Navigated minimally invasive thoracolumbar pedicle screw placement with flat panel 3-D imaging. A feasibility study.

STUDY DESIGN

The current study involves a cadaveric specimen with navigated pedicle screw placement using conventional reference markers and isocentric 3D fluoroscopy and also minimally invasive reference marker use with a flat panel 3D scanner.

OBJECTIVE

To test the feasibility of a novel minimally invasive reference marker system for navigated pedicle screw placement in combination the use of a new imaging modality i.e. flat panel 3D imaging.

SUMMARY OF BACKGROUND DATA

A major limiting factor of navigated pedicle screw placement is the requirement for intraosseous fixation of reference markers. This usually necessitates an open approach to the spinous process. To address this issue, the current authors have developed a minimally-invasive fixation device for spinal reference marker fixation.

METHODS

A fresh-frozen cadaver with no history of spinal injury or deformity was positioned prone on a radiolucent table. L3 and L4 vertebrae were randomly selected for conventional pedicle screw insertion while T5 and T6 were selected for the percutaneous technique. A flat detector 3D C-arm (Ziehm vision FD 3D; Ziehm, Nuremberg, Germany) was used to evaluate the position of the pedicle screws at the vertebral levels targeted in the study.

RESULTS

All screws placed within the lumbar spine involved conventional reference markers. The average depth deviation was 0.73 mm and the average axis deviation was 1.67 mm. Within the thoracic spine, the minimally-invasive marker fixation devices were used. The average depth deviation was 0.85 mm and the average axis deviation was 1.75 mm. In both cases, the plan and navigation were performed satisfactorily. The Y-jaw clamp for minimally-invasive reference fixation seemed to provide stable and robust fixation of the markers, requiring only two small incisions.

CONCLUSIONS

The minimally invasive reference marker system produced results which were comparable to the conventional intra-osseous markers while the flat detector-based navigation was shown to be easier to use and faster than isocentric Iso-3D technology.