Results
A total of 176 patients who had initial RIRS for kidney stones were included in this study. Age, gender, follow-up period, stone side, BMI, operative difficulty were not significantly different between groups, except for size and density (detailed demographic and clinical data of the patients are summarized in Table 1).
Immediate intraoperative SFRs for the group 1 and group 2 were 43.14% (n=22/51) and 57.6% (n=72/125), respectively. Postoperative radiologically controlled residual stone fragments after initial RIRS for group 1 and group 2 were 37.25% (n=19/51) and 40.8% (n=51/125), respectively. SFR after second-look flexible URS improved from 40.8% to 93.6% (n=117/125); for the eight patients who were not considered stone-free, the RSFs were visibly smaller than 1 mm and were not retrievable with a basket.
The univariable analysis indicated that BMI, size, operative difficulty, and type of intervention (group 1 vs. group 2) were significantly associated with SREs (Table 2). The SRE rate increased by 19.6% for each 5 mm increment in stone size.
Age, stone density, stone type, side, gender, and radiologic RSF were not significantly associated with SREs (data not shown).
Accordingly, the final model variables were the type of intervention, operative difficulty, stone size, BMI, residual stone, and stone density (p<0.001). Type of intervention, stone size, and BMI were independent prognostic factors for SREs. When group 2 was taken as a reference, the odds ratio was 8.48 (95% CI: 2.95-24.42) for SREs in group 1. The odds ratio was 1.62 (95% CI: 1.21-2.18) for increasing stone size (Table 2).
In 69% (n=121) of the whole cohort, no postoperative SRE was recorded. Urinary infection, asymptomatic stone growth, and re-operation were recorded in 10.2% (n=18), 6.8% (n=12), and 6.2% (n=11) of the patients, respectively. Nine patients had postoperative SWL, four patients reported renal colic, and one patient was admitted to the emergency room due to unrelieved colic symptoms.
Renal colic (5.9% vs. 1%), urinary tract infection (16% vs. 8%), emergency room admission (2% vs. 0), SWL (15.69% vs. 0.8 %), and reoperation (13.8% vs. 3%) rates were significantly higher in the group 1, while asymptomatic stone growth (4% vs. 8%) was higher in the group 2 (Table 1). Initial stone sizes were larger than 20 mm in patients who had reoperations in group 2.