# Stone extraction during flexible ureterorenoscopy with or without the hydrogel method: a randomized, multicenter safety and feasibility study

## TL;DR

A new hydrogel method improves kidney stone removal during surgery, especially for small fragments, without increasing risks.

## Contribution

The hydrogel method was shown to safely and effectively extract smaller stone fragments during flexible ureterorenoscopy.

## Key findings

- The hydrogel method retrieved significantly more fragments < 1 mm and > 1 mm compared to standard methods.
- No serious adverse events were reported with the hydrogel method.
- Surgery duration was longer with the hydrogel method, but it was still feasible.

## Abstract

Achieving the highest possible stone-free rate is the primary goal of kidney stone surgery, yet standard flexible ureterorenoscopy often leaves small residual fragments that predispose to recurrence. The hydrogel method using mediNiK® was developed to embed and extract even the smallest fragments with conventional baskets. This study aimed to evaluate the safety and feasibility—defined as the ability to extract fragments < 1 mm—of stone extraction during flexible ureterorenoscopy with or without the hydrogel method.

This prospective, randomized, multicenter proof-of-concept trial included patients > 18 years with kidney stones > 8 mm and no anatomical abnormalities. Patients were randomized to flexible ureterorenoscopy + hydrogel (Group 1) or flexible ureterorenoscopy (Group 2) alone. After laser lithotripsy, fragments were retrieved either embedded in hydrogel or individually, and categorized by size (< 0.5 mm, 0.5–1.0 mm, > 1.0 mm). Explorative statistical analyses included Mann-Whitney U, Student’s t-test, and Chi-square test. Adverse events were monitored intraoperatively and during a 6-week follow-up.

Of 65 screened patients, 40 were analysed (Group 1: n = 23; Group 2: n = 17). The hydrogel method significantly retrieved more fragments < 1 mm (1716 vs. 209) and > 1 mm (310 vs. 118). On a per-patient level, more < 1 mm fragments were removed in Group 1 (median 7 [IQR 21] vs. 0 [2], p < 0.003). Surgery duration was longer in Group 1 (80 [28] vs. 62 [20] minutes, p = 0.02). No serious adverse events were reported.

The hydrogel method was a safe and feasible addition to fURS, allowing improved retrieval of even the smallest fragments without added risk. The main limitations are the small sample size and absence of long-term stone-free and recurrence data, underscoring the need for larger confirmatory studies.