CPT code 27635 – Excision or curettage of tibia or fibula bone cyst or tumor

Key takeaways

CPT code 27635 reports excision or curettage of a bone cyst or benign tumor of the tibia or fibula when no bone graft is placed.

Grafting the cavity changes the code: 27637 covers autograft, including the graft harvest, and 27638 covers allograft.

Partial excision of tibial or fibular bone without a cyst or tumor, such as craterization for osteomyelitis, belongs to 27640 or 27641.

The diagnosis code must name the lesion and the side, such as M85.461 for a solitary bone cyst of the right tibia and fibula.

CMS lists 27635 with a 90-day global period and a 150% bilateral payment rule, and Medicare does not pay an assistant at surgery.

What CPT code 27635 covers

CPT code 27635 covers excision or curettage of a bone cyst or benign tumor of the tibia or fibula, with no bone graft placed. The official AMA CPT code set descriptor reads “Excision or curettage of bone cyst or benign tumor, tibia or fibula.” Two indented child codes share that stem and add a graft: 27637 and 27638.

The lesion defines the code. The surgeon may remove the lesion whole or scrape it out with a curette, and both count as 27635. A malignant tumor removed with a margin of healthy tissue moves to the radical resection codes, 27645 for the tibia and 27646 for the fibula.

Surgical technique and clinical context

A typical 27635 case starts with a lesion seen on X-ray or MRI, often after pain, swelling, or a fracture through weakened bone. Common lesions include unicameral and aneurysmal bone cysts, enchondromas, fibrous dysplasia, and giant cell tumors of bone.

The surgeon exposes the bone, opens a cortical window over the lesion, and removes its contents with curettes, a high-speed burr, or both. Some surgeons also treat the cavity wall with a local adjuvant, such as phenol or cryotherapy, to lower the recurrence risk.

• Approach: Open exposure of the tibia or fibula, with a cortical window large enough to reach the whole cavity.
• Removal: Excision of the lesion or curettage of its lining, often extended with a burr.
• Specimen: Tissue goes to pathology, and the final pathology diagnosis drives the ICD-10-CM code.
• Defect management: An ungrafted cavity stays on 27635. Packing it with bone graft moves the claim to 27637 or 27638.
• Fixation: Prophylactic fixation of a weakened tibia is a separate procedure (27745) with its own documentation.

27635 vs 27637, 27638, 27640 and 27641: Choosing the correct code

The tibia and fibula excision codes split on two questions. Was the lesion a cyst or benign tumor, and was the cavity grafted? The work RVUs below come from the 2026 CMS relative value file and show how much each answer changes the claim.

Use the operative note and the pathology report together to pick the code:

• Cyst or benign tumor, cavity left empty: Report 27635.
• Same lesion, the patient’s own bone packed into the defect: Report 27637, which already includes harvesting the graft.
• Same lesion, donor bone packed into the defect: Report 27638.
• No cyst or tumor, such as osteomyelitis or a bony spur: Look at 27640 for the tibia or 27641 for the fibula.
• Malignant tumor resected with margins: Report 27645 or 27646.

Laid out as a decision path, those questions sort every tibia or fibula excision into one of seven codes.

The same graft split runs through the bone cyst codes for other sites. A clavicle or scapula cyst packed with donor bone, for example, is reported with 23146.

No excludes note in the CPT code set sends spur, osteophyte, or exostosis removal to 27635. If an older reference says otherwise, check it against the current AMA descriptor before you code.

ICD-10-CM codes commonly paired with CPT 27635

Payers expect a diagnosis that names a cyst or benign tumor of the tibia or fibula, with laterality. These ICD-10-CM codes match the lesions 27635 describes:

Code from the final pathology report once it is available. A lesion treated as a simple cyst can come back as a giant cell tumor, and the diagnosis code must follow the report.

Codes for spurs and other bone disorders do not describe a cyst or tumor. Examples are M89.8X6 (Other specified disorders of bone, lower leg) and M89.8X7 (Other specified disorders of bone, ankle and foot). On their own, they do not support 27635.

Modifiers for CPT code 27635

Modifier choice for 27635 depends on the side treated, whether both legs were operated on, and who assisted. The CMS payment indicators in the relative value file settle the bilateral and assistant questions.

Some commercial payers want two lines, 27635-RT and 27635-LT, instead of modifier 50. Check the payer’s billing manual before you submit a bilateral claim, because Medicare rules do not carry over automatically.

Medicare payment for CPT code 27635

Medicare pays CPT code 27635 under the physician fee schedule. The figures below come from the 2026 CMS relative value file, October release, before any geographic adjustment.

These are national amounts. Your MAC locality’s geographic practice cost indices move the final payment, so pull the locality rate from the CMS physician fee schedule look-up tool. Confirm which conversion factor applies to your practice before you build payer contracts.

Documentation requirements for a 27635 claim

The operative report has to show that a cyst or benign tumor was removed from the tibia or fibula, and that no graft went in. These elements carry the claim through audit:

• Bone and side: Tibia or fibula, right or left, and where on the bone the lesion sat (proximal, shaft, or distal).
• Lesion type: The imaging diagnosis and the working diagnosis, such as unicameral bone cyst or enchondroma.
• Technique: Excision or curettage, the size of the cortical window, and any burr or adjuvant used.
• Defect management: A clear statement that no graft was placed, or the graft type if one was.
• Specimen: Confirmation that tissue went to pathology, with the final result added once it returns.
• Additional procedures: Any biopsy, fixation, or second site, each described on its own.

Reference the preoperative imaging report in the operative note. Payers often request it when they review 27635 for medical necessity. Pabau, the practice management platform we build, keeps that imaging, the operative note, and the claim in one patient record.

Prior authorization and payer requirements

Traditional Medicare does not list 27635 in its hospital outpatient prior authorization program. Commercial and Medicare Advantage plans set their own rules, so check each plan’s surgical authorization list before you schedule.

• Authorize all three graft options: The surgeon often decides on a graft during the operation. Request authorization that covers 27635, 27637, and 27638 so the final code is not left unauthorized.
• Imaging: Send the X-ray or MRI report that shows the lesion, its size, and its location on the bone.
• Clinical reason: State why the lesion needs surgery, such as pain, growth on serial imaging, or fracture risk.
• Medicare Advantage: A plan can require authorization that traditional Medicare does not. Verify it for each plan your practice works with.

Keeping current medical billing compliance protocols for prior authorization cuts surgical cancellations and protects revenue. Record the authorization number, the approval date, and the codes covered in the patient record before the day of surgery.

Common denial reasons for CPT code 27635 and how to avoid them

Common 27635 denials trace back to a code that does not match the operative note or a diagnosis that does not match the code. These are the patterns to watch:

A structured denial management strategy for orthopedic claims should track 27635 denials by root cause as well as by code. Grouping them shows whether the fix is coder training, note templates, or payer rules. For a full reference to common denial codes in medical billing, review the CARC table before you write appeal letters.

Codes billed with CPT 27635 and NCCI edits

A few codes appear alongside 27635 in bone cyst and benign tumor surgery. NCCI edits decide which pairs are payable and which need a modifier, and they update quarterly. Check the current CMS NCCI procedure-to-procedure edits before you bill any pair.

How claims management software reduces errors for CPT code 27635

A bone cyst claim can only be coded once the surgery is over. The final code depends on what happened to the cavity and what pathology found, and both arrive after the booking.

In Pabau, the pathology result lands in the same record as the operative note. Its claims software for surgeons lets your billing team check the graft line and the diagnosis before the claim is built.

Claims go out electronically through Claim.MD, with eligibility checks before surgery and remittance posted back to the same record. When a 27635 claim is denied, your team can trace the CARC to its cause and fix it once.

Get bone cyst and tumor claims right the first time

Pabau keeps operative notes, pathology results, and claims in one record, so your team codes 27635, 27637, or 27638 from what happened in surgery.

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Conclusion

CPT 27635 is a narrow code: One lesion type, two bones, and no graft. The costly errors come from stretching it over procedures it does not describe, such as spur removal or a grafted cyst.

Code from the operative note and the final pathology report, not from the booking. Ask for authorization that covers all three graft options, and remember that Medicare will not pay an assistant at surgery on 27635.

Book a demo to see how Pabau keeps operative notes, pathology, and claims together so your orthopedic claims go out right the first time.

Continue your research

Need to understand how the clearinghouse processes your 27635 claim? Pabau’s Claim.MD clearinghouse guide explains how electronic claims are validated, scrubbed, and routed to payers.

Confused by the 837 file format your clearinghouse requires? 837 file billing guide covers the transaction set structure and common submission errors.

Want to reduce denial rates across your orthopedic billing? Electronic remittance advice (ERA) processing guide shows how automated ERA posting surfaces denial patterns faster than manual EOB review.

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