Lag screw fixation is a technique used in surgical treatment (internal fixation) of fractures or broken bones. It involves the use of special half threaded orthopedic bone screws, which are smooth from the head up to half or two-thirds of their length. Even a fully threaded cortical screw can be used as a lag screw if the proximal cortex is over drilled. The function of a lag screw is to achieve compression between the fracture fragments (pieces of bone), which helps in providing lag screw strength for better bone fracture healing.
Lag Screw Strength Principle
The threads of the lag screw engage in the distal (away from the insertion point) piece of bone and hold it firmly. Thus, this piece of bone can be controlled by moving the head of the lag screw. The smooth portion of the lag screw passes through the proximal fragment of bone and hence, this piece is free to slide along the shaft of the screw. However, the head of the screw serves as a stopper to restrict this motion. When the lag screw is tightened, the head fits snugly on the entry point of the screw and forces the proximal fragment over the distal fragment. Thus, the 2 fragments of bone are not just aligned but compressed over each other. This provides tremendous lag screw strength for stabilization of broken bones and also for earlier and better bone fracture healing.
Lag Screw Uses
- Elbow Fractures (Broken Elbow)
- Ankle Fractures (Broken Ankle)
- Scaphoid Fracture (Broken Wrist)
- Proximal Tibial Fracture (Broken Leg near Knee)
- Hip Fracture (Broken Hip)