Symmetry matching of the medial acetabular surface - A quantitative analysis in view of patient specific implants.

Objective: To quantify intrapelvic surface symmetry in reference to a preshaped suprapectineal acetabular implant. Methods: In this cross-sectional study, an anatomically preshaped acetabular fracture implant was fitted on 3D surface models of 516 pelvises from a preexisting bone database using a software tool for automated implant fitting (SOMA, Stryker Orthopaedic Modeling and Analytics) of a CAD model of the implant. The distances between bone and the reference implant were measured at 2310 reference points for each hemipelvis. Results: The average distance between the left hemipelvis and the plate was 1.98 mm (median, 10% percentile: 1.45, 90% percentile: 2.78) and 2.0 mm (median, 10% percentile: 1.45, 90% percentile: 2.92) between the right hemipelvis and the plate. There was no significant difference between the 2 hemipelvises (median absolute pairwise delta: 0.25 mm; 10% percentile: 0.04, 90% percentile: 0.82; Wilcoxon, P = 0.064). Conclusions: With regard to the periacetabular surface of the inner pelvis, the pelvis can be considered sufficiently symmetric for using the mirrored contralateral hemipelvis as a template for patientspecific implants in acetabular fracture fixation.