Relationship between the frequency of piezoelectric shock waves and the quality of renal stone fragmentation. In vitro study and clinical implications.

Nine renal stones were separated into 5 fragments of similar weight and size. One fragment was analyzed chemically and the other 4 fragments were submitted to treatment by piezoelectric shock waves according to the following modalities: 3,000 shock waves at firing frequencies of 1.25, 2.5, 5 and 10 shock waves/s. In the case of hard stones, better quality fragmentation was obtained with low frequencies than with high frequencies. With friable stones, using only 800 shock waves, the result was the same regardless of the frequency used. Treatment of hard stones by shock waves for 20 min at various frequencies revealed that a slightly better result was obtained with a frequency of 5 shock waves/s, although the result was not significantly better. In conclusion, slow frequencies of 1.25 or 2.5 shock waves/s allow better fragmentation of hard stones at the cost of a longer mean treatment than at high frequencies. High frequencies do not give significantly better results than low frequencies when the same firing time is used. In the clinical situation, it is therefore preferable to use low frequencies which allow treatment without anesthesia or analgesia and without admission to hospital.