Fracture-table-mounted versus bone-mounted dynamic reference frame tracking accuracy using computer-assisted orthopaedic surgery--a comparative study

Fluoroscopy-based computerized navigation systems enable accurate implant placement while reducing radiation exposure. The navigation process normally requires the attachment of a dynamic reference frame (DRF) to a bone, causing additional surgical trauma. The aim of this study was to compare the accuracy of navigation with the DRF either attached to the bone or mounted on the fracture table. We conducted a prospective study on 10 consecutive patients who underwent operative fixation of femoral neck fractures with cannulated screws using computerized navigation. After insertion of the three guide wires, the DRF was moved from the patient's bone to the fracture table. For each screw, angular and translational deviations of the navigated images as compared to the conventional fluoroscopic images were analyzed. The accuracy of navigated Kirschner wire placement was similar with both techniques, resulting in an average translational error of less than 2 mm in both groups and around 1 degrees in angulation error--both of these accuracy measurements are acceptable and sufficient for the insertion of cannulated screws into the femoral head. Our study suggests that attaching the DRF to a fracture table during navigated femoral neck fixation allows for acceptable accuracy with the possible added benefit of reducing patient morbidity.