Comparison of Freehand Sagittal Trajectories for Inserting Pedicle Screws Between C7 and T5

Abstract

Study Design:Anatomic study using computed tomographic scans.Objective:The purpose of this paper was to determine the trajectory of pedicle screw insertions, in regard to posterior bony landmarks encountered during standard posterior exposure of the spine between the seventh cervical (C7) and the fifth thoracic (T5) vertebrae, when lateral fluoroscopic and radiographic guidance may be obstructed by the scapula and shoulders.Summary of Background Data:Only a few studies have evaluated the intraoperative sagittal trajectory of pedicle screw insertion.Materials and Methods:We assessed 64 participants of a health screening program using whole-spine computed tomographic scans. On the basis of 5 previously reported methods, we designed 3 freehand trajectories: lamina surface method (angle between the superior vertebral endplate and the surface of the lamina), spinous process method (angle between the superior vertebral endplate and a line connecting the tips of the index spinous process and the one cephalad to it), and facet tilt method (angle between the superior endplate and the superior facet tilt). We calculated each of the angles for the C7–T5 vertebrae and determined the most reliable method using coefficients of variation (CV) and intraobserver and interobserver reliability.Results:The lamina surface method had the smallest CVs for C7 and T1, and the mean angles were larger than 90 degrees (range, 94.7–102.4 degrees). The spinous process method had the smallest CVs between T2 and T5, and the mean angles were <90 degrees (range, 85.0–87.0 degrees). The intraobserver and interobserver reliabilities were good or excellent for both methods.Conclusions:The ideal sagittal trajectories for pedicle screw insertion are nearly orthogonal to the lamina surface or the line connecting the spinous processes, but were different for each of the vertebrae. The lamina surface method was the most reliable for C7 and T1, whereas the spinous process method was most reliable between T2 and T5.Level of Evidence:Level III.

The Concept of Lamina–Pedicle Perpendicularity: Part 2: Thoracic Spine

“…However, detailed measurements of the individual vertebrae or the identification of vertebral zones were not analyzed. Furthermore, Oshina et al [15] reported that the ideal sagittal trajectories for pedicle screw insertions were nearly orthogonal to the lamina surface or to the line connecting spinous processes. However, they were different for each vertebra, although the lamina surface method was most reliable for the C7-T1 vertebrae [15].…”

“…While many studies have focused on screw inclination in the mediolateral direction [1,[8][9][10], few have addressed sagittal plane assessment [11][12][13][14]. To determine the correct sagittal trajectory of the thoracic pedicle screw, bony landmarks, such as the lamina surface, the spinous process, and the facet joint tilt can be used as anatomic references [15]. Based on observations in different spinal disorders, including deformities, it was noted that following a sagittal cranial-caudal trajectory perpendicular to the interlaminar line (ILL) joining the two adjacent vertebrae would work well at most vertebral levels.…”

A Novel Intraoperative Technique to Determine Cranio-Caudal Angulation of Pedicle Screws in Thoracolumbar Spine: A Prospective Computerized Tomography–Based Analysis of 428 Screws

“…In the upper thoracic spine, obtaining a proper lateral view with fluoroscopy is difficult due to the superimposition of the shoulder. 5 Furthermore, in patients with vertebral body fracture, there is significant kyphosis in the proximal vertebral levels that will alter the sagittal angulation of screws. For accurate pedicle screw placement, many image-guided technologies have been developed; however, its cost-effectiveness is debatable.…”

“…6 There are a few studies that have addressed assessing the sagittal-plane orientation of the pedicle screw. 5,[7][8][9][10][11][12] The previously published methods of determining the sagittal angulation of a pedicle screw in vivo can only provide a vague visual cue to the surgeon, which will result in human errors. 5,[7][8][9][10][11][12] It is known that even experienced spine surgeons cannot aim for a predefined angulation.…”

“…5,[7][8][9][10][11][12] The previously published methods of determining the sagittal angulation of a pedicle screw in vivo can only provide a vague visual cue to the surgeon, which will result in human errors. 5,[7][8][9][10][11][12] It is known that even experienced spine surgeons cannot aim for a predefined angulation. 13 The human eye can identify orthogonal angles more accurately; therefore, when a reference frame is added, the accuracy of execution of the screw can increase.…”