Clin Orthop Surg.  2016 Jun;8(2):133-139. 10.4055/cios.2016.8.2.133.

Measurement of Optimal Insertion Angle for Iliosacral Screw Fixation Using Three-Dimensional Computed Tomography Scans

• Kim JJ
• Jung CY
• Eastman JG
• Oh HK

• KMID: 2412336
• DOI: http://doi.org/10.4055/cios.2016.8.2.133

Abstract

BACKGROUND
Percutaneous iliosacral screw fixation can provide stable fixation with a minimally invasive surgical technique for unstable posterior pelvic ring injuries. This surgical technique is not limited by cases of difficult fracture patterns, sacral dysplasia, and small sacral pedicles that can occur in Asians. The purpose of this study was to investigate the incidence of the sacral dysplasia in the Korean population and determine the optimal direction of iliosacral screws by analyzing pelvic three-dimensional computed tomography (3D-CT) scans.
METHODS
One hundred adult patients who had pelvic 3D-CT scans were evaluated. The upper sacral morphology was classified into three groups, i.e., normal, transitional, and dysplastic groups; the cross-sectional area of the safe zone was measured in each group. S1 pedicle with a short width of more than 11 mm was defined as safe pedicle. The incidences of safe pedicles at different angles ranging from 0° to 15° were investigated in order to determine optimal angle for screw direction.
RESULTS
The incidence of normal, transitional, and dysplastic group was 46%, 32%, and 22%, respectively. There were significant increases of the cross-sectional area of the safe zones by increasing the angles from 0° to 15° in all groups. The incidence of safe pedicles increased similar to the changes in cross-sectional area. The overall incidence of safe pedicles was highest at the 10° tilt angle.
CONCLUSIONS
The incidence of sacral dysplasia in Koreans was 54%, which is higher than previous studies for Western populations. The cross-sectional area of the safe zone can be increased by anteromedial direction of the iliosacral screw. Considering the diversity of sacral morphology present in the Korean population, a tilt angle of 10° may be the safest angle.

Keyword

Pevis; Fracture; Bone screws; Anatomy; Radiography

MeSH Terms

Adult
*Bone Screws
Cohort Studies
Female
Fracture Fixation, Internal/*methods
Humans
Ilium/diagnostic imaging/injuries/*surgery
Incidence
Male
Middle Aged
Republic of Korea
Sacrum/diagnostic imaging/injuries/*surgery
Surgery, Computer-Assisted/*methods
Tomography, X-Ray Computed/*methods

Figure

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  Fig. 1 Multiplanar reformation images on the same screen. The oblique sagittal image (A) could be simultaneously generated after choosing the points and cross section on the axial (B), sagittal (C), and coronal (D) images and show their cross sections perpendicular to the sliced plane.

• 

  Fig. 2 Classification of upper sacrum morphology for iliosacral screw fixation using transparent three-dimensional reconstruction image. (A) Normal group has no radiologic signs of sacral dysplasia. (B) The transitional group has some radiologic characteristics of sacral dysplasia with less than half of the S1 body protruding above the iliac cortical density (ICD). (C) The dysplastic group has some radiologic characteristics of sacral dysplasia and has more than half of the S1 body located above the ICD.

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  Fig. 3 Oblique sagittal images were obtained along the given axis (arrow) (A). Area of safe zone was defined as the area inside the greatest common outer lines that did not violate the cortex of the sacrum anteriorly or superiorly nor the neuroforaminal tunnel posteriorly. This area was calculated from the lateral side of the first sacral neural foramen (B) to its medial side (C).

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  Fig. 4 Sagittal computed tomography image showing the cross-sectional area and short width of the safe zone.

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  Fig. 5 Incidences of safe pedicle according to tilt angle.

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