The biomechanical properties of the urethra in boys with hypospadias: a preliminary study.
PURPOSE
The ventral aspect of the penis in boys with hypospadias is composed of dysplastic tissue of the skin and the urethra. The aim of this study was to assess the pre-operative size and biomechanical properties of urethrae in boys with and without hypospadias using a more objective catheter-based system.


MATERIALS & METHODS
In this non-blinded clinical observation study, the study population consisted of 19 boys with hypospadias-the case group (median age 13.9 months [range: 12.2-21.3])-and seven boys without hypospadias-the control group (median age 8.5 months [range: 3.8-18.1]). Modified measurements of impedance were used to assess the size, compliance and viscoelasticity of the urethrae under stepwise increased pressures (between 0, 40 and 60 cmH2O) using a customised Endolumenal Functional Lumen Imaging probe (EndoFLIP®).


RESULTS
The sizes of the urethrae in boys with hypospadias are variable but tend towards being narrower and less compliant than those of the control subjects i.e. median diameter for meatus urethra was 3.2 mm (range: 2.98-3.92) in the hypospadias group compared with 3.64 (range: 3.22-4.44) in the control group at 40 cmH2O, and the median change in diameter at meatus urethra was 0.08 mm (range: -0.02 to 0.52) in the hypospadias group compared with 0.23 mm (range: -0.02 to 0.34) when the pressure was increased from 40 to 60 cmH2O. This biomechanical analysis found that there was no significant viscoelasticity of the urethral meatus in both the groups, whereas the remainder of the urethral structure generally had viscoelastic properties in the control group, seen as a creep on the time/diameter curves (Figure). In the group of boys with hypospadias, evaluations of the urethrae revealed varying viscoelastic abilities, ranging from abilities that were comparable with those of the control subjects to no sign of viscoelasticity at all.


CONCLUSIONS
This study is the first to measure the biomechanical properties of the urethra in children, which might help to provide an understanding as to the structural and functional changes associated with hypospadias. The urethrae in the subjects with hypospadias were variable in diameter but tended to be narrower overall, especially in the distal portion of the urethra. Furthermore, the urethrae in boys with hypospadias were frequently less viscoelastic than those of controls.


CLINICAL RELEVANCE
The EndoFLIP® system may be a future way of objectively estimating the severity of a urethral obstruction and could potentially be included in the postoperative assessment of patients with signs of hampered voiding.