The capitellum is a difficult target: almost spherical, covered in cartilage, and reached through bone that gets thinner with age and fracture. Screws that converge on it from the posterior aspect find its best remaining stock, but only if they keep their planned direction. In soft condylar bone a conventional screw drifts as it tightens.
The locking posterolateral plate removes that drift. Its distal screws engage the plate at fixed angles, so the corridor chosen at planning is the corridor the screw actually travels — forward into the capitellum, clear of the joint surface. As the posterolateral element of a dual construct it gives the lateral side of the elbow fixed-angle stability to match the medial plate. Screw planning and construct design stay with the operating surgeon.