Prediction of Residual Fragments After Flexible Ureteroscopic Stone Management: A Critical Evaluation Based on Patient- and Stone-Related Parameters

<b>Aim</b>: This study aimed to evaluate the potential impact of stone characteristics, patient factors, and upper tract anatomical parameters in the prediction of residual fragments (RFs) following the flexible ureteroscopic (fURS) management of renal stones. <b>Patients and Methods</b>: Between June 2023 and July 2024, a total of 104 cases underwent fURS for the minimally invasive management of medium-sized renal stones (10-25 mm), and 28 cases presenting with RFs 3 months after these procedures were included for further evaluation. In addition to the assessment of patient-related factors, non-contrast computed tomography (NCCT) was performed in all cases in an attempt to assess specific stone characteristics and upper tract anatomical parameters in detail during the 3-month follow-up period. <b>Results</b>: An evaluation of our findings indicated that, among the evaluated parameters, a higher degree of hydronephrosis (>Grade 2), a larger stone size (>15 mm), and the presence of multiple stones were found to affect the presence of RFs significantly (<i>p</i> = 0.020, <i>p</i> = 0.012, and <i>p</i> = 0.040, respectively). On the other hand, although the analysis of other parameters such as patient gender, stone side, stone hardness, and the use of an access sheath with univariate regression demonstrated potential correlations, none of these parameters demonstrated a significant impact when analyzed using backward logistic regression. Logistic regression revealed that Grade 2 hydronephrosis (OR = 18.3, <i>p</i> = 0.020), stone size > 15 mm (OR = 7.0, <i>p</i> = 0.012), and multiple stones (OR = 3.7, <i>p</i> = 0.040) significantly increased the risk of residual fragments following fURS. <b>Conclusions</b>: In light of our findings and published data, we can conclude that endourologists should consider the likelihood of RFs' presence after successful stone disintegration with fURS. A detailed evaluation of the relevant factors revealed that patients with larger stones, higher degrees of hydronephrosis, and multiple calculi may carry the risk of residual fragments after these procedures. Thus, the utilization of such reliable predictive parameters may aid in selecting optimal stone removal strategies and planning subsequent interventions in the rational management of RFs.