Casts are a common form of treatment to hold fractured bones in their properplace so that healing can take place over time, thus reduce pain. It may also beused to relieve pain from severe sprains. They would need to stay on your armor leg for 4 to 12 weeks, depending on the severity of your injury.Different types of casts and splints can be applied. Plaster of Paris slabs areapplied during the early stages of treatment to hold the fractured bones intheir proper place. Synthetic casts will be applied once the broken bones havestarted to heal.