NAVIGATED PLACEMENT OF SCAPHOID SCREWS WITH 3-D FLUOROSCOPY -TECHNIQUE AND FIRST LABORATORY RESULTS-

Abstract

Introduction: Image based navigation is able to increase precision and reduce intraoperative radiation time in drilling procedures in orthopeadic trauma indications. Due to specific anatomic conditions and necessary adequate fluoroscopic visualizing, specific indications need intraoperative 3-D fluoroscopy based navigation modalities. This kind of navigation has already been successfully used in several orthopaedic interventions. The complex anatomic structure of the scaphoid, the suggested minimal invasiveness and misplacement rates of the screws make 2-D based fluoroscopic navigation impossible. Missing options for a stable reference marker fixation at the scaphoid or carpus did not allow an intraoperative registration for the navigation. We report about the development of an adequate non invasive fixation technique of the reference marker for navigated interventions and the first implementation of 3-D fluoroscopy based scaphoid screws.

Materials and method: Fixation of the reference marker was achieved by immobilisation of the complete hand and forearm in maximum dorsal extension of the wrist. We used a completely new developed radiolucent hand fixation device (HFD) fixed nonivasively to the carpus and a conventional navigation system (Brainlab, Germany) in combination with 3-D fluoroscopic imaging (Iso-C, Siemens, Germany).

Tests were done on 10 intact specimen and the process included the initial drilling and final placement of an osteosynthetic screw. Postoperative placement was controlled with a 3-D scan. Results concerning a defined optimal screw positioning and drill failures attempts were done by another independent surgeon.

Results: All 3-D scans were done without complications. The multiplanar reconstructions allowed a proper visualisation of the scaphoid in all cases. No additional movement of the fixed extremity occurred during the operation. No registration failures were detected. An optimally defined screw placement in the scaphoid was achieved in 9 cases. Two repeated drill attempts were necessary in one case, another case needed three drill attempts. The scaphoid was never perforated.

Discussion: Our development of a new immobilizing device for the complete hand and forearm allows proper use of 3-D fluoroscopy based navigation at the scaphoid including a placement of an osteosynthetic screw. Further movements of the hand or fingers are intraoperatively only possible after the definite drill placement has been performed.

The 3-D imaging modality allows a direct control of the reduction and screw placement intraoperatively. Our tests did not include simulated fracture conditions, a general use of our new technique can now only be implemented to non displaced fracture types, while clinical and further laboratory tests have to improve our findings for all types of scaphoid fractures.