Anatomic evaluation and relationship between the lumbar pedicle and adjacent neural structures: an anatomic study

Transpedicular spinal fixation has recently been the focus of increased attention in several institutions throughout the world, but its safety and efficacy are still important questions for orthopedic surgeons. Accurate screwing through the pedicle will avoid neurologic complications and increase the stability of the instrumentation. In this study, it was aimed to analyze the anatomic relations quantitatively between the lumbar pedicle and the adjacent dural sac and nerve roots, to determine the risky areas for neural injury during transpedicular screw placement.

Ten adult cadavers were used for observation of the lumbar pedicle and its relations. After removal of the laminas and facets, the lumbar pedicles, dural sac, and nerve roots were exposed. Interpedicular distance (IPD), pedicle-inferior nerve root distance (PIRD), pedicle-superior nerve root distance (PSRD), and pedicle-dural sac distance (PDSD) were measured.

Average distance from the lumbar pedicle to the dural sac medially and to the adjacent nerve roots superiorly and inferiorly through the cranial to caudal lumbar levels ranged from 1.29 to 1.56, from 4.12 to 5.52, and from 1.10 to 1.06 mm, respectively. The mean IPD ranged from 32.77 to 41.24 mm. There were statistically significant differences between the L5 level and other lumbar levels for IPD, PSRD, and PDSD measurements.

These results indicate that although L5 is safer than other lumbar levels for pedicle screw insertion, an improper medial and caudal placement of a pedicular screw will carry a great risk of injury to the dural sac and inferior nerve root.