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Defining the Differences in Transverse Plane Trajectories for Thoracic Pedicle Screw Insertion: Anatomic Versus Medial

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Abstract

Study Design

Comparing thoracic pedicle screw trajectories, screw lengths, and starting points by examining osteologic specimens.

Objective

Describe a medial screw trajectory (MST) compared to a screw trajectory along the anatomic pedicle angle (APA) in terms of trajectory, screw length, and starting point.

Summary of Background Data

Although thoracic pedicle screw insertion is commonly used for posterior fusion and instrumentation, there is little data to quantify an MST that avoids the great vessels and allows for greater screw purchase.

Methods

Thirty adult female skeleton thoracic vertebral columns from the University of New Mexico Maxwell Museum of Anthropology Osteology Collection were photographed from axial and right and left lateral views from T1 to T12. Axial plane measurements included APA and MST (both measured from the midline), screw lengths, and APA/MST intersection on the superior articular facet (SAF). The MST was defined as an insertion angle through the midpoint of the pedicle isthmus intersecting the anterior midpoint of the vertebral body. The intersection of each trajectory with the SAF was measured in relation to the lateral base of the SAF, reported as a percentage of the SAF base width from the lateral SAF border.

Results

At every vertebral level, the APAwas different from the MST for angle, screw length, and SAF intersection (p <.0001), with the largest difference at T12. The T12 differences were APA versus MST angles (−25.5°, 95% CI −22.7° to −28.4°), screw lengths (11.0 mm, 95% CI 9.2 mm to 12.9 mm), and percentage of SAF width from the lateral border of the SAF base (38.6%, 95% CI 29.1% to 48.1%).

Conclusions

The MST was approximately 8° to 10° greater at T1eT10 (19° at T11 and 25° at T12) than the traditional APA insertion angle. This resulted in a much more lateral starting point on the SAF and longer screw length, greatest at T12.

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Authors and Affiliations

  1. Department of Orthopaedic Surgery, University of Texas-Southwestern Medical Center, 1801 Inwood Rd, Dallas, TX, 75235, USA

    William R. Hotchkiss MD

  2. Department of Orthopaedic Surgery, Children’s Mercy Hospital Kansas City, 2401 Gillham Rd, Kansas City, MO, 64108, USA

    Richard M. Schwend MD

  3. Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, 200 Lothrop St, Pittsburgh, PA, 15213-258, USA

    Patrick P. Bosch MD

  4. Department of Anthropology, University of New Mexico, Albuquerque, MN, 87131, USA

    Heather J. H. Edgar PhD & Bonnie N. Young PhD

Authors
  1. William R. Hotchkiss MD
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  2. Richard M. Schwend MD
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  3. Patrick P. Bosch MD
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  4. Heather J. H. Edgar PhD
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  5. Bonnie N. Young PhD
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Corresponding author

Correspondence to Richard M. Schwend MD.

Additional information

Author disclosures: WRH (none); RMS (none); PPB (none); HJHE (none); BNY (none).

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Hotchkiss, W.R., Schwend, R.M., Bosch, P.P. et al. Defining the Differences in Transverse Plane Trajectories for Thoracic Pedicle Screw Insertion: Anatomic Versus Medial. Spine Deform 4, 22–26 (2016). https://doi.org/10.1016/j.jspd.2015.05.004

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  • DOI: https://doi.org/10.1016/j.jspd.2015.05.004

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