U.S. Department of Health and Human Services

Design Change May Improve Kidney Stone Treatment

New research has shown that changes to a medical machine called a lithotripter may improve kidney stone treatment.  Kidney stones are one of the most common disorders of the urinary tract.  Kidney stones can form when substances in the urine—such as calcium, oxalate, and phosphorus—become highly concentrated.  A small stone may pass on its own, causing little or no pain.  A larger stone may get stuck along the lower urinary tract and can block the flow of urine, causing severe pain and/or bleeding.  The lower urinary tract is primarily made up of the ureter (the tube that connects the kidney to the bladder), bladder, and urethra (tube that carries urine from the bladder to the outside).  One treatment option for a person with a larger stone, or one that blocks urine flow and causes great pain, is non-invasive shock wave lithotripsy.  In shock wave lithotripsy, the lithotripter generates shock waves that pass through the person’s body to break the kidney stone into smaller pieces to pass more readily through the urinary tract.  The lens component of the lithotripter serves to focus the shock wave at the selected target (stone).  Although current lithotripters are more powerful and more reliable than previous iterations of the machine, their treatment effectiveness is reduced.
 
NIDDK-supported researchers have recently determined that the more powerful lithotripters shift the shock wave off-target, which contributes to efficiency loss.  In addition, this same group of investigators made modifications to the lens while keeping all other aspects of the lithotripter the same.  By introducing a groove around the outer portion of the lens, the researchers were able to re-direct the shock wave to its proper target when tested in an animal model.  The newly designed lithotripter pulverized 89 percent of the stones to sufficient size for passage through the urinary tract compared to 54 percent of the stones by the current generation of lithotripter.  Moreover, it is anticipated that the newly designed lithotripter will cause less damage to surrounding tissue.  If future research shows similar benefits in people with kidney stones, this newly designed lens may be adaptable by other manufacturers to improve their lithotripters currently in medical practice.
 
Neisius A, Smith NB, Sankin G, Kuntz NJ, Madden JF, Fovargue DE, Mitran S, Lipkin ME, Simmons WN, Preminger GM, Zhong P. Improving the lens design and performance of a contemporary electromagnetic shock wave lithotripter. Proc Natl Acad Sci USA 111:E1167-75, 2014.