Background and aims Pulsed radiofrequency (PRF) has been shown in structural studies to selectively impact small-diameter fibers. Herein, we demonstrate that PRF attenuates function hosted by small-diameter axons while preserving function of large-diameter fibers, and these effects were coincident with structural changes.
Methods Fifteen Sprague-Dawley rats were anesthetized. Animals were randomly assigned to PRF (20ms,2Hz,120s,42°C,55–75V) or sham (120s, no PRF) groups after placement of a radiofrequency probe tip-down on the sciatic nerve (≤0.5 V threshold). the Nociceptive Flexion Reflex (NFR) was elicited by stimulation on the foot (8 ms,20–80 V) and motor function was assessed by proximal sciatic-nerve stimulation (50 μs,5–30 V). the average electromyogram (EMG) area corresponding with the NFR (latency: 150–650 ms; small-diameter unmyelinated-fibers) and motor function (latency: 1–10 ms; large-diameter myelinated fibers) was recorded before and after treatment. Welch’s t-tests were performed with Bonferroni correction. Nerves were preserved and assessed by a third-party histologist (H&E or electron microscopy).
Results PRF reduced the NFR and motor responses by a between-animal average of 70.0% and 12.4%, respectively, while sham treatment reduced these by 10.4% and 2.0%, respectively (figure 1a). Significant differences were observed for the NFR in PRF-treated animals vs. sham animals (p < 0.0001) and between the NFR and motor response in PRF-treated animals (p < 0.0001). No detectable nerve damage was observed via light microscopy (n=3). Electron microscopy (n=3) suggested preferential disruption to mitochondria of small-diameter fibers (figure 1b).
Conclusions PRF selectively attenuates the NFR while sparing motor conduction. Disruption of subcellular structures is one of many possible explanations for the selectivity of PRF.
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