In vitro evaluation of ureteral perforation forces

Ureteroscopy has become a very effective treatment option for ureteral and upper tract abnormalities. The reported complication rates have ranged from 1.5% to 13% for perforations and have been less than 1% for avulsions. We present a study that quantified the ureteral avulsion force in porcine ureters and ureteral perforation forces in human and porcine ureters.

The avulsion force was measured in six porcine kidneys. A 2.4F stainless steel flat-wire basket was advanced through an incision made in the renal pelvis, and a 10-mm stone was placed in the extraction basket. The external end of the basket (handle) was attached to a miniature, low-force load cell and slowly pulled with increasing force until the ureter avulsed. The ureteral perforation forces were measured in 10 fresh porcine and 9 human ureters. Perpendicular perforation with either the blunt end of a CT-1 needle (0.038 in.) or the back end of a stiff guidewire (0.035 in.) was measured using the miniature, low-force load cell.

The average maximal force to avulse the pig ureter was 2.21 +/- 0.43 pound-mass (lb(m)). The force required to perforate the porcine ureter was significantly greater than that required to perforate the human ureter, irrespective of whether a needle (1.70 +/- 0.26 lb(m) versus 1.05 +/- 0.29 lb(m), P = 0.019) or guidewire (1.30 +/- 0.25 lb(m) versus 0.79 +/- 0.25 lb(m), P = 0.013) was used. Greater force was required to perforate with the needle than with the guidewire in both the porcine (P = 0.037) and the human (P = 0.26) ureter.

Quantifying the ureteral perforation forces will facilitate the design of endourologic devices, open the door for "smart devices" that sense forces and provide feedback, provide information critical to the design of endourologic and suturing simulators, and, finally, establish competency parameters for professionals in training.