The main goal of this type of injury is to allow the bone and soft tissues to heal. At the same time, it's important to keep the elbow joint from freezing up. Usually, the device, called an external fixator allows elbow flexion and extension. It prevents torque or load from side to side.
This side-to-side stress is called varus or valgus load. It occurs most often when the bones of the elbow are rotated. This happens when you turn your hand palm up (supination) and palm down (pronation).
Without these motions, the hand is fairly limited in function. The fixator helps maintain motion without stiffness while protecting the healing tissue.