A Novel Paraboloid Intracorporeal Lithotripter: Computer Aided Design Analysis and In Vitro Comparison with Holmium Laser for Large Renal Calculi

Abstract

An intracorporeal lithotripsy probe tip was designed with a paraboloid shaped tip and compared with holmium laser for stone pulverization. The paraboloid tip concept was developed and designed using computer aided design (CAD), fabricated, and patented. CAD analysis and in vitro comparison (with laser) of pulverization and propulsion dynamics were performed in an underwater hands-free bench arrangement using phantom stones. SPSS analysis for different energy cohorts was performed. CAD analysis: At "point contact" with the tip, the paraboloid lithotripter generated 3590 bars at generator settings of 4 bars. During "follow-up impacts," the tip pressure exponentially decreased (graduated tip pressure) and the lateral/centrifugal forces increased, converting the probe into a side-firing energy source. Bench analysis: At point contact, the paraboloid lithotripter at 2, 3, and 4 bars was comparable to that of a 6, 10, and 15 W laser, respectively (P<0.005). The paraboloid lithotripter showed a statistically significant advantage in breaking the phantoms, as against a laser that always bored through the phantom. Stone propulsion was comparable within all energy cohorts (P>0.05). The paraboloid lithotripter generates highly focused impact force with low propulsion, at point contact. As stone pulverization progresses, the tip forces exponentially decrease and the probe converts into a lateral firing energy source resulting in pulverization into larger fragments. Thus, the paraboloid lithotripter has all the advantages of laser at point contact and advantages of pneumatic lithotripter at follow-up hits, akin to being a bimodal energy source.