Results
A total of 621 patients were included in the study. The patient characteristics are presented in Table 1. The median age of the patients was 46 (36-56) years, and their median BMI was 26.0 (24.0-28.6) kg/m2. Of the patients, 30.8% had a history of ESWL and 21.7% required preoperative stents. Stones were located in the pelvis in 35.9% of the patients, lower calyx in 17.9%, and multi-calyceal in (13.0%). In addition, 68 (11.0%) patients had proximal stones and 38 (6.1%) patients had stones in the middle ureter. According to the localization classification of the T.O.HO. scoring system, 46.2% of the stones were located in the middle pole and 31.2% in the lower pole, while 17.6% of the patients had multiple stones. The median stone size was 16 (12-22.5) mm, and the median stone area was 126 (77-204) mm2. Total SFR was 79.9%. Complications rate was 10.6% and the majority of complications were grade I-II (n=58, 9.3%).
Table 1 presents the comparison of patient and stone characteristics according to SFS. SFR was higher in patients with higher BMI (p = 0.018). There was statistically significant difference in SFS according to stone localization (p < 0.001). In the post-hoc analysis, the multi-calyceal stones had significantly lower SFR compared to the pelvic and proximal ureteral stones, while lower the lower calyceal stones had significantly lower SFR compared to only proximal ureter stones. According to the localization classification of T.O.HO., the lower pole stones had lower SFR compared to the stones located in the middle pole and ureter. Multiple stone number, high HU value, high stone size and stone area, and prolonged operation time and length of hospital stay were determined to be associated with fURS failure. The median T.O.HO., STONE and modified T.O.HO. scores were determined as 8, 11, and 8, respectively for the failure group and 7, 10, and 6, respectively, for the patients with SFS (p < 0.001 for all).
Table 2 shows the multivariate logistic regression analysis results of possible predictive factors associated with SFS given in Table 1. According to the results, stone area had better predictive power than stone diameter (p = 0.025). Lower pole (reference), middle pole (OR = 0.492 p = 0.016) and middle ureteral (OR = 0.227, p = 0.024) localizations, stone density (OR = 1.001, p < 0.001), and stone volume (OR = 1.008, p < 0.001) were determined as independent predictive markers for SFS. A nomogram was constructed to predict fURS failure (Figure 1). Based on the effect size of stone surface area in the nomogram, stone volume was divided into five categories, at 1-point intervals, as <120 mm2, 120-240 mm2, 240-360 mm2, 360-480 mm2 and >480 mm2. The newly created scoring system was defined as modified T.O.HO. (Figure 1). The nomogram was found to have high predictive power, with an area under the curve (AUC) value of 0.838 (Figure 2).
The T.O.HO., STONE and modified T.O.HO. scores were calculated for each patient included in our dataset. The external validation of the original T.O.HO. and STONE systems and the internal validation of the modified T.O.HO. system were undertaken. The AUC value was calculated as 0.758 for original T.O.HO., 0.634 for STONE, and 0.821 for modified T.O.HO. at the asymptotic significance of <0.001 for each scoring system (Figure 2). The cut-off value and sensitivity-specificity results for each scoring system are shown in Table 3. The modified T.O.HO. created by adding stone volume was statistically significantly superior to the original version (ROC curve comparison, p < 0.001).