Retrieval and releasing capabilities of stone-basket designs in vitro

A serious problem during calculus retrieval is the inability to release a stone from the basket. We evaluated a variety of basket designs to address this issue in two in-vitro models.

Four baskets--a modified, flat-wire, a double-helical, and two tipless Nitinol models (a passive and an articulating type)--were evaluated. The ability to retrieve and release beads of 4, 6, 8, 10, 12, and 14 mm diameter was compared in both a ureteral and a caliceal model.

In the ureteral model, all baskets were successful in retrieving all sizes of beads as long as the bead was smaller than the measured basket diameter. Only the articulating (all sizes) and larger non-articulating Nitinol models were able to release each of the bead sizes once engaged. The double-helical basket (larger size only) was able to release only the 4- and 6-mm beads after retrieval. For the 10- and 12-mm beads, the respective articulating Nitinol baskets could liberate the bead only when the articulating mechanism was used. In the caliceal model, the flat-wire and double-helical baskets were unsuccessful in all attempts at retrieval. The larger non-articulating Nitinol model was successful for beads >8 mm but had difficulty retrieving those smaller. Only the articulating Nitinol models were able to engage and release each of the beads.

From these in-vitro studies, it is apparent that the Nitinol basket designs have the best retrieval capabilities. The ability to articulate the basket improves release of a stone once engaged.