The research on the effect of different application durations of pulsatile radiofrequency (PRF) and conventional radiofrequency (CRF) for treatment of pain syndromes on nerve structure under microscope

Objective: Radiofrequency treatment is being used for many years by forming neuroablation in chronic pain treatment. CRF shows its effect by creating a coagulation necrosis in the tissue by heat. But the ablation process that takes place by applying heat may cause deafferentation sequelae. For this reason, recently, the pulsed radiofrequency is developed by applying RF current in a pulsatile manner with lower temperatures. In this study, we studied the neuroablative effects of PRF in contrast to CRF in periferic nerves by working on the sciatic nerve, a nerve that includes both motor, sensory and autonomous fibers. Material and Method: In this study, a total of 60 rattus norvegicus rats were used in 6 groups after getting the permission of Animal Studies Ethics Committee. No procedure was performed on the control group (n:10). After the induction of general anesthesia, the electrodes were placed near the sciatic nerve. In the Sham group (n:10) the electrodes were placed but no current was applied. In the 3. group, 120 seconds of 42C PRF was applied. In the 4. group, 240 seconds of 42C PRF was applied. In the 5. group, 120 seconds of 42C CRF was applied. In the 6. group, 240 seconds of 42C CRF was applied. After 2 days, the sciatic nerves of the rats were dissected under general anesthesia and examined with an optic and electron microscope. Results: The motor and sensory functions of all subjects were normal before the experiment. No wound infection was recorded in any of the subjects. The effects of the procedure on sciatic nerve were examined by comparing the findings of the Sham and other procedural groups with the control group. The examination of the specimens from Sham group under optic and electron microscope showed normal findings similar to control group and no morphological abnormality was recorded. The examination of the specimens from PRF 120 seconds and CRF 120 seconds under optic and electron microscope showed no structural difference in morphology. The images were similar to control group. In the PRF 240 seconds group, while no general structural abnormality was observed, very rarely, abnormal findings were recorded such as myelin sheath deformations and particularly axoplasmic lysis and electron dense material deposits. When all of the specimens were examined, it was concluded that these findings were extremely rare and could be ignored. In some of the specimens from CRF 240 seconds group, heavy deformation of both myelinated and non-myelinated nerve fibers was observed under both electron and optic microscope. The deformations were: myelin sheath destruction, openings in layers, axoplasmic destruction, mesaxon destruction and endonorial myelin residues. In many of the axons, loss of neurotubule and neurofilament structure, mitochondrial crista destruction and contraction was observed. Dramatic structural deformities in Schwann cells were observed. The loss of basal lamina, loss of integrity of membranes, the breakup of cytoplasma into the endonorium, the loss of heterochromatic appearance due to the electron density increase in nucleoplasma were the deformative changes that were observed. Conclusion: 120 second and 240 second PRF treatments did not produce any deformities in the sciatic nerve. No pathology was observed in 120 second CRF group. The application of CRF for 240 seconds produced pathological alterations in the nerve structure.