Abstract
Background: To assess the accuracy of pedicle instrumentation placement using an image guidance system ( Medi Vision) in a pig cadaveric model.
Methods: A 4mm diameter (10cm long) screw was inserted transversely into the spinous process of a pig cadaver percutaneously using fluoroscopic guidance. The dynamic reference base (DRB) of the image guidance system was then attached to the screw. Using the navigation system both pedicles at each level were identified and 3.2mm guide wires inserted percutaneously. This process was performed for each level from D7 to L4. Actual wire placement was recorded using standard anteroposterior and lateral fluoroscopic images. Virtual trajectories generated by the image guidance system were recorded on the guidance system database. Accuracy of wire placement was then evaluated in an automated way by linear correlation between corresponding images.
Results: 20 pedicles were instrumented at 10 levels from D7 to L4. Mean estimate of accuracy for dorsal levels AP and lateral (mm). Mean = 1.452mm, standard deviation 1.57mm. Mean for lumber levels= 1.047mm, standard deviation 1.187mm
Conclusion: Lumbar pedicle instrumentation showed more accuracy when compared to dorsal pedicle instrumentation. The error of navigation that was accommodated by the image guidance system was 2mm.
There was correlation between fluoroscopic copies and virtual trajectories.
This image guidance system may not only aid in the placement of pedicle instrumentation but also assist the senior surgeon in trainee supervision.
The abstracts were prepared by Mr Colin E. Bruce. Correspondence should be addressed to Colin E. Bruce, Consultant Orthopaedic Surgeon, Alder Hey Children’s Hospital, Eaton Road, Liverpool, L12 2AP.
