Lag screw fixation
1. Screw direction
The screws are inserted in lag fashion. To achieve maximal interfragmentary compression, anatomic reduction must be present, and the screws must be directed perpendicular to the fracture plane.
2. Screw insertion
A glide hole (outer diameter of the screw) is first drilled into the cis (near) cortex followed by the thread hole (smaller diameter) in the trans (far) cortex using the appropriate drill bits and drill sleeves. The drill sleeve for the thread hole must be inserted through the cis cortex, touching the far cortex, to ensure proper placement and compression.
The hole is slightly countersunk to enlarge the contact area of the screw head to the bone.
The screw length is measured with a depth gauge. The longest measurement should be used.
The thread hole is tapped, and a screw of appropriate length is inserted.
The screw should exit the trans cortex by 2mm.
Note: If two lag screws are placed, take care not to place them too close to each other. Safe distance is at least 1 screw diameter away from any fracture line and 2 screws should be separated by 2 x their diameter.
