gms | German Medical Science

Objectives/Interrogation: Scaphoid non-union results in humpback deformity, pronation of the distal fragment, and a bone defect in the non-union site with shortening. To improve accuracy of scaphoid fracture fixation or non-union reconstruction with bone grafting, we hypothesize that pre-operative planning and computer navigated reduction is feasible and results in good correction of alignment. We propose a method of anatomical reconstruction in scaphoid non-union by computer-assisted preoperative planning combined with intraoperative computer navigation, which can be performed in conjunction with arthroscopic bone grafting technique.

Methods: The first model consisted of a scaphoid bone with a simulated fracture, a forearm model, and an attached patient tracker was used. 'Pre-operative' CT scan was done. The proximal scaphoid fragment was attached to the model. 2 titanium K-wires were inserted into the distal scaphoid fragment. 3D images were acquired (3D Iso-C, Siemens) and matched to those from the computed tomography (CT) scan. In an image processing software, the non-union was reduced and pin tracts were projected 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 2 cadaveric upper limbs. A scaphoid fracture was created and a patient tracker was inserted into the radial shaft. Simulated reduction and planning of pin tracts into the proximal fragment was done as in the first model. Using these planned tracts, the K-wires were driven into the proximal fragment under computer navigation. Direct visual assessment of reduction was done and post-fixation CT was obtained to assess reduction.

Results and Conclusions: In both models, articular stepping was less than 1mm, and scaphoid length was restored with less than 1mm discrepancy. Part analysis of the CT showed good matching with mean root mean square analysis of 0.5mm (Figure 1 [Fig. 1]).

This is the first report on the use of computer navigation on reduction of malalignment in the wrist. Further study in real patients is warranted to demonstrate clinical benefit.