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 publ ished. The lumbar pedicle and its relationships to adjacent neural structur es were investigated through an anatomic study. Our objective is to highlig ht important considerations in performing transpedicular screw fixation in the lumbar spine. Twenty cadavers were used for observation of the lumbar p edicle and its relations. After removal of whole posterior bony elements in cluding spinous processes, laminae, lateral masses, and inferior and superi or facets, the isthmus of the pedicle was exposed. Pedicle width and height (PW and PH), interpedicular distance (IPD), pedicle-inferior nerve root di stance (PIRD), pedicle-superior nerve root distance (PSRD), pedicle-dural s ac distance (PDSD), root exit angle (REA), and nerve root diameter (NRD) we re measured. The results indicated that the average distance from the lumba r pedicle to the adjacent nerve roots superiorly, inferiorly and to the dur al 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 PI-I 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. Tile mean REA increased consistently from 35 degrees to 39 d egrees. The NRD was between 3.3 and 3.9 mm. Levels of significance were sho wn for the P <0.05 and P <0.01 levels. On the basis of this study, we can s ay that improper placement of the pedicle screw medially and inferiorly sho uld be avoided.