Variation in the size and number of stone fragments after gallbladder lithotripsy

Ninety-four gallbladder ultrasound examinations were carried out in 11 patients at intervals for the first 40 days after lithotripsy. No dissolution or other active therapy was carried out during this time. Fragment size and number were measured to determine the postlithotripsy variability. Analysis of variance (ANOVA) showed no significant changes in fragment size or number over time. The changes in fragment size and number compared to the previous measurements were then evaluated. Again, ANOVA showed no significant changes between times. The average change in absolute size was 3.1 +/- 0.6 mm, and the average change in absolute number was 1.4 +/- 0.5. We conclude that fragment size and number as determined by ultrasound do not vary significantly with time during the first 40 days. The absolute size change measured to the nearest millimeter should be at least 4 mm to surpass the 95% confidence interval. Similarly, the absolute change in number should be at least 2 to be regarded as significant.