The Cortical Bone Trajectory for Pedicle Screw Insertion.

P edicle screw fixation for spinal stabilization is now commonplace in spine surgery. Traditionally, pedicle screws are placed through a trajectory in which screw insertion utilizes a transpedicular path through the axis of the pedicle, either paralleling the end plate, as in the straightforward trajectory, or following the anatomic axis of the pedicle with an approximately 22° cephalocaudal trajectory through the pedicle, as in the anatomic trajectory. In 2009, Santoni et al. introduced a novel pedicle screw trajectory and called the path the cortical bone track. Traditional pedicle screws obtain 60% to 80% of their stability within the denser cortical bone of the pedicle, with the remainder of fixation obtained through the weaker cancellous bone located in the vertebral body. In osteoporosis, as primarily trabecular bone is compromised, the fixation strength of these screws diminishes and increased rates of loosening are seen. Compared with traditional pedicle screws, the cortical bone track screws (from here on referred to as cortical screws) take advantage of a cortically based track through the pedicle and were developed precisely to address loosening rates seen in osteoporotic bone. This new track follows a laterally directed trajectory in the transverse plane and a superiorly directed track in the sagittal plane (Figs. 1-A and 1-B). The hope was that this modified technique would provide enhanced screw purchase and interface strength independent of trabecular bone mineral density, which may be advantageous in the setting of compromised bone.