PROJECTION OF THE THORACIC PEDICLE AND ITS MORPHOMETRIC ANALYSIS

Study Design. This study defined the projection point of the thoracic pedicles on their posterior aspect and its relation to a reliable land mark. It also reported pedicle dimensions based on 43 thoracic spines. Objectives. To determine the projection point of the pedicle axis on the posterior aspect of the thoracic spine, quantitatively describe re lations of the projection point to some reliable landmarks, and evalua te linear and angular dimensions of the thoracic pedicle. Summary of b ackground data. Posterior segmental screw fixation is the current stan dard of internal fixation at the level of the second lumbar vertebrae or below. However, pedicular screw fixation in the thoracic spine, esp ecially in the middle and upper thoracic region, is not common because the small dimensions of the pedicle in this region make screw inserti on difficult. More information about pedicle axis projection (not pedi cle zone) and its quantitative relationship to some reliable landmarks is essential. Methods. Forty-three dry thoracic specimens (516 verteb rae) were obtained for study of the thoracic pedicle. Anatomic evaluat ion focused on the determination of the projection point of the thorac ic pedicle axis on its posterior aspect and the anatomic relationship of this point to the lateral edge of superior facet and the midline of the transverse process. Also, pedicle dimensions, including linear an d angular, were measured. The mean, range, and standard deviation were calculated for all of the specimens and for male and female specimens separately. Results. Sexual difference was found to be significant st atistically in more than half of parameters. For T1-T2, the projection point of the pedicle axis was approximately 7-8 mm medial to the late ral edge of the superior facet adn 3-4 mm superior to the midline of t he transverse process. For T3-T12, this point was 4-5 mm medial to the lateral margin of the facet and 5-8 mm superior to the midline of the transverse process. The transverse angle of the pedicle axis was foun d to be 30-40 degrees at T1-T2, 20-25 degrees at T3-T11, and 10 degree s at T12. Conclusions. This information, in conjunction with preoperat ive computed tomography evaluation, may enhance our knowledge of trans pedicular screw fixation in the thoracic pedicle.