Edge targeting reduces the number of shock waves required for biliary ESWL in vitro

In vitro experiments were conducted to determine if differences in targeting would effect stone fragmentation. Ten pairs of twin gallstones were used. The stones in each pair were identical in volume, diameter, radiolucency, and gross shape. One stone from each pair was subjected to shock waves focused at the center of the stone; the other was treated with shock waves targeted at the edge. Lithotripsy was terminated when all fragments were less than 5mm in diameter. The total number of shock waves used for each stone was recorded. In 7 of 10 pairs, fewer shock waves were required to fragment the edge targeted stone than the center targeted stone. In two of the remaining three pairs, equal numbers of shock waves were required for complete fragmentation. The difference between edge targeting and center targeting was shown to be statistically significant using the nonparametric Wilcoxin Signed Rank Test. (1 tailed = p less than 0.02, 2 tailed = p less than 0.04). These findings suggest that the outcome of biliary lithotripsy may be improved by targeting the edge of the stone.