Computer navigated reduction of scaphoid non-unions and displaced scaphoid fractures- a cadaveric study

Abstract

IntroductionScaphoid non-union results the typical humpback deformity, pronation of the distal fragment, and a bone defect in the non-union site with shortening. Bone grafting, whether open or arthroscopic, relies on fluoroscopic and direct visual assessment of reduction. However, because of the bone defect and irregular geometry, it is difficult to determine the precise width of the bone gap and restore the original bone length, and to correct interfragmentary rotation. Correction of alignment can be performed by computer-assisted planning and intraoperative guidance. The use of computer navigation in guiding reduction in scaphoid non-unions and displaced fractures have not been reported.ObjectiveWe propose a method of anatomical reconstruction in scaphoid non-union by computer-assisted preoperative planning combined with intraoperative computer navigation. This could be done in conjunction with a minimally invasive, arthroscopic bone grafting technique.MethodsA model consisting of a scaphoid bone with a simulated fracture, a forearm model, and an attached patient tracker was used. 2 titanium K-wires were inserted into the distal scaphoid fragment. 3D images were acquired and matched to those from a computed tomography (CT) scan. In an image processing software, the non-union was reduced and pin tracts were planned into the proximal fragment. The K-wires were driven into the proximal fragment under computer navigation. Reduction was assessed by direct measurement.These steps were repeated in a cadaveric upper limb. A scaphoid fracture was created and a patient tracker was inserted into the radial shaft. A post-fixation CT was obtained to assess reduction.Results and DiscussionIn both models, satisfactory alignment was obtained. There were minimal displacement and articular stepping, and scaphoid length was restored with less than 1mm discrepancy. This study demonstrated that an accurate reduction of the scaphoid in non-unions and displaced fractures can be accurately performed using computed navigation and computer-assisted planning. It is the first report on the use of computer navigation in correction of alignment in the wrist.