CPT Code 27299: Unlisted Procedure, Pelvis or Hip Joint

Key Takeaways

CPT Code 27299 is the correct unlisted procedure code for any surgical or medical intervention on the pelvis or hip joint that lacks a specific Category I CPT code.

Common procedures reported under 27299 include periacetabular osteotomy (PAO), core decompression for avascular necrosis, triple innominate osteotomy, and abductor muscle transfer.

Payers require the operative report and a cover letter comparing the procedure to a similar Category I code – submitting without these attachments almost always results in denial.

Pabau’s claims management workflows help orthopedic practices track unlisted code submissions, attach supporting documentation, and monitor payer-specific reimbursement outcomes.

Orthopedic claims for hip preservation and pelvic reconstruction procedures are among the most frequently denied in surgical billing. The core problem: many of these operations are technically complex and clinically well-established, yet no specific Category I CPT code exists for them. That forces coders to reach for CPT Code 27299 – the unlisted procedure, pelvis or hip joint – and navigate a reimbursement process that is anything but automatic.

Unlike standard CPT codes, 27299 carries no built-in RVU value in the Medicare Physician Fee Schedule. Each claim is reviewed on its individual merits. Reimbursement depends on the quality of the operative report, the persuasiveness of the cover letter, and the comparison code chosen as a billing benchmark. This guide covers the code’s definition, which procedures trigger its use, what documentation payers actually want, modifier rules, and how to benchmark reimbursement – including the ICD-10 diagnoses most commonly paired with it.

CPT Code 27299: Definition and Clinical Description

CPT Code 27299 is maintained by the American Medical Association (AMA) as part of the musculoskeletal surgical range 26990-27299, which covers surgical procedures on the pelvis and hip joint. The full official description is: Unlisted procedure, pelvis or hip joint.

As the AAPC (American Academy of Professional Coders) notes, unlisted CPT codes are used when no specific code in the CPT code set accurately describes the procedure performed. Typically, these codes end in “99” – and 27299 follows that convention as the terminal unlisted code for the pelvis and hip joint section. It is a Category III-equivalent placeholder, not a Category I code with a defined work value.

Coders should reach for CPT Code 27299 only after confirming that no existing Category I code adequately describes the procedure. HIPAA’s administrative simplification rules require use of the most specific code available. If a Category I code covers the work, 27299 is not appropriate. Related unlisted codes in adjacent anatomical sections include CPT 27599 (unlisted procedure, femur or knee), which applies when a femoral or knee procedure lacks a specific code.

Code Range and Category Context

Within the CPT code set, 27299 sits at the end of the surgical range dedicated to the pelvis and hip joint. Practices that manage claims management workflows for orthopedic surgeons will encounter this code frequently when hip preservation surgery volumes are high. Knowing which procedures legitimately belong here, versus which have been assigned their own Category I codes, is the first step to clean claims submission.

Procedures Commonly Billed Under CPT Code 27299

Several well-recognised hip preservation and pelvic reconstruction procedures have no dedicated Category I CPT code, making CPT Code 27299 their correct billing vehicle. Each carries its own documentation requirements and comparison code considerations.

Periacetabular Osteotomy (PAO)

The Bernese periacetabular osteotomy is the surgical standard for correcting symptomatic hip dysplasia in skeletally mature patients. No Category I CPT code exists for this procedure. According to Karen Zupko and Associates, a nationally recognised orthopedic coding consultancy, the correct code is CPT 27299 (Unlisted procedure, pelvis or hip joint). Coders must attach the operative report and a cover letter identifying a similar procedure for benchmarking. PAO is technically complex and time-intensive, so the comparison code chosen should reflect the procedure’s complexity. Coding consultancies note that selecting a similar musculoskeletal osteotomy code from the same anatomical region is standard practice, though no single comparison code is universally accepted; for non-Medicare payers, HCPCS S2115 may also be considered where the payer recognises it.

Core Decompression for Avascular Necrosis

Core decompression involves drilling one or more channels into the femoral head to relieve intraosseous pressure and encourage revascularisation in patients with avascular necrosis (AVN). The AAPC Orthopedic Coding Alert confirms that unlisted procedure code 27299 is the correct vehicle for this procedure. AVN of the femoral head is typically documented with ICD-10 code M87.052 (Idiopathic aseptic necrosis of left femur) or M87.051 (right femur), providing the payer with medical necessity context.

Triple Innominate Osteotomy

The triple innominate osteotomy cuts the ilium, ischium, and pubis to reorient the acetabulum – most often performed in pediatric and adolescent patients with residual hip dysplasia. A peer-reviewed article in the Journal of the Pediatric Orthopaedic Society of North America (JPOSNA) confirms that because no CPT code reflects this procedure, it is correctly reported as 27299. The JPOSNA guidance also notes that practices serve their own interests by proactively providing payers with thorough documentation, because unlisted code claims default to manual review and can stall for weeks without supporting materials.

Abductor Muscle Transfer

When significant fatty atrophy is present, transfer of the anterior portion of the gluteus maximus to the greater trochanter may be performed as part of a hip preservation case. A peer-reviewed article in PMC on hip preservation procedural coding confirms that this procedure is billed as CPT 27299, with CPT 23420 (reconstruction of complete shoulder cuff avulsion) used as the comparison code for reimbursement benchmarking. Using an appropriate comparison code from a similar anatomical region and complexity tier is standard practice for unlisted code billing.

Other procedures that share the unlisted code challenge across surgical specialties include certain Dega osteotomies (which may require 27299 alongside CPT 27151, the iliac osteotomy with femoral osteotomy code, when both pelvic and femoral components are performed) and hip tendon repairs where no specific tendon code adequately captures the work performed.

Documentation Requirements for Unlisted Procedure Claims

Submitting CPT Code 27299 without supporting documentation is the most common reason these claims are denied. Unlike standard procedure codes, unlisted codes have no built-in fee schedule value. The payer’s medical review team must manually evaluate the claim and assign a reimbursement amount – and they cannot do that without the operative report and a structured cover letter.

The Operative Report

The operative report is the clinical anchor of any unlisted code claim. It must describe: the patient’s diagnosis and the clinical indication for the procedure, the specific technique used (including approach, landmarks, instrumentation, and time), any intraoperative findings, and the surgeon’s assessment of complexity. Vague operative notes – “periacetabular osteotomy performed without complication” – are insufficient. Payers need enough detail to compare the work described against the comparison code proposed in the cover letter. Accurate clinical records maintained in real time during the encounter produce the most defensible operative reports.

The Cover Letter

The cover letter is where the coder and surgeon make the case for reimbursement. It should include:

• A plain-language description of the procedure – what was done, why, and how it differs from the comparison code
• The specific comparison (similar) code – the Category I CPT code that most closely resembles the work in scope, time, and complexity
• A rationale for any upward or downward variance – if the procedure is more complex than the comparison code, explain why
• The surgeon’s signature – payers treat unsigned cover letters as informal correspondence, not clinical justification
• Relevant ICD-10 diagnosis codes – linking the procedure to the diagnosis establishes medical necessity

For periacetabular osteotomy, the cover letter should note that no Category I code exists and cite the comparison code (e.g., CPT 27151) as the closest analogue. For abductor muscle transfer, cite CPT 23420 as the comparison, as confirmed in the PMC hip preservation coding literature. Keeping a practice management system that logs each unlisted code submission and its outcome helps build an internal reference library for future claims.

Modifiers and Billing Rules for CPT 27299

Modifier usage with unlisted procedure codes follows the same general rules as standard CPT codes, but practices should verify modifier applicability with each payer before submission. CPT Code 27299 does not appear in the National Correct Coding Initiative (NCCI) edit tables in the same way Category I codes do, because it lacks a standard descriptor that NCCI edits can target. That does not mean modifiers are irrelevant – it means the payer applies its own review criteria.

Commonly Used Modifiers

• Modifier -22 (Increased Procedural Services): Used when the procedure required substantially greater work than typically expected. For complex PAO cases with revision elements or unusual anatomy, -22 may be appropriate. Supporting documentation explaining the additional complexity is mandatory.
• Modifier -51 (Multiple Procedures): Applied when CPT 27299 is billed alongside another procedure on the same date. For example, if CPT 27151 (iliac osteotomy with femoral osteotomy) is performed in the same session as the unlisted procedure, -51 may apply to the secondary code. Verify with the payer.
• Modifier -RT/-LT (Right/Left): Laterality modifiers apply to hip procedures and should be included to identify the operative side. Omitting laterality is a common reason for claim delays on bilateral anatomical sites.
• Modifier -80 (Assistant Surgeon): If a surgical assistant participated, append -80 to the assistant surgeon’s claim line. As with all modifier usage, confirm coverage under the specific payer’s policy.

Prior authorisation requirements for CPT 27299 vary significantly by payer and by the underlying procedure. Medicare does not publish a standard prior auth rule for unlisted codes – coverage decisions are made at the payer level, often by regional Medicare Administrative Contractors (MACs). Commercial payers frequently require pre-authorisation before hip preservation surgery. Practices that operate across sports medicine and orthopedic settings should establish payer-specific pre-auth protocols for each procedure regularly billed under 27299.

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Reimbursement and Fee Schedule Considerations

CPT Code 27299 has no assigned Relative Value Unit (RVU) in the CMS Medicare Physician Fee Schedule. This means there is no published national rate. Reimbursement is negotiated on a case-by-case basis, benchmarked against the comparison code provided in the cover letter. The practical implication: the quality of the documentation package directly determines the reimbursement amount.

For Medicare and most commercial payers, the reimbursement for CPT 27299 is typically pegged to the comparison code’s allowed amount, adjusted up or down based on the payer’s assessment of the procedure’s relative complexity. Submitting CPT 27151 (iliac osteotomy with femoral osteotomy) as a comparison code for a periacetabular osteotomy, for example, may result in reimbursement at a rate similar to that code’s fee schedule value in your geographic area. Selecting a comparison code that genuinely reflects the work performed is therefore not only accurate – it directly affects revenue.

Medicare vs. Commercial Payer Rates

Medicare rates for unlisted codes are set by the MAC’s medical review process and can vary by region. Commercial payer rates depend on the practice’s contracted fee schedule, the comparison code submitted, and the payer’s internal unlisted code policy. Practices using compliance management tools should maintain a log of comparison codes used, reimbursement outcomes, and payer responses to build a benchmarking reference over time.

ICD-10 Diagnosis Codes Commonly Paired with 27299

Pairing CPT 27299 with the correct ICD-10 diagnosis code establishes medical necessity – a prerequisite for reimbursement on any unlisted code claim. The ICD-10 code should reflect the primary diagnosis driving the procedure. Common pairings include:

• M16.11 / M16.12 – Primary osteoarthritis, right/left hip (post-surgical hip degeneration requiring reconstruction)
• M87.051 / M87.052 – Idiopathic aseptic necrosis of right/left femur (AVN – core decompression cases)
• Q65.81 – Developmental dysplasia of hip (DDH – periacetabular osteotomy and triple innominate osteotomy)
• M16.31 / M16.32 – Unilateral osteoarthritis resulting from hip dysplasia (PAO cases with arthritic progression)
• M25.551 / M25.552 – Pain in right/left hip (general hip pathology requiring unlisted procedure)

Orthopedic and physical therapy practices that work alongside orthopedic surgeons should confirm which ICD-10 codes the operating surgeon uses in the operative report, as the diagnosis codes on the claim must match.

Managing CPT 27299 Workflows in Practice

Unlisted codes create more administrative friction than any other category in orthopedic billing. Standard claim scrubbing tools flag 27299 for manual review by default. Clearinghouses may reject the claim if the supporting documentation is not attached in the correct format. Payer portals have varying rules about how to upload operative reports alongside electronic claims.

For practices managing high volumes of hip preservation surgery, a standardised workflow pays dividends. The surgeon dictates the operative note immediately post-procedure and flags the case as a 27299 submission. The coder assembles the cover letter and comparison code within 48 hours. The billing team attaches both documents before claim submission and sets a follow-up reminder at 14 days. Practices that use HIPAA-compliant documentation systems can route the operative report directly from the clinical record to the billing queue, eliminating the manual handoff where documents are most often lost.

Pabau’s claims management software is designed for exactly this kind of complex submission. Operative reports stored in the patient record can be attached to claims directly, comparison codes noted in the billing notes field, and reimbursement outcomes tracked per procedure type. For practices submitting multiple unlisted procedure codes across orthopedic subspecialties, having that data organised reduces the time spent reconstructing documentation when a payer requests reconsideration.

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Conclusion

CPT Code 27299 is not a code of last resort – it is the correct, compliant code for a defined set of hip preservation and pelvic reconstruction procedures that lack Category I status. The challenge is not the code itself but the documentation process that determines whether the claim pays, and at what rate.

Practices that standardise their operative report quality, build procedure-specific cover letter templates, and select comparison codes that genuinely reflect procedural complexity will see materially better reimbursement outcomes than those treating unlisted code claims as exceptions. Pabau’s claims management tools help orthopedic practices bring that structure to every 27299 submission. To see how it works in your billing workflow, book a demo.

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