Vesicoureteral reflux (VUR) is the backward flow of urine from the bladder into the kidneys. There are many reasons for this reflux. In 1959, Paquin recommended a tunnel length 5 times the diameter of the ureter to prevent VUR based on anatomical comparisons of postmortem specimens of patients with and without VUR [1]. This has become the standard for current ureteral reimplantation surgery. In 1969, Lyon proposed that the shape of the ureteral orifice was more important than the intravesical tunnel for ureterovesical junction (UVJ) competence [2]. However, this was only considered as a supplement to Paquin’s theory. Lyon’s theory might come into play when using bulking agents to affect the shape and configuration of the ureteral orifice but is not directly taken into consideration during surgical ureteral reimplants. Since Paquin and Lyon, little research has looked at parameters regulating the prevention of VUR or leaking from Mitrofanoff type conduits. A case-control study of megaureter reimplants with and without ureteral tailoring demonstrated equivalent outcomes [3], raising concerns about the validity of the 5:1 rule. Most recently, Villanueva et al. reported that the tunnel length of ureter, which can be modified depending on different surgery cases, is not strictly required to have a 5:1 ratio of the diameter to the length [4]. Accurate quantification of the parameters that affect the ureter mechanics is helpful to improve surgical technique.

The aim of this work was to quantitatively inspect Lyon’s theory, i.e., the relationship of intravesical tunnel length and orifice shape with respect to VUR by measuring the pressure required to collapse the ureter for preventing backflow. An enhanced three-dimensional (3D) numerical model was developed considering the interaction between the ureteral orifice and the bladder wall. Parametric studies were then conducted to determine the sensitivity of UVJ competence to the spatial configuration of the intravesical tunnel as well as the ureteral orifice (UO). Two common ureteral orifice shapes, “golf” and “volcano,” as well as different intravesical ureteral tunnel length/diameter ratios, were examined. The required closure pressure was then compared.

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