Surgical And Radiological Anatomical Study Of Accuracy Entrance Point For The Placement Of Pedicle Screw Through Posterior Approach

Objective: Pedicle screw systems have been widely used in spine surgery for reconstruction of spinal stability and realignment of the spine. The key to success of this technique is to find reliable landmark of the accuracy entrance point for insertion of the pedicle screw to decrease the complications. Several entrance points for this purpose have been reported since 1970 by Roy- Camille et al. They are almost located at the intersection point of lines bisecting transverse process and the lateral border of the superior articular process, but the directions of insertion is quite different between their reports, that makes difficult and risk in clinical practice. To approach this problem, ideal entrance point on posterior aspect of the lumbar spine should secure correctly to insert pedicle screw through the pedicle to the vertebral body. The purpose of this study were â‘  to determine the "^" shape crest of the lumbar spine as a landmark of insertion of pedicle screw; â‘¡to describe quantitatively relations of the top point of the crest to the pedicle center; â‘¢ to define the direction and depth of insertion; â‘£to compare the new method with others.Material and Methods: â‘ 100 dry lumbar specimens(500 lumbar vertebrae) were obtained for the study. Anatomical evaluation focussed on determination of the "^" shape crest and the relationship between the top point of the "^" shape crest with the lumbar pedicle center. The distance from the point to the anterior cortex of the vertebral through the center of the pedicle in each level of the lumbar spine was measured. The distance from the center of the pedicle to the axis of the transverse process was also measured, the relationship between the lateral margin of the superior facet with the pedicle center, the degenerative changes and variant of the posterior part of the lumbar spine were also observed. â‘¡The 310 pedicles (in 155 vertebrae) that were twined with the wire of 1.0 mm in diameter were taken for radiological study. The anteroposterior, lateral and superoinferior roentgenograph were performed, the relationship between the top point of the "^" shape crest with the pedicle center were observed, the pedicle and its adjacent neural structures were also investigated.Results: â‘  the appearance rate of the "^" shape crest was 96.7% in L₁, 98.9% in...