A simple method for calculating acetabular posterior wall fracture fragment percentages on three-dimensional computed tomography scan reconstruction images

Background: Hip joint congruency and stability in fractures are affected by posterior wall fragment size and percentage compared with the normal side. Computed tomography (CT) scan is a useful tool to precisely evaluate the morphologic features of acetabular fractures. Aim: The aim of this study was to establish an accurate and reliable method of measuring acetabular posterior wall fracture fragment percentages on three-dimensional (3D) CT scan reconstruction images. Methods: CT scans of eight patients with acetabular posterior wall fractures were reviewed by five orthopedic surgeons. Posterior wall fracture fragment percentages were measured using three methods: (1) linear measurement percentages on axial CT images, (2) linear measurement percentages on 3D reconstruction images, and (3) acetabular posterior surface area measurements using computer software (gold standard). Analysis of variance testing was used to compare these methods. Dunn's multiple comparison test was used to compare the accuracy of the axial CT scan and 3D reconstruction methods to the gold standard method. Results: There were no significant differences between two of the eight patients (25%) in fracture fragment percentage measurements using all methods. Dunn's multiple comparison test showed that the axial CT scan method measurement was significantly different from the gold standard measurement in four of the eight patients (50%), three of whom sustained more than an 80% fracture. However, there was no significant difference between the 3D reconstruction and gold standard methods in all study patients. Inter- and intra-observer reliabilities were excellent for all three methods. Conclusion: The 3D reconstruction image method is reliable and accurate for measuring acetabular posterior wall fracture fragment percentages.