The Synthes Locking Compression Plate (LCP) with its patented combination plate holes (combi‐holes) that accommodate conventional or locking screws was released in 2001 [1, Chapter 2]. Cortical or cancellous screws can be inserted in the dynamic compression unit (DCU) of the combi‐hole to provide axial compression. The other half of the combi‐hole is threaded and conical to accept a locking screw, allowing for fixed‐angle stability. As such, an LCP can be applied in two manners: as a compression plate or as a bridging “internal fixator” plate.

The strength of the locking fixation depends less on the integrity of the bone than on fixations using conventional compression plates. Locking plates allow rigid fixation of comminuted fractures using biological fixation and are ideal for fractures in weak bone. Furthermore, locking plates are the ultimate implant for minimally invasive plate osteosynthesis (MIPO).

The locking drill guide threads into the threaded portion of the combi‐hole in the plate in a fixed direction (uniaxial) for an angle‐stable construct (Figure 12.1). The threads of the locking screw are smaller than cortical screws, as they do not have to create compression between the bone and the plate. Locking screws also have a larger core diameter than conventional screws, allowing them to be stronger in bending and shear forces. The thread leads on the shaft and the head of the locking screw are 1 mm. The pitch on the threads in the head is 0.5 mm, or two threads per 1 mm of space, also known as a 2‐start thread. In a 2‐start thread, there are two sets of threads 180° apart. During screw insertion, the shaft and head spin at the same rate but the threads in the head travel twice the distance. If the screwhead threads come in contact with the plate threads and become 90° out of phase, a height/distance of 0.25 mm is created. The plate/screw/bone will adjust to allow the screwhead to properly thread into the plate without stripping the threads into the bone. The leading screwhead thread will tend to compress the plate against the bone until the threads come into phase. When the threads mate together, the plate will release some of the built‐up compression. Per the manufacturer, the Synthes stardrive screwhead design is 65% stronger in insertional torque than conventional hexagonal screwhead design (Synthes publication #036.001.395). Locking screws offer less risk of screw loosening than do conventional screws.