Introduction: Currently two technologies, super pulsed thulium fibre laser (TFL) and the Moses laser using the holmium fibre (HLM) are most effective for lithotripsy by flexible ureteroscopy(f-URS) for renal stones. The primary aim of our study is to compare and contrast the outcomes of these two laser technologies in our cohort of 2075 patients enrolled in the FLEXible ureteroscopy Outcomes Registry (FLEXOR) project .Our secondary aim is to evaluate if either technology was superior in stone free rate(SFR) and complications. Methods: Patients who underwent f-URS for renal stones between January 2018 and August 2021 were retrospectively analysed . Patients aged <18 years, ureteral stones, concomitant bilateral procedures, or musculoskeletal abnormalities were excluded .Kolmogorov-Smirnov test was used to check data distribution for normality. Continuous data presented as mean and standard deviation and categorical data as absolute numbers and percentages. Analyses repeated after propensity score matching (PSM) to adjust for bias. One-to- one matching for age, gender, stone location, single/multiple stone, and HU estimated. Univariate logistic regression analysis was performed to evaluate factors for SFR from PSM population. Multivariable assessment done and estimated as odds ratio (OR) and 95% confidence interval (CI), and p-value. Results: Before PSM matching, there were 508 patients in the HLM and 1567 in the TFL groups. The population in the TFL group were significantly younger (mean age 46.44±14.01 years), larger stone diameter (14.35±7.37 mm p<0.001), single stones (65.6% vs 42.5%, p<0.001) and stones located in the pelvis (46.4% vs 17.1%, p<0.001).Mean stone density was significantly higher in HLM group (1115±386 vs 1068±331 HU, p=0.016). Mean lasing time was significantly longer with HLM (29.40±14.25 vs 20.90±16.47 minutes, p=0.01) and longer total surgical time in TFL (73.41±51.14 vs 61.03±29.47 minutes, p<0.001).TFL group experienced more infective complications. SFR was significantly higher in the TFL group (89.9% vs 61.6%, p<0.001). There were 297 patients in each group after PSM matching. Pure dusting was performed in 5.7% of the HLM group compared with 28.8% in TFL group. A larger proportion of patients required stone extraction in the HLM group compared to the TFL group. (89.2% vs 40.5%, p<0.001). Lasing time did not differ significantly. Total operation time was significantly longer in the TFL group (74.75±51.38 vs 62.42±29.98 minutes, p<0.001). There were 11 patients who had sepsis in the TFL group and none in the HLM group (p=0.002). SFR was significantly higher with TFL (84.8% vs 56.6%, p<0.001). Conclusions: In our global study TFL was the winner with significantly higher SFR and a better laser for treating renal stones by dusting especially in larger stones A higher rate of sepsis cautions its careful use. MOSES laser lithotripsy is equally effective for fragmentation and extraction but need for ancillary treatment for RF was higher and urologists should counsel patients accordingly. SOURCE OF Funding: NIL
