Efficacy of supine versus prone biliary lithotripsy: an in vitro study

Clinical extracorporeal shock wave lithotripsy (ESWL) results have shown that the smaller the gallstone fragments following ESWL, the faster the patient will become stone-free. At ESWL, an attempt is made to produce sand-like fragments that will easily pass through the cystic and common bile ducts. Sixteen pairs of gallstones of equal shape, size, and composition were harvested from cholecystectomy specimens and then fragmented on the Dornier MPL-9000 lithotripter (Dornier Medical Systems, Inc.), individually, in a phantom oriented to duplicate either supine or prone patient positions. The number and size of remaining fragments were compared following the supine versus prone treatments. The 32 stones, ranging from 5-15 mm in diameter, received 1,500 shock waves at 21 kV. Fragments with a maximal diameter of greater than or equal to 4 mm were measured and counted after 750 and 1,500 shock waves. Fragments greater than or equal to 4 mm were found in four out of 16 stones treated supine (25%) and 16 out of 16 stones treated prone (100%). The largest residual fragment regardless of size for each stone pair occurred in the prone group in 14 out of 16 cases (88%). Biliary lithotripsy performed with supine positioning results in more efficacious gallstone fragmentation in this in vitro model; these findings suggest that supine positioning for patients could improve fragmentation and treatment success.