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).