In Vivo Biomechanical Assessment of Anterior Rabbit Urethra After Repair of Surgically Created Hypospadias

Abstract

We studied the in vivo biomechanical properties of the anterior urethra in a rabbit hypospadias simulation model at long-term followup after urethroplasty. A total of 38, 9-week-old white New Zealand male rabbits were randomized into active treatment and control groups. The active treatment group included hypospadias-like simulation and acute repair (sham, mobilization and advancement, tubularized incised posterior urethral plate). After 23 weeks all groups underwent biomechanical investigation using impedance planimetry. Cross-sectional area pressure measurements during bag distention were conducted at 3 different positions along the urethra, and biomechanical (tension-strain) relations were computed. The biomechanical parameters studied were urethral luminal dimension (cross-sectional area pressure relation) and its deformability to luminal pressure (tension-strain relation). The urethral cross-sectional area was significantly larger in the mobilization and advancement group compared to the tubularized incised plate group (p <0.001), shams and controls at the distal distention site (p <0.05), and other groups at the intermediate distention site (p <0.05). The strain-tension curves were not significantly different between the groups. All groups showed a nonlinear cross-sectional area pressure and circumferential wall tension-strain relationships in the 3 distention sites. The urethras exhibited a decreasing ability to be distended with increasing pressures, indicating self-protection against damage. At long-term followup no differences in tension-strain relations were found between groups, despite the fact that the mobilization and advancement group had enlarged urethras. Our hypospadias simulation animal model could be useful to test commonly used or new urethroplasty techniques and their functional (biomechanical) long-term results before clinical use.