Among the possible confounders from penile photographies that can affect its reliability, the optical effect that happens when you represent a 3D curved structure in 2D has never been directly studied. Again, most urologists have seen pictures in clinical practice where the angle was not exactly the one they would like it to be. How can this impact the measurements? It was a "common sense" heard across urological meetings that this could underestimate the curvature. Is this really true? And to what extent?
Our aim with this project was to better understand those points. Using an experiment and a mathematical model we were able to exclude other known confounders and have a detailed appreciation of this phenomenon.
Our results showed that this is a complex phenomenon that can either under or overestimate the readings depending on the axis of the camera deviation and the penile curvature degree itself. This error can be significant and get up to almost 100% but is always less than 5% for a camera deviation smaller than 20 degrees.
Therefore, in clinical practice, we recommend urologist to ask for an extra picture perpendicular to the curvature plane, knowing that a small error (<5%) is expected if he stays below a 20-degree deviation.
It must be said, however, that there are other sources of possible errors that can impact the reliability of this method not accounted for in our study, notably the erectile rigidity. In addition to that, complex deformities with a biplanar curve or volume-loss deformities may never be correctly evaluated with a single 2D picture.
Therefore, in office curvature assessment using a goniometer following a pharmacologically induced rigid erection is still the gold standard method to avoid OR surprises in clinical practice.
Written by: Bruno Nascimento and Jose Cury, Sexual Medicine Service, Division of Urology, Hospital das Clinicas, University of São Paulo Medical School, São Paulo, Brazil
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