A biomechanical investigation of the retentive force of pedicle screw structures for different screw tulip designs

In monoaxial screws, when the axis of the shaft isn't perpendicular to the axis of the rod, a gap is formed between the tulip-rod interface. This results in a decreased retentive force. In polyaxial and uniplanar screws, the contact surfaces were the same in different tilt angles, therefore, the retentive force remained constant, which was attributed to the adjustable tulips always being perpendicular to the axis of the rods.

Source: Clinical Biomechanics - July 9, 2019 Category: Orthopaedics Authors: Po-Yi Liu, Po-Liang Lai, Chun-Li Lin Source Type: research