|Cannulated screws have a hollow
central shaft. Both cortical and cancellous screws can be cannulated.
Cannulated cancellous screws are used for metaphyseal fractures while
cannulated and noncannulated cortical screws are used as lag screws for
fixation of diaphyseal fractures. The main advantage of cannulated screws is that they can be
inserted over a guide wire or guide pin.
The diameter of the guide pin is much smaller than the cannulated screw and can be more
accurately placed using fluoroscopy in the operating room. In addition,
given its small diameter, the guide pin can be reinserted several times if
necessary for accurate placement without excessive damage to bone. One
special type of cannulated cancellous screw is the Knowles pin which is a
cannulated screw used for fixation of slipped capital femoral epiphysis in
Two cannulated cancellous screws used as lag screws for dynamic
compression of a subcapital fracture of the femoral neck in an adult.