Urinary system stone treatment management varies according to the characteristics of the stone and patient preference and physician experience. Treatment options include medical therapy, extracorporeal shock wave treatment (ESWL), percutaneous nephrolithotomy (PCNL), and ureterorenoscopy (URS).1 In addition to PCNL being recommended for stones of >2 cm in size, with the recent developments in the device and laser technologies and increase in surgeon experience, flexible URS (fURS) is also reported to result in satisfactory stone-free rates (SFRs) in these stones.2,3 Xu et al. reported that effective treatment could be applied even in stones with a cumulative burden of >4 cm.4 The usage area and popularity of fURS is increasing day by day.5 With the widespread use of fURS in large renal stones, the choice of treatment will become more and more difficult.
Many scoring systems have been developed to predict the success of ESWL, URS, and PCNL in urinary system stones.6–9 It has been proven that stone-free status (SFS) and development of complications can be effectively predicted with scoring systems, especially in PCNL.10 In the literature, several scoring systems, including Resorlu-Unsal11, STONE12, S-ReSC13, and R.I.R.S.14 and one nomogram15 have been defined to predict the success of fURS. Among these scoring systems, only STONE score is used for kidney and ureter stones. The STONE scoring system consists of the parameters of (S)ize, (T)opography (stone localization), (O)bstruction, (N)umber of stones, and (E)valuation of stone density (Hounsfield unit, HU). Although the developing authors reported high predictive values for this system, their patient data belong to 2006-2012.12 Considering that the STONE scoring system would not preserve its predictive value in the face of developing technology, Hori et al. developed a practical scoring system comprising the (T)allness, (O)ccupied lesion, (HO)unsfield unit components and named it T.O.HO.16 In the current study, we aimed to evaluate factors associated with SFS in patients treated with fURS for ureteral and kidney stones and perform the external validation of the T.O.HO. and STONE score. We also aimed to derive a modified version of the T.O.HO. score and perform the internal validation of this version.