Villanueva Carlos A, Nelson Carl A, Stolle Cale
University of Nebraska Medical Center/Children's Hospital and Medical Center, Omaha, NE, USA.
Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, USA; Department of Surgery, University of Nebraska Medical Center, Lincoln, NE, USA.
J Pediatr Urol. 2015 Jun;11(3):144.e1-5. doi: 10.1016/j.jpurol.2015.01.015. Epub 2015 Mar 13.
In 1959, Paquin recommended a tunnel length five times the diameter of the ureter to prevent vesicoureteral reflux (VUR) during ureteral reimplants. In 1969, Lyon et al. challenged Paquin's conclusions and proposed that the ureteral orifice was more important than the intravesical tunnel for UVJ competence. It is not known if the two mechanisms of UVJ competence (tunnel length and UO spatial orientation) are interdependent or if one is more critical. Although in clinical practice Paquin's rule has stood the test of time, classical mechanics of materials would predict more coaptation (less reflux) with larger diameter ureters and this contradicts Paquin's rule. The aim of this study was to test Paquin's tunnel length theory by parametrically modeling the ureterovesical junction (UVJ) to determine variables critical for ureteral closure.
LS-DYNA finite-element simulation software was use to model ureteral collapse (Figure). Intravesical tunnel length, ureteral diameter, ureteral thickness and ureteral stiffness were all modeled. Changes in the pressure required to collapse the ureter were studied as each variable was changed on the model. The modeled ureteral orifice was not affected by changes in bladder volume (in a real bladder, bladder distention would pull the ureteral office open) and had no constraints (which could occur by suturing the ureteral orifice to a stiff bladder).
As predicted by classical mechanics of materials, the pressure required to collapse the ureter was inversely related to its diameter. Above 1 cm tunnel length, pressures required to collapse a ureter did not decrease by any significant amount. Increasing ureteral thickness or ureteral stiffness did increase the pressure required to collapse the ureter, but only significantly for ureteral thicknesses not commonly seen in practice (i.e. wall thickness of 2.5 mm in a 6.4 mm ureter).
Our model showed that for most ureters seen in clinical practice (3-30 mm in diameter), and when the ureteral orifice is not constrained by the bladder mucosa, a 1 cm tunnel would allow the ureter to collapse under low pressures. Contrary to Paquin's belief, larger diameter ureters collapsed more easily. It is important to understand that our model's main limitation was that it did not study the effects of the ureteral orifice, which in light of our findings must play an important role in preventing reflux as suggested by Lyon et al., in 1969. For example, a 3 cm ureteral orifice sutured to the bladder mucosa would be difficult to collapse as the bladder distends and pulls open the orifice. One way of compensating for a difficult to collapse ureteral orifice would be creating a larger diameter tunnel, but another would be to create a better ureteral orifice, perhaps by narrowing the diameter of the UO (distal ureteral tapering) and making it protrude into the bladder like a volcano (i.e. advancement sutures, or creating an intravesical nipple).
We hope that this new understanding of the variables involved in ureterovesical junction competence can lead to further refinement in our surgical techniques to correct vesicoureteral reflux.
1959年，帕昆建议输尿管再植术中隧道长度为输尿管直径的5倍，以防止膀胱输尿管反流（VUR）。1969年，里昂等人对帕昆的结论提出质疑，并提出输尿管口对膀胱输尿管连接部（UVJ）的功能完整性比膀胱内隧道更重要。目前尚不清楚UVJ功能完整性的两种机制（隧道长度和输尿管口空间方向）是相互依存的，还是其中一种更为关键。尽管在临床实践中帕昆的规则经受住了时间的考验，但材料经典力学预测，直径较大的输尿管会有更多的贴合（更少的反流），这与帕昆的规则相矛盾。本研究的目的是通过对输尿管膀胱连接部（UVJ）进行参数化建模来检验帕昆的隧道长度理论，以确定对输尿管闭合至关重要的变量。
使用LS-DYNA有限元模拟软件对输尿管塌陷进行建模（图）。对膀胱内隧道长度、输尿管直径、输尿管厚度和输尿管硬度均进行了建模。研究了模型中每个变量改变时输尿管塌陷所需压力的变化。建模的输尿管口不受膀胱容积变化的影响（在真实膀胱中，膀胱扩张会拉开输尿管口），且没有约束（输尿管口缝合到坚硬膀胱上可能会出现这种情况）。
正如材料经典力学所预测的，输尿管塌陷所需的压力与其直径成反比。隧道长度超过1厘米时，输尿管塌陷所需的压力没有显著降低。增加输尿管厚度或输尿管硬度确实会增加输尿管塌陷所需的压力，但仅在实践中不常见的输尿管厚度时（即6.4毫米输尿管的壁厚为2.5毫米）才显著增加。
我们的模型表明，对于临床实践中常见的大多数输尿管（直径3 - 30毫米），且当输尿管口不受膀胱黏膜约束时，1厘米的隧道会使输尿管在低压下塌陷。与帕昆的观点相反，直径较大的输尿管更容易塌陷。需要理解的是，我们模型的主要局限性在于它没有研究输尿管口的影响，根据我们 的研究结果，正如1969年里昂等人所指出的，输尿管口在防止反流方面肯定起着重要作用。例如，一个3厘米的输尿管口缝合到膀胱黏膜上，随着膀胱扩张并拉开开口，很难塌陷。弥补难以塌陷的输尿管口的一种方法是创建更大直径的隧道，但另一种方法是创建更好的输尿管口，也许可以通过缩小输尿管口的直径（输尿管远端变细）并使其像火山一样突出到膀胱中（即推进缝合，或创建膀胱内乳头）。
我们希望对输尿管膀胱连接部功能完整性相关变量的这种新认识能够进一步完善我们纠正膀胱输尿管反流的手术技术。
