J Korean Neurosurg Soc.  2020 Mar;63(2):210-217. 10.3340/jkns.2019.0090.

Accuracy Analysis of Iliac Screw Using Freehand Technique in Spinal Surgery : Relation between Screw Breach and Revision Surgery

• Lee S
• Jung SK
• Keshen SG
• Lewis SJ
• Park JH

• KMID: 2501707
• DOI: http://doi.org/10.3340/jkns.2019.0090

Abstract

Objective
: To analyze the accuracy of iliac screws using freehand technique performed by the same surgeon. We also analyzed how the breach of iliac screws was related to the clinical symptoms resulting in revision surgery.
Methods
: From January 2009 to November 2015, 100 patients (193 iliac screws) were analyzed using postoperative computed tomography scans. The breaches were classified based on the superior, inferior, lateral, and medial iliac wall violation by the screw. According to the length of screw extrusion, the classification grades were as follows : grade 1, screw extrusion <1 cm; grade II, 1 cm ≤ screw extrusion <2 cm; grade III, 2 cm ≤ screw extrusion <3 cm; and grade IV, 3 cm ≤ screw extrusion. We also reviewed the revision surgery associated with iliac screw misplacement.
Results
: Of the 193 inserted screws, 169 were correctly located and 24 were misplaced screws. There were eight grade I, six grade II, six grade III, and four grade IV screw breaches, and 11, 8, 2, and 3 screws violated the medial, lateral, superior, and inferior walls, respectively. Four revision surgeries were performed for the grade III or IV iliac screw breaches in the lateral or inferior direction with respect to its related symptoms.
Conclusion
: In iliac screw placement, 12.4% breaches developed. Although most breaches were not problematic, symptomatic violations (2.1%) could result in revision surgery. Notably, the surgeon should keep in mind that lateral or inferior wall breaches longer than 2 cm can be risky and should be avoided.

Keyword

Sacropelvic fixation; Iliac screw; Breach; Accuracy; Freehand technique

Figure

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  Fig. 1. A : Intraoperative photograph showing a screw trajectory with a pedicle probe after removal of the PSIS. First, the GT is palpated to identify it (white dotted line) and then it is used as a marker to advance the pedicle probe 15° above (yellow arrows). B : A model showing the screw entry point (center of the PSIS) and inferior angle (15° above the GT, yellow arrow). C : Postoperative computed tomography image showing that the screw entry point is located in the center of the PSIS (yellow arrows) and the pelvic lateral wall slope used for creating a lateral angle of the screw trajectory (yellow dotted lines). D : After screw insertion, portable anterior-posterior (AP) and lateral radiographs were obtained before the closure. In these images, the screw location was considered acceptable if it was above the sciatic notch (yellow arrows). PSIS : posterior superior iliac spine, GT : greater trochanter.

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  Fig. 2. A : Lateral wall violation, grade III (2.44 cm). B : Medial wall violation, grade III (2.38 cm). C : Superior wall violation, grade I (0.97 cm). D : Inferior wall violation, grade III (2.21 cm); none of the above cases needed revision surgery.

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  Fig. 3. A : Lateral wall violation, grade III (2.89 cm). B : Lateral wall violation, grade IV (3.12 cm). C : Inferior wall violation, grade III (2.32 cm). D : Inferior wall violation, grade IV (4.20 cm); all the above cases underwent revision surgery.

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  Fig. 4. Anterior-posterior radiographs of the spine in a 63-year-old woman with degenerative scoliosis. A : After the first surgery, both iliac screws were located above the sciatic notch on the image. However, the patient had severe pain in his right lower limb, and there was a grade IV screw breach on the right side; 4.20 cm inferior wall violation (Fig. 3D). B : Thus, we performed revisional surgery to replace the iliac screw toward a superior direction through another trajectory (yellow arrow).

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  Fig. 5. The learning curve of iliac screw placement using the freehand technique (the violation rate is shown in the graph for each period).

Reference

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