First off, if you have a bunny with an injury, PLEASE take it to a vet immediately. They are well-trained and far better equipped than any home, regardless of the veterinary skill of the homeowner.
If your pet has a leg injury, the treatment will depend entirely on the type and severity of the injury. If there is a broken bone, treatments will vary from simply resetting the limb and casting it to performing minor surgery in the event the bone can't be manually set. A sprained leg among rabbits, as far as I know, is a very unlikely event, but should fix itself.
As I stated before, if your pet has an injury that you are concerned may be a broken bone, it must have the attention it will receive at a veterinary clinic. Even if it turns out to be a minor injury, at least you will not risk an improperly set bone.