Ultrasonic lithotripsy can only be employed when there is a straight path to the stone. This technique uses a probe to break small stones with shock waves generated by electricity. The physician positions the tip of the probe 1 mm from the stone through a flexible ureteroscope and projects electrically generated hydraulic shock waves at the stone. These fragments can be passed by the patient or removed by extraction methods. EHL requires general anesthesia and is generally not used in close proximity to the kidney because the shock waves can cause tissue damage.
Fragments tend to scatter widely, making retrieval or extraction difficult.
Extracorporeal shock wave lithotripsy uses highly focused impulses projected from outside the body to pulverize kidney stones. The patient is positioned on a cushion atop a table and may be given a sedative. Lithotripters are effective at crushing cystine stones and those in the lower ureter. The stone usually is reduced to granules that can be passed in the patient's urine. Large struvite stones, because of their jagged shape, sometimes become lodged in positions or locations that make them difficult to treat effectively with shock waves.