A novel 3D technique to assess symmetry of hemi pelvises

Anatomical reconstruction of pelvic fractures has been shown to affect functional outcome. Using the contra lateral side of the extremities to create a template for an ipsilateral reconstruction is common practice in orthopedic surgery. We aimed to assess whether hemi pelvises are symmetrical in terms of translation and rotation using 3D reconstruction, point to point mirroring and merging of the 3D created volumes, a method with previous proven high precision and accuracy. CT images of ten randomly selected patients were used. The DICOM images were converted to STL files. Three dimensional images of left hemi pelvis were reversed and merged with the right side. The posterior aspect of the pelvises was considered static and the anterior aspect as moving. Differences in translation and rotation were measured. There were no statistically significant differences between right and left hemi pelvis. The 95% confidence interval (CI) for all mean angular differences between right hemi pelvis and mirrored left hemi pelvis were - 2° to 1.5°. The 95% CI for all mean translational differences between these two objects were - 2.3 to 2.9 mm. Differences between the right hemi pelvis and the mirrored images of the left hemi pelvis for any patient greater than 3 mm or 2 degrees could be excluded with a 95% confidence. The left and right hemi pelvis of healthy adults are symmetrical enough. The pre-operative planning based on a healthy contra lateral side seems reasonable.