Pathological effects and motor response threshold changes following radiofrequency application at various distances from the L-5 nerve root: an experimental study

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Radiofrequency (RF) ablation is a minimally invasive technique often used percutaneously in the treatment of many conditions such as spasticity, pain, and osteoid osteoma. The purpose of this study was to assess the value of motor response threshold (MRT) as an indirect indicator of the RF generator's electrode to nerve distance, and to evaluate the effects of RF at various distances from a nervous structure.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>The L-5 nerve root was studied in 102 Sprague-Dawley rats (sham contralateral side). Motor response thresholds at 0, 2, 4, 5, and 6 mm from the nerve root were assessed before and after RF application for 2 minutes at 80° C on Days 0 and 7. Radiofrequency was applied 0, 2, 4, 5, and 6 mm away from L-5 and with the addition of interposed cortical bone. The effects of RF application on MRT were studied, and subsequent nerve injury was evaluated using light microscopy pathological examination.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>There is a significant correlation between MRT and the distance between the electrode tip and L-5, with MRT less than 0.5 V when the electrode was in direct contact with the root. Electrical and pathological changes following RF application were more pronounced at 0 mm, with worsening seen on Day 7. Radiofrequency at 2 and 4 mm produced fewer electrical and histological deleterious effects on the nerve on Days 0 and 7, with an obvious improvement on Day 7. At 5 mm, electrical and histological abnormalities were minimal on Day 0 and were fully reversible on Day 7. At 6 mm and with interposed cortical bone, MRT and pathological findings were unchanged on Days 0 and 7.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>The MRT proved to be a useful and reliable tool in decreasing nerve morbidity following RF ablation in animals and may be used in humans for the same purpose. It serves as an indirect indicator of the proximity of the RF generator's electrode tip to any adjacent motor nervous structure. A minimum safe distance of 5 mm between the electrode tip and the nerve is required to avoid irreversible nerve injury, unless a bony wall is interposed between them, thus serving as a nerve shield. In medical conditions that require RF ablation of the nerve, such as spasticity and pain, the MRT must be lower than 0.5 V. When a nerve lesion is to be avoided such as in cases of osteoid osteoma, an MRT higher than 2.5 V is considered safe, reflecting a distance greater than 5 mm.</jats:p></jats:sec>

Radiofrequency ablation of spinal osteoid osteoma: a prospective study

“…Based on the results of a previous experimental study in which we determined the safety parameters for the use of radiofrequency in the spine, 8 we found in the current prospective clinical study that radiofrequency is a safe and valid method for the treatment of spinal osteoid osteomas, with excellent long-term results. This condition may thus be managed in a mini-invasive way, avoiding more aggressive neurosurgical treatment.…”

“…When no motor response is observed until 2.5 V, the tip of the electrode is considered to be at a safe distance of at least 5 mm of the adjacent nervous elements, based on the experimental study published by our team. 8 After the motor response threshold test was performed, the electrode was connected to a radiofrequency generator (Neuro N50, [IEC 601-1, FDA, UL-listed, Med.GB]), which delivered a radiofrequency of 500 kHz with a controlled temperature of 82°C. This temperature was maintained for 4 minutes.…”

“…3 Therefore, we conducted an experimental study in rats in our laboratory to test the safety of the procedure when performed in the spine. 8 The study demonstrated that a motor response threshold to electrical stimulation higher than 2.5 V is considered to be safe, reflecting a distance greater than 5 mm between the tip of the electrode and the adjacent nervous structure. Indeed, in this study, the presence of a cortical bone between the tip of the electrode and the nervous structure proved to be safe to these structures.…”

Effects of Supraorbital Foramen Variations on the Treatment Efficacy of Radiofrequency Therapy for V1 Trigeminal Neuralgia: A Retrospective Study

“…High temperature could induce cellular apoptosis and necrosis. e damage caused at high temperatures of 95°C could evidently damage the neurons and nerve fibers [19,20]. Active damaging of the nerves for the treatment of some diseases has been highly accepted by the patients.…”

Computed tomography-guided resection of osteoid osteoma of the sacrum: a case report

“…It has been reported that when treating osteoid osteoma, 90°C of heat should be applied for approximately five minutes for the necrosis of the entire tumor [9,13]. When this energy is applied to the tumor, a 2 to 5mm margin from the nerve has been postulated to be the safety threshold [14,15]. Although epidural vein plexus and cerebrospinal fluid may reduce the possible side effects, when the tumor is within 5mm of the spinal canal, it is prudent to undergo an open resection of the nidus.…”