Grade two sprains can take 4 to 6 weeks to heal. This involves partial tearing of the ligaments. Signs of a grade two sprain include instability, moderate to severe pain, swelling, stiffness and possible bruising.
Grade three sprains can take 8 to 12 weeks to heal. This is a complete tear of the ligament. With grade three sprains, there is a lot of instability within the joint, severe pain when the injury occurs and no pain after injury, severe swelling and excessive bruising. (This answer provided for NATA by the California University of Pennsylvania Athletic Training Education Program.)