X-Plan
Fluoroscopy based navigation in hip surgery
Introduction
In the framework of this project a planning system for hip surgery is developed. Incontrast to CAS systems which make use of preoperative CT datasets, intraoperativefluoroscopic images are used. This supports a reduction of intraoperative x-ray doses,minimal invasive or even perkutaneous interventions and enables the surgeon to define andadapt the surgical strategy intraoperatively in some cases.
Image dewarping
Intraoperative plain x-ray images suffer from distortions due to a number of mechanicaland physical effects (fig. 1). To eliminate this problem a so called intrinsic calibrationprocedure was implemented decreasing locally these errors with the help of the givengeometry of a intrinsic calibration disk.
Fig. 1: Spiral radiograph distorsion
3D-Camera calibration
In a further step the determination of the co-ordinate transformation for the transitionof the conical projection space to the two-dimensional radiograph image takes place. The determination of the co-ordinate transformation enables a specifically developedradiolucent calibration body equipped with metal spheres at defined positions (fig. 2).Moreover the fluoroscope position is tracked by an optical localiser system.
Fig. 2: Installed calibration body
and corresponding x-ray image
Intraoperative step
The system can be used for manual navigation with optically tracked instruments (Optotrak) or with robot assistance (CRIGOS). Both possibilities were developed and tested for hip surgery applications (femoral neck fractures and total hiprevision surgery) in laboratory set-ups.
Fig. 3: Simulation of fluoroscopic navigation on the hip