Validation of a CT image based software for three-dimensional measurement of acetabular cup orientation

The purpose of our study was to develop a simple and reproducible method for calculating post-operative acetabular cup position based upon computed tomographic images. Next, we sought to examine the reliability, objectivity and accuracy of this method. We developed a 3D CT evaluation software based upon Amira(R) (data visualisation, analysis and modelling software) to calculate the abduction and anteversion of the acetabular cup relative to the APP (anterior pelvic plane). To test the accuracy of the method, we constructed a special phantom pelvic model as the gold standard, in which the acetabulum was mounted at various abduction and anteversion angles that had previously been measured digitally. This phantom was then CT scanned in 12 different cup positions (30 degrees to 50 degrees abduction, 0 degrees to 30 degrees anteversion) and then evaluated using the 3D CT evaluation software. In addition, we also examined the reliability and objectivity of this method in 10 patients following implantation of a hip prosthesis, as a clinical trial. We observed an average accuracy of the 3D CT evaluation software of -0.3 degrees (range -1.4 degrees to 1.3 degrees ; SD 0.6 degrees ) for abduction and 0.2 degrees (range -1.4 degrees to 1.4 degrees ; SD 0.6 degrees ) for anteversion compared with the gold standard. Moreover, a high intra -and interindividual agreement in the resulting ICC well above 0.8 for abduction and abduction values in the phantom study and the clinical trial were observed. This study found that the 3D CT evaluation software provides high reliability, objectivity and accuracy. Thus, the 3D CT software is a method that permits very precise evaluation of the post-operative cup position independent of patient positioning or pelvic til

Ultrasound-based computer navigation of the acetabular component: a feasibility study

This feasibility study investigated the accuracy of anterior pelvic reference plane (APP) registration and acetabular cup orientation in two cadavers with different BMIs. Method Five observers each registered the APP five times in the 2 cadavers (BMIs: 32 kg/m² and 25 kg/m²) using an ultrasound-based navigation system. By comparison against the CT-derived reference landmarks, the errors in determining the individual landmarks defining the APP, as well as the resulting errors in the orientation of the APP and the acetabular cup orientation were determined. Results Across all measurements obtained with the ultrasound navigation system, the errors in rotation and version in determining the APP were 0.5° ± 1.0° and ?0.4° ± 2.0°, respectively. The cup abduction and anteversion errors determined from all measurements of the five investigators for both cadavers together were ?0.1° ± 1.0° and ?0.4° ± 2.7°, respectively. The data further demonstrated a high reproducibility of the measurements for the resulting cup adduction and anteversion angle. Conclusion Our preliminary results confirm that ultrasound navigation is a highly accurate tool that allows a reproducible registration of the APP and thereby enables accurate and precise intraoperative determination of the acetabular cup orientation also in patients with increased BMI