Voided stone fragments retrieved after extracorporeal shock wave lithotripsy (ESWL) in 200 patients were sorted by size and analyzed by optical microscopy for composition. The most common size by volume or weight was 0.85–1.4 mm, with the largest fragment in each sample usually being 1.4–2.0 mm in diameter. However, 30 specimens contained fragments of 2.8–5.6 mm. Hydroxyapatite/struvite and uric acid stones produced the largest fragments (>4 mm), probably because of the larger pretreatment stone burden. Calcium oxalate monohydrate stones produced larger fragments than did calcium oxalate combined with uric acid, hydroxyapatite, or calcium oxalate dihydrate. Stone size and location, the number of shock waves delivered, and patient habitus and ureteral size affect the size distribution of voided stone fragments. Chemical composition is not the sole determinant of particle size and extent of stone destruction by ESWL.
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