Influence of chemolysis on physical properties and comminution of artificial stones (BON(N)-STONES)

Purpose: Acoustic and mechanical properties show significant differences among various stone compositions and are important parameters for the determination of stone fragility under shock wave impact. Suggesting that stone fragility and thus shock wave lithotripsy (SWL) can be altered by varying the physical properties of stones through chemolysis calcium oxalate monohydrate (COM) stones were treated with EDTA and stones composed of uric acid (UA) with tromethamine. Material and Methods: Synthetic urine served as a control. Using an ultrasound transmission technique longitudinal wave propagation speeds were measured at different time intervals. We also measured stone density using a pycnometer based on Archimedes' principle. From these measurements we calculated transverse (shear) wave speed, wave impedance and dynamic mechanical properties of the artificial stones. Moreover the microhardness of artificial stones was measured and investigations on shock wave lithotripsy (SWL) combined with initial chemolytic treatment of the stones were performed. Results: Both, wave speeds and wave impedances as well as dynamic mechanical properties only showed a decreasing trend in test groups regarding COM and UA treated stones suggesting an improvement of stone fragility, whereas no change was seen concerning all COM and UA control groups. Microhardness of COM and UA treated stones decreased compared to control groups. Combining medical treatment and SWL the investigations showed a significant impact of solvents on stone comminution concerning COM and UA stones. Conclusion: In conclusion, the results indicate that appropriate chemical treatments may provide a useful adjunct modality for improving the efficacy of stone comminution during SWL.