Accuracy of pedicular screw placement in vivo.

The accuracy of pedicular screw placement was assessed in 40 consecutive patients treated with the AO "Fixateur Interne." Postoperative CT scans were used to measure canal encroachment from the medial border of the pedicle, the angle of insertion and the point of entry. Eighty-one percent of the screws were placed within 2 mm of the medial border of the pedicle and 6% had 4-8 mm of canal encroachment with two patients developing minor neurological complications that spontaneously resolved. Four percent were inserted lateral to the pedicle. The parameters linked to satisfactory screw placement include entry point, angle of insertion and pedicular isthmus widths. Improvement in accuracy was noted in the latter 25% of screw insertions, reflecting the learning curve associated with this technique.