Stone fragility--a new therapeutic distinction

Area of Science:

• Urology
• Biomaterials Science
• Medical Physics

Background:

• Extracorporeal shock wave lithotripsy (ESWL) is a common treatment for urinary calculi.
• Stone composition is known to influence treatment outcomes, but the specific mechanical properties related to fragmentation remain under investigation.

Purpose of the Study:

• To investigate the relationship between urinary stone composition, structural characteristics, and fragmentation susceptibility to extracorporeal shock waves.
• To introduce the concept of "stone fragility" as a critical factor in ESWL treatment planning.

Main Methods:

• In vitro analysis of urinary calculi (1.1–3.0 cm) of varying compositions (calcium oxalate monohydrate, calcium oxalate dihydrate, struvite/apatite).
• Fine detail radiography to assess structural differences.
• In vitro fragmentation using Dornier HM3 lithotriptor (200 shocks at 18 KV) and determination of fragment size distribution via a two mm sieve.
• Measurement of linear density using single photon emission absorptiometry.

Main Results:

• ESWL retreatment rates varied by stone composition: COM (10.3%), COD (2.8%), struvite/apatite (6.4%).
• In vitro fragmentation showed significant differences: COD and uric acid (100% fragmentation), COM (64%), struvite (57%), brushite (47%), and cystine (16%).
• Linear density correlated with radio-density, not stone fragility.

Conclusions:

• Urinary calculi of different compositions exhibit distinct structural properties influencing their fragility and response to shock wave lithotripsy.
• Stone fragility, determined by composition and structure, is a crucial factor that should be considered alongside stone size in ESWL treatment selection.