[Implementation of a scale on stone baskets]

Complications after endoscopic retrieval of kidney and ureter stones are obviously related to the size of the stones as well as the experience of the surgeon and other factors. During the procedure it is sometimes difficult for surgeons to estimate stone size and therefore give prognostic advises. The visual perception of the stone size depends on the shape, colour, distance to the renoscope and dilatation of the ureter. This is the so-called binding problem, because shape, color and direction of motion are processed separately by different population of optical neurons. In order to establish a better prognostic ratio, especially for less experienced surgeons we established an intraoperative semi-quantitative measurement of the stone size supported by a stone basket.

We modified the tipped nitinol stone baskets from the company Urotech with diameters of 2.5, 3.0 and 4 Ch. The handle of this basket has a spring mechanism, which automatically closes the basket and provides a predefined fixation force of the stones within the basket. On the handle we established a non-linear scale in mm by grabbing standardized balls or standardized screws.

The scales are nonlinear because of the nonlinear relation between the diameter of the stone and the distance of the slider. Also the scales differ in between the basket size, because of the different strain conditions due to the different wire sizes and materials or the spring and basket.

This scale could be an important orientation for a surgeon during endourological procedures to estimate stone sizes. It could be used also for the documentation of the size of fragments after an endourologic lithotripsy and could help in the decision for or against an extraction. Finally it could be very interesting for other disciplines like gastroenterology. The scale should be validated in further clinical trials.