  Vital for spinal fracture treatment, pedicle screw fixation is the gold
standard for spinal fixation procedures. Nevertheless, due to the screw pullout
and loosening issues, this surgery often fails to be effective for patients
suffering from osteoporosis (i.e., having low bone mineral density). These
failures can be attributed to the rigidity of existing drilling instruments and
pedicle screws forcing clinicians to place these implants into the osteoporotic
regions of the vertebral body. To address this critical issue, we have
developed a steerable drilling robotic system and evaluated its performance in
drilling various J- and U-shape trajectories. Complementary to this robotic
system, in this paper, we propose design, additive manufacturing, and
biomechanical evaluation of a transformative flexible pedicle screw (FPS) that
can be placed in pre-drilled straight and curved trajectories. To evaluate the
performance of the proposed flexible implant, we designed and fabricated two
different types of FPSs using the direct metal laser sintering (DMLS) process.
Utilizing our unique experimental setup and ASTM standards, we then performed
various pullout experiments on these FPSs to evaluate and analyze their
biomechanical performance implanted in straight trajectories.
