Orthopaedic surgeons use variations of cortical or cancellous screws to repair and stabilise bones. Factors such as the location of the injury, the type of injury and the type of bone that will be anchoring the screw determine the type used. Screws may be used alone or in conjunction with other orthopaedic hardware or devices. They may be used temporarily and then removed or left in place indefinitely.
Cortical screws are designed to anchor into cortical bone. According to Encyclopedia Britannica, 80 per cent of the human body is comprised of this dense type of bone. Cortical screws are commonly used alone or with other orthopaedic hardware for fixation of fractures. They come in various lengths and diameters with a fine threading that runs the entire length of the screw for firm anchoring.
In contrast to cortical bone, cancellous bone is porous like a sponge. Cancellous screws are intended for use with this softer type of bone. The threads of a cancellous screw are spaced wider apart to provide better grip into bone that is less dense. Metaphyseal and osteoporotic fractures are commonly repaired using this type of screw. Like cortical screws, they come in various lengths and diameters.
The cannulated screw is made of stainless steel or Titanium and has a hollowed out centre for a guidewire such as a Kirschner wire (or K-wire). This makes it easier for surgeons to place them and makes them popular for limited-incision operations, as well as femoral neck fixation. They are self-drilling, so surgeons do not have to tap them into place. Cannulated screws are used only when needed, as they are much more expensive than non-cannulated screws.
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