Introduction of a three-dimensional computed tomography measurement method for acetabular fractures

Introduction Acetabular fractures consist of complex fracture patterns whereby bone fragments are displaced in different directions. Two-dimensional computed tomography (2DCT) gap and step-off measurements tend to underestimate the multidirectional features of these fractures. The aim was to develop a three-dimensional computed tomography (3DCT) measurement method for acetabular fractures and validate whether this method will provide an observer independent fracture characterization. Materials and methods Sixty patients, operated for an acetabular fracture between 2007 and 2018, were included. The displacement was measured on the pre- and postoperative CT scans. Pre- and postoperative CT-based 3D models were made for each patient. Multiple 3D measurements, namely the 3D step-off, gap and the total gap area were introduced to quantify the preoperative and postoperative displacement. The Wilcoxon signed rank analysis was used to compare the 2DCT and 3DCT measurements. Results The preoperative displacement was significantly underestimated by 2DCT measurements in comparison with 3DCT measurements (2D vs. 3D; step-off 8 vs. 16 mm with P < 0.001; gap 19 vs. 21 mm with P = 0.001). The same applies to the postoperative residual displacement (2D vs. 3D; step-off 0 vs. 6 mm; gap 3 vs. 8 mm; P < 0.001). The total gap area, defined as the surface area between all fracture lines in the 3D model, was measured for each patient, resulting in a median value of 722 mm2 preoperatively and 168 mm2 postoperatively, with excellent inter- and intra-rater reliability. Conclusion 2DCT measurements tend to underestimate the initial and residual displacement in complex acetabular fractures. A 3DCT analysis of these injuries was developed to overcome this and should be used in addition to the Judet/Letournel and AO/OTA classification systems, in order to provide an observer independent quantifiable fracture description and accurate assessment of the fracture reduction.