An ex vivo comparison of cooled-radiofrequency and bipolar-radiofrequency lesion size and the effect of injected fluids.

Background And Objectives: Radiofrequency (RF) neuroablation is a common therapy for alleviating chronic pain. Larger lesion volumes lead to higher chance of ablating small sensory nerves; therefore, bipolar-RF and cooled-RF are improved alternatives to conventional monopolar-RF. This work provides an ex vivo comparison of bipolar-RF to cooled-RF lesioning in the presence of bone structure using some conventional temperature and time programs and in conjunction with injection of a variety of clinically used substances.

Methods: Studies were performed using chicken muscle near a bone structure. Cooled-RF was applied using standard parameters at 60°C for 150 seconds and perpendicular to the bone. Bipolar-RF was applied using interelectrode distances (IEDs) of 5, 10, or 15 mm at 80°C for 90 or 150 seconds with the electrodes positioned either paralleled between the bone and muscle or perpendicular to the bone. The effect of injection of various fluids (sterile water, 0.9% saline, 7.3% saline, 2% lidocaine, 0.25% bupivacaine, lidocaine/methylprednisolone (Depo-Medrol), or lidocaine/betamethasone (Celestone) on lesion size was compared with no fluid injected in the muscle. Temperature profiles of lesioning were also obtained using an infrared camera.

Results: The volume of bipolar-RF lesions is dependent on IED, being more favorable at IED equals 10 mm. The injection of some fluids induces significant (P < 0.05) changes in bipolar-RF lesion volume, although the changes are dependent on IED. Cooled-RF induces larger lesions than bipolar-RF, with no changes in volume induced by injecting fluids.

Conclusions: Cooled-RF yields larger lesions than bipolar-RF under the conditions used in this study. The spherical shape of cooled-RF lesions provides larger volume coverage than lesions obtained with bipolar-RF at IED equals 5, 10, or 15 mm under similar electrode tip temperature and lesioning time.