Table 1 Example of code denial due to inappropriate code modifier. In this scenario, because the injections were performed at different sites/on different structures, modifiers 59 or XS could be appropriately used to bypass the edit, as allowed by CMS due to the indicator modifier 1.
SOURCE:, National Correct Coding Initiative Edits


Published 7/27/2021
Michelle AbrahamMHA, CCS-P; Sarah Wiskerchen, MBA, CPC

Navigating the National Correct Coding Initiative

Editor’s note: AAOS partners with KarenZupko & Associates, Inc. (KZA), on the organization’s coding education, and KZA often provides content for AAOS Now. For more information, visit

For procedural coding in orthopaedic surgery, physicians, and their staff primarily rely on two information sources: Current Procedural Terminology (CPT) and the AAOS publication Complete Global Service Data for Orthopaedic Surgery (GSD). Practices may also be subject to payer-created coding and reimbursement guidelines, the most prevalent of which is called the National Correct Coding Initiative (NCCI), which was created by the Centers for Medicare and Medicaid Services (CMS). Understanding the differences between these guideline sources is key to accurate coding and appropriate reimbursement.

What are CPT guidelines?

CPT codes, created by the American Medical Association (AMA), are the set of five-digit/character codes that describe procedures and services performed by physicians or other providers. The codes are accompanied by descriptions, and some codes have parenthetical notes and/or narrative guidelines that provide explanatory details for sections and subsections of the code book. The CPT guidelines often indicate when codes may or may not be reported together and are used to help prevent coding errors. The CPT guidelines do not encompass every potential correct or incorrect code combination, so orthopaedic practices benefit from the availability of a second resource, GSD, created by AAOS.

What are GSD guidelines?

The AAOS two-volume publication, Global Service Data for Orthopaedic Surgery, or GSD, is a comprehensive coding resource that explains details behind the CPT definitions of musculoskeletal CPT codes. With a full page devoted to each orthopaedic-related CPT code, the GSD contains an extensive list of the component services that are included in each CPT code, as well as services that are not included in the CPT code, which may be separately reported when performed.

When creating the guidelines in 1991, AAOS relied on the CPT code vignettes that were created by the AMA. Where no vignette was available, the policy was outlined to reflect common clinical practice. The GSD guidelines are an essential tool to help prevent incorrect coding, particularly when additional services should not be separately reported because they are considered inherent in the primary procedure. Equally importantly, the guidelines can be used as a resource with payers to combat incorrect denials. It is important to note that services that are listed as “not included” in GSD are not exhaustive lists and represent procedures that are most commonly performed with the CPT code. Although third-party vendors may offer electronic options for accessing and viewing CPT codes, the GSD guidelines are only available through AAOS in book, e-book, and software formats (Code-X).

What is NCCI?

Beginning in 1996, CMS created the NCCI to “promote national correct coding methodologies and to control improper coding that leads to improper payment in Part B claims.” The NCCI policies rely on multiple parameters, including procedure-to-procedure (PTP) code pair edits, narrative guidelines, and medically unlikely edits (MUEs). The component parameters are used together but are updated at different intervals.

Who follows NCCI?

Because Medicare Part C plans (Medicare Advantage) must follow CMS policies, NCCI codes should also be applied for those payers. The Affordable Care Act requires CMS to notify states of Medicaid-compatible NCCI methodologies and state programs to incorporate them. The NCCI guidelines for Medicaid often mirror those for Medicare, but the manuals are not identical. For example, with state workers’ compensation programs and private payers, practices must look to their contracts to see whether and how NCCI policies are applied. Payers that adhere to NCCI edits and guidelines may have software systems that reject claims submitted with code pairs containing NCCI edits. Likewise, some clearinghouses may reject claims that contain NCCI code pair edits.

What is an NCCI PTP code pair edit?

The NCCI PTP code pair edits are designed as an extensive table of code pair combinations, available on the CMS website in an Excel format. The edits are updated quarterly. Within the Excel tables, numeric modifiers are used to indicate whether a code pair is reportable in some circumstances, or whether the code combination is never reportable together. The spreadsheet contains the following information:

  • columns 1 and 2, which list the CPT (or Healthcare Common Procedure Coding System [HCPCS]) codes
  • effective date of the code pair edit
  • deletion date, where applicable
  • modifier (indicates whether one can bypass the code pair edit)
  • PTP code pair edit rationale

The modifier options are “0,” “1,” and “9.” The number “0” indicates that the two codes may not be reported together and that there are no CPT modifiers to append to bypass the edit. The number “1” indicates that one of the CPT codes requires an NCCI-associated CPT modifier to bypass the code pair edit. The number “9” indicates that the code pair is not applicable, such as code pairs 20610 (drainage of finger abscess) and 61650 (endovascular intracranial prolonged administration of pharmacologic agent), which would never be performed together. Many third-party coding programs, including Code-X, have incorporated the NCCI PTP code pair edits because they are used so frequently by non-CMS–contracted payers.

When and how can an NCCI PTP edit be bypassed?

If a PTP code pair edit has the modifier “1” listed, the codes must have a CPT modifier appended to the claim to indicate that the two procedures meet criteria for separate reporting. In most cases, the NCCI edit is bypassed with CPT modifier 59, Distinct Procedural Service, defined as, “Under certain circumstances, it may be necessary to indicate that a procedure or service was distinct or independent from other non-E/M services performed on the same day. Modifier 59 is used to identify procedures/services, other than E/M services, that are not normally reported together, but are appropriate under the circumstances. Documentation must support a different session, different procedure or surgery, different site or organ system, separate incision/excision, separate lesion, or separate injury (or area of injury in extensive injuries) not ordinarily encountered or performed on the same day by the same individual.”

Anatomic modifiers RT (right), LT (left), FA-F9 (fingers), and TA-T9 (toes), are even more specific than modifier 59, and may be allowed by payers instead of modifier 59. X{EPSU} modifiers also may be considered to explain that services are separately reportable because they are separate structures (XS), separate encounters (XE), separate practitioners (XP), or unusual, non-overlapping services (XU).

For example, if an orthopaedic surgeon performs an injection to the right wrist without ultrasound guidance and also performs an injection to the flexor tendon sheath of the right index finger at the same encounter, both codes are reportable because they are performed on separate anatomic sites and there is no overlap of work performed. The CPT codes for these procedures, 20605, Arthrocentesis, aspiration and/or injection, intermediate joint or bursa (eg, temporomandibular, acromioclavicular, wrist, elbow or ankle, olecranon bursa); without ultrasound guidance, and 20550, Injection(s); single tendon sheath, or ligament, aponeurosis (eg, plantar “fascia”), are subject to an NCCI PTP code pair edit. Without an appropriate modifier, one of the codes would be denied by any payer that uses the NCCI PTP code pair edits in claims adjudication, as illustrated in Table 1 (page 16).

According to the CPT manual, “When another, already established modifier is appropriate, it should be used rather than modifier 59. Only if no more descriptive modifier is available, and the use of modifier 59 best explains the circumstances, should modifier 59 be used.” This measure is consistent with AAOS coding instructions. As CMS moves to the use of the “most specific modifier,” anatomic modifier F6 (right index finger) would be the most specific and appropriate for the tendon injection. Some payers may require only the anatomic modifiers, whereas others may require both the anatomic modifier and 59. The medical necessity of each procedure should be documented, and the claims should be supported by appropriate procedure notes and supporting diagnoses.

There are frequent occurrences when certain NCCI guidelines conflict with CPT and AAOS GSD guidelines, which poses a challenge. Examples include: multiple closed nondisplaced fractures treated with the same cast or splint, knee arthroscopy, shoulder procedures, spine decompression with interbody fusion, and other joint debridement. Unfortunately, the more restrictive NCCI guidelines have reduced reimbursement for orthopaedic surgeons. The unilateral adoption of NCCI guidelines by non-Medicare and Medicaid payers increases the potential for lost revenue.

Recommendations for AAOS members

Orthopaedic surgeons can assign a physician/staff team to perform a quarterly or annual review of the NCCI guidelines and to educate their group’s members. Pay attention to policies for services performed in the practice that diverge from CPT and GSD.

For private payers, it is essential that practices review their contracts and associated online reimbursement policy manuals to assess whether contracted plans adhere to some or all components of NCCI. If possible, remove references to NCCI entirely. If that is not possible, request carve-out exceptions when the NCCI policies conflict with CPT and GSD guidelines. If the contract mandates that the practice apply all aspects of NCCI, billing staff will have no foundation to appeal unpaid services.

However, if physicians and their staff are experiencing claim denials based on clinically inaccurate NCCI edits, AAOS members can raise the issue with the AAOS Coding and Reimbursement department for intervention. If the physician advisors on the AAOS Coding Coverage and Reimbursement Committee (CCRC) deem the NCCI edits as incorrect and in conflict with CPT and GSD guidelines, then AAOS will address the inaccurate code pair edit directly with CMS and NCCI and request a change. This intervention has overturned several NCCI edits in recent years.

Recent victories with NCCI for orthopaedic surgeons

In 2017, after AAOS input and urging for change, NCCI deleted selected arthroscopic shoulder debridement code pair edits (codes 29823/29824, 29823/29827, and 29823/29828). AAOS referenced GSD guidelines that described the services as separate in their supporting documentation to CMS.

Effective Jan. 1, 2020, CMS deleted language from the NCCI Policy Manual which stated that the shoulder was a “single anatomic structure,” driven by petitions from AAOS and other specialty societies.

AAOS works tirelessly on advocating for NCCI changes by submitting supporting documentation that substantiates the medical necessity of performing and reporting certain procedures together, in the case of NCCI edits, or performing and reporting certain procedures more than once per day, as in the case of MUEs, which limit the maximum units of services allowed per encounter.

However, not every request is a victory. Often, despite compelling clinical evidence submitted, NCCI maintains the decision to apply a code pair edit or MUE limitation to a procedure. Just as listed in the June edition of AAOS Now, “AAOS Responds to NCCI Code Edit to Distal Radial Fracture and Carpal Tunnel Release,” regardless of the significant data and justification given to support the performing of these two procedures (64721 with 25607) in different anatomic areas of the upper extremity with distinctly different diagnoses, NCCI moved forward with the implementation of the erroneous PTP code pair edit.

In such instances, physicians should voice their concerns with NCCI directly. There is power in numbers, and it may take the action of AAOS and its members to achieve a favorable result. For PTP and MUE issues, please report via email to

For payers that do not contractually require the use of NCCI, surgeons must be aware of the NCCI PTP code pair edits, along with CPT and GSD guidelines, and appeal all inappropriately denied and bundled claims. Appeals should state if the denial of the code conflicts with AMA CPT guidelines and/or AAOS GSD guidelines, which state the two codes are separately reportable.

For additional information on the NCCI program, review the “How to Use the Medicare National Correct Coding Initiative (NCCI) Tools” from CMS, as well as other Medicare Learning Network resources at

Michelle Abraham, MHA, CCS-P, is the coding and reimbursement coordinator for the AAOS Office of Government Relations.

Sarah Wiskerchen, MBA, CPC, is a senior consultant and coding educator with KZA, which develops and delivers the AAOS annual coding and reimbursement workshops.