An in vitro assessment of the flow characteristics of spiral‐ridged and smooth‐walled JJ ureteric stents

Objective To assess drainage through spiral‐ridged and smooth‐walled JJ ureteric stents (designed to ensure upper tract drainage) and thus determine whether drainage preferentially occurs around rather than through the spiral‐ridged stent, promoting renal flow and potentially facilitating the passage of urinary stone fragments. Materials and methods A mechanical ureteric model was constructed to mimic the funnel characteristics of the renal pelvis. A motor pump was used to help simulate respiratory and skeletal movement, resulting in differential motion between the intraluminal stent and the surrounding ureteric wall. Tubes of varying internal diameters were used to simulate different sizes of ureter. Flow rates of standard 7 F smooth‐walled stents were compared with 7 F spiral‐ridged stents with and without occluded lumens, and with and without standardized excursions. Results Extraluminal flow (mean rates) with and without movements simulating respiratory excursions were significantly higher with the spiral stent for all stent diameters evaluated. All flow rates increased as the ureteric diameter increased. Total flow past the spiral stent was significantly greater than flow with the smooth‐walled stent under all conditions tested. Flows measured around the spiral stent under conditions of excursion were the highest of all categories, 20‐fold higher than in smooth‐walled, closed, stationary stents. Conclusion Spiral‐ridged JJ stents provided substantially greater flow in this in vitro model. Extraluminal flow was markedly increased with the spiral‐ridged configuration. The difference in flow rates was more pronounced at the smaller pseudo‐ureteric tube diameters, simulating dimensions found in clinical practice. The flow rate also was increased when the central lumen remained open, and was greater still when there was dynamic excursion with respiratory movements.