Influence of coil number on the retention strength of ureteral stents: an experimental investigation.

Ureteral stents are temporary implantable devices used to maintain urinary drainage and prevent obstruction. Most designs incorporate pigtail coils to reduce migration; however, the contribution of terminal coil configuration to retention strength remains unclear. This study evaluated the retention behavior of five commercially available Double-J ureteral stents commonly used in Indonesia, representing different intended indwelling durations and terminal coil configurations. Stent length, outer diameter, inner diameter, material, angular sweep, and estimated coil number were recorded. Terminal coil number was estimated from available pre-test photographs using manual image-based angular sweep analysis. Specimens were immersed in artificial urine for one month and tested according to ASTM F1828-22 using a custom pull-out device. 1.5 coil stents showed higher mean retention forces (0.061-0.065 N) than 1 coil stents (0.010-0.034 N). Statistical analysis confirmed significant differences among stent types (F = 72.76, p = 4.665 × 10-10). However, because the tested specimens differed in material and geometry, the observed differences should be interpreted as the combined effect of coil configuration and associated stent design rather than coil number alone. These findings represent comparative in vitro retention behavior and should not be interpreted as direct clinical thresholds for migration prevention.