An ankle sprain is graded based on severity of injury. It may only involve stretching of a few fibres, may be partially or completely torn. A complete tear of the ligaments is uncommon.
However it is very important, not to simply regard any ankle injury as an "ankle sprain" because other injuries can occur as well, for example, the peroneal tendons (the tendons that are behind the outer ankle bone) can be torn, fractures in other bones around the ankle could be a possibility.
In some cases, an MRI may be warranted to rule out other problems in the ankle such as damage to the cartilage (a flexible connecting tissue). An MRI, however, is not necessary to diagnose a sprain.
Minor injuries recover quickly within a few weeks. More severe injuries and injuries in athletic individuals, may take a longer time to recover. Outcome is generally good and most patients heal from an ankle sprain and are able to get back to their normal lives, sports, and activities. Some people, however, who do not properly rehabilitate their ankle or have had a severe sprain, may go on to have ankle instability. Repeated episodes can be dangerous because they can lead to cartilage damage within the ankle and may require surgery.
Surgery is rarely indicated when in spite of appropriate conservative treatment and physical therapy, the ankle joint continues to feels unstable and frequently gives way. Here, the ligaments are either repaired or reconstructed (using tendon grafts which involves replacing damaged tendons by borrowing them from a different area in the body)