Analysis of anatomic morphometry of the pedicles and the safe zone for through-pedicle procedures in the thoracic and lumbar spine

Abstract

Posterior instrumentation through the pedicle is a common surgery. Understanding the morphometry of the pedicle and the anatomy of adjacent neural structures should help decrease the risk of postoperative complications. T1-L5 segments from 15 sets of human vertebrae were separated into individual vertebrae and the morphometric characteristics of the thoracic and lumbar spine and the safe zone of the pedicle were analyzed. T11-L5 segments from six human cadavers were dissected. Measurements were taken from the pedicle to the dura and nerve roots superiorly, inferiorly, medially, and laterally, and the transverse angles of the nerve roots were measured. Pedicles were widest in L5 and narrowest in T4 in the transverse plane, and widest in T11 or T12 and narrowest in T1 in the sagittal plane. In individual pedicle, the ranges of the safe zone width and height were 3.4-7.7 and 8.6-13.7 mm, respectively, in T1-T10; and 7.2-17.8 and 13.9-16.7 mm, respectively, in T11-L5. The transverse angle of the pedicle decreases progressively from T1 to T12, then increase from L1 to L5.In sagittal angle, the largest angle localized at T2 and the smallest at L5. The mean distances from pedicles to adjacent neural structures were greater superiorly and laterally than inferiorly and medially. The lateral distance between nerve root and the pedicle ranged from 2.4 to 9.6 mm in lumbar spine. This study provides potential safe zones for the application of through-pedicle procedures to help decrease the risk of postoperative complications.

Benefit and accuracy of intraoperative 3D-imaging after pedicle screw placement: a prospective study in stabilizing thoracolumbar fractures

“…Our figures also make clear that the risk of penetration of the pedicle and a suboptimal screw position is greatest in the thoracic area T1-T10, caused by the narrow pedicle and corpus anatomy [5,15]. The 3D imaging process shows the highest error rate of 6% in the area of the most frequent false positioning rates.…”

“…However, an intraoperative measurement in millimeter steps is not practicable and not decisive for the objective. In the middle thoracic area, the average pedicle diameter amounts to \4 mm [5,15]. This must result in a penetration of the pedicle walls by even the smallest pedicle screws (4 mm), but this has no clinical consequences.…”

“…The intraosseous corridor of the pedicle for the positioning of the screws is limited [15]. Even lateral deviations in millimetre scale can damage the stability of the fixation and medial pedicle penetrations can cause damage to the bone marrow and the nerve roots.…”

“…Even lateral deviations in millimetre scale can damage the stability of the fixation and medial pedicle penetrations can cause damage to the bone marrow and the nerve roots. While Castro et al first anticipate a lesion of the nerve root in the lumbar portion of the spine with a medial false position of the screw as of 6 mm, more recent anatomical examinations by Lien et al show that the distance between the pedicle wall and the nerve root varies considerably in the lumbar region of the spine and occasionally amounts to only 2.4 mm [7,15].…”

Use of computed tomographic reconstruction to establish the ideal entry point for pedicle screws in idiopathic scoliosis

“…The transverse angle of the pedicle is another major factor affecting the screw placement [22]. Many reports have been published achieving a reliable transverse angle as a result of CT-based measurement [23].…”