Int J CARS (2012) 7:433–444 DOI 10.1007/s11548-011-0634-9 ORIGINAL ARTICLE Volume slicing of cone-beam computed tomography images for navigation of percutaneous scaphoid fixation Erin J. Smith · Hisham A. Al-Sanawi · Braden Gammon · Paul J. St. John · David R. Pichora · Randy E. Ellis Received: 10 January 2011 / Accepted: 7 June 2011 / Published online: 25 June 2011 © CARS 2011 Abstract Purpose Percutaneous scaphoid fixation (PSF) is growing in popularity as a treatment option for non-displaced fractures. Success of this procedure demands high-precision screw placement, which can be difficult to achieve with standard 2D imaging. This study aimed to develop and test a system for computer-assisted navigation using volume slicing of 3D cone-beam computed tomography (CBCT). Methods The navigated technique involved a distinctive workflow in which a 3D CBCT imager was calibrated preop- eratively, circumventing the need for intraoperative patient- based registration. Intraoperatively, a 3D CBCT image was acquired for both preoperative planning and direct naviga- tion using volume-rendered slices. An in vitro study was conducted to compare the navigated approach to two con- ventional fluoroscopic methods for volar PSF. The surgical goal was to insert a guide wire to maximize both length and central placement. Results There was no significant difference in the mean central placement of guide wire, although the variance in cen- tral placement was significantly lower using VS navigation E. J. Smith · R. E. Ellis Department of Mechanical Engineering, Queen’s University, Kingston, ON, Canada e-mail: smith@me.queensu.ca H. A. Al-Sanawi · B. Gammon · D. R. Pichora · R. E. Ellis Department of Surgery, Queen’s University, Kingston, ON, Canada P. J. St. John · D. R. Pichora · R. E. Ellis Human Mobility Research Centre, Queen’s University, Kingston, ON, Canada R. E. Ellis (B ) School of Computing, Queen’s University, Kingston, ON, Canada e-mail: ellis@cs.queensu.ca (P < 0.01). The lengths of the drill paths were significantly longer for the VS-navigated group compared with one 2D group (P < 0.1). Each navigated trial required only one drilling attempt and resulted in less radiation exposure than conventional C-arm (P < 0.01). Conclusions Volume-sliced navigation achieved a more repeatable and reliable central pin placement, with fewer drilling attempts than conventional 2D techniques. Volume- sliced navigation had a higher number of drill paths within the optimal zone maximizing both length of the path and depth from the surface. Keywords Computer-aided surgery · Preoperative planning · Navigation · Volume slicing · Percutaneous fixation · Scaphoid fractures Introduction The scaphoid bone is the most commonly fractured of the eight small carpal bones in the human wrist, usually the result of a fall on an outstretched arm [1]. Although conven- tional casting of a non-displaced scaphoid for approximately 10–12 weeks is usually an effective treatment option, cast- ing can be poorly tolerated by active individuals, particularly those dependent on their upper extremities for work or sports. Furthermore, delayed unions and malunions following cast immobilization are not uncommon, even with minimally dis- placed or proximal pole fractures, and may lead to pain and loss of function at the wrist. For these reasons, there is a grow- ing popularity in offering internal fixation as a treatment for minimally displaced and non-displaced fractures [2]. The scaphoid bone is tiny, measuring on average 26.0mm in length and as little as 7.2 mm at its narrowest point, the waist [3], so placement of standard fixation screw does not leave much tolerance for error. Because of the complex 123