Computational and experimental study on kidney stone removal in the renal pelvis

Kidney stones, mineral and salt deposits that can obstruct the urinary tract and impede urine flow, cause significant discomfort and pain to affected individuals. Surgical techniques are commonly employed to break down large stones into smaller ones, making the resulting fragments easier to remove by urine flow. However, the precise optimal size that maximizes stone clearance, reduces intervention times, and ensures effective treatment is still unclear. To determine this critical dimension, it is crucial to comprehend the forces involved in stone motion and transportation within the renal pelvis. The clinical scenario studied in the current work involved a patient resting on a hospital bed after undergoing a procedure for renal calculi ablation. Given the horizontal orientation of the kidney, stone fragments resulting from surgery were considered to settle at the bottom of the pelvic cavity. Based on these assumptions, the impact of kidney fluid dynamics on the dislodgment of the deposited grains was investigated by following two approaches. Firstly, computational fluid dynamics (CFD) was employed to simulate the urine flow field within the renal pelvic cavity. Incipient motion criteria were then applied to interpret the computational results and served as a predictive tool for grain entrainment. Additionally, the clinical scenario was replicated experimentally. Stone-like grains were introduced into a 3D-printed model of the renal pelvis and water was injected into the model at physiological flow rates using a peristaltic pump. A camera was used to visualize and record any particle displacement at the bottom of the pelvis. Overall, both computational and experimental results suggested that, when determining the critical diameter at which stones should be reduced, urine flow dynamics does not significatively contribute to grain dislodgment. As an innovative exploration of this issue, the current work lays the foundation for future research on the processes occurring in the kidney that influence stone motion and evacuation. This can provide clinicians with more effective guidelines for stone surgical interventions, leading to a relevant enhancement in surgical outcomes.