Development and biomechanical test of a new pedicle screw for thoracolumbar spinal surgery

Rupture of the medial pedicle wall often occurs during pedicle screw insertion. This allows the pedicle screw to compress or cut the nerve root and/or spinal cord. In this paper, we designed a new double-threaded pedicle screw that has a cylindrical outer diameter and a conical core diameter, with a wide thread at the front, no thread in the middle, and a narrow thread at the rear, according to an analysis of the shortcomings of the conventional pedicle screw and anatomical parameters in 300 healthy adult volunteers. After the screw was placed, the non-threaded portion of the screw was located at the vertebral pedicle. No nerve root cutting occurred if the screw was misplaced and the medial wall of the vertebral pedicle was broken. We then performed biomechanical tests using a static universal testing machine and compared the new double-threaded screws with the conventional full-threaded pedicle screws, however, the differences were not obvious. In compression bending fatigue tests, the novel double-threaded pedicle screws were subjected to 5 million fatigue cycle loads without failure. The current study demonstrated that the new pedicle screw possesses similar biomechanical features as those of the conventional fully threaded pedicle screw. This provides a basis for further clinical applications.