The lumbosacral angle is a significant predictor for using a semi-rigid ureteroscopic approach in middle ureteral stones

BACKGROUND: Ureteroscopy for middle ureteral stones is often difficult from an anatomical view. This study aimed to evaluate the pelvic anatomy in three dimensions and investigate the relationship between the pelvic anatomy and potential semi-rigid ureteroscopic approach for treating middle ureteral stones. METHODS: From a total of 967 patients who underwent ureteroscopy from December 2017 to January 2021, 124 patients who had middle ureteral stones were included in this retrospective cohort study. The pelvic transverse diameter, pelvic vertical diameter, pelvic depth, and lumbosacral angle were measured through preoperative non-contrast computed tomography to define the shape of the pelvic cavity. The relationship between the reachability of the middle ureteral stone using a semi-rigid ureteroscope and the aforementioned anatomical factors, as well as treatment outcomes, was examined retrospectively. RESULTS: The lumbosacral angle and female sex were significant predictors of the possibility of a semi-rigid ureteroscopic approach to middle ureteral stones [odds ratio =1.08; 95% confidence interval (CI): 1.03–1.14; P=0.003, and odds ratio =3.23; 95% CI: 1.12–9.32; P=0.03, respectively]. The cutoff value of the lumbosacral angle was 149.9°, with a sensitivity of 55.1% and a specificity of 72.7%. The time to reach the stone was longer in the lumbosacral angle <150° group than in the lumbosacral angle ≥150° group (P=0.049). CONCLUSIONS: In this study, gradual lumbosacral angle and female sex are positive predictors of the reachability of the middle ureteral stone with a semi-rigid ureteroscope.