Surgical · Knee

Open knee arthrotomy performed solely to obtain a synovial tissue sample for pathologic examination.

Verified May 8, 2026 · 6 sources ↓

Medicare: $412.84
Total RVUs: 12.36
Global, days: 90
Region: Knee

Drawn from CMSAAPCEohhsFastrvu

Documentation requirements

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

Source · Editorial brief grounded in 6 cited references ↓

Specify that the procedure was limited to synovial biopsy only — any additional intra-articular work documented changes the correct code.
Record the laterality (left or right knee) in both the operative note and the diagnosis/procedure fields.
Confirm pathology specimen was sent; note the tissue site and quantity harvested.
Document the medical necessity and pre-operative diagnosis driving the biopsy (e.g., suspected inflammatory arthropathy, pigmented villonodular synovitis, crystalline arthropathy).
Record the surgical approach and arthrotomy location (e.g., medial parapatellar, suprapatellar pouch) — vague references to 'standard approach' invite audit flags.
Include the pathology report or pending order in the chart to confirm the specimen was processed.

Applicable modifiers

Modifiers commonly billed with this code.

Source · AMA CPT modifier descriptors · CMS NCCI Policy Manual

22 Increased complexity 51 Multiple procedures 52 Reduced services 58 Staged or related 59 Distinct service 78 Unplanned return — related 79 Unrelated during global LT Left side RT Right side XS Separate structure

What this code covers

Source · Editorial summary grounded in 6 cited references ↓

CPT 27330 describes an open arthrotomy of the knee joint performed for the sole purpose of synovial biopsy. The surgeon incises the knee joint capsule, harvests synovial tissue, and closes the wound. Because the code's scope is limited to biopsy only, it does not cover joint exploration, removal of loose bodies, or synovectomy — each of those scenarios maps to a different arthrotomy code (27331 through 27335).

Code selection within the 27330–27335 family hinges on exactly what was done inside the joint. If your operative note documents anything beyond tissue sampling — exploration, loose body removal, or synovectomy — 27330 is not the right code. Upgrade to 27331 for exploration or loose body removal, 27334/27335 for synovectomy. Laterality modifiers LT and RT apply when the payer requires them; always confirm payer-specific requirements before submitting.

The 90-day global period means all routine post-op visits through day 90 are bundled. The MUE for 27330 is 1 unit per outpatient encounter. If a separate, distinct procedure is performed at the same session that isn't bundled into the arthrotomy, append modifier 59 or an X-modifier with documentation supporting a separate indication.

RVU & reimbursement

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

Source · CMS Physician Fee Schedule, RVU26A · January 2026

Work RVU	4.98
Practice expense RVU	6.31
Malpractice RVU	1.07
Total RVU	12.36
Medicare national rate	$412.84
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	$412.84
HOPD (APC 5113) Hospital outpatient department	$3,342.87
ASC (PI A2) Ambulatory surgical center (freestanding)	$1,644.87

Common denial reasons

The recurring reasons claims for CPT 27330 get rejected.

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

Code mismatch: operative note documents joint exploration or loose body removal, making 27330 a down-coded error that triggers post-payment audit.
Missing laterality when payer policy requires LT or RT modifier — claim routes to manual review or rejects outright.
Lack of documented medical necessity: payer requires evidence of failed conservative workup or specific clinical indication before authorizing an open synovial biopsy.
Unbundling attempt: billing 27330 alongside a same-session arthroscopic knee procedure on the same joint — arthroscopic synovial sampling is captured within the arthroscopy code family.
Global period conflict: post-op visit or related service billed without modifier 24 within the 90-day global window following a prior knee procedure.

Frequently asked questions

Source · Generated from the editorial pipeline, verified against 6 cited references ↓

01What is the difference between 27330 and 27331?

27330 is biopsy only. The moment your operative note documents joint exploration or removal of a loose or foreign body in addition to the biopsy, you must use 27331. Billing 27330 when exploration occurred is a coding error, not a conservative choice.

02Can 27330 be billed on the same day as a knee arthroscopy on the same joint?

No. Arthroscopic procedures include diagnostic evaluation of the joint by NCCI policy. Billing an open synovial biopsy alongside a same-session knee arthroscopy on the same joint constitutes unbundling and will generate an NCCI edit.

03Do I need a laterality modifier for 27330?

Most commercial payers and many Medicare contractors require LT or RT. Confirm your payer's policy. Submitting without laterality when it's required typically routes the claim to manual review or triggers a rejection.

04What ICD-10 diagnoses typically support 27330?

Common supporting diagnoses include inflammatory arthropathies (M06.x, M05.x), pigmented villonodular synovitis (M12.2x), crystal-induced synovitis, and unspecified joint effusion with synovial thickening when prior imaging and aspiration have been inconclusive. The diagnosis must reflect why open biopsy — rather than arthroscopic or needle biopsy — was medically necessary.

05What is the MUE for 27330 and what does it mean practically?

The MUE is 1. You can bill only one unit of 27330 per outpatient encounter regardless of how many synovial samples were taken. Multiple specimens from the same arthrotomy do not create additional billable units.

06If a planned 27330 is converted to an open synovectomy intraoperatively, how do I code it?

Bill the synovectomy code (27334 or 27335 depending on extent), not 27330. You cannot bill both. The arthrotomy access and any incidental biopsy are bundled into the synovectomy code. Document the intraoperative finding that changed the surgical plan.

07Does the 90-day global period for 27330 affect billing for a subsequent knee replacement on the same knee?

If the total knee arthroplasty is a planned staged procedure, use modifier 58 on the TKA. If it's unrelated to the biopsy, modifier 79 applies. Do not leave the global period relationship undocumented — payers will deny the subsequent surgery claim without the correct modifier and supporting documentation.

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 stated scope of the arthrotomy from dictation — confirming that the procedure was limited to synovial biopsy with no concurrent exploration, loose body removal, or synovectomy. It also logs laterality and the specific intra-articular location of tissue harvest. This prevents the most common audit trigger for 27330: an operative note that inadvertently describes a more extensive procedure, forcing a code upgrade or triggering a post-payment take-back.

See how Mira captures CPT 27330 documentation