In vitro evaluation of ureteral stent compression

Objectives. To evaluate the force required to radially compress ureteral stents and the impact of compression on stent performance across a broad range of stent sizes and manufacturers. Methods. Fourteen ureteral stents ranging in size from 6F to 10.3F were evaluated for radial compression using an MTS Micro Bionix Testing System using Testworks II software, 5N load cell, vibration isolation table, and socket set screws with rounded caps. Radial compression was exerted in 0.2-mm increments. Cycles of compression and a 100-second hold time were repeated for each stent to maximal compression. Three trials were completed for each stent. The Young's Modulus, E, was calculated from each trial using the engineering stress. Simultaneous flow data using normal saline were collected for the Amplatz stent. Results. The Cook C-Flex (E = 30,355 +/- 910 Pa), Microvasive Percuflex Plus 6F (E = 28,973 +/- 250 Pa), Cook EncloSof (E = 28,403 +/- 471 Pa), and Fossa Open Lumen (E = 28,627 +/- 5,338) were the most resistant to compression and the Cook Amplatz 10.2F (E = 11,922 +/- 220 Pa) and Microvasive Percuflex Plus 10.3F (E = 8,247 +/- 286 Pa) were the least resistant to compression. Stress relaxation occurred similarly in all stents. Flow through the Cook Amplatz stent decreased at a rate of 5 mL/s/mm of compression linearly (R-2 = 0.95). Conclusions. Stents resistant to radial compression are critical for function in the face of extrinsic ureteral obstruction. The Cook C-Flex ureteral stent resisted extrinsic compressive forces best. Although large-lumen stents are often used in this clinical situation, they were the most susceptible to compressive forces.