Original Article

Radiological Evaluation of SI Posterior Screw Placement

Yong Jae Cho
Author Information & Copyright
Department of Neurosurgery, Ewha Womans University, School of Medicine, Korea.

Copyright ⓒ 2007. Ewha Womans University School of Medicine. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Published Online: Mar 30, 2007

Abstract

Axial computed tomographic scans were obtained from 40 normal sacrum for evaluation of screw length and angle in the posterior lumbosacral screw fixation. The best scans close to the inferior portion of S1 superior facet and the middle of S2 pedicle were chosen to evaluate various screw paths. Measurements of screw paths included the screw path lengths and angulations as well as the distances between the screw and the sacral canal. The results showed that no significant differences between male and female were found in any parameters, although the linear measurements were greater for male than for female. In Sl, the greatest value of screw path lengths was noted in screw path VI(anterolaterally directed) with an average of 34.8±2.97mm. The mean distance between screw path I and the lateral cortex of the sacral canal was 5.6±0.4mm. For S2, the mean value(30.6±2.08mm) of screw path II (anterolaterally directed) was significantly greater than that(23.8±1.93mm) of screw path I(30° anteromedially directed) (p≤0.001). The mean distance between screw path I and the lateral cortex of the sacral canal was 4.0±0.36mm. This study showed that computed tomography(CT) scans provide more accurate information of screw path lengths. Preoperative CT evaluation of the sacral screw path angle and length is recommended.

Keywords: Computed tomography; Sacrum; Sacral pedicle