Interspinous process devices for spinal surgery are designed to keep the spine in a flexed position, to achieve indirect decompression of the mobile segment. Such devices have been fabricated using numerous materials and designs. In this study, the fundamental knowledge required for choosing an appropriate interspinous process device for spinal surgery was reviewed.

Purpose
To evaluate the method of inserting cortical bone trajectory pedicle screws (cortical screws) and potential complications when performing lumbar fusion.
Methods
Lumbar fusion with cortical screw fixation in the hard cortical bone of the pars interarticularis of vertebrae was introduced to replace conventional pedicle screws. We review the literature on the biomechanics of cortical screw insertion and on the clinical outcomes.
Results
In vitro biomechanical testing has shown that cortical screws have greater pullout strength than traditional pedicle screws due to the strong bone–screw interface in cortical bone. Cortical screws have the advantages of requiring minimal muscle dissection and shortening the surgery. However, early screw loosening and loss of reduction have been reported.
Conclusions
When inserting cortical screws, the entry point and trajectory of the screws are important and a meticulous surgical technique is needed to prevent potential screw-related complications.