There are many types of screws used in orthopedic procedures, including corcal and cancellous screws, fully and partially threaded screws, locking and non-locking screws, cannulated screws, Poller screws, and more. The main differences in design features relate to thread pitch, tip design, core to outer diameter ratio, threading, and whether the screw is cannulated or has a locking mechanism. Cortical screws are designed to gain maximal purchase in dense cortical bone with a small pitch and greater number of threads, while cancellous screws have wider threads and a larger pitch to gain maximum purchase in less dense cancellous bone. Locking screws have additional threads around the head for mechanical coupling with plates and increased angular stability. Cannulated screws have a hollow core for use with a guide wire and accurate positioning near articular surfaces. Screw function can vary depending on the type of procedure, from producing interfragmentary compression to locking an intramedullary nail in place or blocking movement of a main fragment around an intramedullary nail.

The lag screw technique involves creating a gliding hole through the near cortex and a threaded hole through the far cortex. The screw is inserted perpendicular to the fracture plane, only engaging in the far cortex and sliding through the near cortex, resulting in interfragmentary compression and absolute stability. Proper countersinking and over-drilling of the near cortex are necessary to prevent screw threads from engaging both near and far cortex. This technique is best suited for simple fractures such as spiral or oblique.

The factors affecting screw pull-out strength include contact surface area between screw threads and bone, outer and core diameter, thread density, number of threads engaged in the bone cortex, use of locking mechanisms and surgical techniques. Poor surgical technique, such as making a large pilot hole or repeatedly withdrawing and reintroducing a screw, can also lead to reduced pull-out strength.