Locking plate/screw system offer several advantages over conventional plate/screw systems. Conventional plate/screw systems require precise adaptation of the plate to the contour of the underlying bone in order to avoid drawing the bone segments toward the plate with tightening of the screws. Locking plate/screw systems, on the other hand, do not need to intimately contact the underlying bone in all areas, because the screws lock to the plate as they are tightened and stabilize the fracture fragments.
Because locking plate/screw systems do not need to intimately contact bone, they do not disrupt the underlying cortical bone perfusion as much as conventional plates that require intimate contact of the undersurface of the plate to the cortical bone.
Locking screws are also unlikely to loosen from the plate, which is important in cases where the screw is inserted into a fracture gap or into unincorporated bone graft.
Modern plates have two connected holes. One accepts conventional screws (including lag screws), and the other has threads and accepts locking screws. The image above shows a combination plate used with conventional screws (note that the screw heads aren't flush with the plate).