Cannulated screw with solid core insert: stronger than cannulated screws. 
We conducted a study to determine if there is a significant difference in ultimate load, yield strength, and fatigue strength between solid core screws and cannulated screws and if a solid core insert placed inside a cannulated screw would have biomechanical effects similar to those of a solid core screw.  Five screw designs were tested: Synthes 4.5-mm solid core and 4.5-mm cannulated and our prototype 4.0-mm solid core, 4.0-mm cannulated, and 4.0-mm cannulated with solid core insert.  Biomechanical testing with 3-point bending was used to determine ultimate load, yield strength, and cycles to failure for 6 screws of each design.  Ultimate load, yield strength, and cycles to failure were significantly (P < .05) lower in the Synthes 4.5-mm cannulated screws than in the Synthes solid core screws and significantly lower in the prototype cannulated screws than in the prototype solid core screws (P < .05) and prototype cannulated screws with solid core inserts (P < .05).  There was no significant difference (P > .05) in ultimate load, yield strength, or cycles to failure between the prototype cannulated screws with solid core inserts and the prototype solid core screws.