Ergonomics in Endourology: Measurement of Force for Deflection in Contemporary Ureteroscopes.

Few studies have examined the ergonomic hazards to endourologists during endoscopic procedures. We have evaluated the forces required to deflect different flexible ureteroscopes across a range of measurements with several different standard instruments within the working channel. Five ureteroscopes were studied: the Uscope, Neoflex, LithoVue, URF-P6, and the Flex-X2. A pull-force meter (Nextech DFS 500) was attached to the thumb lever to deflect the tip from 30° to 210° at 30° intervals. Measurements were made with upward and downward deflection separately. The forces were reported in Newtons (N) to the nearest 10th, as positive values regardless of the direction of the force. Measurements were made with the channel empty or containing an instrument: a 365 μm laser fiber, a 2.4F Nitinol basket, 3F biopsy forceps, or a 0.038" guidewire using the flexible or the stiff tip. The maximum downward deflection force, measured at 210° of deflection, with an empty channel range from a minimum of 5.7 N in one scope to a maximum of 33.4 N in another. The force necessary for deflection ranges from 2.0 to 7.0 N (0.45-1.57 foot-pounds) at 30° to 8.5 to 25.3 N (1.8-5.69) at 180°. Maximum upward deflection shows similar results with a minimum of 7.9 N in one scope and a maximum of 43.1 N of force in another. Working instruments in the channel increased the force needed for deflection. Forces required for steep deflection of the tip of a flexible ureteroscope reach extremely high levels or limit the deflection capability of the scope. The force is higher with increased deflection and with instruments within the channel.