Abstract
Pedicle screws allow for biomechanically secure fixation of the spine. However if they are misplaced they may effect the strength of the fixation, damage nerve roots or compromise the spinal cord. For these reasons image guidance systems have been developed to help with the accuracy of screw placement. The accuracy of pedicle screw placement outside the lumbar spine is not well published. To determine the accuracy of pedicle screw placement using CT scanning post operatively. Cortex perforations were graded in 2mm steps.
Prospective observational study. Plain x-rays are inaccurate for determining screw placement and therefore high definition CT scanning was used. The screw positioning on the post-operative CT scans was independently determined by a research registrar who was not present at the time of surgery. Screw position and clinical sequelae of any malposition.
Thirty patients (13 F:17 M) with segmental instability. Twelve were for metastatic disease, seven for trauma, seven for spondylolisthesis, three for atlanto-axial instability and one for a vertebral haemangioma. All patients were operated on by the senior author.
One hundred and seventy six pedicle screws were inserted in the thirty patients over the 20 month study period. Six screws violated the lateral cortex of the pedicle but none perforated the medial cortex. There were no adverse neurological sequelae.
The findings from this study will serve as a good comparison with future studies on pedicle screw placement, which may claim to improve accuracy and safety by the use of image guidance systems, electrical impedance or malleable endoscopes.
The abstracts were prepared by Mr Simon Donell. Correspondence should be addressed to him at the Department of Orthopaedics, Norfolk & Norwich Hospital, Level 4, Centre Block, Colney Lane, Norwich NR4 7UY, United Kingdom
