Prospective randomized controlled single-blind parallel-group trial in order to compare symptoms related to loop-tail (Polaris Loop) stents versus conventional double J (Vortek) stents after uncomplicated flexible URS.

Patients undergoing RIRS for a single renal stone < 2 cm are asked to participate in a prospective randomized controlled single-blind parallel-group study. Ureteral stent is always placed after flexible URS. Patients are prospectively randomized into two groups with a 1:1 allocation: group LT receive loop-tail stents (Polaris ™ Loop - Boston Scientific, Natick, USA), while group DJ receive conventional double J stents (Vortek ® - Coloplast, Humlebaek, DK). Stent removal is planned 4 weeks after the procedure.

Participants are asked to fill in the Italian validated version of the Ureteral Stent Symptoms Questionnaire (USSQ) 2 days and 4 weeks after surgery. The USSQ is further submitted 4 weeks after stent removal (8 weeks after surgery) and these results are used as baseline evaluation, on the assumption that SRS persist for a few days after removal.

Inclusion Criteria:

• patients undergoing flexible ureteroscopy and laser lithotripsy for kidney stones < 2 cm
• given informed consent
• WHO PS 0-2

Exclusion Criteria:

• significant residual fragments at the end of the procedure
• intraoperative complications (i.e. ureteral damage or ureteral stricture)
• urinary tract infections
• anatomic abnormalities
• chronic diseases or medications potentially influencing pain perception and urinary symptoms (i.e. alpha blockers and antimuscarinics)
• preoperative ureteral stenting.