Patellar arthroplasty with insertion of a prosthetic implant to resurface the kneecap.

Verified May 8, 2026 · 6 sources ↓

Medicare: $781.92
Total RVUs: 23.41
Global, days: 90
Region: Knee

Drawn from CMSNimblercmZimmerbiometAAPC

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 a prosthetic implant was placed — not just patellar shaping or debridement without prosthesis
Identify the implant used (manufacturer, model, lot number) and confirm it is distinct from a full TKA patellar component
Document preoperative diagnosis with imaging (e.g., standing X-rays, MRI) confirming isolated patellar pathology warranting prosthetic replacement
Describe the surgical technique: patellar preparation, sizing, cementing or press-fit fixation method, and tracking assessment
If performed alongside another knee arthroplasty code, clearly describe each component addressed to support separate billing
When infection, pain, or functional disability is the indication, document how conservative treatment failed prior to surgical intervention

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 25 Significant separate E/M 51 Multiple procedures 52 Reduced services 58 Staged or related 59 Distinct service 62 Co-surgeons 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 27438 covers arthroplasty of the patella with prosthesis — specifically, the surgical resurfacing or replacement of the patellar articulating surface using an implanted component. This is distinct from 27437, which is the same procedure performed without a prosthesis. The 90-day global period means all routine post-op care through day 90 is bundled into the payment; separate E/M services during that window require modifier 24.

27438 is used when the patella alone is being addressed with an implant — not when a full patellofemoral arthroplasty (trochlear groove + patella) is performed. Per updated AMA guidance, patellofemoral arthroplasty — which involves both patellar resurfacing and trochlear groove resurfacing — should be reported with the unlisted knee code 27599, not 27438. Using 27438 for a combined patellofemoral case understates the work and invites downcoding disputes.

When 27438 is performed in the same operative session as a tibial or femoral component arthroplasty (e.g., as an add-on to 27446 or 27447), modifier 51 applies to the secondary procedure. If billing the patellar component as part of a revision scenario — for example, isolated patellar component exchange within an existing TKA — review whether 27486 or 27487 more accurately captures the full scope of work before defaulting to 27438.

RVU & reimbursement

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

Source · CMS Physician Fee Schedule, RVU26A · January 2026

Work RVU	11.59
Practice expense RVU	9.39
Malpractice RVU	2.43
Total RVU	23.41
Medicare national rate	$781.92
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	$781.92
HOPD (APC 5115) Hospital outpatient department	$13,116.76
ASC (PI A2) Ambulatory surgical center (freestanding)	$6,804.43

Common denial reasons

The recurring reasons claims for CPT 27438 get rejected.

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

27438 billed for patellofemoral arthroplasty (combined trochlear + patellar resurfacing) — correct code is unlisted 27599
Missing implant documentation: payer cannot confirm a prosthesis was placed versus a non-prosthetic patellar arthroplasty (27437)
Global period conflict: post-op E/M billed without modifier 24 when an unrelated condition is the stated reason
Modifier 51 missing when 27438 is billed same-day with a primary knee arthroplasty code such as 27446 or 27447
Medical necessity not supported: preoperative imaging or documented failure of conservative care absent from the record

Frequently asked questions

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

01What is the difference between 27437 and 27438?

27437 is patellar arthroplasty without a prosthesis — typically a patelloplasty or reshaping procedure. 27438 requires placement of an implant. The distinction is binary: if a prosthetic component was implanted, use 27438; if not, use 27437.

02Can I bill 27438 for patellofemoral arthroplasty?

No. The AMA updated its guidance: patellofemoral arthroplasty — which resurfacts both the patella and the trochlear groove — should be reported with unlisted code 27599. Using 27438 alone understates the work performed and will not capture trochlear groove resurfacing.

03How do I bill 27438 when it is performed at the same session as a unicompartmental or total knee arthroplasty?

Append modifier 51 to 27438 as the secondary procedure. Ensure the operative note documents both components separately and that 27438 represents distinct patellar work with a prosthesis beyond what is included in the primary arthroplasty code.

04Does the 90-day global period apply to 27438?

Yes. All routine post-op care is bundled through day 90. Separately billing an E/M during that window requires modifier 24 (unrelated condition) or modifier 25 (significant, separately identifiable service on the day of the procedure). Document clearly why the visit is outside the global.

05If a patellar component from an existing TKA is being exchanged in isolation, is 27438 the right code?

Not automatically. Isolated patellar component exchange within an existing TKA system can be a gray area — review whether 27486 (revision TKA, one component) better reflects the work. 27438 is more appropriate when the patella is being primarily resurfaced and the rest of the joint is native or not being revised.

06What HCPCS code reports the implant in an outpatient or ASC setting?

Report C1776 (joint device, implantable) alongside 27438 when billing under OPPS or ASC. This is required for Medicare outpatient facility claims to capture the device cost separately under the pass-through or device-intensive payment structure.

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 implant type and fixation method from dictation, flags whether the procedure was isolated to the patella or included trochlear groove work (which would shift the code to 27599), and logs the patellar tracking assessment. This prevents the most common audit trigger — operative notes that don't explicitly confirm prosthesis placement or that conflate isolated patellar arthroplasty with full patellofemoral arthroplasty.

See how Mira captures CPT 27438 documentation