The Use of a Novel Reverse Thermosensitive Polymer to Prevent Ureteral Stone Retropulsion During Intracorporeal Lithotripsy: A Randomized, Controlled Trial

Purpose: We present the first randomized clinical study using BackStop (TM), a novel reverse thermosensitive water-soluble polymer that is dispensed above the stone(s) and temporarily occludes the ureter to prevent retropulsion of stone fragments during ureteroscopic lithotripsy. After fragmentation is completed and concretions are extracted, conventional irrigation with saline dissolves the polymer, which is then flushed out. Materials and Methods: A total of 68 subjects with a single stone in the proximal ureter and an indication for ureteroscopic lithotripsy were enrolled in this prospective, randomized, single-blind, controlled, multisite clinical study. Each subject was randomly assigned to the Back Stop group (34) or the control group (34 with no antiretropulsion device). For subjects in the experimental group Back Stop was dispensed into the ureter above the stone using a 3Fr or 5Fr catheter. Ureteroscopic lithotripsy was performed in all subjects using pneumatic or laser energy. Measured end points included the retropulsion rate, the need for subsequent procedures, the stone-free rate at followup, the occurrence of adverse events and ureteral occlusion, if any, and post-stone fragmentation and extraction. Results: Subjects randomized to the Back Stop group experienced a statistically significant (p = 0.0002) lower rate of retropulsion (8.8%, 3 of 34) vs the control group (52.9%, 18/34). There were no adverse events in the Back Stop group and Back Stop was successfully dissolved in every subject, resulting in a patent ureter. Conclusions: Back Stop appears to be a novel, safe and effective means of preventing stone fragment retropulsion during ureteroscopic lithotripsy for the management of ureteral stones.