Eighty in vitro experiments were performed with single (n = 51) or multiple (n = 29) gallstones in order to find out which parameters are of prime importance for their disintegration by extracorporeal shock waves. A Dornier lithotripter and an upper limit of 1,500 discharges were employed.
Although computed tomography density was significantly lower in cholesterol stones than in the noncholesterol stones (p < 0.0001) and although the latter were significantly more often radiopaque (p < 0.0001), we found no clear-cut correlation between the cholesterol content or computed tomography density and the degree of fragmentation of the stones. The most important variable which limited successful disintegration was the total stone volume. In stones with a mean total volume of 0.83 ml ± 0.25 S.E. (diameter for single stones = 11.5 ± 0.9 mm), none of the fragments exceeded 2 mm, whereas in stones with a mean volume of 3.6 ml ± 0.64 (diameter = 17.2 ± 1.5 mm) at least one fragment larger than 2 mm remained (p < 0.002). Under the in vitro conditions, fragmentation was similar in multiple and solitary stones, provided the volume of the stones was comparable.
These data show that, in general, the number and size of the stones, i.e. their total volume, and much less significantly their chemical composition are the major determinants of fragmentation by extracorporeal shock waves.