Subchondral lag screw
Once the reduction of the articular surface is achieved, it is maintained
with a subchondral lag screw which runs from lateral anteromedially into the
“constant” medial subchondral fragment.
Thus, when drilling the hole for the lag screw, the drill bit must be directed
carefully in these three directions:
a) Lateral to medial
b) Posterior to anterior
c) Cephalad to caudad
In this way, the threaded portions of the screw will be directed into the
strong medial sustentacular cortical bone.
The surgeon must use caution while inserting the lag screw.