Arthroscopy · Knee

Open arthrotomy of the knee joint for exploration, biopsy, or removal of loose or foreign bodies.

Verified May 8, 2026 · 6 sources ↓

Medicare: $459.60
Total RVUs: 13.76
Global, days: 90
Region: Knee

Drawn from CMSAAPCFindacodeAAOS

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 an open arthrotomy (not arthroscopic) and document the incision size and location
Identify the clinical indication: loose body size and location, foreign body description, or biopsy target — including why an open approach was required
If converted from arthroscopic to open, document what was accomplished arthroscopically before conversion and why the open approach became necessary
Record all findings within the joint compartments explored (e.g., patellofemoral, medial, lateral), including cartilage and synovial status
Document specimen sent to pathology if biopsy was taken, including the tissue source
If modifier 22 is appended, include a narrative in the operative note explaining the increased complexity, additional time, or unusual circumstances

Applicable modifiers

Modifiers commonly billed with this code.

Source · AMA CPT modifier descriptors · CMS NCCI Policy Manual

22 Increased complexity 24 Unrelated E/M during global 51 Multiple procedures 52 Reduced services 58 Staged or related 59 Distinct service 78 Unplanned return — related 79 Unrelated during global 80 Assistant surgeon AS PA/NP/CNS assistant LT Left side RT Right side

What this code covers

Source · Editorial summary grounded in 6 cited references ↓

CPT 27331 covers an open arthrotomy of the knee — not an arthroscopic procedure — performed to explore the joint, obtain a biopsy, or extract loose or foreign bodies. The code applies when the surgeon opens the knee joint through an incision to accomplish one or more of those goals. A classic trigger: an arthroscopic approach is initiated but converted to open surgery because a loose body (e.g., a fragment too large to extract through the scope) cannot be retrieved arthroscopically. In that scenario, both 27331 and the arthroscopic code (e.g., 29881 for meniscectomy) can be reported if the arthroscopic work was distinct and separately completed.

The 90-day global period means all routine post-op care is bundled through day 90. Any E/M visit in that window for a new or unrelated problem requires modifier 24; a separate procedure during the global for an unrelated condition requires modifier 79. If a complication requires a return to the OR for a related procedure, use modifier 78. Modifier 22 is appropriate when the procedure is substantially more complex than typical — document the added time and difficulty explicitly in the operative note.

Site of service matters here: HOPD and ASC reimbursement differ significantly (see the Site of Service comparison table). Most 27331 cases are performed in an ASC or hospital outpatient setting. Payers including Medicare require medical necessity documentation linking the open approach to a specific clinical indication — a loose body that could not be addressed arthroscopically is a well-supported justification.

RVU & reimbursement

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

Source · CMS Physician Fee Schedule, RVU26A · January 2026

Work RVU	5.87
Practice expense RVU	6.66
Malpractice RVU	1.23
Total RVU	13.76
Medicare national rate	$459.60
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	$459.60
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 27331 get rejected.

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

Lack of medical necessity documentation justifying an open approach over arthroscopic technique
Bundling conflict when 27331 is billed same-day with an arthroscopic knee code without adequate documentation that each procedure was distinct and separately performed
Missing or insufficient operative note detail — noting only 'exploration performed' without describing findings, approach, and clinical rationale
Modifier 22 appended without a supporting narrative, triggering automatic downcode or denial on review
Billing 27331 during the global period of a prior knee procedure without modifier 79 (unrelated) or 78 (related complication)

Frequently asked questions

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

01Is 27331 an arthroscopic code?

No. 27331 is an open arthrotomy. Arthroscopic knee procedures bill under the 29870–29889 range. If you started arthroscopically and converted to open, you can bill the completed arthroscopic work separately alongside 27331, with appropriate modifiers and documentation of what each approach accomplished.

02Can 27331 and 29881 be billed together on the same date?

Yes, when the arthroscopic meniscectomy (29881) was fully performed and then a separate open arthrotomy (27331) was required to remove a loose body too large for arthroscopic retrieval. Document each procedure independently. Modifier 59 or XS on the secondary code may be required to bypass NCCI edits — verify current edit status before billing.

03What modifiers are most commonly needed with 27331?

LT or RT to lateralize the procedure. Modifier 51 when it's the secondary procedure in a multi-procedure session. Modifier 59 or XS if billed alongside an arthroscopic knee code to establish procedural independence. Modifier 22 for unusually complex cases, supported by a written narrative in the operative note.

04What is the global period for 27331, and what does it cover?

27331 carries a 90-day global period. That covers the day-before surgical visit, the procedure itself, and all routine post-op care through day 90 — including dressing changes, suture removal, and standard follow-up. Unrelated E/M visits in that window need modifier 24; unrelated procedures need modifier 79.

05When does modifier 78 apply after 27331?

Use modifier 78 if the patient returns to the OR within the 90-day global for a complication directly related to the original 27331 procedure — for example, evacuation of a post-op hematoma. Do not use 78 for unrelated procedures; that's modifier 79.

06What ICD-10 diagnoses typically support 27331?

M23.40–M23.42 (loose body in knee), M23.200–M23.202 (derangement of unspecified meniscus), S80–S89 range codes for acute traumatic foreign body, and M65/M67 codes for synovial pathology requiring biopsy. The diagnosis must directly support the open approach — payers flag 27331 with diagnoses that would typically be managed arthroscopically.

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 approach (open arthrotomy vs. arthroscopic), the joint compartments entered, the specific pathology addressed (loose body dimensions and location, foreign body description, or biopsy site), and — if conversion from arthroscopy occurred — what was accomplished before conversion and the clinical reason for it. That level of detail prevents the most common denial: a payer downgrading or rejecting 27331 because the operative note doesn't justify why an open approach was necessary.

See how Mira captures CPT 27331 documentation