Resistance to Extrinsic Compression and Maintenance of Intraluminal Flow in Coil-Reinforced Stents (Silhouette® Scaffold Device): An In Vitro Study

Introduction: Stenting is the best approach to manage ureteral extrinsic compression and depends on intraluminal patency, which is mainly determined by cross-sectional stability. We evaluated the resistance to extrinsic compression of the Silhouette (R) Scaffold Device and its ability to simultaneously maintain intraluminal flow. Materials and Methods: Four 8 F Silhouette stents of different lengths were evaluated for radial compression and intraluminal flow by an MTS Micro Bionix Testing System using Testworks II software. Compression was exerted in 0.2 mm increment cycles until a maximum load cell of 5 N was reached. The Young's modulus, E, was calculated from each trial using engineering stress. Flow rates were compared with the 10.2 F Cook Amplatz. Analysis of variance was used to detect differences between Scaffold stents, and Student's t-test for differences between baseline flow rates. A level of significance of p < 0.05 was used. Results: Cross-sectional area and E did not differ throughout different length Scaffold stents (average 28,856 +/- 2592; 95% confidence interval 27,447, 30,265; p - 0.426). The inner lumen of the 10.2 F Cook Amplatz was larger by 0.125 mm. Baseline flow rate of the Cook Amplatz was significantly higher than that of the Silhouette Scaffold (1.089 vs. 0.660 mL/second, p = 0.001), but the drop in the flow rate was four times faster for the Amplatz. Conclusion: The resistance of 8 F Silhouette Scaffold Device is extremely higher than that of previously tested stents, and it is uniform along the shaft and does not vary with length. The Cook Amplatz 10.2 F stent has higher flow at baseline and 2 mm compression, but its flow rate drops four times faster than the Silhouette Scaffold.