Cortical, Cancellous and Self-tapping Screw Types
Cortical and cancellous screws are available as fully as well as partially threaded screws. A cortical bone screw is often fully threaded. In plate fixation, a bone screw must purchase firmly on both the cortices. The purchase on the near cortex contributes 80 percent of the grip and the distal cortex contributes around 20 percent. A fully threaded cortical screw may function as lag screw only once the near cortex is over-drilled. A fully threaded cortical screw can be either self-tapping or non-self-tapping.
A partially threaded cortical screw is known as a shaft screw. The shaft diameter resembles the outer diameter of the thread. This screw has better strength as well as stiffness than a fully threaded screw which is a benefit when it’s used as a lag screw and as an axial compression screw. It’s a non-self-tapping screw.
A locking cancellous screw can be fully threaded or partially threaded. A fully threaded cancellous screw is utilized as a placement screw to fix a bone plate in metaphyseal as well as epiphyseal regions. A partially threaded cancellous screw is utilized as a lag screw.
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