Intra-articular ultrasonic stimulation and intracutaneous electrical stimulation: evoked potential and visual analogue scale data

The reproducibility of focussed ultrasound-induced intra-articular pain was compared with that of electrically induced cutaneous pain over a period of time by measuring both the evoked potential (EP) amplitude and visual analogue scale (VAS) score. The responses to ultrasound were more variable than those to electrical stimulation. A greater degree of accommodation occurred during electrical stimulation compared with ultrasound stimulation. A statistically significant correlation between the EP amplitude and the VAS score was found for each form of stimulation. Changes in EP amplitude correlated with changes in the perception of pain as measured by the VAS score, rather than stimulus intensity, which remained constant for each subject throughout the duration of the experiment. A single oral dose of pethidine produced a statistically significant decrease in the EP amplitude and the VAS score in each case.