BACKGROUND: A specific aspect of the hypospadias phenotype that may contribute to long-term outcomes is the presence of ventral penile curvature and the adequacy of its surgical correction. The current gold standard to assess this angle is intraoperative goniometry of an erect penis. Beyond its potential technical limitations, an angle measured by goniometry cannot be re-evaluated retrospectively once the curvature is corrected. 3-dimensional (3D) modeling technologies may overcome these limitations through their combination of digital image and geometric replication to produce 3D digital forms of a physical structure. These technologies have previously been used in orthopedics, plastics and craniofacial surgery to document dysmorphism and perioperative anatomy. The aim of this study is to evaluate the measurement accuracy and reliability of modern handheld 3D modeling technologies versus standard goniometry for angle assessment in a laboratory setting.

METHODS: Blocks with specified angles (10 to 45 degrees; 1”x1” base, 2” height) were printed using a Zortrax M200 3D printer (±0.2% accuracy). Following the completion of standardized education, blinded participants measured each block angle using a Baseline digit goniometer. Participants were classified as expert or novice based on urological training. Complete digital models of the blocks were created using 3 modeling technologies. Structured light scanning was completed using an Artec Space Spider and Artec Studio 13. Traditional photogrammetry was completed using a Canon Eos Rebel T5i DSLR camera and Agisoft Metashape Pro. Finally, photogrammetry with a 3D camera was completed using the VECTRA H1 and VECTRA Analysis Module. Regardless of the modeling modality, all 3D models were then imported into the software Autodesk Inventor in which the mean of six automated angle measurements through the central plane was obtained. The reliability for using goniometry and the 3 modeling technologies were tested using two-way random effect models with absolute agreement. All the analyses were performed using SAS (9.4) NC Cary.

RESULTS: Six 3D printed blocks were evaluated. 5 digital models per block were created using each of the 3 modeling technologies. 12 participants completed goniometry (7 expert, 5 novice). Inter-rater reliability of goniometry was moderate (ICC 0.76, 95% CI 0.46, 0.92). There was no significant difference between naive and expert participants in assessment of goniometric angle (p=0.7). Test-retest reliability of the 3 modeling technologies were excellent: structured light scanning (ICC 0.99; 95% CI 0.99, 0.999); traditional photogrammetry (0.99; 0.998, 0.999); 3D camera (0.99; 0.998, 0.999). Mean angle measurements and standard error for each angle and modality are listed in the attached table.

CONCLUSIONS: This study demonstrated excellent reliability of off-the-shelf, readily used, handheld 3D modeling technologies in comparison to goniometry when applied to measurements of angulation in small blocks. In particular, we have demonstrated high-fidelity model creation of angles that have historically been most challenging to measure using either goniometry or eyeball analysis in a 3D printed penile model (Villanueva SPU 2019). These 3D modeling technologies may provide reliable, reproducible phenotypic analysis of congenital genitourinary conditions for future intraoperative and database development applications.

Authors: Allen E. D. Siapno BA, Brendan C. Yi BA, Doug Daniels BA, Aswani Bolagani MPH, Lorna Herbert MPH, Shantanu Joshi PhD, Renea Sturm MD