Surgical · Knee

Surgical disarticulation at the knee joint, separating the tibia and fibula from the femur without cutting through bone.

Verified May 8, 2026 · 6 sources ↓

Medicare: $645.31
Work RVU: 10.94
Global, days: 90
Region: Knee

Drawn from CMSAAPCMdclarityCodingmasteryEmedny

Documentation requirements

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

Source · Editorial brief grounded in 6 cited references ↓

Operative note must identify the procedure as disarticulation at the knee joint, not transtibial or transfemoral amputation
Document the surgical indication explicitly — trauma, vascular disease, infection, or oncologic necessity — with supporting clinical findings
Specify laterality (right or left) in both the operative note and the diagnosis codes to support LT/RT modifier use
Record the technique used for soft-tissue management, including handling of cruciate ligaments, collateral ligaments, and patella
Note the wound closure method or whether the wound was left open (guillotine/open circular), as this affects subsequent staging claims
Include pre-operative imaging, vascular studies, or infectious workup findings that support the medical necessity decision

Applicable modifiers

Modifiers commonly billed with this code.

Source · AMA CPT modifier descriptors · CMS NCCI Policy Manual

22 Increased complexity 50 Bilateral procedure 51 Multiple procedures 58 Staged or related 59 Distinct service 62 Co-surgeons 76 Repeat, same physician 78 Unplanned return — related 79 Unrelated during global 80 Assistant surgeon LT Left side RT Right side

What this code covers

Source · Editorial summary grounded in 6 cited references ↓

CPT 27598 describes disarticulation at the knee — an amputation performed through the knee joint itself rather than through the tibial or femoral shaft. Because no bone is transected, the surgeon works through soft tissue and cartilaginous structures to disengage the tibia and fibula from the distal femur. The intact femoral condyles remain, allowing the patient to bear partial weight on the residual limb end, which has functional advantages over transfemoral amputation.

This procedure carries a 90-day global period. All routine post-op wound checks, dressing changes, and stitch removals through day 90 are bundled — bill unrelated E/M visits in that window with modifier 24 or unrelated procedures with modifier 79. A planned staged procedure (e.g., revision or formal closure after open/guillotine preparation) uses modifier 58.

Indications typically include severe lower extremity trauma, vascular disease with non-viable tissue, uncontrolled infection, or malignancy requiring limb-level sacrifice. Document the specific indication with supporting ICD-10 diagnosis codes, because payers routinely request medical necessity records on amputation claims.

RVU & reimbursement

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

Source · CMS Physician Fee Schedule, RVU26A · January 2026

Work RVU vs. total RVU

The work RVU (10.94) is the surgeon's own effort — the figure physician pay and productivity targets are built on. The total RVU (19.32) adds practice overhead and malpractice, and is what drives the Medicare payment below.

Work RVU	10.94
Practice expense RVU	5.71
Malpractice RVU	2.67
Total RVU	19.32
Medicare national rate	$645.31
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	$645.31
HOPD (APC 5113) Hospital outpatient department	$3,342.87
ASC (PI G2) Ambulatory surgical center (freestanding)	$1,644.87

Common denial reasons

The recurring reasons claims for CPT 27598 get rejected.

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

Medical necessity not established — payer requests vascular studies, wound care records, or prior treatment history before approving amputation
Laterality missing or mismatched between the claim modifier and the operative/diagnostic documentation
Procedure billed as transtibial (27880) or transfemoral (27590) instead of disarticulation at knee (27598), driven by an ambiguous operative note
Global period violation — post-op E/M visits billed without modifier 24 within the 90-day window
Incorrect modifier 78 vs. 79 on a return-to-OR claim during the global period, causing the related/unrelated distinction to fail edit

Frequently asked questions

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

01What is the difference between CPT 27598 and CPT 27880?

27598 is disarticulation through the knee joint — no bone is cut. CPT 27880 is amputation of the leg through the tibia and fibula (transtibial). The distinction is anatomic level: 27598 preserves the full femur and disengages at the joint; 27880 transects the tibial and fibular shafts below the knee. Choose the code that matches where the surgeon actually separated the limb.

02Does 27598 require a laterality modifier?

Yes. Append LT or RT on every claim. Bilateral amputation at the knee is exceptionally rare but would use modifier 50. Payers routinely deny amputation claims lacking laterality because the diagnosis codes also need to reflect side, and a mismatch triggers medical review.

03How long is the global period for 27598?

90 days. The global period begins the day of surgery and covers all routine post-operative care through day 90. Unrelated E/M visits in that window require modifier 24; unrelated procedures require modifier 79; a planned staged procedure (such as formal closure after an open amputation) requires modifier 58.

04Can 27598 be billed with a wound closure or revision code in the same session?

Generally no — myodesis, soft-tissue shaping, and primary closure are considered part of the amputation procedure and bundled into 27598. If a separate, distinct reconstructive procedure is performed that is not integral to the amputation, use modifier 59 with strong operative note support. Expect scrutiny and a medical review request.

05What ICD-10 codes most commonly support 27598 for medical necessity?

Common supporting diagnoses include critical limb ischemia (I70.261–I70.269 range), gas gangrene or necrotizing fasciitis (A48.0, M72.6), traumatic crush injury or open fracture with non-reconstructible soft tissue, and malignant neoplasm of the knee region. The specific code should match the clinical documentation precisely — payers match diagnosis to procedure for amputation claims.

06Is 27598 performed in an ASC, and does the site of service affect payment?

27598 is on the ASC covered procedures list. The HOPD and ASC payment rates differ — see the Site of Service comparison table on this page. Most disarticulations at the knee are performed in a hospital outpatient or inpatient setting given the acuity of the underlying condition, but ASC billing is valid when the clinical situation permits.

Sources & references

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

Mira Scribe

Mira's AI scribe captures the exact level of amputation (disarticulation through the knee joint vs. transtibial or transfemoral), the surgical indication with supporting clinical context, laterality, and wound management approach from the surgeon's dictation. That prevents the most common upcoding or downcoding flag — where a vague operative note triggers a re-audit to determine whether 27598, 27880, or 27590 was actually performed.

See how Mira captures CPT 27598 documentation