Goniometer not better than unaided visual inspection at estimating ventral penile curvature on plastic models

The assessment of penile curvature is a key component of hypospadias surgery, as it often determines if a one- or two-stage procedure should be performed. The objective of this study was to compare unaided visual inspection (UVI) against goniometry estimations of ventral penile curvature (VC) among pediatric urologists.

A total of nine different penile models (1.5 cm wide and 5-6 cm long) representing each decile of curvature from 10° to 90° were created. The nine models were divided in two groups: one with five models (group 1: 10°, 30°, 50°, 70°, and 90°) and the other with four models (group 2: 20°, 40°, 60°, and 80°). Each subject measured the VC of each model in group 1 using one method (i.e. UVI) and the curvature of each model in group 2 using the other method (i.e. goniometry). The next subject then used the opposite method for group 1 (goniometry) and group 2 (UVI), and so on, alternating the methods used to measure each group in between the subjects (Figure). The mean error (difference in between the true curvature and the subject estimation) was compared in between the two measurement methods (UVI and goniometry). A statistician calculated that 20-30 subjects would be needed to detect more than 10° difference in between the methods.

A total of 25 subjects were recruited for the study (24 pediatric urologists and 1 adult urologist). Mean errors for all degrees of penile curvature and methods ranged from 3.5° (90° model) to 13.6° (30° model). The mean error was not statistically different in between UVI and goniometry methods for any degree of curvature. A subgroup analysis of only goniometry estimations comparing subjects with and without prior experience with goniometry showed a statistically significant difference only for the 60° model. If choosing the correct surgery depended on determining if the curvature was ≤30° or >30°, all subjects would have chosen the right surgery for all except the 20°, 30°, and 40° models, where wrong surgery was chosen in 6/25, 15/25, and 7/25, respectively.

In this preliminary study, goniometry was not superior to UVI at estimating VC. There is pressing need in the field of hypospadias surgery to develop a tool that can measure VC in a reproducible and reliable fashion.