Radiographic analysis of hexapod external fixators: fundamental differences between the Taylor Spatial Frame and TrueLok-Hex.

Hexapod circular external fixators are extremely accurate at correcting deformities in three dimensions. In order to exploit this accuracy, however, the surgeon must be able to accurately analyse the deformity and mounting parameters on post-operative radiographs. A Sawbone® model was created to simulate a mid-shaft tibial fracture with deformity. A 180 mm ring was applied oblique to the proximal segment of the Sawbone® model, in both the sagittal and coronal planes. Standard radiographs were taken of the model and analysed using the described Taylor Spatial Frame and TrueLok-Hex methods. The TrueLok-Hex software allows the surgeon the ability to program reference rings that are not orthogonally mounted. Apart from this software difference, the described analysis methods resulted in variation in all translational measurements for both deformity and mounting parameters. In conclusion, the radiographic analysis of the Taylor Spatial Frame and TrueLok-Hex are fundamentally different. These differences must be appreciated in order to use these systems effectively.