Taking A Knee
By Beth W. Orenstein
Radiology Today
Vol. 26 No. 8 P. 14
Effective, Minimally Invasive Procedure Relieves Osteoarthritis Joint Pain
In the United States, more than 32.5 million adults have osteoarthritis (OA), with the knee being the most common site, according to the CDC. Between 1990 and 2021, the prevalence of knee OA increased by more than 100%, and it is only expected to continue to rise due to factors such as an aging global population and rising obesity rates, according to a study published in June 2025 in PLoS One. OA of the knee can cause severe pain, stiffness, and swelling and is often disabling.
Traditional treatments range from physical therapy and pain medications to joint replacement surgery. A relatively new, minimally invasive IR procedure known as genicular artery embolization (GAE) is gaining traction worldwide.
“It is one of the hottest topics in IR today,” says John David Prologo, MD, FSIR, a professor and division director of IR and vice chair of imaging interventions in the department of radiology and imaging sciences at Emory University School of Medicine in Atlanta. Prologo is an early adopter of GAE who has been performing the procedure for about seven years.
Yuji Okuno, MD, and colleagues at the Okuno Clinic in Tokyo, Japan, were the first to write about the modern clinical concept, 10 years ago. Prior to that, GAE had been used for recurrent bleeding into the knee joint after knee replacement but not generally for OA.
“Then it spread around the world,” says Florian Nima Fleckenstein, MD, an interventional radiologist at Charité – University Hospital Berlin in Germany.
Today, Prologo adds, GAE is performed at most academic centers and at several free-standing centers in the United States. “Finding an interventional radiologist near you will likely result in finding someone who does it, but, if not, they certainly will know someone who does,” Prologo says. Also, Prologo notes, quite a few clinical trials involving GAE are enrolling patients.
Fleckenstein says interventional radiologists routinely block blood vessels to stop bleeding and treat fibroids or enlarged prostates. They also use blood vessel blocking to treat cancers and other conditions. “The idea of doing that in the setting of osteoarthritis was revolutionary and brilliant,” he says.
Interrupts Disease Process
During GAE, an interventional radiologist uses fluoroscopy to guide a microcatheter through the femoral artery to target the genicular arteries that supply blood to the inflamed synovium—the thin, soft, connective tissue membrane that lines the inner surface of the knee. Then the interventional radiologist injects embolic particles that selectively block blood flow to the inflamed area of the knee, which reduces pain and inflammation.
The entire procedure is performed through a single pinhole puncture, Prologo says. The procedure is performed on an outpatient basis and generally takes about two to three hours, says Ryan Hickey, MD, an interventional radiologist at the NYU Grossman School of Medicine in New York, who also performs the procedure at NYU Langone.
Current treatments such as pain medication and steroid injections only mask the symptoms of OA. They do not slow progression of the disease. As OA worsens and conservative treatments become ineffective, many people turn to joint replacement surgery.
Studies have shown that GAE is a promising alternative for those with knee OA who are unable or don’t want to undergo knee replacement, Fleckenstein says. “GAE could potentially offer a new lease on life for many patients who suffer from debilitating pain and mobility issues caused by OA and especially for people who haven’t had success with other treatments such as physical therapy or pain meds,” he adds. “I personally like it because it interrupts the disease process, which is so much different from simply blocking pain.”
Positive Research Findings
Research has shown that GAE is safe and effective. At RSNA 2024, Fleckenstein reported on a retrospective analysis that he performed with colleagues at his institution. They looked at 403 cases of patients, aged 40 to 90, with moderate to severe knee OA who did not respond to conservative treatments. All patients underwent GAE. The research was designed to evaluate both the safety and efficacy of GAE across a broad spectrum of OA severities. The researchers used patient-reported outcome measures—Visual Analogue Scale and Knee Injury and Osteoarthritis Outcome Score—to measure pain and quality of life. These standardized scores were recorded at baseline and during follow-up visits at six weeks, three months, six months, and one year postprocedure.
Technical success was achieved in 100% of procedures. Temporary slight skin discoloration and mild knee pain immediately after the procedure were noted in 18% of all cases. No severe complications were reported. The quality-of-life index and pain score improved by 87% and 71%, respectively, at one-year follow-up.
“Our study was unique and interesting in that it closely followed patients at regular intervals to 12 months postprocedure to assess clinical outcomes (pain scores and another score called WOMAC [Western Ontario and McMaster Universities Osteoarthritis Index], which measures pain, stiffness, and physical function) but also to look at what we call biomarkers, namely chemicals in the body that are related to the inflammatory process,” Fleckenstein says. “Our study showed that there was a sustained reduction one year after the procedure in two of these important inflammatory biomarkers.” The study was published online in July 2025 in Radiology.
Additional Study Results
A study published online in August 2025 in the Journal of Vascular Interventional Radiology by researchers at NYU Langone also found that GAE is a safe and effective, minimally invasive treatment for those with moderate to severe symptomatic knee pain tied to OA. Hickey, an author of the study, says, “This work also provides evidence that GAE is offering more than just pain relief and could be modifying the disease process itself.”
For their study, the NYU Langone researchers looked at 25 patients with knee OA who were resistant to conservative therapy for greater than three months and who underwent GAE using 250- μm microspheres. Patients ranged in age from 50 to 78 years old, and all had their embolization procedures performed between January 2021 and January 2023.
Widely used patient-reported outcome measures were evaluated at baseline and one-, three-, and 12-months following GAE. In addition to rating their knee pain and stiffness, patients were asked to evaluate their ability to bend, stand up, and walk up and down stairs freely. Biomarker analysis was also done from blood samples that were collected. MRI was obtained at baseline and three months after GAE.
The researchers reported that the technical success was 100%, with no significant adverse events. The clinical success rate was 62%. Pain scores improved by nearly 40% at one month, and more than 50% at three months and 12 months.
Another key result of the study was a decline in blood levels of vascular endothelial growth factor (VEGF), a protein that is needed to stimulate the formation of new blood vessels. Past research has linked VEGF to other structural changes in the knee from OA. A second protein biomarker, interleukin-1 receptor agonist (IL-1Ra) showed a similar decrease (15%). IL-1Ra is known for its role in countering inflammation. A half dozen other immune molecules involved in inflammation were also tested but found to be inconclusive. Hickey says the reductions in serum VEGF and IL-1Ra levels following GAE that the researchers observed “may contribute to local pain relief and decreased inflammation in the knee joints.”
Adverse side effects were minimal, the researchers reported. “Patients may have some skin discoloration around the knee as a result of the embolization, but this is generally not clinically significant,” Hickey says. Otherwise, he says, the procedure is generally well tolerated.
Notable Improvement
Patients who undergo the procedure reported improvement in their knee pain and stiffness at their first follow-up at six weeks and continued to improve out to 12 months, Fleckenstein says. “One good thing about GAE and embolization for chronic joint disorder is that patients can continue with their normal lives the day after the procedure,” he says. “However, we do recommend that they stay home for at least the following three days.”
Prologo says his patients usually improve two to four weeks after their procedure and have shown lasting improvement for up to two years. “The important point to make here, though,” he says, “is that this procedure is not performed simply to mask/relieve pain. It is performed to interrupt the progression of the disease. In my mind, of course symptom improvement is nice, but I will get mine to extend the life of my native knees.”
The procedure could potentially be repeated, if needed. “There’s not necessarily a finite number of times,” Hickey says. “It would depend on what the angiography looked like at repeat procedures, if the vessels had not been completely embolized or not all vessels had been embolized during the initial procedure.”
Prologo agrees: “It can be repeated, but the nuance here is that it would be to block additional or new vessels that might form abnormally. We don’t necessarily have to repeat what we have done but, perhaps, would perform it again to improve on the original procedure outcome.”
Fleckenstein also says that if symptoms recur, repeated GAE can be considered. “There is published experience with successful retreatment around 12 months in selected cases. In practice,” he says, “we reassess at six weeks based on clinical course, rather than on a fixed schedule.”
Spreading the Word
Cost also favors GAE vs other treatments, especially knee replacement surgery. While the cost of GAE varies by location and insurance, it typically ranges from $5,000 to $15,000. The cost of a knee replacement can range from $30,000 to $50,000 or more, including the surgery, hospital stay, and other associated expenses such as rehabilitation. An analysis published in December 2024 in the American Journal of Roentgenology found that GAE is likely to be more cost-effective than radiofrequency ablation or corticosteroid injections for the treatment of symptomatic knee OA.
Fleckenstein says GAE is not recommended for patients with inflammatory arthritides (eg, active rheumatoid arthritis) or who have active joint infections. Also, he says, patients who have marked coronal malalignment (>about 15 degrees) where mechanical factors dominate symptoms would not be good candidates. “These points are consistent with our inclusion/ exclusion criteria and contemporary reporting standards,” Fleckenstein says. GAE can also be used in patients after knee replacement, after exclusion of infectious and mechanical causes for their pain, he says.
The NYU Langone team plans to further investigate precisely how embolization alleviates inflammation and leads to pain relief. Hickey says more research is needed to establish how long the benefits of embolization last and which OA patients are most likely to benefit from it. Work also needs to be done on some of the technical nuances of the procedures to favor the best outcomes, he says. Studies are also underway that are looking at the use of embolization to treat inflammatory conditions in other joins of the body, as well.
Prologo says interventional radiologists need to do a better job promoting GAE for patients who would benefit from it. Interventional radiologists have been operating as advanced interventional pain management providers for many years—at least 10—performing procedures that require advanced imaging guidance to solve difficult pain problems, he says.
“Interventional radiologists are uniquely equipped to solve pain problems because of their ability to use advanced imaging guidance to reach and treat virtually any pain generator, anywhere in the body, with medication injections, ablations, implants, and an entire host of advanced options,” he says.
Prologo says he meets someone at least once a week who could have been helped many months prior with procedures such as GAE. “Again,” he says, “it’s poor PR” on behalf of IR.
Fleckenstein agrees that convincing orthopedic surgeons to collaborate with interventional radiologists on GAE is probably the “hardest thing.”
— Beth W. Orenstein of Northampton, Pennsylvania, is a freelance medical writer and regular contributor to Radiology Today.
