An ankle fracture is typically caused by a twisting or impact injury. When the ankle twists, it can fracture in many different ways. It may fracture just above the joint, breaking or fracturing the tibia and/or the fibula, like this.
In other cases, the tibia may be fractured in a way that damages the articular cartilage on the joint surface. Notice how this makes the smooth surface of the articular cartilage become rough or jagged. Fractures such as these can be more serious because even a little roughness or irregularity in the joint surface can lead to painful movement of the joint and the early development of arthritis.
In most cases, surgery allows for the roughness of the joint surface to be returned to its original or near original smoothness. This offers the greatest chance for the return of normal function.