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  • Title: Pullout Strength of Pedicle Screws Following Redirection After Lateral or Medial Wall Breach.
    Author: Maeda T, Higashino K, Manabe H, Yamashita K, Hayashi F, Goda Y, Tsuruo Y, Sairyo K.
    Journal: Spine (Phila Pa 1976); 2018 Sep 01; 43(17):E983-E989. PubMed ID: 29470278.
    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. LEVEL OF EVIDENCE: 1.
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