What this is
A reference note on genicular artery embolisation (GAE), why a procedure aimed at the blood supply makes sense for knee osteoarthritis pain, the anatomy on the screen, and what the embolic options look like. We see this very rarely, no more than a case every couple of years, so these notes are background reading rather than a working protocol.
Why This Procedure Works at All
The thing GAE turns on is a relatively recent shift in how knee osteoarthritis is understood. The classical story is that pain comes from cartilage wear, bone-on-bone contact, and joint mechanics. That’s still partly true. But a lot of the chronic pain in OA, particularly the deep ache that doesn’t track tightly with how the cartilage looks on MRI, is driven by inflammation of the synovium and the small new blood vessels that grow into it.
Picture a quiet road that, over time, has sprouted dozens of little side roads supplying new buildings. Those side roads are the neovascular sprouts that grow into the inflamed synovial lining of an arthritic knee, and along every one of them are tiny pain-carrying nerve fibres. Blood flow, inflammation, and pain end up reinforcing each other in a feedback loop.
The whole logic, in one line
Cut the neovascular blood supply feeding the inflamed synovium, and the inflammation, and the pain that travels with it, settle down.
The literature describes meaningful pain relief in roughly two thirds to four fifths of patients at twelve months, and the patients who do best are the ones with moderate radiographic OA (Kellgren-Lawrence grade 2 or 3) and pain that’s well out of proportion to what their imaging says it should be. Bone-on-bone end-stage knees do less well, the joint mechanics are doing most of the work at that point.
The patients described in the literature are typically in one of two camps. Patients with moderate OA who’ve exhausted conservative measures (analgesia, physio, weight loss, intra-articular steroid or hyaluronic injections) but aren’t ready for a knee replacement, either because they’re not bad enough or because surgery isn’t an option for them. And patients with persistent pain after a knee replacement, sometimes from residual synovial inflammation, where GAE has a separate evidence base.
The Anatomy
The screen during the case is essentially a moving map of the small arteries supplying the knee. The popliteal artery, which runs down the back of the knee, gives off a fan of named branches that wrap around the joint. There are five main ones to know.
Femoral artery
→ Popliteal artery
→ Descending genicular artery (a small branch off the femoral)
→ Superior medial genicular artery
→ Superior lateral genicular artery
→ Middle genicular artery (supplies the cruciate ligaments)
→ Inferior medial genicular artery
→ Inferior lateral genicular artery
The descending genicular comes off the femoral artery before the popliteal proper begins, and supplies the upper inner part of the knee. The superior and inferior pairs flank the joint at four corners. The middle genicular feeds the cruciate ligaments and is often left alone because it doesn’t tend to supply the painful synovium.
What the doctor is looking for in the angiogram is hypervascular blush in one or more of these territories, a fluffy patch of contrast in the synovium that corresponds to the part of the knee that hurts. It looks much like the blush in a tumour case, just smaller and at the edge of a joint instead of in an organ. A patient with medial knee pain almost always has the densest blush in the superior or inferior medial genicular territory. The match between where the pain lives and where the blush lights up is the thing that decides whether the case will actually help.
Variant anatomy is common
The number, calibre, and exact origins of the genicular branches vary between people. Most patients have all five, but a third have some sort of variant, an accessory branch, a shared origin, a smaller-than-expected middle genicular. The diagnostic run at the start of the case is what sorts this out for the individual knee.
The connections worth knowing about are the anastomoses around the patella, the so-called peripatellar arterial ring. These link the superior and inferior genicular arteries at the front of the knee, and a few of them run close to the skin. Non-target embolisation through the peripatellar ring is the mechanism behind one of the more common minor complications, a patch of skin discolouration over the knee that fades over weeks.
How a Case Unfolds
Access is through the common femoral artery, usually on the opposite side from the knee being treated so the catheter has a clean angle into the popliteal. Radial access is also possible and is used in some centres, but the catheter lengths required (around 150 cm to reach the knee from the wrist) and the gentler angles available from the groin make the femoral approach the default for most operators.
Once the sheath is in, a diagnostic catheter goes down the aorta, across the bifurcation, and into the superficial femoral artery on the side of interest. Iodinated contrast (we use Omnipaque) is run through to map the genicular branches. A cone-beam CT through the knee at this point is becoming standard. It picks up small branches that flat fluoroscopy misses and gives the operator a clear picture of which territories the symptomatic synovium is sitting in.
A microcatheter (Progreat, Renegade, or similar) is then advanced over a fine wire into each genicular branch that maps to the patient’s pain. Common targets in a medial-pain case are the superior medial and inferior medial genicular arteries. Selectivity matters here, the microcatheter needs to sit beyond the takeoff of any non-target vessels, particularly any branches running toward skin, before any embolic goes in.
The match between pain and blush is what makes the case work
Embolising every visible branch isn’t the point, and isn’t safe. The operator is treating the territories that light up and correspond to where the patient says the pain is. A case where the pain map and the angiographic map don’t agree is a case where embolisation probably won’t help, and the team may stop at the diagnostic run.
The embolic agent is where international practice splits. Two main options are used.
Imipenem-Cilastatin sodium suspension (IPM/CS) is the original Japanese protocol, developed by Okuno’s group, and still the dominant agent in much of Asia. It’s an antibiotic powder mixed with iohexol to form a slurry, and the particles transiently occlude the small vessels before dissolving over a few hours. The advantage is the temporary nature of the blockage, the disadvantage is the off-label status and the variability in particle size between batches.
Calibrated microspheres, typically 100 to 300 micron Embospheres or similar (Embozene, HepaSphere), are the Western default. They permanently occlude the small synovial vessels but are easier to deliver, more predictable in behaviour, and on-label for peripheral embolisation. Most US and European centres use these.
The injection is slow and deliberate. The doctor watches for the moment the blush stops filling and pruning of the small branches becomes visible. That’s the endpoint, not a complete arterial cutoff. The peripatellar ring and any cutaneous branches are watched throughout because a small amount of reflux toward the skin can be enough to cause discolouration afterwards.
A final angiogram confirms the treated territories are quiet and the surrounding non-target vessels are intact. The sheath comes out, the groin gets either firm pressure for 15 to 20 minutes or a small closure device, and the patient walks to recovery once the leg checks are clean.
The whole case typically runs 45 minutes to a couple of hours depending on how many territories need treating and how much CBCT work the operator does.
What Follows the Procedure
Most patients walk out the same day. The immediate post-procedure observation is the standard groin-access protocol, 2 to 4 hours flat in bed (or shorter if a closure device was used), monitoring the puncture site, distal pulses, and the leg for colour and warmth.
The pain relief is not immediate. The synovium needs time to settle after the embolisation, and most patients describe a gradual improvement over two to six weeks, with the full effect usually present by three months. About a third of patients have a transient flare in knee pain in the first few days, which is the post-embolisation inflammatory response, manageable with simple analgesia and settles within a week.
Worth flagging to the patient before they go
The procedure isn’t a one-off cure. It’s a way of buying time and quality of life for a knee that isn’t ready for replacement yet. The literature suggests average durability of around two to three years before pain begins to creep back, though some patients hold their improvement for considerably longer. Repeat embolisation is feasible and sometimes done.
Complications are mostly minor. The most common is a patch of skin discolouration over the front of the knee, seen in roughly 1 in 10 patients, from minor non-target embolisation through the peripatellar arterial ring. It fades over weeks. Transient mild knee pain or stiffness in the first few days is expected. Groin haematoma is the standard access-site risk, no more common here than for any femoral case. Rarer events include skin or muscle ischaemia from significant non-target embolisation, infection, and the usual contrast reactions.
What needs a phone call back
Severe or escalating knee pain not settling with analgesia, fever, expanding skin discolouration or skin breakdown over the knee, new neurological symptoms in the leg, signs of significant access-site bleeding. None of these are common, but they’re what gets flagged on the discharge sheet.
Where This Sits in Practice
GAE is still a relatively young procedure outside Japan. The first case series were published in the early 2010s, and the bigger randomised trials are only now starting to mature. The current evidence supports it as a reasonable option for patients who fit the indication profile, but it isn’t a default treatment yet and isn’t reimbursed everywhere. Most centres doing it position it as an option between failed conservative care and knee replacement, particularly for patients who want to delay or avoid surgery.
For us this is an occasional procedure at most, a couple of cases across several years, usually one of the doctors taking on a referral where the patient has run out of other options. The technique itself overlaps with the small-vessel embolisation work the team does regularly, so the catheter side isn’t the issue. The bits that get cold between cases are patient selection, the angiogram-to-pain mapping, and the careful titration of embolic delivery. That’s the actual reason for keeping a reference note like this.
Numbers Worth Knowing
| Stat | Value | Why it matters |
|---|---|---|
| Pain relief at 12 months | ~70–80% of well-selected patients | Most published series; effect is meaningful, not curative |
| Patients with KL grade 2–3 OA respond best | Grade 4 (bone-on-bone) does worse | Patient selection is where the case is won or lost |
| Skin discolouration (most common minor complication) | ~10% | From peripatellar collateral non-target embolisation, transient |
| Onset of pain relief | 2 to 6 weeks, full effect by 3 months | Manage patient expectations on the day |
| Typical durability before pain returns | 2 to 3 years in series with longer follow-up | Repeat treatment is feasible |
| Embolic particle size (microspheres) | 100 to 300 µm | Small enough to reach synovial neovasculature |
| Genicular arteries usually targeted | 2 to 4 of the 5 | Driven by the pain map, not the angiogram alone |
| Case duration | ~45 to 120 minutes | Variable with number of targets and CBCT use |
Related
- Bland TAE — Embolisation Agents, deeper look at the embolic agents used here and elsewhere
- Liver Tumour Embolisation, same arterial-catheter approach, different territory
- Acetabulum Tumour Embolisation, another small-vessel embolisation around bone and joint
Sources
- Transcatheter Arterial Embolization as a Treatment for Medial Knee Pain in Patients with Mild to Moderate Osteoarthritis — Okuno et al., CVIR
- Geniculate Artery Embolization for the Treatment of Knee Osteoarthritis — JVIR Review
- Genicular Artery Embolization for Knee Pain — Radiology Society Practice Parameters
- Long-term outcomes of geniculate artery embolization for moderate to severe osteoarthritis — Cardiovascular and Interventional Radiology
- Systematic Review and Meta-Analysis of Genicular Artery Embolization for Knee Osteoarthritis — JVIR
- Genicular Artery Embolization for the Treatment of Knee Osteoarthritis Pain — RSNA RadioGraphics
- Cilastatin Sodium as an Embolic Agent — technical note
- The Peripatellar Anastomotic Ring and Implications for Genicular Artery Embolization — Skeletal Radiology
- Genicular Artery Embolization for Persistent Pain After Total Knee Arthroplasty — JVIR
- Embospheres Microspheres — Merit Medical product information
Last updated May 18, 2026.