• Toru Maeda, Kosaku Higashino, Hiroaki Manabe, Kazuta Yamashita, Fumio Hayashi, Yuichiro Goda, Yoshihiro Tsuruo, and Koichi Sairyo.
• Department of Orthopaedics, Institute of Biomedical Sciences, Tokushima University Graduate School, Tokushima, Japan.
• Spine. 2018 Sep 1; 43 (17): E983-E989.

Study DesignA cadaveric biomechanical study designed to test the pullout strength of pedicle screws.ObjectiveTo 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 DataScrew malposition is one of the main pitfalls of inserting pedicle screws. Intraoperatively a malpositioned screw is redirected and inserted along the correct axis.MethodsForty-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.ResultsFollowing 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.ConclusionRedirected 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.Level Of Evidence1.

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