Mechanisms responsible for diminished fragmentation of ureteral calculi : an experimental and clinical study

AbstractWe molded 24 synthetic stones (mean weight 680mg., range 641 to 715) from a commercial mixture of gypsum, silica, cellulose and polyvinyl acetate. Each stone was subjected to 400 shocks on a Wolf 2300 Piezolith and groups of 6 stones were treated in 4 different modes. Mean amounts fragmented were 243 ± 18mg. in a free environment, 62 ± 18mg. confined loosely in a latex tube, 22 ± 8mg. impacted in the tube and 30 ± 8mg. impacted alongside a 7F stent.During a 30-month period 118 patients received in situ extracorporeal shock wave lithotripsy for ureteral calculi using the same lithotriptor. The mean stone burden was 11.4mm. (range 4 to 29). Success was greater for patients with calculi 10mm. or less than for those with stones greater than 10mm. (71% versus 51%, p <0.05), despite the former group receiving less shocks (5,404 versus 7,491). The influence of size was then excluded by studying the number of shocks delivered per mm. of calculus. Patients receiving 500 to 699 shocks per mm. showed a highe...