Objectives: The increasing application of ureterorenoscopy for the treatment of urolithiasis has produced a myriad of different help-tools for stone retrieval. In this study, we compared the retrieval capabilities of different baskets and graspers in ex vivo models and attempted to find the most appropriate tool for stone extraction considering the location and size of stone, number of stones and potential harm to urinary tract tissue.
Methods: We created four different ex vivo models with porcine kidneys and ureters and natural human stones: (1) single ureteral stone (4mm); (2) single impacted ureteral stone (6mm); (3) Steinstrasse; (4) single lower-pole stone (5mm). With the aid of four baskets of different design (flat-wire basket Segura and Nitinol basket Zerotip, helical Gemini, and Parachute) and three graspers (two-prong, three-prong Tricep, and Nitinol grasper Graspit) we performed repeated stone extraction 10 times in each model. The time for complete stone removal was calculated. Macroscopical evaluation of tissue damage was performed after each series. In the Steinstrasse model the frequency of instrument reinsertion into the ureter was also calculated.
Results: In the single ureteral stone model, the fastest stone removal was achieved with the two-prong graspers, three-prong graspers and helical basket (20, 26 and 31s, respectively). Segura and Parachute needed more time (55 and 86s, respectively). Impacted stones were removed fastest with the two- and three-prong graspers (38 and 52s, respectively), Segura and Gemini were slower (89 and 114s, respectively). The Steinstrasse was cleared fastest by the helical basket with the lowest frequency of endoscope reinsertion (66s, 1.4 reinsertion). The Segura, 149s with 3.2 reinsertion was needed for the same procedure. With the Parachute and two-prong graspers 163s, 1.8 reinsertion and 261s, 4.6 reinsertion were needed, respectively. During postprocedural macroscopical evaluation of uretral tissue, the Parachute basket and three-prong graspers demonstrated the highest risk of mucosal and muscle damage. In the lower-pole kidney model, the poor deflectability of the ureterorenoscope prevented access to the lower-pole with the two- and three-prong graspers. There was no significant difference in stone retrieval time between the remaining Nitinol basket Zerotip and Nitinol grasper Graspit (87 and 61s, respectively ). The number of failures was 4/10 for Zerotip and 5/10 for Graspit. No significant mucosal damage was noted with these tools.
Conclusions: Our ex vivo models demonstrated that the design of graspers and baskets affects the time of stone retrieval in different situations and causes the various grades of tissue damage.