The Lag Screw

The lag screw is the basic implant for stable interfragmental fixation. A 1.5 mm (0.062 or 1/16) cortical screw has the same thread diameter as the largest Kirschner wire used in the United States. The thread diameter of a 2.0 mm cortical screw is equal to the diameter of the largest Kirschner wire used in Europe. From this, it can be seen that cortical screws designed for the hand are only slightly larger, in general, than Kirschner wires that might be chosen for the same fixation. Whereas Kirschner wires can only splint the fracture and provide coaptive fixation, screws can provide firm fixation by compression. Screws, in addition, can be measured precisely for the desired length required and do not protrude through the bone.