A comparison of the pull out resistance of different pedicle screws in different positions on sheep vertebrae specimens

AIM: In this study we try to explain influencing factors for reducing screw pull out, that is the most general problem of osteoporotic patients, which surgical technique and instruments should be used. We aimed to show this with a biomechanical experiment. MATERIALS AND METHODS: The pull out resistance of different pedicle screws measured in different positions on sheep vertebrae specimens. Specimens divided into four groups including different screw types and insertion techniques and tested for mechanical force to pull out. RESULTS: PMMA canulated screw is the most powerful one. Also, trapezoidal screw's pullout resistance is higher than the others. Extrapedicular position has the highest pullout resistance after that bicortical, CBT and unicortical. CBT has higher resistance than unicortical and it was significantly. And also PMMA has no effect to CBT position. CONCLUSIONS: Either surgical techniques or instruments (screws) effect the pullout resistance. PMMA canulated and trapezoidal shaped screws were showed stronger resistance to pull out. Our opinion is PMMA canulated screws and CBT technique are very useful and powerful alternative for osteoporotic patients and also recovery operations. KEY WORDS: Spinal stabilization, osteoporosis, salvage surgery, screw pull out, malposition