot-Check” Protocol
Select a Random Sample: Pull 10–15 surgical claims from the last 90 days, specifically focusing on those involving modifiers 24, 57, 58, 78, and 79.
Verify the “Global Shield”
Ensure no E/M visits were billed as “routine” post-op care. If a visit was billed during the global period, check for a separate, distinct diagnosis.
Check for “Note Cloning”
Compare notes from three different patients. If the HPI (History of Present Illness) and MDM (Medical Decision Making) look identical, you have a documentation compliance issue that needs immediate training.
Confirm Anatomical Modifiers
Cross-reference the operative report with the claim form. Does the report describe work on the right foot while the claim lists the left?
Review DME Log
Ensure every dispensed boot or orthotic has a corresponding signed “Proof of Delivery” (POD) and a clinical note explaining why it was medically necessary.
The Gold Standard for Audit-Proofing
The following snapshot of the table helps podiatry clinics to comply with regulations and have audit-ready documentation:
| Audit Area | The Risk | The Compliance Solution |
| Global Modifiers | Automatic denial or recoupment | Ensure separate ICD-10 codes for every “unrelated” visit. |
| Documentation | Insufficient “proof” of work | Use unique descriptions for each patient; avoid copy-pasting. |
| DME | “Same or Similar” denials | Check Medicare’s “Common Working File” before dispensing. |
| Anatomy | Mismatched T-modifiers | Double-check the operative note against the claim line. |
Conclusion: Transforming Your Post-Op Podiatry Revenue Cycle
Podiatry post-op billing is a high-wire act of clinical excellence and administrative precision. By mastering the Global Surgical Package, using Modifiers strategically, and leveraging EMR technology, your practice can capture every dollar earned while remaining fully compliant.
To facilitate foot and ankle care institutions’ practices across the US, BillingPodiatry offers its dedicated billing services. We are an award-winning medical billing company serving more than 1200 podiatry clinics. We help providers maximize efficiency in coding and billing while remaining compliant with HIPAA, AMA, and payer policies.
Frequently Asked Questions (FAQs)
If I treat a post-operative infection in my office during the 90-day global period, why can’t I bill an E/M code or a procedure code?
Under CMS and most private payer guidelines, the “Global Surgical Package” includes the treatment of all complications associated with a surgery—unless that treatment requires a return to the Operating Room (OR). If you manage an infection in the office with oral antibiotics or a simple bedside I&D, it is bundled into your original surgical fee. However, if the infection is deep and requires a formal trip back to the OR or an ASC, you can bill the surgical intervention using Modifier 78.
Can I bill for a CAM boot (L4361) if it’s dispensed on the same day as a bunionectomy?
Yes. Durable Medical Equipment (DME) is generally excluded from the surgical bundle. While the surgery (CPT 28296) has a 90-day global period, the “L-code” for the boot is a separate HCPCS claim.
To ensure payment, your documentation must clearly state the medical necessity of the boot for post-operative stabilization. Be wary of “Same or Similar” rules; if the patient received a boot elsewhere within the last five years, you may need a signed Advanced Beneficiary Notice (ABN) to bill the patient if the insurance denies the claim.
When should I use Modifier 24 instead of Modifier 79?
Think of the distinction as Office Visit vs. Procedure:
Modifier 24 is used strictly for Evaluation and Management (E/M) services (office visits) for an unrelated issue during a global period (e.g., seeing a post-op bunion patient for a new wart on the other foot).
Modifier 79 is used for Procedures performed during a global period that are unrelated to the original surgery (e.g., performing a matrixectomy on the left foot while the right foot is in a 90-day surgical window).