Lumbar pedicle: surgical anatomic evaluation and relationships

Although several clinical applications of transpedicular screw fixation in the lumbar spine have been documented for many years, few anatomic studies concerning the lumbar pedicle and adjacent neural structures have been published. The lumbar pedicle and its relationships to adjacent neural structures were investigated through an anatomic study. Our objective is to highlight important considerations in performing transpedicular screw fixation in the lumbar spine. Twenty cadavers were used for observation of the lumbar pedicle and its relations. After removal of whole posterior bony elements including spinous processes, laminae, lateral masses, and inferior and superior facets, the isthmus of the pedicle was exposed. Pedicle width and height (PW and PH), interpedicular distance (IPD), pedicle-inferior nerve root distance (PIRD), pedicle-superior nerve root distance (PSRD), pedicle-dural sac distance (PDSD), root exit angle (REA), and nerve root diameter (NRD) were measured. The results indicated that the average distance from the lumbar pedicle to the adjacent nerve roots superiorly, inferiorly and to the dural sac medially at all levels ranged from 2.9 to 6.2 mm, 0.8 to 2.8 mm, and 0.9 to 2.1 mm, respectively. The mean PH and PW at L1-L5 ranged from 10.4 to 18.2 mm and 5.9 to 23.8 mm, respectively. The IPD gradually increased from L1 to L5. The mean REA increased consistently from 35 degrees to 39 degrees. The NRD was between 3.3 and 3.9 mm. Levels of significance were shown for the P < 0.05 and P < 0.01 levels. On the basis of this study, we can say that improper placement of the pedicle screw medially and inferiorly should be avoided.