Cannulated Screws

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 children.


  Two cannulated cancellous screws used as lag screws for dynamic compression of a subcapital fracture of the femoral neck in an adult.