Digital and mechanical characterisation of ureteral stent luminal reduction in response to extrinsic compression forces.

Abstract

Purpose To investigate the principles that govern ureteral stent failure by digitally and mechanically characterising their luminal reduction in response to various extrinsic compression forces. To explore the relationship between ureteral stent 'material area', 'luminal area' and 'cross-sectional area (CSA)' for resisting extrinsic compression forces. Materials and Methods 4.8 French (Fr, n=9), 6Fr (n=9), and 7Fr (n=9) ureteral stents were mechanically investigated to determine parameters that contribute to resisting radial compression forces. Digitalised images of luminal reduction values under incrementally increased reductions of stent outer diameters were obtained (0%, 25%, 50% and 60% of original outer diameter). Forces (N) and percentage (%) luminal reduction that resulted in complete ureteral stent obstruction were determined. Results Uniaxial incremental compression in the radial direction demonstrated complete luminal reduction (95-100%) when 58-62% of the outer stent diameter was compressed. 6Fr ureteral stents demonstrated the greatest resistance to extrinsic compression and the greatest 'material area' relative to 'cross-sectional area' (CSA, mm2). The force (Newton, [N]) required for 50% compression of outer stent diameter was 10.44N, 28.13N and 25.39N for 4.8Fr, 6Fr and 7Fr ureteral stents respectively. The 'material area'/'CSA' at 50% compression of outer stent diameter was 76%, 86% and 78% for 4.8Fr, 6Fr and 7Fr ureteral stents respectively Conclusions Maintenance of intraluminal stent diameter in the presence of extrinsic compressive forces is primarily dependent on the stent's ratio of 'material area' to 'cross-sectional area'. Urologists should be aware of these findings to decrease the risk of ureteral stent failure when treating extrinsic ureteral obstruction.