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Modeling the Effects of Gravity and Patient Positioning on Stone Migration during Ureteroscopy with Laser Lithotripsy
Juanita Velasquez Ospina1, Ashley Gordon1, Julio Ojalvo2
1Miller School of Medicine, Desai Sethi Urology Institute, University of Miami, Miami, Florida, USA.
Introduction:
Residual lower pole fragments are a common limitation of ureteroscopy, yet the optimal patient positioning to minimize stone migration remains undefined. This study aimed to evaluate the impact of Trendelenburg (head tilt) and lateral body roll (body tilt) on stone migration within the kidney using physics-based simulation.
Methods:
Three-dimensional collecting system models were generated from delayed-phase CT urograms using RadiAnt™. These hollowed models and an open-source stone model were imported into NVIDIA Isaac Sim™ (physics-based simulator). Stones were placed in the upper pole and subjected to gravity and a random contact force directed toward renal pelvis to simulate stone migration during laser fragmentation. Five angles (0°, 5°, 10°, 15°, 20°) of head tilt and body tilt, independently and in combination, were tested with 100 simulations per configuration to evaluate lower pole migration. Stone migration between sides was compared with a Mann-Whitney U test. Two-way analysis of variance (ANOVA) assessed head tilt and body tilt effects, with paired t tests and Pearson's correlation quantifying their impact.
Results:
From 20 CTs, 20 left and 18 right collecting systems were extracted. Average lower pole migration was 14.0 ± 5.5 (left) vs. 13.2 ± 5.4 (right), with no significant difference (U = 120,568, p = 0.056). Two-way ANOVA revealed significant effects of head tilt (F = 929.99, p < 0.0001) and body tilt (F = 513.42, p < 0.0001), without interaction (p = 0.37). Paired t test showed no difference between tilt types (p = 0.056). Increased head tilt and body tilt correlated with reduced lower pole migration (r = -0.744 and -0.552, p < 0.0001).
Conclusion:
Simulation findings suggest combined head and body tilt can reduce stone migration to the lower pole but challenge the convention of one ideal angle. These adjustments may improve stone clearance during ureteroscopy.
