How is trimalleolar fracture curable by insertion of metal plates and screws?

It will help to. Position of the bone correctly so it will heal correctly.
Stabilization. Metal plates and screws are used to stabilize bone fragments that might otherwise easily become displaced. They allow the fragments to stay in juxtaposition and proper alignment so they can grow bony interconnections to re-establish the natural stability of these bones after fracture displacement.

Related Questions

I feel a screw protruding slightly from the bottom of a plate inserted to repair a trimalleolar fracture. Is it possible to have that one screw removed or must all the hardware come out?

Yes. Most likely you can have one screw removed without jeopardizing the stability of the plate or the repair. Read more...
Sometimes. It could just be the one screw removed but it would all depend on the plate configuration. See your orthopedist. Read more...

I suffered a trimalleolar fracture in April I had hardware put in, screws broke and the doctor says it will be fine but I have a lot of pain and swell?

A thought. Acupuncture is sometimes helpful in accelerating healing. It can help to reduce inflammation and pain. You might consider discussing this option with your orthopedic surgeon. Read more...
Second Opinion. The surgery was 5 months ago. A lot of pain and swelling means that something could be amiss. At this point in time some swelling is acceptable and consistent with appropriate healing, but pain should not be to an exaggerated level. It could be the time for a second opinion. Read more...