Is the impaired flow after hypospadias correction due to increased urethral stiffness?

PURPOSE A low flow rate without clinical symptoms is commonly found in boys after hypospadias correction. Urethral calibration usually shows no abnormalities. We investigated whether this impairment might be caused by increased neo-urethral wall stiffness. METHODS From polyvinyl alcohol cryogel two models of the urethra were made, hypospadias and control; both had a constant and equal inner diameter and equal compliance. The hypospadias model had a less compliant distal segment mimicking the distal neo-urethra after hypospadias correction. In both models, flow rate was recorded as a function of bladder pressure. To test whether the length of the less compliant segment had an effect on the flow rate, both models were shortened by cutting off 1-cm segments. RESULTS In a physiological range of bladder pressures (10-130 cmH(2)O) the mean flow rate (+/-1 SEM) in the hypospadias model was 2.8+/-0.3 ml/s, significantly lower (P<0.05) than in the control model (5.4+/-0.6 ml/s). Shortening of the hypospadias model showed some increase in flow rate, but this was not statistically significant. In the control model there was also no significant variation in flow rate. CONCLUSION A low-compliant segment of a urethral model reduced the flow rate. Extrapolating these results to asymptomatic boys with a low urinary flow rate after hypospadias repair might justify a watchful waiting policy.