Working Channel Position and Flexible Ureteroscope Performance: An In Vitro Comparative Study

Flexible ureteroscopy (fURS) is a mainstay of treatment for intrarenal stones, and the position of the working channel determines the direction from which a basket or other instrument enters the endoscopic field. Working channel position (WCP) has nevertheless received little systematic evaluation as a design variable, and ureteroscopes with a 6 o'clock channel have not previously been compared with conventional 3 and 9 o'clock designs. It was hypothesized that ureteroscopes with different working channel configurations would show measurable, task-specific differences in navigation, stone interaction, and operator ergonomics under standardized conditions. Four digital ureteroscopes representing 3 o'clock (Flex-Xc, LithoVue), 6 o'clock (URUS), and 9 o'clock (Lscope) configurations were evaluated in a life-size three-dimensional printed model of the right and left collecting systems reconstructed from a de-identified patient computed tomography dataset. A single experienced endourologist performed timed navigation to each color-coded calyx, quantification of calyceal visualization using predefined intracalyceal surface dots, ureteroscope-tip contact with artificial stones, basket relocation of a stone from the lower-posterior to the upper-posterior calyx, and assessment of wrist range of motion and self-reported fatigue. Differences in navigation time, calyceal visualization, relocation time, wrist range of motion, and operator-reported comfort were observed among ureteroscopes with different working channel configurations, and these differences varied by kidney side and calyx location. Flex-Xc showed the shortest navigation times in selected calyces, URUS showed more consistent stone relocation between the two kidneys together with favorable operator-reported comfort, and Lscope required longer completion times in the right kidney. Because the devices also differed in diameter, deflection, weight, and single-use versus reusable design, these differences cannot be attributed to WCP alone. The findings identify working channel configuration as a potentially relevant design factor that requires controlled and clinical validation.