Titanium Locking plates. A paradigm shift in plating technology.
Standard DCP or round hole plates are held into position by friction between the head of the screw and the bone. When the screw is tightened against the bone the threads of the screw pull the plate into position. This requires time consuming and difficult contouring of standard plates to achieve anatomical reduction.
Locking screws and plates are different in how they behave. They behave more like “internal” External Skeletal Fixators. Although the threads of the screw shaft do engage the bone, the interface between bone and screw is not related to the attachment of the plate and screws. In locking plates it is the interface between the screw head and the plate that holds the plate to the screw. As the screw is tightened the bone maintains its position relative to the plate, it is not drawn up to it. This means perfect anatomical contouring is not required. The increased angular igidity of Locking Plate constructs places greater stresses onto the screw. Because Locking plates are not relying on the threads of the screw in the bone to hold the plate against the bone they do not need to be as coarse a thread as standard cortical screws. They need, only, to hold their position in the bone. Thus for the same outside diameter of screw the core diameter is increased, without increasing the likelihood of bone/screw interface failure. This increase in core diameter increases the resistance to bending and breakage of the screws.
Locking plates require the screw to be inserted at a fixed angle relative to the hole in the plate. Hence why locking plates are sometimes referred to as Fixed Angle systems. Drill guides, which screw into the locking plate’s holes allow accurate drilling of the screw holes (in the larger plates k-wire holes allow the plate to be fixed to the bone prior to drilling the screw holes). The rigid attachment of the screw to the plate gives Locking plates a high degree of angular rigidity relative to a DCP construct. This means in any given situation to achieve the same rigidity as a DCP construct a locking construct needs less screws. This has particular implications in terms of time and morbidity. The Titanium Locking Plate system has limited contact to the bone thus helping preserve the blood supply to the healing bone. Titanium is extremely biocompatible compared to stainless steel limiting the chances of a reaction to the plate.
Locking plates allow for a more “biological fracture fixation”