Does working channel position influence the effectiveness of flexible ureteroscopy? Results from an in vitro study.

Objective: To evaluate whether the position of the working channel affects the effectiveness of flexible ureteroscopy. Materials and Methods: We compared the ureteroscopes Flex‐X2S and Flex‐XC (working channel at the 9 and 3 o'clock positions, respectively) in eight cavities of a K‐Box model, simulating the distribution of the right and left intrarenal calyces. In the first and second settings, each cavity contained a 1‐cm stone, lying on the bottom and fixed on the anterior sheet covering the box, respectively. In the third setting, the posterior and lateral surface of each cavity was draped with graph paper. Once the flexible ureteroscope entered each cavity, we measured and compared (i) the proportion of stone surface targeted by the laser (STL) and (ii) the proportion of graph paper burned by the laser (PBL) obtained with the two instruments. Results: Higher STLs and PBLs were obtained with the 3 o'clock position than the 9 o'clock position in the right posterior and left anterior cavities (mean ± sd STL 87% ± 15% vs 46% ± 38% and 78% ± 35% vs 43% ± 24%, respectively; P < 0.05), and on the right posterior surfaces of the middle‐lower/lower cavities (PBL 72% vs 31% and 77% vs 35%, respectively; P < 0.01) and on the left lateral surface of the lower cavities (PBL 45% vs 25%; P = 0048), respectively. Conversely, the 9 o'clock position provided higher STLs and PBLs than the 3 o'clock position in the left posterior and right anterior cavities (mean ± sd STL 84% ± 20% vs 65% ± 28% and 79% ± 30% vs 44% ± 35%, respectively; P ≤ 0.02), and on the left posterior and right lateral surfaces of the lower cavities (PBL 59% vs 34% and 50% vs 21%, respectively; P ≤ 0.04). Conclusions: The position of the working channel of the flexible ureteroscope should be considered when planning flexible ureteroscopy, especially when dealing with the lower pole. [ABSTRACT FROM AUTHOR]