Intraoperative planning and computer assisted navigation of complex multi-planar correction osteotomies at the proximal femur using a standard C-arm fluoroscopy

摘要

Objectives/Background: Besides great advances in hip-alloarthroplasty there are still numerous indications for joint saving procedures especially for younger patients. Of special importance in this context are different forms of correction osteotomies (OT) at the proximal femur. Often these procedures include more-dimensional multi-planar 3D rearrangements of the proximal femur, which are for the surgeon technically very demanding because of the (1) complexity of a precise 3D planning of the rotation and/or additional translation of the proximal fragment and as a second step (2) the exact operative realization of the plan. The aim of this project was to minimize these two major problems by using computer assisted techniques for an (1) exact intraoperative virtual 3D planning including a detailed biomechanical analysis (as change of head offset, torsion, leg length etc.) and a (2) precise 3D visualization of the position of the wedge and the used implant without changing the operative standard procedure. The intention was to extend a former developed geometry based approach using 2 fluoroscopy frames from different angles of the proximal femur to inversely reconstruct the femoral head sphere [1, 3] and additionally mark the head-neck axis and the anatomical femur axis. Similar geometric approaches had been used for navigated fragment treatment [2]. Methods: For navigation a passive infrared based optical system was used with a Polaris-camera, a C-arm calibration kit and PC-based developed software. For in vitro evaluation multi-planar correction osteotomies were performed on 5 femora under simulated OR conditions. To measure the accuracy the virtual planning data were compared to the real outcome after the correction osteotomy. Results: The analysis of the essential steps showed that the difference between the planning and real outcome for the wedge size was <3掳 and for the femur head center position <4mm. The osteosynthesis plate was in all femora completely intraosseous, but in 2 femora the position of the plate resulted in a lateral space of maximal 2mm between the OT-planes, which was by higher plate tensioning before screw fixation completely removable. The planning process as well as the operative execution were practicable and tune efficient. Conclusions: According to the results the used method demonstrated from a clinical view point a high accuracy. Beside that the method can open new areas of better reproducible and predictable operative treatment strategies because of the detailed 3D planning and of the new option of a precise navigation of the 2 fragments according to the real-time visualized planning data in all 6 degrees of freedom. Additionally it is now for the surgeon directly visible during the planning process what biomechanical impacts his planned procedure will have on the femur head offset, torsion, leg length etc.