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Validation of STONE nephrolithometry scoring system in the management of large renal stones by percutaneous or open nephrolithotomy

Objective To assess the validity of STONE nephrolithometry scoring system in the prediction of surgical outcome following percutaneous nephrolithotomy (PCNL) for large renal stones and for the first time we further tested its applicability in open stone surgery (OSS). Patients and methods The STONE score was retrospectively calculated from preoperative noncontrast computed tomography of 100 adult patients treated for more than or equal to 20 mm renal stones with either PCNL (65 patients) or OSS (35 patients) from January 2019 till July 2020. Correlations of STONE score with operative time, estimated blood loss, primary stone-free rate (SFR), complications, and hospital stay within each group were assessed. Results The OSS group was older than the PCNL group (mean, 53 ± 11 vs. 47 ± 12 years, P=0.008), had higher stone size (mean, 7.1 ± 2.7 vs. 3.1 ± 1.5 cm, P<0.001), and STONE score (median, 10 vs. 7, P<0.001), respectively. STONE score showed an inverse correlation (P<0.001) with primary SFR within PCNL and OSS (r=−0.581 and r=−0.567, respectively). Primary SFR was more than 90% with STONE score less than or equal to 8 in PCNL and less than or equal to 10 in OSS. STONE score also directly correlated with intraoperative estimated blood loss within PCNL (r=0.389, P=0.001) and OSS (r=0.355, P=0.036) and with the operative time (r=0.400, P=0.001) only in the PCNL group. However, the score was not correlated with postoperative hospital stay or complications in both groups. Conclusions The STONE nephrolithometry score is a valid tool in the prediction of surgical outcomes following both PCNL and OSS. Additional validation of this scoring system is important particularly to confirm its general applicability for OSS.