• Tetsutaro Mizuno, Toshihiko Sakakibara, Takamasa Yoshikawa, Tadashi Inaba, Takaya Kato, and Yuichi Kasai.
• Mie University Graduate School of Medicine, Department of Spinal Surgery and Medical Engineering, Japan.
• Turk Neurosurg. 2019 Jan 1; 29 (1): 53-58.

AimTo assess biomechanical problems related to pedicle screw (PS) systems.Material And MethodsFunctional spinal units (L3-4) of deer were evaluated using a 6-axis material testing machine. For the specimen models, we prepared an intact model, a damaged model, a PS model, and a crosslink model. We checked the range of motion (ROM) during bending and rotation tests. Eight directions were measured in the bending test: anterior, right-anterior, right, right-posterior, posterior, left-posterior, left, and left-anterior, and 2 directions were measured in the rotation test (right and left).ResultsROMs of the PS model were smaller than those of the intact model in all directions. However, ROMs of the PS model in the rotation test were smaller than those of the damaged model and larger than those of the intact model. The stability of the crosslink model was better than that of the PS model during the bending test, but ROMs of the crosslink model were larger than those of the intact model during the rotation test.ConclusionExcessive bending rigidity and rotational instability are the biomechanical problems related to PS systems. Based on these results, we speculate that one of the most significant causes of adjacent segment disease is excessive bending rigidity and one of the most important causes of instrumentation failure is rotational instability.

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