Bipolar vs Monopolar Radiofrequency Ablation for Osteoarthritis Knee Pain

Bipolar radiofrequency (RF) ablation of the genicular nerves using ultrasound guidance was more effective than monopolar RF ablation at relieving knee osteoarthritis (OA) pain, according to findings of a randomized, prospective, double-blind study, published in the Annals of Medicine and Surgery.

Radiofrequency ablation interrupts pain conduction by producing a thermal lesion that disrupts nociceptive signals, with bipolar RF ablation producing a larger lesion than monopolar RF ablation. Investigators for the current study sought to compare the effects of bipolar vs monopolar RF ablation of genicular nerves — using ultrasound guidance without fluoroscopic confirmation — in treating OA knee pain. The primary study outcome was knee pain postprocedure. Patients were followed for 24 weeks for changes in pain measured by the visual analogue score (VAS) and Oxford knee score.

Patients (N=50) with chronic OA pain that was unresponsive to other treatments or physiotherapy were recruited at the Mansoura University in Egypt between 2020 and 2021. One week prior to RF ablation, patients received a diagnostic nerve block. Patients who responded to the diagnostic block were randomized to receive monopolar (n=25) or bipolar (n=25) RF ablation of the genicular nerve. The monopolar and bipolar cohorts were aged mean 58±7 and 57±6 years, respectively, with male:female ratios of 11:14 and 12:13, respectively, and with Kellgren-Lawrence classifications of 4 in 36% and 32% of patients, respectively.

Patients undergoing both procedures reported significant reductions in pain following the procedure (all P <.05). At 12 weeks postprocedure, the investigators found that patients who received bipolar RF ablation reported greater improvements to VAS (mean change from baseline, 3.96 vs 2.8; P <.001). Similar trends were observed at week 24 (mean change from baseline, 3.56 vs 2.2; P <.001). The Oxford knee score was lower among the bipolar ablation cohort at weeks 12 (mean, 26 vs 34; P <.001) and 24 (mean, 27 vs 35; P <.001).

Associated adverse events rates for monopolar vs bipolar ablation were: infection, 4% vs 8%, respectively; numbness, 4% vs 8%, respectively; and anesthesia dolorosa, 8% vs 12%, respectively.

Notably, the monopolar intervention was quicker (mean, 36 vs 47 minutes; P <.001) and patients reported less pain during the intervention (median, 4 vs 5; P =.002).

The major limitations of this study was that the treatment was applied to the 3 main articular branches, not all branches innervating the knee joint, and the lack of a control condition.

The study authors concluded, “Ultrasound-guided bipolar radiofrequency ablation without fluoroscopic confirmation is more effective than monopolar radiofrequency ablation in controlling chronic osteoarthritis knee pain.”