Pullout Strength of Pedicle Screws Following Redirection After Lateral or Medial Wall Breach

    loading  Checking for direct PDF access through Ovid

Abstract

Study Design.

A cadaveric biomechanical study designed to test the pullout strength of pedicle screws.

Objective.

To evaluate the pullout strength of redirected pedicle screws with a larger diameter following lateral wall breach, redirected pedicle screws of the same diameter following medial wall breach, and redirected pedicle screws with a larger diameter following medial wall breach.

Summary of Background Data.

Screw malposition is one of the main pitfalls of inserting pedicle screws. Intraoperatively a malpositioned screw is redirected and inserted along the correct axis.

Methods.

Forty-seven vertebrae (T9-L5) were harvested from eight fresh cadaveric spines. The 18 pedicle screws that breached the lateral wall were then removed and redirected using a pedicle screw of 1 mm larger in diameter. The 16 pedicle screws that had breached the medial wall were then removed and redirected using a pedicle screw of the same diameter. The other 13 pedicle screws that had breached the medial wall were then removed and redirected using a pedicle screw of 1 mm larger in diameter. The pullout strength was measured.

Results.

Following lateral wall breach, mean pullout strength for the larger redirected screws was 46.9% greater than that of the correctly aligned screws. Following medial wall breach, mean pullout strength for the redirected screws of the same diameter was 20.6% less than that of the correctly aligned screws. Mean pullout strength for the larger pedicle screws following medial wall breach was 27.3% more than that of the correctly aligned screws.

Conclusion.

Redirected pedicle screws of larger diameter after a lateral or medial pedicle breach show recovery of pullout strength. However, the pullout strength of redirected pedicle screws of the same diameter after a medial pedicle breach is significantly less than that of correctly aligned screws.

Conclusion.

Level of Evidence: 1

Related Topics

    loading  Loading Related Articles