Turkish Neurosurgery 2019 , Vol 29 , Num 1
Biomechanical Problems Related to the Pedicle Screw System
Tetsutaro MIZUNO1,Toshihiko SAKAKIBARA1,Takamasa YOSHIKAWA2,Tadashi INABA2,Takaya KATO3,Yuichi KASAI1
1Mie University Graduate School of Medicine, Department of Spinal Surgery and Medical Engineering, Japan
2Mie University, Graduate School of Engineering, Department of Mechanical Engineering, Japan
3Mie University, Community-University Research Cooperation Center, Japan
DOI : 10.5137/1019-5149.JTN.21002-17.2 AIM: To assess biomechanical problems related to pedicle screw (PS) systems.

MATERIAL and METHODS: Functional 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).

RESULTS: ROMs 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.

CONCLUSION: Excessive 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. Keywords : Biomechanics, Bending rigidity, Lumbar spine, Pedicle screw, Rotational instability

Corresponding author : Tetsutaro MIZUNO, tmiz1102@yahoo.co.jp