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Biomechanical Comparison of Spinopelvic Fixation Constructs: Iliac Screw Versus S2-Alar-Iliac Screw

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Abstract

Study Design

Biomechanical cadaveric study.

Objective

To compare the biomechanical properties of the iliac and S2-Alar-Iliac (S2AI) screw in a similar spinopelvic fixation construct.

Summary of Background Data

Spinopelvic fixation is used in the correction of pelvic obliquity, high-grade spondylolisthesis, and long spinal fusions. With the development of pedicle screw fixation, the iliac screw has been used as an anchor point to the pelvis. The associated morbidity with this fixation has led to the development of the S2AI screw. Many studies have examined the biomechanical properties of iliac and S2AI screws; however, a direct comparison has not been performed.

Methods

Eight cadaveric spines were instrumented with pedicle screws bilaterally at L5 and S1. Four specimens were further instrumented with iliac screws placed with a starting point at the posterior superior iliac spine, and four specimens were instrumented with S2AI screws placed with a starting point 1 mm inferolateral to the S1 foramen. Screws were connected with 6.35 mm rods. Subfailure testing was performed by loading at 1°/second to a torque of 10 Nm in four directions: left bending, right bending, extension, and flexion. Specimens then underwent a monotonic load to failure under flexion at a rate of 1°/second.

Results

There were no significant differences for torsional stiffness in extension, flexion, left bending, or right bending between S2AI and iliac screw constructs. There were no significant differences in S2AI versus iliac screws for failure torque (30.9 × 12.00 Nm vs. 22.61 × 6.25 Nm) and yield torque (11.86 × 0.41 Nm vs. 12.01 × 1.70 Nm).

Conclusion

Iliac screws have been associated with increased dissection, wound complications, an additional construct failure point, and hardware prominence. The S2AI screw was developed as an alternative and has been associated with less morbidity. The iliac and S2AI screw demonstrate no statistical difference in stiffness and load-to-failure in a spinopelvic fixation model.

Level of Evidence

Level V.

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Authors and Affiliations

  1. Department of Orthopaedic Surgery, Stony Brook University School of Medicine, Stony Brook, NY, 11794, USA

    Camden B. Burns MD, Karan Dua BA, Nicholas A. Trasolini BSE, David E. Komatsu PhD & James M. Barsi MD

Authors
  1. Camden B. Burns MD
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  2. Karan Dua BA
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  3. Nicholas A. Trasolini BSE
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  4. David E. Komatsu PhD
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  5. James M. Barsi MD
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Corresponding author

Correspondence to James M. Barsi MD.

Additional information

Author disclosures: CBB (reports grants from Medtronic, during the conduct of the study); KD (reports grants from Medtronic Sofamor Danek USA, Inc., during the conduct of the study); NAT (reports grants from Medtronic Sofamor Danek USA, Inc., during the conduct of the study); DEK (reports grants and non-financial support from Medtronic Sofamor Danek USA, Inc., during the conduct of the study); JMB (reports grants from Medtronic, during the conduct of the study).

A Medtronic External Research Program Grant provided funding for this study.

IRB approval: Deemed nonhuman subjects research by Stony Brook University IRB.

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Burns, C.B., Dua, K., Trasolini, N.A. et al. Biomechanical Comparison of Spinopelvic Fixation Constructs: Iliac Screw Versus S2-Alar-Iliac Screw. Spine Deform 4, 10–15 (2016). https://doi.org/10.1016/j.jspd.2015.07.008

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  • DOI: https://doi.org/10.1016/j.jspd.2015.07.008

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