The 5:1 rule overestimates the needed tunnel length during ureteral reimplantation

Paquin asserts that in order for ureterovesical junctions (UVJs) to prevent reflux, the ureteral tunnel length-to-diameter ratio needs to be 5:1. We hypothesize that the surgical implementation of this observation results in an overestimation of the needed length-to-diameter ratio to prevent vesicoureteral reflux.

With finite elements, we model the urine storage phase of the bladder under nonlinear conditions. In the reference state, the bladder is assumed to be a sphere with an oblique straight elliptical hole as the UVJ. Broad parametric studies on different length-to-diameter ratios are performed as the bladder volume increases from 10% to 110% capacity.

The capability of the UVJ to prevent reflux during storage depends on its length-to-diameter ratio. UVJs with larger length-to-diameter ratios lengthen and narrow as the bladder volume increases, causing the closure of the UVJ and rise in its flow resistance. Our model shows that the UVJ length-to-diameter ratio decreases as the bladder volume increases. The 5:1 ratio implemented at 80% capacity-approximate volume or bladder wall stretch during ureteroneocystostomy (UNC)-corresponds to 7:1 at the reference state-used by Paquin. The 5:1 ratio implemented at the reference state corresponds to 3:1 at 80% capacity.

Our modeling results are consistent with Paquin's original observation on the significance of the UVJ length-to-diameter ratio in preventing reflux. They, however, indicate that the surgical implementation of this rule during UNC results in an overestimation of the requisite tunnel length-to-diameter ratio to prevent reflux. They also suggest that the UVJ closure is due to the bladder wall deformation rather than the pressure.