CPT code 27331: Knee arthrotomy, anterior or posterior synovectomy2026 Medicare rate & RVUs

Medicare pays $459.60 for 27331 nationally in a facility.

Medicare allowed amount for participating (non-QP) physicians, before deductible, coinsurance and claim adjustments. Not a patient’s bill or a hospital charge.

What 27331 covers

Code 27331 represents open entry into the knee joint to remove synovial tissue from either its anterior or posterior portion. Orthopedic surgeons may perform it for symptomatic synovial disease requiring direct surgical treatment. The operative report should establish the open approach and identify the portion of the joint treated. The procedure is typically performed in an operating room, including hospital outpatient and inpatient settings.

Select this code when the documented work is an anterior or posterior synovectomy, rather than a biopsy alone or a major synovectomy involving multiple compartments. Documentation should describe the synovial abnormality, surgical approach, area treated, and extent of tissue removal. CMS assigns a 90-day global period, including the day-before preoperative visit and 90 days of related postoperative care. In a same-session multiple-procedure claim, the highest-valued procedure is paid in full and other procedures at 50%. Bilateral procedures with modifier 50 are paid at 150%. Assistant-at-surgery payment may be made; co-surgeons require supporting documentation, and team surgery is not permitted.

This summary was written with AI assistance from CMS physician fee schedule data and checked against the CMS billing rules shown here. Rates on this page come directly from CMS files.

Where 27331 pays more and less

The same RVUs, adjusted for each area’s costs. Open a locality for its calculation, history and nearby areas.

109 of 109 payment localities

27331 rates by state

Office rate range in each state. Select a state to see its payment localities.

How the 27331 rate is calculated

Each of 27331’s three RVUs is multiplied by a geographic index (GPCI) for the payment locality, added up, and multiplied by the conversion factor. Drag the indexes or enter a ZIP to see what moves the rate.

Payment rules and modifiers for 27331

27331 has a 90-day global period: related visits in that window are included in the surgery payment.

What modifiers do to the payment

When to use modifier 50

27331 compared with similar codes

How to choose

27330Knee biopsyOpen synovial tissue sampling

Choose 27330 when the arthrotomy is performed to obtain a biopsy. Choose 27331 when the operative work removes synovial tissue from an anterior or posterior portion of the joint.

27334Knee synovectomyAnterior or posterior approach

27334 describes a major synovectomy involving two compartments. Distinguish it from 27331 by the documented extent and compartments treated.

27335Knee synovectomyAnterior and posterior

27335 describes a major synovectomy involving three compartments; 27331 describes an anterior or posterior synovectomy.

Codes related to 27331

Related codes aren’t interchangeable: bill the code that matches the service performed.

Where these rates come from

FeeBase calculates base physician payments from CMS work, practice-expense and malpractice RVUs, adjusted by each locality’s geographic indexes and the conversion factor. Services without a published rate are labeled, never given a made-up amount. Amounts are Medicare allowed amounts before claim adjustments: not a patient’s bill or a commercial rate.

CMS RVU26D · effective Oct 1, 2026 through the day before Jan 1, 2027

Open CMS sourceHow we calculate rates