What is a Cortex Screw? The answer is that is stronger and have larger core-to-outer diameter ratio as compared to the cancellous screws having exactly same outer diameter. Further, these also are blunt ended. The threads present in these screws are shallow and closely-spaced. Cortex Screws are also the answer to âWhat type of screws are used in surgery?â. These are designed to be placed in the cortical bone. In conditions, where it is required to fix plates to long bones, the fully-threaded cortex screws are used in order to achieve optimum stability.