The stone cone: a new generation of basketry

We designed a device to minimize ureteral stone migration during intracorporeal lithotripsy, decrease the likelihood of stone and/or basket entrapment, and extract whole stones and fragments.

Nitinol and stainless steel wires were configured into expandable tapered cones, which were placed cephalad to in vitro and in vivo concretions, and used to trap and extract stones as well as other test material. Safety features were evaluated by measuring the release of ball bearings and the tension needed to unwind the coils of the cone, which were greater than 4 mm. in diameter. We treated 4 patients with ureteral calculi using the Stone Conedagger to prevent migration and extract fragments.

The cone-shaped devices expanded to occlude the test devices and human ureters, and prevented stone migration. They extracted whole concretions and fragments greater than 1.5 mm. The cone-shaped basket released a 5.5 mm. ball bearing at an average 0.127 pounds of tension when pulled through a 5 mm. plastic orifice. Coils greater than 4 mm. in diameter were straightened at a tension of 0.10 to 0.14 pounds. Stone migration during intracorporeal lithotripsy was prevented in the 4 patients with ureteral calculi, in whom large and small fragments were safely extracted.

The Stone Cone may be placed via a ureteral catheter and opened cephalad to a ureteral stone to prevent stone migration during intracorporeal lithotripsy. It may extract whole stones and fragments greater than 1.5 mm. It is designed, so that its coils greater than 4 mm. in diameter release concretions too wide for the ureter or ureteral orifice after approximately 0.127 pounds of tension are applied. Because of these features, the Stone Cone represents a new generation of basketry appropriate to the era of ureteroscopy and intracorporeal lithotripsy. It is worthy of further clinical study.