Stone Fragility--a New Therapeutic Distinction

The ESWL retreatment rates for calculi of 1.1 to 3.0 cm. varied according to stone composition: calcium oxalate monohydrate (COM) 10.3%, calcium oxalate dihydrate (COD) 2.8%, struvite/apatite calculi 6.4%. Fine detail in-vitro radiographs of approximately equal sized calculi composed of COM, COD, struvite, brushite, uric acid and cystine showed structural differences which may account for differences in their fragility. The same six calculi were fragmented in vitro in the Dornier HM3 lithotriptor by 200 shocks at 18 KV and the percent weight of each calculus able to be filtered through a two mm. sieve was determined; COD and uric acid (100%); COM (64%); struvite (57%); brushite (47%); cystine (16%). The linear density of these calculi, measured by single photon emission absorbtiometry, correlated with radio-density, not fragility. Calculi of varying composition respond differently to shock wave fragmentation. The assessment of the capability of ESWL to fragment a stone will determine the size stone selected for treatment. Therefore, "stone fragility" is a new distinction which deserves to be included in the conversation about urinary calculi.