Comparison Between Holmium:YAG Laser with MOSES Technology vs Thulium Fiber Laser Lithotripsy in Retrograde Intrarenal Surgery for Kidney Stones in Adults: A Propensity Score–matched Analysis From the FLEXible Ureteroscopy Outcomes Registry

Purpose: We evaluated stone-free rate and complications after flexible ureteroscopy for renal stones, comparing thulium fiber laser and holmium:YAG laser with MOSES technology. Materials and Methods: Data from adults who underwent flexible ureteroscopy in 20 centers worldwide were retrospectively reviewed (January 2018-August 2021). Patients with ureteral stones, concomitant bilateral procedures, and combined procedures were excluded. One-to-one propensity score matching for age, gender, and stone characteristics was performed. Stone-free rate was defined as absence of fragments >2 mm on imaging within 3 months after surgery. Multivariable logistic regression was performed to evaluate independent predictors of being stone-free. Results: Of 2,075 included patients, holmium:YAG laser with MOSES technology was used in 508 patients and thulium fiber laser in 1,567 patients. After matching, 284 patients from each group with comparable baseline characteristics were included. Pure dusting was applied in 6.0% of cases in holmium:YAG laser with MOSES technology compared with 26% in thulium fiber laser. There was a higher rate of basket extraction in holmium:YAG laser with MOSES technology (89% vs 43%, P < .001). Total operation time and lasing time were similar. Nine patients had sepsis in thulium fiber laser vs none in holmium:YAG laser with MOSES technology (P = .007). Higher stone-free rate was achieved in thulium fiber laser (85% vs 56%, P < .001). At multivariable analysis, the use of thulium fiber laser and ureteral access sheath ≥8F had significantly higher odds of being stone-free. Lasing time, multiple stones, stone diameter, and use of disposable scopes showed significantly lower odds of being stone-free. Conclusions: This real-world study favors the use of thulium fiber laser over holmium:YAG laser with MOSES technology in flexible ureteroscopy for renal stones by way of its higher single-stage stone-free rate. Flexible ureteroscopy (F-URS) is a first-line option for kidney stones up to 2 cm in diameter1,2 and is suitable even for patients with larger stones,3 renal malformations,4 obesity, bleeding diathesis, and calyceal diverticula5 under general and spinal anesthesia,6 with good stone-free rate (SFR) and low morbidity. Over the past 3 decades, holmium laser lithotripsy has been predominantly carried out using standard-power machines (ie, 20 W). More recently, the availability of high power has allowed a wider range of pulse energy, frequency, and power settings to improve lithotripsy.7 In holmium:YAG laser (HL), variations in pulse modulation have introduced the concept of holmium:YAG laser with MOSES technology (HLM), virtual basket, and vapor tunnel allowing for more efficient stone ablation and less retropulsion.8 In vitro studies demonstrated that pulse modulation technology resulted in more efficient stone ablation together with less retropulsion for both hard and soft stones.9,10 Thulium fiber laser (TFL), which emerged in 2018,11 was found in preclinical studies to allow for ablation at twice the speed of HL with 4 times the amount of dust generated.12 Despite a recent single-center randomized clinical trial demonstrating no significant clinical advantage of one technology over the other,13 no direct comparison has been published comparing HLM with TFL in F-URS for renal stones in real-world practice, and much controversy continues to exist among experts in the field.14,15 The purpose of the present study was to evaluate outcomes and complications after F-URS for renal stones, comparing patients who were operated on using HLM vs TFL.