Open arthrotomy with complete synovectomy of the knee, excising synovial tissue from both the anterior and posterior compartments, including the popliteal area.

Verified May 8, 2026 · 8 sources ↓

Medicare: $719.12
Total RVUs: 21.53
Global, days: 90
Region: Knee

Drawn from CMSAAOSMdclarityEmednyAAPC

Documentation requirements

What must appear in the operative or office note to support the claim.

Source · Editorial brief grounded in 8 cited references ↓

Specify compartments addressed: anterior, posterior, and popliteal area must all be documented to support 27335 over 27334
Document the primary diagnosis driving medical necessity — e.g., rheumatoid arthritis, PVNS, or chronic synovitis with failed conservative treatment
Operative note must confirm open arthrotomy approach, not arthroscopic, with named incision sites (anterior and posterior)
Record pre-operative imaging or lab findings supporting synovial disease severity and necessity of bilateral-compartment resection
If billed same-day with another knee procedure, document that the synovectomy was performed in compartments distinct from those addressed by the companion procedure
Include anesthesia type and laterality (left vs. right knee) clearly in the operative report

Applicable modifiers

Modifiers commonly billed with this code.

Source · AMA CPT modifier descriptors · CMS NCCI Policy Manual

22 Increased complexity 51 Multiple procedures 59 Distinct service 76 Repeat, same physician 78 Unplanned return — related 79 Unrelated during global LT Left side RT Right side 50 Bilateral procedure AS PA/NP/CNS assistant

What this code covers

Source · Editorial summary grounded in 8 cited references ↓

CPT 27335 describes an open knee synovectomy performed through arthrotomy with removal of inflamed or diseased synovial membrane from both the anterior and posterior aspects of the joint, extending into the popliteal area. This distinguishes it from 27334, which covers only the anterior or posterior compartment — not both. The procedure is typically indicated for refractory inflammatory arthropathy (e.g., rheumatoid arthritis, pigmented villonodular synovitis) when conservative management and less invasive approaches have failed.

The 90-day global period covers the operative session, the day-before preoperative visit, and all routine postoperative management through day 90. Synovectomy performed as a 'clean up' adjunct to a more extensive knee procedure — including total knee arthroplasty (27447) — is not separately reportable. AAOS global service data explicitly bundles 27334 and 27335 into 27447.

For arthroscopic cases, note that 29875 (arthroscopic synovectomy, single compartment) cannot be billed with any other ipsilateral knee arthroscopy code. CPT 29876 (two or more compartments) has limited separate billing permitted only when the additional compartments involved are distinct from those addressed by the companion arthroscopic procedure. Open synovectomy (27335) and arthroscopic synovectomy codes are not interchangeable — use the code that matches what was actually performed and documented.

RVU & reimbursement

Component RVUs and Medicare national rate. Actual payment varies by GPCI locality.

Source · CMS Physician Fee Schedule, RVU26A · January 2026

Work RVU	10.29
Practice expense RVU	9.05
Malpractice RVU	2.19
Total RVU	21.53
Medicare national rate	$719.12
Global period	90 days

Payment by site of service

Medicare pays different rates by setting. HOPD typically pays substantially more than ASC for the same procedure.

Source · CMS OPPS Addendum B·ASC HCPCS payment rates·2026

Setting	Medicare rate (national)
Office (PFS non-facility) Procedure performed in physician's office	$719.12
HOPD (APC 5114) Hospital outpatient department	$7,413.38
ASC (PI A2) Ambulatory surgical center (freestanding)	$3,695.53

Common denial reasons

The recurring reasons claims for CPT 27335 get rejected.

Source · Editorial brief grounded in CMS NCCI edits, AAOS coding appeals, and cited references ↓

Bundling denial when billed alongside 27447 (TKA) — synovectomy is included in the arthroplasty global and is not separately payable
Upcoding flag when 27335 is billed but the operative note only documents single-compartment (anterior or posterior) synovectomy, which maps to 27334
Medical necessity denial for lack of documentation showing failure of conservative management prior to open surgical synovectomy
NCCI edit denial when arthroscopic synovectomy codes (29875/29876) are billed on the same claim as 27335 for the same knee on the same date
Laterality missing or mismatched — claim submitted without LT or RT modifier causing payer-side rejection or processing error

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 8 cited references ↓

01What is the difference between CPT 27334 and 27335?

27334 covers open knee synovectomy in the anterior OR posterior compartment only. 27335 requires both anterior AND posterior resection, including the popliteal area. If the op note doesn't explicitly document posterior and popliteal involvement, auditors will downcode to 27334.

02Can I bill 27335 with a total knee arthroplasty (27447)?

No. Synovectomy — including 27334 and 27335 — is bundled into 27447 per AAOS global service data. Billing both on the same claim will result in denial of 27335 without a valid modifier and supporting documentation showing the synovectomy was a separate, distinct service, which is rarely supportable in the TKA context.

03Can 27335 be billed with arthroscopic knee codes on the same day?

Not for the same knee. Mixing open and arthroscopic synovectomy codes on the same joint same day triggers NCCI edits. If the open procedure was genuinely distinct from an arthroscopic portion of the same encounter, document thoroughly and append modifier 59 — but payer scrutiny will be high.

04What modifier do I use if the patient returns to the OR within the 90-day global for a related knee problem?

Use modifier 78 for an unplanned return to the OR for a complication or related procedure during the global period. Use modifier 79 if the return procedure is unrelated to the original synovectomy. Never invert these two.

05Does 27335 require prior authorization?

Prior auth requirements vary by payer and plan. Medicare does not require prior authorization for 27335, but many commercial payers do — particularly when the indication is inflammatory arthritis. Washington State HCA (Medicaid) lists 27335 under chondral defect criteria requiring medical necessity review. Verify with each payer before scheduling.

06How does site of service affect payment for 27335?

HOPD and ASC payments differ substantially — see the site of service comparison table on this page. The procedure is typically performed in a hospital OR or ASC given the open approach and 90-day global period.

Sources & references

Editorial content was developed using the following public sources. Last verified May 8, 2026.

Mira AI Scribe

Mira's AI scribe captures the specific compartments addressed (anterior, posterior, popliteal), the open arthrotomy approach, the disease process driving the procedure, and any companion procedures performed on the same knee. That documentation prevents the two most common denials: downcoding to 27334 when only one compartment is mentioned, and bundling denials when the note fails to establish that synovectomy was performed in compartments distinct from those of a co-billed procedure.

See how Mira captures CPT 27335 documentation