A total knee replacement (the procedure code is 27447) is one of the most common major surgeries in the country, and nearly every insurer requires prior authorization for it. The good news is that the criteria are remarkably consistent across insurers — they converge on the same clinical standard — so once you know what the checklist looks like, you can walk in with everything it needs.
Across Aetna, Cigna, Anthem, UnitedHealthcare and Medicare, a knee replacement for osteoarthritis is considered medically necessary when all of the following are documented:
The differences between insurers are smaller here than for many procedures — but they exist, mostly in how long the conservative-care trial has to be and how the criteria are administered:
| Insurer | Imaging requirement | Conservative-care trial | Source policy (2026) |
|---|---|---|---|
| Cigna | Kellgren-Lawrence Grade 3–4 | ≥ 3 months (provider-directed) | eviCore MSK CMM-311 |
| Aetna | Kellgren-Lawrence Grade 3–4 | ≥ 3 months (provider-directed) | eviCore MSK CMM-311 |
| Anthem / Elevance | Kellgren-Lawrence Grade 3–4 | ≥ 12 weeks (waived at Grade 4) | Carelon Joint Surgery |
| UnitedHealthcare | Advanced OA grade (via InterQual) | Required (via InterQual) | Surgery of the Knee → InterQual |
| Medicare | Advanced osteoarthritis | Expected (per-MAC LCD) | CMS — no national prior auth |
| Medicaid | Varies by state — check your state's policy | State Medicaid manual | |
One nuance worth knowing: Anthem waives the conservative-care trial when your X-ray is already Kellgren-Lawrence Grade 4 (truly bone-on-bone) — at that point the imaging speaks for itself. Most other insurers still want the trial documented, or a surgeon's note explaining why it isn't appropriate.
Denials almost never say "we don't think you need a new knee." They say the request is missing a piece the checklist expects:
Walk in with the recent X-ray showing the grade, the three months of conservative care, and the functional limitations documented, and most knee-replacement requests turn into approvals.
Answer a few plain questions about your X-ray and treatment so far, and see exactly where you stand against your insurer's real criteria — plus what to document if you're not there yet.
Check my knee coverageMost insurers require severe osteoarthritis at Kellgren-Lawrence Grade 3 or 4 — commonly called "bone-on-bone" — on a weight-bearing X-ray, or the equivalent severe cartilage loss on MRI or arthroscopy. Moderate (Grade 2) changes generally don't qualify yet, regardless of how much pain you're in. A recent weight-bearing film that clearly documents the grade is the single most important piece of the request.
Generally yes. Insurers want about three months of documented provider-directed conservative care — physical therapy, anti-inflammatory or pain medication, injections, and activity modification — before approving the surgery. The exception is when your surgeon documents a specific reason that non-surgical care isn't appropriate for you, and Anthem also waives the trial when your X-ray is already Kellgren-Lawrence Grade 4.
Medicare has no national prior-authorization requirement for inpatient knee replacement, and the procedure is no longer on the "inpatient-only" list. Coverage still depends on medical necessity — advanced arthritis plus a failed conservative-care trial — and some regional contractors (MACs) publish local coverage determinations with their own specifics.
A high BMI usually isn't an absolute denial, but surgeons are expected to optimize modifiable risks — weight, blood sugar (A1c), and smoking — before surgery, and a very high BMI can pause approval for optimization first. It's worth addressing early so it doesn't delay the procedure.
Almost always one of three things: the X-ray wasn't severe enough (or wasn't recent), the conservative-care trial wasn't documented, or modifiable risk factors hadn't been addressed. These are fixable — a fresh weight-bearing X-ray documenting Grade 3–4, the dates and details of your physical therapy and medications, and a note on your functional limitations usually turn a denial into an approval.
Yes, all of them cover medically necessary knee replacement. Cigna and Aetna administer the criteria through eviCore (Kellgren-Lawrence Grade 3–4 plus a roughly three-month conservative-care trial); UnitedHealthcare adjudicates through InterQual on the same advanced-arthritis-plus-failed-conservative-care standard. The documentation they want is essentially the same across all three.
It varies by insurer and how complete the request is, but a clean request — recent X-ray showing the grade, documented conservative care, and functional limitations — is typically decided within a few business days. Missing documentation is what causes delays, because it triggers a request for more information or an outright denial that then has to be appealed.
Yes. A partial knee replacement has its own criteria — the severe arthritis must be isolated to one compartment of the knee with the others relatively preserved, the ligaments intact, and the deformity within set limits. If arthritis involves more than one compartment, insurers generally expect a total knee replacement instead.
Related: Knee & hip replacement coverage checker · Why prior authorizations get denied · all coverage tools