Comparison of 2 generations of piezoelectric lithotriptors using matched pair analysis

The Piezolith 3000 (Richard Wolf, Knittlingen, Germany) is the newest piezoelectric lithotriptor. Using a matched pair analysis model we compared treatment outcomes of this machine with those of an older generation Piezolith 2300 lithotriptor (Richard Wolf).

Patients with solitary, radio-opaque urinary calculi undergoing primary lithotripsy using the Piezolith 3000 were identified. All patients had a 3-month followup. These patients were matched with those from our database treated between 1992 and 1999 with a Piezolith 2300. Patients were initially matched for gender, side and site of the stone. For stones other than those in the lower calix and lower ureter, matching was performed for size in terms of maximum and minimum diameter of the index stone. Additional anatomical factors of caliceal pelvic height and vertical distance of the lower ureteral stone from pubic symphysis were also measured. Thereafter stones with size +/- 1 mm of the index stone were selected and the stone with the best matched anatomical factors was chosen. The initial stone fragmentation rate and stone-free rates at 3 months in the matched pairs were then compared.

A total of 25 matched pairs were found between October 2002 and December 2002. There was no statistical difference between the initial fragmentation rate for the Piezolith 3000 (68%) and the Piezolith 2300 (84%, McNemar's test p = 0.388). The stone-free rate at 3 months for the Piezolith 3000 and the Piezolith 2300 were 36% and 48%, respectively, again with no statistical difference (McNemar's test p = 0.581).

Despite significant design changes and technical modifications, the new piezoelectric lithotriptor does not appear to provide a better treatment outcome than the older generation machine.