Abstract
Purpose
Primary internal fixation of uncomplicated scaphoid fractures offers many advantages compared to conventional casting. However, ideal fixation placement along the central scaphoid axis can be challenging, especially if the procedure is performed percutaneously. Because of the lack of direct visualization, percutaneous procedures demand liberal use of imaging, thereby increasing exposure to harmful radiation.
It has been demonstrated that computer-assisted navigation can improve the accuracy of guidewire placement and reduce X-ray exposure in procedures such as hip fracture fixation. Adapting the conventional computer-assist paradigm, with preoperative imaging and intraoperative registration, to scaphoid fixation is not straightforward, and thus a novel tactic must be conceived.
Method
Our navigation procedure made use of a flatpanel C-arm (Innova, GE Healthcare) to obtain a 3D cone-beam CT (CBCT) scan of the wrist from which volumetrically-rendered images were created. The relationship between the Innova imager and an optical tracking system (OptoTrak Certus, Northern Digital Inc.) was calibrated preoperatively so that an intraoperatively-acquired image could be used for real-time navigation. Optical markers fitted to a drill guide were used to track its orientation, which was displayed on a computer monitor relative to the wrist images for navigation.
Randomized trials were conducted comparing our 3D navigated technique to two alternatives: one using a standard portable C-arm, and the other using the Innova flatpanel C-arm with 2D views and image intensification. A model forearm with an exchangeable scaphoid was constructed to provide consistency between the trials. The surgical objective was to insert a K-wire along the central axis of a model scaphoid.
An exposure meter placed adjacent to the wrist model was used to record X-ray exposure. Procedure time and drill passes were also noted. CT scans of the drilled scaphoids were used to determine the shortest distance from the drill path to the scaphoid surface.
Results
The closest distance from the drill path to the scaphoid surface was significantly larger using navigation compared to the 2D Innova method (p<0.05). Fewer drill passes were required using navigation compared to a conventional C-arm (p<0.01). Navigated procedures were significantly longer, although the overall time remained clinically acceptable (∼4min). There was no significant difference in radiation exposure to the patient between the three methods. The 3D CBCT image was acquired remotely in the navigated approach, so conceivably the exposure to the surgeon was much less than the other techniques.
Conclusion
Computer-assisted navigation was successfully adapted to percutaneous scaphoid fixation without requiring the tedious preoperative imaging and intraoperative registration that typically plague these procedures. Navigation resulted in superior central screw placement with fewer drilling attempts in comparison to conventional techniques.
