The Effect of Holmium Laser Fiber Bending Radius on Power Delivery During Flexible Ureteroscopy

Flexible ureteroscopy is a mainstay of upper urinary tract stone treatment. Holmium laser lithotripsy is a particularly common and notable technique for the dusting and fragmenting of renal stones. During ureteroscopy, optical fibers are subject to sharp bends in pursuit of stones, particularly those at the lower pole. Following from principles of fiber optics, subjecting these fibers to sharp bending angle has the potential to reduce the efficiency of power transmission at the fiber tip. Due to the potential implications this hypothesis could have on endourological practice and research, we aimed to explore the potential impact of fiber bending on end-fiber power output. Using a highly sensitive oscilloscope and a urological holmium laser, we assessed the end-fiber power output under a variety of bending conditions. To ensure maximal confidence in our results, the maximal bending conditions explored substantially exceeded any condition, which could occur during ureteroscopic surgery. We found evidence that bending radius alone has a clinically insignificant impact on the light power transmission in the fiber. At certain bending conditions, we observed a clinically unimportant but statistically significant reduction in power transmission. This was verified using two commonly used delivery fiber types exposed to 8-second bursts for each bending condition.