Fracture of polyurethane double pigtail stents: an in vivo retrospective and prospective fluoroscopic study

To study the behaviour of pigtail polyurethane ureteric stents during breathing and change in body habitus and thereby explain some side-effects of stenting, particularly spontaneous stent fracture.

The study comprised retrospective evaluation of records and radiographs of seven patients (five men and two women, mean age 41; SD 10.9 years) who were admitted with fractured polyurethane pigtail stents, and a prospective fluoroscopic study of the behaviour of 14 stents in 12 patients (11 men and one woman; mean age 40; SD 9.3 years) during breathing, spinal flexion, extension and rotation.

Five of the seven pigtail stents fractured where the stent crossed the lateral edge of psoas muscle, 7-10 cm below the renal coil of the stent. The sixth stent was fractured at its lower third and the seventh fractured just proximal to the stent's bladder coil. The prospective study revealed a 20-80 degrees bend in the upper third of 11 of the 14 stents and a 35 degrees bend in the lower third of two stents. A 1-5 cm craniocaudal movement and a 0-2 cm vertical movement of the stents occurred during breathing and spinal flexion and extension. There were no changes in stent configuration during spinal lateral rotation or at the sacral promontary. The bend in the upper third of the ureter was profound in two stents whose vertical movement was restricted by other conditions.

As the kidney-to-bladder distance shortens during inspiration and spinal flexion, the stent adapts by bending and/or moving. Fracture of the stent may be caused by repeated mechanical stress, particularly across the side-holes, and by diminution of its tensile strength by depolymerization during long indwelling times. Large polyurethane stents tended to bow, displacing the upper ureter anteriorly, while small, soft stents conformed to the anatomical course of the ureter, suggesting that they should be used after open or endoscopic surgery to the upper two-thirds of the ureter. Stress on the stent can be minimized by choosing the correct length, particularly where vertical stent movement is limited by other conditions.