Stimulation of the obturator nerve during extracorporeal shock wave lithotripsy.

This paper presents eigth patients with lithiasis of the lower third of the ureter that were treated by extracorporeal shock wave lithotripsy (ESWL). All the procedures were performed with a Dornier HM4 lithotriptor in the sitting position. In all cases clinical signs of stimulation of the obturator nerve were presented. Because of the continuing movement of the patient and the possibility of damage to the obturator nerve, the lithotripsy was interrupted in the sitting position and was performed successfully with patients in the prone position. One possible explanation for the above phenomenon is that the increased abdominal pressure in the sitting position pushes the ureter with the stone towards the side walls of the pelvis and the obturator nerve. In this way, both obturator nerve and stone were included either in the zone of the high concentration of the shock waves, or in the secondary focal point, with the final result of stimulation of the nerve. By placing the patient into the prone position, the abdominal pressure is reduced, the ureter moves towards the center line, the obturator nerve gets away from the shock waves and the ESWL is completed freely without stimulation of the nerve.