Placing a plate on the back of the lateral column changes what the construct can do. Screws from a dorsolateral plate run forward into the capitellum — a different corridor from the lateral plate's sideways trajectory — and the plate buttresses the condyle against the posterior displacement that many fracture patterns want to produce.
This is the logic behind perpendicular plating: one plate on the medial ridge, one on the posterolateral aspect, with the two constructs crossing at right angles for stiffness that parallel arrangements do not reach. Traditional dorsolateral plates keep the technique flexible — they contour to the column at the table and compress as they are fixed. Plane selection and construct design remain decisions for the operating surgeon.